Author name code: schou
ADS astronomy entries on 2022-09-14
author:"Schou, Jesper" 
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Title: The on-ground data reduction and calibration pipeline for
    SO/PHI-HRT
Authors: Sinjan, J.; Calchetti, D.; Hirzberger, J.; Orozco Suárez,
   D.; Albert, K.; Albelo Jorge, N.; Appourchaux, T.; Alvarez-Herrero,
   A.; Blanco Rodríguez, J.; Gandorfer, A.; Germerott, D.; Guerrero,
   L.; Gutierrez Marquez, P.; Kahil, F.; Kolleck, M.; Solanki, S. K.; del
   Toro Iniesta, J. C.; Volkmer, R.; Woch, J.; Fiethe, B.; Gómez Cama,
   J. M.; Pérez-Grande, I.; Sanchis Kilders, E.; Balaguer Jiménez,
   M.; Bellot Rubio, L. R.; Carmona, M.; Deutsch, W.; Fernandez-Rico,
   G.; Fernández-Medina, A.; García Parejo, P.; Gasent Blesa, J. L.;
   Gizon, L.; Grauf, B.; Heerlein, K.; Korpi-Lagg, A.; Lange, T.; López
   Jiménez, A.; Maue, T.; Meller, R.; Michalik, H.; Moreno Vacas, A.;
   Müller, R.; Nakai, E.; Schmidt, W.; Schou, J.; Schühle, U.; Staub,
   J.; Strecker, H.; Torralbo, I.; Valori, G.
Bibcode: 2022arXiv220814904S
Altcode:
  The ESA/NASA Solar Orbiter space mission has been successfully launched
  in February 2020. Onboard is the Polarimetric and Helioseismic Imager
  (SO/PHI), which has two telescopes, a High Resolution Telescope
  (HRT) and the Full Disc Telescope (FDT). The instrument is designed
  to infer the photospheric magnetic field and line-of-sight velocity
  through differential imaging of the polarised light emitted by the
  Sun. It calculates the full Stokes vector at 6 wavelength positions
  at the Fe I 617.3 nm absorption line. Due to telemetry constraints,
  the instrument nominally processes these Stokes profiles onboard,
  however when telemetry is available, the raw images are downlinked and
  reduced on ground. Here the architecture of the on-ground pipeline
  for HRT is presented, which also offers additional corrections not
  currently available on board the instrument. The pipeline can reduce
  raw images to the full Stokes vector with a polarimetric sensitivity
  of $10^{-3}\cdot I_{c}$ or better.

Title: Using birefringent elements and imaging Michelsons for the
    calibration of high-precision planet-finding spectrographs
Authors: Schou, J.
Bibcode: 2022A&A...662A.119S
Altcode: 2022arXiv220213421S
  Context. One of the main methods used for finding extrasolar planets
  is the radial velocity technique, in which the Doppler shift of a star
  due to an orbiting planet is measured. These measurements are typically
  performed using cross-dispersed echelle spectrographs. Unfortunately,
  such spectrographs are large and expensive, and their accurate
  calibration continues to be challenging. <BR /> Aims: The aim is
  to develop a different way to provide a calibration signal. <BR />
  Methods: A commonly used way to introduce a calibration signal is
  to insert an iodine cell in the beam. Disadvantages of this include
  that the lines are narrow, do not cover the entire spectrum, and
  light is absorbed. Here I show that inserting a birefringent element
  or an imaging Michelson, combined with Wollaston prisms, eliminates
  these three shortcomings while maintaining most of the benefits of
  the iodine approach. <BR /> Results: The proposed designs can be
  made very compact, thereby providing a convenient way of calibrating
  a spectrograph. Similar to the iodine cell approach, the calibration
  signal travels with the stellar signal, thereby reducing the sensitivity
  to spectrograph stability. The imposed signal covers the entire visible
  range, and any temperature drifts will be consistent and describable
  by a single number. Based on experience with similar devices that were
  used in a different configuration by the Helioseismic and Magnetic
  Imager, it is shown that the calibration device can be made stable
  at the 0.1 m/s level over a significant wavelength range on short to
  medium timescales. <BR /> Conclusions: While the design is promising,
  many details still need to be worked out. In particular, a number of
  laboratory measurements are required in order to finalize a design
  and estimate actual performance, and it would be desirable to make a
  proof of concept.

Title: The magnetic drivers of campfires seen by the Polarimetric
    and Helioseismic Imager (PHI) on Solar Orbiter
Authors: Kahil, F.; Hirzberger, J.; Solanki, S. K.; Chitta, L. P.;
   Peter, H.; Auchère, F.; Sinjan, J.; Orozco Suárez, D.; Albert,
   K.; Albelo Jorge, N.; Appourchaux, T.; Alvarez-Herrero, A.; Blanco
   Rodríguez, J.; Gandorfer, A.; Germerott, D.; Guerrero, L.; Gutiérrez
   Márquez, P.; Kolleck, M.; del Toro Iniesta, J. C.; Volkmer, R.;
   Woch, J.; Fiethe, B.; Gómez Cama, J. M.; Pérez-Grande, I.; Sanchis
   Kilders, E.; Balaguer Jiménez, M.; Bellot Rubio, L. R.; Calchetti,
   D.; Carmona, M.; Deutsch, W.; Fernández-Rico, G.; Fernández-Medina,
   A.; García Parejo, P.; Gasent-Blesa, J. L.; Gizon, L.; Grauf, B.;
   Heerlein, K.; Lagg, A.; Lange, T.; López Jiménez, A.; Maue, T.;
   Meller, R.; Michalik, H.; Moreno Vacas, A.; Müller, R.; Nakai,
   E.; Schmidt, W.; Schou, J.; Schühle, U.; Staub, J.; Strecker, H.;
   Torralbo, I.; Valori, G.; Aznar Cuadrado, R.; Teriaca, L.; Berghmans,
   D.; Verbeeck, C.; Kraaikamp, E.; Gissot, S.
Bibcode: 2022A&A...660A.143K
Altcode: 2022arXiv220213859K
  Context. The Extreme Ultraviolet Imager (EUI) on board the Solar Orbiter
  (SO) spacecraft observed small extreme ultraviolet (EUV) bursts,
  termed campfires, that have been proposed to be brightenings near the
  apexes of low-lying loops in the quiet-Sun atmosphere. The underlying
  magnetic processes driving these campfires are not understood. <BR
  /> Aims: During the cruise phase of SO and at a distance of 0.523
  AU from the Sun, the Polarimetric and Helioseismic Imager on Solar
  Orbiter (SO/PHI) observed a quiet-Sun region jointly with SO/EUI,
  offering the possibility to investigate the surface magnetic field
  dynamics underlying campfires at a spatial resolution of about 380
  km. <BR /> Methods: We used co-spatial and co-temporal data of the
  quiet-Sun network at disc centre acquired with the High Resolution
  Imager of SO/EUI at 17.4 nm (HRI<SUB>EUV</SUB>, cadence 2 s) and the
  High Resolution Telescope of SO/PHI at 617.3 nm (HRT, cadence 2.5
  min). Campfires that are within the SO/PHI−SO/EUI common field
  of view were isolated and categorised according to the underlying
  magnetic activity. <BR /> Results: In 71% of the 38 isolated events,
  campfires are confined between bipolar magnetic features, which seem to
  exhibit signatures of magnetic flux cancellation. The flux cancellation
  occurs either between the two main footpoints, or between one of the
  footpoints of the loop housing the campfire and a nearby opposite
  polarity patch. In one particularly clear-cut case, we detected the
  emergence of a small-scale magnetic loop in the internetwork followed
  soon afterwards by a campfire brightening adjacent to the location
  of the linear polarisation signal in the photosphere, that is to
  say near where the apex of the emerging loop lays. The rest of the
  events were observed over small scattered magnetic features, which
  could not be identified as magnetic footpoints of the campfire hosting
  loops. <BR /> Conclusions: The majority of campfires could be driven
  by magnetic reconnection triggered at the footpoints, similar to the
  physical processes occurring in the burst-like EUV events discussed
  in the literature. About a quarter of all analysed campfires, however,
  are not associated to such magnetic activity in the photosphere, which
  implies that other heating mechanisms are energising these small-scale
  EUV brightenings.

Title: Multi-view magnetic synoptic maps with SO/PHI and SDO/HMI
Authors: Löschl, P.; Hirzberger, J.; Schou, J.; Solanki, S. K.
Bibcode: 2020AGUFMSH0360028L
Altcode:
  With the recent launch of Solar Orbiter (SO) and the first data slowly
  becoming available, it will soon be possible to simultaneously observe
  the Sun from additional vantage points off the Earth-Sun line. One
  of its instruments, the Polarimetric and Heliospheric Imager (PHI),
  is the first spectro-polarimeter to operate outside of this line of
  sight. This opens the possibility for joint observational campaigns
  with similar instruments, such as the Heliospheric and Magnetic Imager
  (HMI) on-board the Solar Dynamics Observatory (SDO). We utilise these
  new observational possibilities to produce combined magnetic synoptic
  maps from magnetograms of the PHI and HMI instruments. Building on the
  existing software infrastructure for HMI synoptic maps, we extended
  its current functionality to include PHI data and correct for the
  different and varying relative orbital characteristics of the two
  spacecraft. The result are joint magnetic synoptic maps, that can
  be produced significantly faster than the approximately 27 days of
  one solar rotation and therefore are less likely to suffer from the
  evolution of the magnetic field over the observation period. Once Solar
  Orbiter leaves the ecliptic plane, we will also be able to include
  observations of the polar magnetic field into our synoptic maps,
  which will give an unprecedented insight into the magnetic field of
  the Sun. This work presents our preparatory modelling efforts and
  gives an outlook for the future capabilities of this novel data product.

Title: First results from SO/PHI's on-board data reduction
Authors: Albert, K.; Hirzberger, J.; Kolleck, M.; Albelo Jorge,
   N.; Busse, D.; Blanco Rodriguez, J.; Cobos Carrascosa, J. P.;
   Fiethe, B.; Gandorfer, A.; Germerott, D.; Guan, Y.; Guerrero, L.;
   Gutierrez-Marques, P.; Hernández Expósito, D.; Lange, T.; Michalik,
   H.; Orozco Suárez, D.; Schou, J.; Solanki, S. K.; Woch, J. G.
Bibcode: 2020AGUFMSH038..05A
Altcode:
  The Polarimetric and Helioseismic Imager (PHI), on-board Solar
  Orbiter (SO), is a spectropolarimeter imaging the solar photosphere
  at the wavelengths of the Fe I 617.3 nm Zeeman sensitive absorption
  line. SO/PHI's aim is to provide data about the magnetic structures and
  the line-of-sight (LOS) velocity in the solar atmosphere. For this, it
  takes time series of data sets consisting of 2048 x 2048 pixel images of
  the Sun at 6 wavelengths, each in 4 different polarisation states. With
  the minimum necessary 17 bits pixel depth, one data set amounts to
  approx. 0.2 GB. The guaranteed data telemetry for PHI, in contrast,
  is only 50 GiB/orbit which would also need to contain any calibration
  data obtained on-board, i.e. our flat and dark fields. To cope with
  this discrepancy, SO/PHI is performing full data reduction on-board,
  including the inversion of the radiative transfer equation. The
  downloaded results are science ready data, containing 5 final images: a
  total intensity image from nearby the spectral line, the magnetic field
  strength, azimuth and inclination (describing the magnetic vector) and
  the LOS velocity. This process maximises the science return by reducing
  the number of necessary images in a data set, as well as rendering the
  download of calibration data unessential. In the commissioning phase
  of SO/PHI we used the on-board data reduction system successfully
  for the first time. We have calibrated the instrument to its optimal
  operational parameters (calculation of exposure time, focus, etc.),
  acquired and processed calibration data (dark and flat fields),
  removed the most significant instrumental artefacts from the data
  (dark field, flat field, polarimetric modulation and polarimetric
  cross-talk), and performed the inversion of the radiative transfer
  equation. The data have then been compressed to further maximise the
  use of our telemetry. This contribution presents and discusses the
  final results from this process.

Title: The Solar Orbiter Science Activity Plan. Translating solar
    and heliospheric physics questions into action
Authors: Zouganelis, I.; De Groof, A.; Walsh, A. P.; Williams, D. R.;
   Müller, D.; St Cyr, O. C.; Auchère, F.; Berghmans, D.; Fludra,
   A.; Horbury, T. S.; Howard, R. A.; Krucker, S.; Maksimovic, M.;
   Owen, C. J.; Rodríguez-Pacheco, J.; Romoli, M.; Solanki, S. K.;
   Watson, C.; Sanchez, L.; Lefort, J.; Osuna, P.; Gilbert, H. R.;
   Nieves-Chinchilla, T.; Abbo, L.; Alexandrova, O.; Anastasiadis, A.;
   Andretta, V.; Antonucci, E.; Appourchaux, T.; Aran, A.; Arge, C. N.;
   Aulanier, G.; Baker, D.; Bale, S. D.; Battaglia, M.; Bellot Rubio,
   L.; Bemporad, A.; Berthomier, M.; Bocchialini, K.; Bonnin, X.; Brun,
   A. S.; Bruno, R.; Buchlin, E.; Büchner, J.; Bucik, R.; Carcaboso,
   F.; Carr, R.; Carrasco-Blázquez, I.; Cecconi, B.; Cernuda Cangas, I.;
   Chen, C. H. K.; Chitta, L. P.; Chust, T.; Dalmasse, K.; D'Amicis, R.;
   Da Deppo, V.; De Marco, R.; Dolei, S.; Dolla, L.; Dudok de Wit, T.;
   van Driel-Gesztelyi, L.; Eastwood, J. P.; Espinosa Lara, F.; Etesi,
   L.; Fedorov, A.; Félix-Redondo, F.; Fineschi, S.; Fleck, B.; Fontaine,
   D.; Fox, N. J.; Gandorfer, A.; Génot, V.; Georgoulis, M. K.; Gissot,
   S.; Giunta, A.; Gizon, L.; Gómez-Herrero, R.; Gontikakis, C.; Graham,
   G.; Green, L.; Grundy, T.; Haberreiter, M.; Harra, L. K.; Hassler,
   D. M.; Hirzberger, J.; Ho, G. C.; Hurford, G.; Innes, D.; Issautier,
   K.; James, A. W.; Janitzek, N.; Janvier, M.; Jeffrey, N.; Jenkins,
   J.; Khotyaintsev, Y.; Klein, K. -L.; Kontar, E. P.; Kontogiannis,
   I.; Krafft, C.; Krasnoselskikh, V.; Kretzschmar, M.; Labrosse, N.;
   Lagg, A.; Landini, F.; Lavraud, B.; Leon, I.; Lepri, S. T.; Lewis,
   G. R.; Liewer, P.; Linker, J.; Livi, S.; Long, D. M.; Louarn, P.;
   Malandraki, O.; Maloney, S.; Martinez-Pillet, V.; Martinovic, M.;
   Masson, A.; Matthews, S.; Matteini, L.; Meyer-Vernet, N.; Moraitis,
   K.; Morton, R. J.; Musset, S.; Nicolaou, G.; Nindos, A.; O'Brien,
   H.; Orozco Suarez, D.; Owens, M.; Pancrazzi, M.; Papaioannou, A.;
   Parenti, S.; Pariat, E.; Patsourakos, S.; Perrone, D.; Peter, H.;
   Pinto, R. F.; Plainaki, C.; Plettemeier, D.; Plunkett, S. P.; Raines,
   J. M.; Raouafi, N.; Reid, H.; Retino, A.; Rezeau, L.; Rochus, P.;
   Rodriguez, L.; Rodriguez-Garcia, L.; Roth, M.; Rouillard, A. P.;
   Sahraoui, F.; Sasso, C.; Schou, J.; Schühle, U.; Sorriso-Valvo, L.;
   Soucek, J.; Spadaro, D.; Stangalini, M.; Stansby, D.; Steller, M.;
   Strugarek, A.; Štverák, Š.; Susino, R.; Telloni, D.; Terasa, C.;
   Teriaca, L.; Toledo-Redondo, S.; del Toro Iniesta, J. C.; Tsiropoula,
   G.; Tsounis, A.; Tziotziou, K.; Valentini, F.; Vaivads, A.; Vecchio,
   A.; Velli, M.; Verbeeck, C.; Verdini, A.; Verscharen, D.; Vilmer, N.;
   Vourlidas, A.; Wicks, R.; Wimmer-Schweingruber, R. F.; Wiegelmann,
   T.; Young, P. R.; Zhukov, A. N.
Bibcode: 2020A&A...642A...3Z
Altcode: 2020arXiv200910772Z
  Solar Orbiter is the first space mission observing the solar plasma
  both in situ and remotely, from a close distance, in and out of the
  ecliptic. The ultimate goal is to understand how the Sun produces
  and controls the heliosphere, filling the Solar System and driving
  the planetary environments. With six remote-sensing and four in-situ
  instrument suites, the coordination and planning of the operations are
  essential to address the following four top-level science questions:
  (1) What drives the solar wind and where does the coronal magnetic field
  originate?; (2) How do solar transients drive heliospheric variability?;
  (3) How do solar eruptions produce energetic particle radiation that
  fills the heliosphere?; (4) How does the solar dynamo work and drive
  connections between the Sun and the heliosphere? Maximising the
  mission's science return requires considering the characteristics
  of each orbit, including the relative position of the spacecraft
  to Earth (affecting downlink rates), trajectory events (such
  as gravitational assist manoeuvres), and the phase of the solar
  activity cycle. Furthermore, since each orbit's science telemetry
  will be downloaded over the course of the following orbit, science
  operations must be planned at mission level, rather than at the level
  of individual orbits. It is important to explore the way in which those
  science questions are translated into an actual plan of observations
  that fits into the mission, thus ensuring that no opportunities are
  missed. First, the overarching goals are broken down into specific,
  answerable questions along with the required observations and the
  so-called Science Activity Plan (SAP) is developed to achieve this. The
  SAP groups objectives that require similar observations into Solar
  Orbiter Observing Plans, resulting in a strategic, top-level view of
  the optimal opportunities for science observations during the mission
  lifetime. This allows for all four mission goals to be addressed. In
  this paper, we introduce Solar Orbiter's SAP through a series of
  examples and the strategy being followed.

Title: Autonomous on-board data processing and instrument calibration
    software for the Polarimetric and Helioseismic Imager on-board the
    Solar Orbiter mission
Authors: Albert, Kinga; Hirzberger, Johann; Kolleck, Martin; Jorge,
   Nestor Albelo; Busse, Dennis; Rodríguez, Julian Blanco; Carrascosa,
   Juan Pedro Cobos; Fiethe, Björn; Gandorfer, Achim; Germerott, Dietmar;
   Guan, Yejun; Guerrero, Lucas; Gutierrez-Marques, Pablo; Expósito,
   David Hernández; Lange, Tobias; Michalik, Harald; Suárez, David
   Orozco; Schou, Jesper; Solanki, Sami K.; del Toro Iniesta, José
   Carlos; Woch, Joachim
Bibcode: 2020JATIS...6d8004A
Altcode:
  A frequent problem arising for deep space missions is the discrepancy
  between the amount of data desired to be transmitted to the ground
  and the available telemetry bandwidth. A part of these data consists
  of scientific observations, being complemented by calibration data
  to help remove instrumental effects. We present our solution for this
  discrepancy, implemented for the Polarimetric and Helioseismic Imager
  on-board the Solar Orbiter mission, the first solar spectropolarimeter
  in deep space. We implemented an on-board data reduction system that
  processes calibration data, applies them to the raw science observables,
  and derives science-ready physical parameters. This process reduces
  the raw data for a single measurement from 24 images to five, thus
  reducing the amount of downlinked data, and in addition, renders the
  transmission of the calibration data unnecessary. Both these on-board
  actions are completed autonomously.

Title: The Polarimetric and Helioseismic Imager on Solar Orbiter
Authors: Solanki, S. K.; del Toro Iniesta, J. C.; Woch, J.; Gandorfer,
   A.; Hirzberger, J.; Alvarez-Herrero, A.; Appourchaux, T.; Martínez
   Pillet, V.; Pérez-Grande, I.; Sanchis Kilders, E.; Schmidt, W.;
   Gómez Cama, J. M.; Michalik, H.; Deutsch, W.; Fernandez-Rico, G.;
   Grauf, B.; Gizon, L.; Heerlein, K.; Kolleck, M.; Lagg, A.; Meller, R.;
   Müller, R.; Schühle, U.; Staub, J.; Albert, K.; Alvarez Copano, M.;
   Beckmann, U.; Bischoff, J.; Busse, D.; Enge, R.; Frahm, S.; Germerott,
   D.; Guerrero, L.; Löptien, B.; Meierdierks, T.; Oberdorfer, D.;
   Papagiannaki, I.; Ramanath, S.; Schou, J.; Werner, S.; Yang, D.;
   Zerr, A.; Bergmann, M.; Bochmann, J.; Heinrichs, J.; Meyer, S.;
   Monecke, M.; Müller, M. -F.; Sperling, M.; Álvarez García, D.;
   Aparicio, B.; Balaguer Jiménez, M.; Bellot Rubio, L. R.; Cobos
   Carracosa, J. P.; Girela, F.; Hernández Expósito, D.; Herranz, M.;
   Labrousse, P.; López Jiménez, A.; Orozco Suárez, D.; Ramos, J. L.;
   Barandiarán, J.; Bastide, L.; Campuzano, C.; Cebollero, M.; Dávila,
   B.; Fernández-Medina, A.; García Parejo, P.; Garranzo-García, D.;
   Laguna, H.; Martín, J. A.; Navarro, R.; Núñez Peral, A.; Royo, M.;
   Sánchez, A.; Silva-López, M.; Vera, I.; Villanueva, J.; Fourmond,
   J. -J.; de Galarreta, C. Ruiz; Bouzit, M.; Hervier, V.; Le Clec'h,
   J. C.; Szwec, N.; Chaigneau, M.; Buttice, V.; Dominguez-Tagle, C.;
   Philippon, A.; Boumier, P.; Le Cocguen, R.; Baranjuk, G.; Bell,
   A.; Berkefeld, Th.; Baumgartner, J.; Heidecke, F.; Maue, T.; Nakai,
   E.; Scheiffelen, T.; Sigwarth, M.; Soltau, D.; Volkmer, R.; Blanco
   Rodríguez, J.; Domingo, V.; Ferreres Sabater, A.; Gasent Blesa,
   J. L.; Rodríguez Martínez, P.; Osorno Caudel, D.; Bosch, J.; Casas,
   A.; Carmona, M.; Herms, A.; Roma, D.; Alonso, G.; Gómez-Sanjuan, A.;
   Piqueras, J.; Torralbo, I.; Fiethe, B.; Guan, Y.; Lange, T.; Michel,
   H.; Bonet, J. A.; Fahmy, S.; Müller, D.; Zouganelis, I.
Bibcode: 2020A&A...642A..11S
Altcode: 2019arXiv190311061S
  <BR /> Aims: This paper describes the Polarimetric and Helioseismic
  Imager on the Solar Orbiter mission (SO/PHI), the first magnetograph and
  helioseismology instrument to observe the Sun from outside the Sun-Earth
  line. It is the key instrument meant to address the top-level science
  question: How does the solar dynamo work and drive connections between
  the Sun and the heliosphere? SO/PHI will also play an important role
  in answering the other top-level science questions of Solar Orbiter,
  while hosting the potential of a rich return in further science. <BR
  /> Methods: SO/PHI measures the Zeeman effect and the Doppler shift
  in the Fe I 617.3 nm spectral line. To this end, the instrument
  carries out narrow-band imaging spectro-polarimetry using a tunable
  LiNbO<SUB>3</SUB> Fabry-Perot etalon, while the polarisation modulation
  is done with liquid crystal variable retarders. The line and the nearby
  continuum are sampled at six wavelength points and the data are recorded
  by a 2k × 2k CMOS detector. To save valuable telemetry, the raw data
  are reduced on board, including being inverted under the assumption of
  a Milne-Eddington atmosphere, although simpler reduction methods are
  also available on board. SO/PHI is composed of two telescopes; one,
  the Full Disc Telescope, covers the full solar disc at all phases of
  the orbit, while the other, the High Resolution Telescope, can resolve
  structures as small as 200 km on the Sun at closest perihelion. The high
  heat load generated through proximity to the Sun is greatly reduced by
  the multilayer-coated entrance windows to the two telescopes that allow
  less than 4% of the total sunlight to enter the instrument, most of
  it in a narrow wavelength band around the chosen spectral line. <BR />
  Results: SO/PHI was designed and built by a consortium having partners
  in Germany, Spain, and France. The flight model was delivered to
  Airbus Defence and Space, Stevenage, and successfully integrated into
  the Solar Orbiter spacecraft. A number of innovations were introduced
  compared with earlier space-based spectropolarimeters, thus allowing
  SO/PHI to fit into the tight mass, volume, power and telemetry budgets
  provided by the Solar Orbiter spacecraft and to meet the (e.g. thermal)
  challenges posed by the mission's highly elliptical orbit.

Title: PMI: The Photospheric Magnetic Field Imager
Authors: Staub, Jan; Fernandez-Rico, German; Gandorfer, Achim; Gizon,
   Laurent; Hirzberger, Johann; Kraft, Stefan; Lagg, Andreas; Schou,
   Jesper; Solanki, Sami K.; del Toro Iniesta, Jose Carlos; Wiegelmann,
   Thomas; Woch, Joachim
Bibcode: 2020JSWSC..10...54S
Altcode:
  We describe the design and the capabilities of the Photospheric Magnetic
  field Imager (PMI), a compact and lightweight vector magnetograph,
  which is being developed for ESA's Lagrange mission to the Lagrange
  L5 point. After listing the design requirements and give a scientific
  justification for them, we describe the technical implementation and
  the design solution capable of fulfilling these requirements. This is
  followed by a description of the hardware architecture as well as the
  operations principle. An outlook on the expected performance concludes
  the paper.

Title: Estimating the nonstructural component of the helioseismic
    surface term using hydrodynamic simulations
Authors: Schou, J.; Birch, A. C.
Bibcode: 2020A&A...638A..51S
Altcode: 2020arXiv200413548S
  Context. As the amount of asteroseismic data available continues
  to grow, the inability to accurately model observed oscillation
  frequencies is becoming a critical problem for interpreting these
  frequencies. A major component of this problem is the modeling of
  the near-surface layers. <BR /> Aims: Our aim is to develop a method
  to estimate the effect of the near-surface layers on oscillation
  frequencies. <BR /> Methods: In the proposed method we numerically
  estimate eigenfunctions in 3D hydrodynamic simulations. We match those
  to the eigenfunctions calculated from the classic equations applied
  to the horizontal averages of the structure variables. We use this
  procedure to calculate the frequency perturbation resulting from the
  dynamical part of the interaction of the oscillations with near-surface
  convection. As the last step we scale the numbers to the Sun. To provide
  a qualitative test of our method we performed a series of simulations,
  calculated the perturbations using our procedure, and compared them
  to previously reported residuals relative to solar models. <BR />
  Results: We find that we can largely reproduce the observed frequency
  residuals without resorting to poorly justified theoretical models. We
  find that, while the calculations of Houdek et al. (2017, MNRAS, 464,
  L124) produce similar frequency perturbations, the density-pressure
  phase differences computed here do not match those of that work.

Title: The Solaris Solar Polar Mission
Authors: Hassler, Donald M.; Newmark, Jeff; Gibson, Sarah; Harra,
   Louise; Appourchaux, Thierry; Auchere, Frederic; Berghmans, David;
   Colaninno, Robin; Fineschi, Silvano; Gizon, Laurent; Gosain, Sanjay;
   Hoeksema, Todd; Kintziger, Christian; Linker, John; Rochus, Pierre;
   Schou, Jesper; Viall, Nicholeen; West, Matt; Woods, Tom; Wuelser,
   Jean-Pierre
Bibcode: 2020EGUGA..2217703H
Altcode:
  The solar poles are one of the last unexplored regions of the solar
  system. Although Ulysses flew over the poles in the 1990s, it did
  not have remote sensing instruments onboard to probe the Sun's polar
  magnetic field or surface/sub-surface flows.We will discuss Solaris,
  a proposed Solar Polar MIDEX mission to revolutionize our understanding
  of the Sun by addressing fundamental questions that can only be answered
  from a polar vantage point. Solaris uses a Jupiter gravity assist to
  escape the ecliptic plane and fly over both poles of the Sun to &gt;75
  deg. inclination, obtaining the first high-latitude, multi-month-long,
  continuous remote-sensing solar observations. Solaris will address key
  outstanding, breakthrough problems in solar physics and fill holes in
  our scientific understanding that will not be addressed by current
  missions.With focused science and a simple, elegant mission design,
  Solaris will also provide enabling observations for space weather
  research (e.g. polar view of CMEs), and stimulate future research
  through new unanticipated discoveries.

Title: Characterizing the spatial pattern of solar supergranulation
    using the bispectrum
Authors: Böning, Vincent G. A.; Birch, Aaron C.; Gizon, Laurent;
   Duvall, Thomas L.; Schou, Jesper
Bibcode: 2020A&A...635A.181B
Altcode: 2020arXiv200208262B
  Context. The spatial power spectrum of supergranulation does not
  fully characterize the underlying physics of turbulent convection. For
  example, it does not describe the non-Gaussianity in the horizontal flow
  divergence. <BR /> Aims: Our aim is to statistically characterize the
  spatial pattern of solar supergranulation beyond the power spectrum. The
  next-order statistic is the bispectrum. It measures correlations
  of three Fourier components and is related to the nonlinearities in
  the underlying physics. It also characterizes how a skewness in the
  dataset is generated by the coupling of three Fourier components. <BR />
  Methods: We estimated the bispectrum of supergranular horizontal surface
  divergence maps that were obtained using local correlation tracking
  (LCT) and time-distance helioseismology (TD) from one year of data
  from the helioseismic and magnetic imager on-board the solar dynamics
  observatory starting in May 2010. <BR /> Results: We find significantly
  nonzero and consistent estimates for the bispectrum using LCT and
  TD. The strongest nonlinearity is present when the three coupling
  wave vectors are at the supergranular scale. These are the same wave
  vectors that are present in regular hexagons, which have been used in
  analytical studies of solar convection. At these Fourier components,
  the bispectrum is positive, consistent with the positive skewness in
  the data and consistent with supergranules preferentially consisting
  of outflows surrounded by a network of inflows. We use the bispectral
  estimates to generate synthetic divergence maps that are very similar to
  the data. This is done by a model that consists of a Gaussian term and
  a weaker quadratic nonlinear component. Using this method, we estimate
  the fraction of the variance in the divergence maps from the nonlinear
  component to be of the order of 4-6%. <BR /> Conclusions: We propose
  that bispectral analysis is useful for understanding the dynamics of
  solar turbulent convection, for example for comparing observations
  and numerical models of supergranular flows. This analysis may also
  be useful to generate synthetic flow fields.

Title: Exploring the latitude and depth dependence of solar Rossby
    waves using ring-diagram analysis
Authors: Proxauf, B.; Gizon, L.; Löptien, B.; Schou, J.; Birch,
   A. C.; Bogart, R. S.
Bibcode: 2020A&A...634A..44P
Altcode: 2019arXiv191202056P
  Context. Global-scale equatorial Rossby waves have recently been
  unambiguously identified on the Sun. Like solar acoustic modes, Rossby
  waves are probes of the solar interior. <BR /> Aims: We study the
  latitude and depth dependence of the Rossby wave eigenfunctions. <BR />
  Methods: By applying helioseismic ring-diagram analysis and granulation
  tracking to observations by HMI aboard SDO, we computed maps of
  the radial vorticity of flows in the upper solar convection zone
  (down to depths of more than 16 Mm). The horizontal sampling of the
  ring-diagram maps is approximately 90 Mm (∼7.5°) and the temporal
  sampling is roughly 27 hr. We used a Fourier transform in longitude
  to separate the different azimuthal orders m in the range 3 ≤ m ≤
  15. At each m we obtained the phase and amplitude of the Rossby waves
  as functions of depth using the helioseismic data. At each m we also
  measured the latitude dependence of the eigenfunctions by calculating
  the covariance between the equator and other latitudes. <BR /> Results:
  We conducted a study of the horizontal and radial dependences of the
  radial vorticity eigenfunctions. The horizontal eigenfunctions are
  complex. As observed previously, the real part peaks at the equator
  and switches sign near ±30°, thus the eigenfunctions show significant
  non-sectoral contributions. The imaginary part is smaller than the real
  part. The phase of the radial eigenfunctions varies by only ±5° over
  the top 15 Mm. The amplitude of the radial eigenfunctions decreases
  by about 10% from the surface down to 8 Mm (the region in which
  ring-diagram analysis is most reliable, as seen by comparing with the
  rotation rate measured by global-mode seismology). <BR /> Conclusions:
  The radial dependence of the radial vorticity eigenfunctions deduced
  from ring-diagram analysis is consistent with a power law down to 8 Mm
  and is unreliable at larger depths. However, the observations provide
  only weak constraints on the power-law exponents. For the real part,
  the latitude dependence of the eigenfunctions is consistent with
  previous work (using granulation tracking). The imaginary part is
  smaller than the real part but significantly nonzero.

Title: An improved multi-ridge fitting method for ring-diagram
    helioseismic analysis
Authors: Nagashima, Kaori; Birch, Aaron C.; Schou, Jesper; Hindman,
   Bradley W.; Gizon, Laurent
Bibcode: 2020A&A...633A.109N
Altcode: 2019arXiv191107772N
  Context. There is a wide discrepancy in current estimates of
  the strength of convection flows in the solar interior obtained
  using different helioseismic methods applied to observations from
  the Helioseismic and Magnetic Imager onboard the Solar Dynamics
  Observatory. The cause for these disparities is not known. <BR />
  Aims: As one step in the effort to resolve this discrepancy, we aim to
  characterize the multi-ridge fitting code for ring-diagram helioseismic
  analysis that is used to obtain flow estimates from local power spectra
  of solar oscillations. <BR /> Methods: We updated the multi-ridge
  fitting code developed by Greer et al. (2014, Sol. Phys., 289, 2823)
  to solve several problems we identified through our inspection of the
  code. In particular, we changed the (1) merit function to account for
  the smoothing of the power spectra, (2) model for the power spectrum,
  and (3) noise estimates. We used Monte Carlo simulations to generate
  synthetic data and to characterize the noise and bias of the updated
  code by fitting these synthetic data. <BR /> Results: The bias in
  the output fit parameters, apart from the parameter describing the
  amplitude of the p-mode resonances in the power spectrum, is below
  what can be measured from the Monte-Carlo simulations. The amplitude
  parameters are underestimated; this is a consequence of choosing to
  fit the logarithm of the averaged power. We defer fixing this problem
  as it is well understood and not significant for measuring flows in the
  solar interior. The scatter in the fit parameters from the Monte-Carlo
  simulations is well-modeled by the formal error estimates from the
  code. <BR /> Conclusions: We document and demonstrate a reliable
  multi-ridge fitting method for ring-diagram analysis. The differences
  between the updated fitting results and the original results are less
  than one order of magnitude and therefore we suspect that the changes
  will not eliminate the aforementioned orders-of-magnitude discrepancy
  in the amplitude of convective flows in the solar interior.

Title: On the latitude dependence of Rossby waves in the Sun
Authors: Proxauf, Bastian Severin Niklas; Gizon, Laurent; Löptien,
   Björn; Schou, Jesper; Birch, Aaron C.; Bogart, Richard S.
Bibcode: 2019AAS...23431801P
Altcode:
  We study the latitude and depth dependence of solar Rossby waves. We
  use horizontal flows from local helioseismology (ring-diagram analysis)
  at different depths in the solar interior. From these we compute maps
  of the radial vorticity. We confirm the existence of solar Rossby waves
  in the sectoral (m = l) power spectra at all depths down to 17 Mm below
  the surface. The depth dependence of the eigenfunctions is consistent
  with r<SUP>m</SUP>, although this is a weak constraint due to the noise
  level. The latitudinal eigenfunctions are observed to be more narrow
  than |sin(θ)|<SUP>m</SUP>, likely indicating that the modes sense the
  latitudinal differential rotation. Furthermore, we detect a non-zero
  imaginary component of the latitudinal eigenfunctions, possibly related
  to viscous dissipation. These new observations provide additional
  constraints on the physics of large-scale Rossby waves in the Sun.

Title: Towards improved multi-ridge fitting method for ring-diagram
    analysis
Authors: Nagashima, Kaori; Birch, Aaron C.; Schou, Jesper; Hindman,
   Bradley; Gizon, Laurent
Bibcode: 2018csc..confE..50N
Altcode:
  Ring-diagram analysis is one of the important methods of local
  helioseismology for probing subsurface flows. In ring-diagram analysis
  the Doppler shifts of oscillation mode frequencies due to flows
  are measured by fitting a model function to the local oscillation
  power spectra. Here we propose alteration of the multi-ridge fitting
  method developed by Greer et al. (2014). It is well known that the
  solar oscillation power is chi-square distributed (with two degrees
  of freedom), and the fitting in the existing multi-ridge fitting is
  done with the maximum likelihood method based on this probability
  distribution function. However, the power is in practice remapped
  from Cartesian to polar coordinates and/or smoothed in azimuth
  of the wavevector. The smoothed power is approximately normally
  distributed. We demonstrate that the probability distribution function
  of the logarithm of the normally-distributed power is approximated
  by a normal distribution with a variance that is independent of the
  expectation value of the power. Therefore, we alter the fitting method
  using the logarithm of the power with a least-square method. In this
  presentation we report the bias and noise levels in the updated fitting
  results as well as the crosstalk between the parameters using a Monte
  Carlo simulation of the power spectra.

Title: HMI Data Corrected for Scattered Light Compared to Hinode
    SOT-SP Data
Authors: Norton, A. A.; Duvall, T. L., Jr.; Schou, J.; Cheung,
   M. C. M.; Scherrer, P. H.; Chu, K. C.; Sommers, J.
Bibcode: 2018csc..confE.101N
Altcode:
  In March 2018, the Helioseismic Magnetic Imager (HMI) team began
  providing full-disk data to the public on a daily basis that were
  corrected for scattered light. In addition to the intensity and
  magnetogram data, the improved vector magnetic field maps are also
  provided. The process uses a Richardson-Lucy algorithm and a known
  PSF. The deconvolution results in a few percent decrease in umbral
  intensity corresponding to a 200 K decrease in temperature, a doubling
  of the intensity contrast of granulation from 3.6 to 7.2%, an increase
  in total field strength values (not only line-of-sight B) in plage by
  1.4, faculae brightening and network darkening, and a partial correction
  for the convective blue-shift. The new data series can be found in
  JSOC with names similar to the original but with the qualifying term
  '_dcon' or '_dconS' appended (denoting whether the deconvolution
  was applied to the filtergrams or Stokes images). Comparisons to
  near-simultaneous Hinode SOT-SP data demonstrate that the correction
  brings the two instruments into much better agreement, including the
  inverted magnetic field parameters. We compare our results to similar
  efforts in the literature such as work by Diaz Baso and Asensio Ramos
  (2018) in which HMI intensity and magnetogram data was enhanced using
  neural networks and super-resolution.

Title: On the depth dependence of solar equatorial Rossby waves
Authors: Proxauf, Bastian; Gizon, Laurent; Löptien, Björn; Birch,
   Aaron C.; Schou, Jesper; Bogart, Richard S.
Bibcode: 2018csc..confE..43P
Altcode:
  Here we use local helioseismology and local correlation tracking of
  granulation to infer horizontal flows on the solar surface and in the
  interior. From these flows, we compute maps of the radial vorticity
  at different depths in order to study Rossby waves. We show that
  the frequencies of these waves agree well with a simple theoretical
  dispersion relation. Also, we show that Rossby waves have significant
  amplitudes in the first 20 Mm below the surface and investigate
  the dependence of the Rossby waves on depth. We find an unexpected,
  presumably spurious dip in the wave power and a depth-independent
  phase and we conclude that further studies are needed.

Title: Interactions of waves with solar convection
Authors: Schou, Jesper
Bibcode: 2018csc..confE..47S
Altcode:
  Some of the most significant problems in our understanding of solar and
  stellar oscillations are believed to be related to their interaction
  with the near surface convection. One such problem is the center
  to limb effect seen in many helioseismic measurements. Another the
  so-called surface term. Here I will briefly describe these problems
  and some preliminary results of trying to address them using large
  scale hydrocode simulations.

Title: Modeling and use of stellar oscillation visibilities
Authors: Schou, J.
Bibcode: 2018A&A...617A.111S
Altcode: 2018arXiv180601055S
  Context. Recently our ability to study stars using asteroseismic
  techniques has increased dramatically, largely through the use of
  space based photometric observations. Work has also been performed
  using ground based spectroscopic observations and more is expected in
  the near future from the SONG network. Unfortunately, the intensity
  observations have an inferior signal-to-noise ratio and details of
  the observations do not agree with theory, while the data analysis
  used in the spectroscopic method has often been based on overly
  simple models of the spectra. <BR /> Aims: The aim is to improve the
  reliability of measurements of the parameters of stellar oscillations
  using spectroscopic observations and to enable the optimal use of the
  observations. <BR /> Methods: While previous investigations have used
  1D models, I argue that realistic magnetohydrodynamic simulations,
  combined with radiative transfer calculations, should be used to model
  the effects of the oscillations on the spectra. I then demonstrate how
  to calculate the visibility of the oscillation modes for a variety of
  stellar parameters and fitting methods. In addition to the methods used
  in previous investigations, I introduce a singular value decomposition
  based technique. This new technique enables the determination of the
  information content available from spectral perturbations and allows
  this content to be expressed most compactly. Finally I describe how
  the time series obtained may be analyzed. <BR /> Results: It is shown
  that it is important to model the visibilities carefully and that the
  results deviate substantially from previous models, especially in the
  presence of rotation. Detailed spectral modeling may be exploited to
  measure the properties of a larger number of modes than possible via
  the commonly used cross-correlation method. With moderate rotation,
  there is as much information in the line shape changes as in the
  Doppler shift and an outline of how to extract this is given.

Title: Autonomous on-board data processing and instrument calibration
    software for the SO/PHI
Authors: Albert, K.; Hirzberger, J.; Busse, D.; Lange, T.; Kolleck, M.;
   Fiethe, B.; Orozco Suárez, D.; Woch, J.; Schou, J.; Blanco Rodriguez,
   J.; Gandorfer, A.; Guan, Y.; Cobos Carrascosa, J. P.; Hernández
   Expósito, D.; del Toro Iniesta, J. C.; Solanki, S. K.; Michalik, H.
Bibcode: 2018SPIE10707E..0OA
Altcode: 2018arXiv181003493A
  The extension of on-board data processing capabilities is an
  attractive option to reduce telemetry for scientific instruments
  on deep space missions. The challenges that this presents, however,
  require a comprehensive software system, which operates on the limited
  resources a data processing unit in space allows. We implemented such
  a system for the Polarimetric and Helioseismic Imager (PHI) on-board
  the Solar Orbiter (SO) spacecraft. It ensures autonomous operation
  to handle long command-response times, easy changing of the processes
  after new lessons have been learned and meticulous book-keeping of all
  operations to ensure scientific accuracy. This contribution presents
  the requirements and main aspects of the software implementation,
  followed by an example of a task implemented in the software frame,
  and results from running it on SO/PHI. The presented example shows
  that the different parts of the software framework work well together,
  and that the system processes data as we expect. The flexibility of
  the framework makes it possible to use it as a baseline for future
  applications with similar needs and limitations as SO/PHI.

Title: Signatures of Solar Cycle 25 in Subsurface Zonal Flows
Authors: Howe, R.; Hill, F.; Komm, R.; Chaplin, W. J.; Elsworth, Y.;
   Davies, G. R.; Schou, J.; Thompson, M. J.
Bibcode: 2018ApJ...862L...5H
Altcode: 2018arXiv180702398H
  The pattern of migrating zonal flow bands associated with the solar
  cycle, known as the torsional oscillation, has been monitored with
  continuous global helioseismic observations by the Global Oscillations
  Network Group (GONG), together with those made by the Michelson
  Doppler Imager (MDI) on board the Solar and Heliospheric Observatory
  (SOHO) and its successor, the Helioseismic and Magnetic Imager (HMI)
  on board the Solar Dynamics Observatory (SDO), since 1995, giving us
  nearly two full solar cycles of observations. We report that the flows
  now show traces of the mid-latitude acceleration that is expected to
  become the main equatorward-moving branch of the zonal flow pattern for
  Cycle 25. Based on the current position of this branch, we speculate
  that the onset of widespread activity for Cycle 25 is unlikely to be
  earlier than the middle of 2019.

Title: Fragile Detection of Solar g -Modes by Fossat et al.
Authors: Schunker, Hannah; Schou, Jesper; Gaulme, Patrick; Gizon,
   Laurent
Bibcode: 2018SoPh..293...95S
Altcode: 2018arXiv180404407S
  The internal gravity modes of the Sun are notoriously difficult to
  detect, and the claimed detection of gravity modes presented by Fossat
  et al. (Astron. Astrophys.604, A40, 2017) is thus very exciting. Given
  the importance of these modes for understanding solar structure and
  dynamics, the results must be robust. While Fossat et al. described
  their method and parameter choices in detail, the sensitivity of their
  results to several parameters was not presented. Therefore, we test the
  sensitivity of the results to a selection of the parameters. The most
  concerning result is that the detection vanishes when we adjust the
  start time of the 16.5-year velocity time-series by a few hours. We
  conclude that this reported detection of gravity modes is extremely
  fragile and should be treated with utmost caution.

Title: Global-scale equatorial Rossby waves as an essential component
    of solar internal dynamics
Authors: Löptien, Björn; Gizon, Laurent; Birch, Aaron C.; Schou,
   Jesper; Proxauf, Bastian; Duvall, Thomas L.; Bogart, Richard S.;
   Christensen, Ulrich R.
Bibcode: 2018NatAs...2..568L
Altcode: 2018NatAs.tmp...54L; 2018arXiv180507244L
  The Sun's complex dynamics is controlled by buoyancy and rotation
  in the convection zone. Large-scale flows are dominated by vortical
  motions<SUP>1</SUP> and appear to be weaker than expected in the solar
  interior<SUP>2</SUP>. One possibility is that waves of vorticity
  due to the Coriolis force, known as Rossby waves<SUP>3</SUP> or
  r modes<SUP>4</SUP>, remove energy from convection at the largest
  scales<SUP>5</SUP>. However, the presence of these waves in the Sun
  is still debated. Here, we unambiguously discover and characterize
  retrograde-propagating vorticity waves in the shallow subsurface layers
  of the Sun at azimuthal wavenumbers below 15, with the dispersion
  relation of textbook sectoral Rossby waves. The waves have lifetimes
  of several months, well-defined mode frequencies below twice the solar
  rotational frequency, and eigenfunctions of vorticity that peak at the
  equator. Rossby waves have nearly as much vorticity as the convection
  at the same scales, thus they are an essential component of solar
  dynamics. We observe a transition from turbulence-like to wave-like
  dynamics around the Rhines scale<SUP>6</SUP> of angular wavenumber
  of approximately 20. This transition might provide an explanation for
  the puzzling deficit of kinetic energy at the largest spatial scales.

Title: On-Orbit Performance of the Helioseismic and Magnetic Imager
    Instrument onboard the Solar Dynamics Observatory
Authors: Hoeksema, J. T.; Baldner, C. S.; Bush, R. I.; Schou, J.;
   Scherrer, P. H.
Bibcode: 2018SoPh..293...45H
Altcode: 2018arXiv180201731H
  The Helioseismic and Magnetic Imager (HMI) instrument is a major
  component of NASA's Solar Dynamics Observatory (SDO) spacecraft. Since
  commencement of full regular science operations on 1 May 2010, HMI
  has operated with remarkable continuity, e.g. during the more than
  five years of the SDO prime mission that ended 30 September 2015, HMI
  collected 98.4% of all possible 45-second velocity maps; minimizing gaps
  in these full-disk Dopplergrams is crucial for helioseismology. HMI
  velocity, intensity, and magnetic-field measurements are used in
  numerous investigations, so understanding the quality of the data is
  important. This article describes the calibration measurements used
  to track the performance of the HMI instrument, and it details trends
  in important instrument parameters during the prime mission. Regular
  calibration sequences provide information used to improve and update the
  calibration of HMI data. The set-point temperature of the instrument
  front window and optical bench is adjusted regularly to maintain
  instrument focus, and changes in the temperature-control scheme have
  been made to improve stability in the observable quantities. The
  exposure time has been changed to compensate for a 20% decrease in
  instrument throughput. Measurements of the performance of the shutter
  and tuning mechanisms show that they are aging as expected and continue
  to perform according to specification. Parameters of the tunable
  optical-filter elements are regularly adjusted to account for drifts
  in the central wavelength. Frequent measurements of changing CCD-camera
  characteristics, such as gain and flat field, are used to calibrate the
  observations. Infrequent expected events such as eclipses, transits,
  and spacecraft off-points interrupt regular instrument operations and
  provide the opportunity to perform additional calibration. Onboard
  instrument anomalies are rare and seem to occur quite uniformly in
  time. The instrument continues to perform very well.

Title: Global-Mode Analysis of Full-Disk Data from the Michelson
    Doppler Imager and the Helioseismic and Magnetic Imager
Authors: Larson, Timothy P.; Schou, Jesper
Bibcode: 2018SoPh..293...29L
Altcode:
  Building upon our previous work, in which we analyzed smoothed and
  subsampled velocity data from the Michelson Doppler Imager (MDI),
  we extend our analysis to unsmoothed, full-resolution MDI data. We
  also present results from the Helioseismic and Magnetic Imager
  (HMI), in both full resolution and processed to be a proxy for the
  low-resolution MDI data. We find that the systematic errors that we saw
  previously, namely peaks in both the high-latitude rotation rate and
  the normalized residuals of odd a -coefficients, are almost entirely
  absent in the two full-resolution analyses. Furthermore, we find that
  both systematic errors seem to depend almost entirely on how the input
  images are apodized, rather than on resolution or smoothing. Using the
  full-resolution HMI data, we confirm our previous findings regarding the
  effect of using asymmetric profiles on mode parameters, and also find
  that they occasionally result in more stable fits. We also confirm
  our previous findings regarding discrepancies between 360-day and
  72-day analyses. We further investigate a six-month period previously
  seen in f -mode frequency shifts using the low-resolution datasets,
  this time accounting for solar-cycle dependence using magnetic-field
  data. Both HMI and MDI saw prominent six-month signals in the frequency
  shifts, but we were surprised to discover that the strongest signal
  at that frequency occurred in the mode coverage for the low-resolution
  proxy. Finally, a comparison of mode parameters from HMI and MDI shows
  that the frequencies and a -coefficients agree closely, encouraging
  the concatenation of the two datasets.

Title: Measuring solar active region inflows with local correlation
    tracking of granulation
Authors: Löptien, B.; Birch, A. C.; Duvall, T. L.; Gizon, L.; Proxauf,
   B.; Schou, J.
Bibcode: 2017A&A...606A..28L
Altcode: 2017arXiv170508833L
  Context. Sixteen years ago local helioseismology detected spatially
  extended converging surface flows into solar active regions. These
  flows play an important role in flux-transport models of the solar
  dynamo. <BR /> Aims: We aim to validate the existence of the inflows by
  deriving horizontal flow velocities around active regions with local
  correlation tracking of granulation. <BR /> Methods: We generate a
  six-year time series of full-disk maps of the horizontal velocity at
  the solar surface by tracking granules in continuum intensity images
  provided by the Helioseismic and Magnetic Imager (HMI) on board
  the Solar Dynamics Observatory (SDO). <BR /> Results: On average,
  active regions are surrounded by inflows extending up to 10° from
  the center of the active region of magnitudes of 20-30 m/s, reaching
  locally up to 40 m/s, which is in agreement with results from local
  helioseismology. By computing an ensemble average consisting of 243
  individual active regions, we show that the inflows are not azimuthally
  symmetric, but converge predominantly towards the trailing polarity
  of the active region with respect to the longitudinally and temporally
  averaged flow field.

Title: Stray Light Correction of HMI Data
Authors: Norton, Aimee Ann; Duvall, Thomas; Schou, Jesper; Cheung,
   Mark; Scherrer, Philip H.
Bibcode: 2017SPD....4820705N
Altcode:
  The point spread function (PSF) for HMI is an Airy function convolved
  with a Lorentzian. The parameters are bound by ground-based testing
  before launch, then post-launch off-limb light curves, lunar eclipse
  and Venus transit data. The PSF correction is programmed in C and runs
  within the HMI data processing pipeline environment. A single full-disk
  intensity image can be processed in less than one second. Deconvolution
  of the PSF on the Stokes profile data (a linear combination of
  original filtergrms) is less computationally expensive and is shown
  to be equivalent to deconvolution applied at the original filtergram
  level. Results include a decrease in umbral darkness of a few percent
  (~200 K cooler), a doubling of the granulation contrast in intensity
  from 3.6 to 7.2%, an increase in plage field strengths by a factor of
  1.5, and a partial correction of the convective blueshift in Doppler
  velocities. Requests for data corrected for stray light are welcome
  and will be processed by the HMI team.

Title: Interactions of Oscillations with Near Surface Convection
Authors: Schou, Jesper
Bibcode: 2017SPD....4840101S
Altcode:
  There are a number of large but unexplained effects in helioseismic
  observations. One is the so-called surface effect, which manifests
  itself as a difference between the theoretical and observed frequencies,
  and which appears to originate close to the surface. Another is a large
  apparent phase shift in the oscillations depending on the center-to-limb
  distance and the observable used.Both of these effects are likely due
  to interactions of the waves with the near surface convection.Here
  I will discuss one of the directly observable consequences of these
  interactions, namely the change in the properties of the modes depending
  on where in the granulation they are observed. To that end I will use
  both observations from HMI and results from hydrodynamic simulations.

Title: Comparison of acoustic travel-time measurement of solar
    meridional circulation from SDO/HMI and SOHO/MDI
Authors: Duvall, Thomas L.; Liang, Zhi-Chao; Birch, Aaron; Gizon,
   Laurent; Schou, Jesper
Bibcode: 2017SPD....4840103D
Altcode:
  Time-distance helioseismology is one of the primary tools for studying
  the solar meridional circulation. However, travel-time measurements
  of the subsurface meridional flow suffer from a variety of systematic
  errors, such as a center-to-limb variation and an offset due to the
  P-angle uncertainty of solar images. Here we apply the time-distance
  technique to contemporaneous medium-degree Dopplergrams produced by
  SOHO/MDI and SDO/HMI to obtain the travel-time difference caused by
  meridional circulation throughout the solar convection zone. The P-angle
  offset in MDI images is measured by cross-correlating MDI and HMI
  images. The travel-time measurements in the south-north and east-west
  directions are averaged over the same observation period for the two
  data sets and then compared to examine the consistency of MDI and HMI
  travel times after correcting the systematic errors.The offsets in the
  south-north travel-time difference from MDI data induced by the P-angle
  error gradually diminish with increasing travel distance. However,
  these offsets become noisy for travel distances corresponding to
  waves that reach the base of the convection zone. This suggests that
  a careful treatment of the P-angle problem is required when studying a
  deep meridional flow. After correcting the P-angle and the removal of
  the center-to-limb effect, the travel-time measurements from MDI and
  HMI are consistent within the error bars for meridional circulation
  covering the entire convection zone. The fluctuations observed in both
  data sets are highly correlated and thus indicate their solar origin
  rather than an instrumental origin. Although our results demonstrate
  that the ad hoc correction is capable of reducing the wide discrepancy
  in the travel-time measurements from MDI and HMI, we cannot exclude
  the possibility that there exist other systematic effects acting on
  the two data sets in the same way.

Title: Limits on radial differential rotation in Sun-like stars from
    parametric fits to oscillation power spectra
Authors: Nielsen, M. B.; Schunker, H.; Gizon, L.; Schou, J.; Ball,
   W. H.
Bibcode: 2017A&A...603A...6N
Altcode: 2017arXiv170510517N
  Context. Rotational shear in Sun-like stars is thought to be
  an important ingredient in models of stellar dynamos. Thanks to
  helioseismology, rotation in the Sun is characterized well, but the
  interior rotation profiles of other Sun-like stars are not so well
  constrained. Until recently, measurements of rotation in Sun-like stars
  have focused on the mean rotation, but little progress has been made on
  measuring or even placing limits on differential rotation. <BR /> Aims:
  Using asteroseismic measurements of rotation we aim to constrain the
  radial shear in five Sun-like stars observed by the NASA Kepler mission:
  <ASTROBJ>KIC 004914923</ASTROBJ>, <ASTROBJ>KIC 005184732</ASTROBJ>,
  <ASTROBJ>KIC 006116048</ASTROBJ>, <ASTROBJ>KIC 006933899</ASTROBJ>,
  and <ASTROBJ>KIC 010963065</ASTROBJ>. <BR /> Methods: We used stellar
  structure models for these five stars from previous works. These models
  provide the mass density, mode eigenfunctions, and the convection
  zone depth, which we used to compute the sensitivity kernels for the
  rotational frequency splitting of the modes. We used these kernels as
  weights in a parametric model of the stellar rotation profile of each
  star, where we allowed different rotation rates for the radiative
  interior and the convective envelope. This parametric model was
  incorporated into a fit to the oscillation power spectrum of each
  of the five Kepler stars. This fit included a prior on the rotation
  of the envelope, estimated from the rotation of surface magnetic
  activity measured from the photometric variability. <BR /> Results:
  The asteroseismic measurements without the application of priors are
  unable to place meaningful limits on the radial shear. Using a prior
  on the envelope rotation enables us to constrain the interior rotation
  rate and thus the radial shear. In the five cases that we studied,
  the interior rotation rate does not differ from the envelope by more
  than approximately ± 30%. Uncertainties in the rotational splittings
  are too large to unambiguously determine the sign of the radial shear.

Title: Comparison of acoustic travel-time measurements of solar
    meridional circulation from SDO/HMI and SOHO/MDI
Authors: Liang, Zhi-Chao; Birch, Aaron C.; Duvall, Thomas L., Jr.;
   Gizon, Laurent; Schou, Jesper
Bibcode: 2017A&A...601A..46L
Altcode: 2017arXiv170400475L
  Context. Time-distance helioseismology is one of the primary tools
  for studying the solar meridional circulation, especially in the lower
  convection zone. However, travel-time measurements of the subsurface
  meridional flow suffer from a variety of systematic errors, such as
  a center-to-limb variation and an offset due to the position angle
  (P-angle) uncertainty of solar images. It has been suggested that the
  center-to-limb variation can be removed by subtracting east-west from
  south-north travel-time measurements. This ad hoc method for the removal
  of the center-to-limb effect has been adopted widely but not tested
  for travel distances corresponding to the lower convection zone. <BR
  /> Aims: We explore the effects of two major sources of the systematic
  errors, the P-angle error arising from the instrumental misalignment and
  the center-to-limb variation, on the acoustic travel-time measurements
  in the south-north direction. <BR /> Methods: We apply the time-distance
  technique to contemporaneous medium-degree Dopplergrams produced by
  SOHO/MDI and SDO/HMI to obtain the travel-time difference caused by
  meridional circulation throughout the solar convection zone. The
  P-angle offset in MDI images is measured by cross-correlating MDI
  and HMI images. The travel-time measurements in the south-north and
  east-west directions are averaged over the same observation period
  (May 2010 to Apr. 2011) for the two data sets and then compared to
  examine the consistency of MDI and HMI travel times after applying
  the above-mentioned corrections. <BR /> Results: The offsets in the
  south-north travel-time difference from MDI data induced by the P-angle
  error gradually diminish with increasing travel distance. However,
  these offsets become noisy for travel distances corresponding to
  waves that reach the base of the convection zone. This suggests that
  a careful treatment of the P-angle problem is required when studying a
  deep meridional flow. After correcting the P-angle and the removal of
  the center-to-limb effect, the travel-time measurements from MDI and
  HMI are consistent within the error bars for meridional circulation
  covering the entire convection zone. The fluctuations observed in both
  data sets are highly correlated and thus indicate their solar origin
  rather than an instrumental origin. Although our results demonstrate
  that the ad hoc correction is capable of reducing the wide discrepancy
  in the travel-time measurements from MDI and HMI, we cannot exclude
  the possibility that there exist other systematic effects acting on
  the two data sets in the same way.

Title: Solar Dynamics, Rotation, Convection and Overshoot
Authors: Hanasoge, S.; Miesch, M. S.; Roth, M.; Schou, J.; Schüssler,
   M.; Thompson, M. J.
Bibcode: 2017hdsi.book...85H
Altcode:
  No abstract at ADS

Title: Helioseismology with Solar Orbiter
Authors: Löptien, Björn; Birch, Aaron C.; Gizon, Laurent; Schou,
   Jesper; Appourchaux, Thierry; Blanco Rodríguez, Julián; Cally,
   Paul S.; Dominguez-Tagle, Carlos; Gandorfer, Achim; Hill, Frank;
   Hirzberger, Johann; Scherrer, Philip H.; Solanki, Sami K.
Bibcode: 2017hdsi.book..257L
Altcode:
  No abstract at ADS

Title: Far side Helioseismology with Solar Orbiter
Authors: Appourchaux, T.; Birch, A.; Gizon, L. C.; Löptien, B.;
   Schou, J.; Solanki, S. K.; del Toro Iniesta, J. C.; Gandorfer, A.;
   Hirzberger, J.; Alvarez-Herrero, A.; Woch, J. G.; Schmidt, W.
Bibcode: 2016AGUFMSH43A2554A
Altcode:
  The Solar Orbiter mission, to be launched in October 2018, will
  carry a suite of remote sensing and in-situ instruments, including
  the Polarimetric and Helioseismic Imager (PHI). PHI will deliver
  high-cadence images of the Sun in intensity and Doppler velocity
  suitable for carrying out novel helioseismic studies. The orbit
  of the Solar Orbiter spacecraft will reach a solar latitude up to
  34 degrees by the end of the extended mission and thus will enable
  the first local helioseismology studies of the polar regions. The
  full range of Earth-Sun-spacecraft angles provided by the orbit will
  enable helioseismology from two vantage points by combining PHI with
  another instrument: stereoscopic helioseismology will allow the study
  of the deep solar interior and a better understanding of the physics
  of solar oscillations in both quiet Sun and sunspots. In this paper
  we will review the helioseismic objectives achievable with PHI, and
  will also give a short status report of the development of the Flight
  Model of PHI.

Title: The Efffect of Image Apodization on Global Mode Parameters
    and Rotational Inversions
Authors: Larson, Tim; Schou, Jesper
Bibcode: 2016usc..confE.127L
Altcode:
  It has long been known that certain systematic errors in the global mode
  analysis of data from both MDI and HMI depend on how the input images
  were apodized. Recently it has come to light, while investigating a
  six-month period in f-mode frequencies, that mode coverage is highest
  when B0 is maximal. Recalling that the leakage matrix is calculated in
  the approximation that B0=0, it comes as a surprise that more modes are
  fitted when the leakage matrix is most incorrect. It is now believed
  that the six-month oscillation has primarily to do with what portion
  of the solar surface is visible. Other systematic errors that depend
  on the part of the disk used include high-latitude anomalies in the
  rotation rate and a prominent feature in the normalized residuals
  of odd a-coefficients. Although the most likely cause of all these
  errors is errors in the leakage matrix, extensive recalculation
  of the leaks has not made any difference. Thus we conjecture that
  another effect may be at play, such as errors in the noise model or
  one that has to do with the alignment of the apodization with the
  spherical harmonics. In this poster we explore how differently shaped
  apodizations affect the results of inversions for internal rotation,
  for both maximal and minimal absolute values of B0.

Title: Solar-cycle variation of the rotational shear near the
    solar surface
Authors: Barekat, A.; Schou, J.; Gizon, L.
Bibcode: 2016A&A...595A...8B
Altcode: 2016arXiv160807101B
  Context. Helioseismology has revealed that the angular velocity of the
  Sun increases with depth in the outermost 35 Mm of the Sun. Recently,
  we have shown that the logarithmic radial gradient (dlnΩ/dlnr) in the
  upper 10 Mm is close to -1 from the equator to 60° latitude. <BR />
  Aims: We aim to measure the temporal variation of the rotational shear
  over solar cycle 23 and the rising phase of cycle 24 (1996-2015). <BR
  /> Methods: We used f mode frequency splitting data spanning 1996 to
  2011 from the Michelson Doppler Imager (MDI) and 2010 to 2015 from
  the Helioseismic Magnetic Imager (HMI). In a first for such studies,
  the f mode frequency splitting data were obtained from 360-day time
  series. We used the same method as in our previous work for measuring
  dlnΩ/dlnr from the equator to 80° latitude in the outer 13 Mm of
  the Sun. Then, we calculated the variation of the gradient at annual
  cadence relative to the average over 1996 to 2015. <BR /> Results:
  We found the rotational shear at low latitudes (0° to 30°) to vary
  in-phase with the solar activity, varying by ~± 10% over the period
  1996 to 2015. At high latitudes (60° to 80°), we found rotational
  shear to vary in anti-phase with the solar activity. By comparing
  the radial gradient obtained from the splittings of the 360-day and
  the corresponding 72-day time series of HMI and MDI data, we suggest
  that the splittings obtained from the 72-day HMI time series suffer
  from systematic errors. <BR /> Conclusions: We provide a quantitative
  measurement of the temporal variation of the outer part of the near
  surface shear layer which may provide useful constraints on dynamo
  models and differential rotation theory.

Title: HMI Data Corrected for Stray Light Now Available
Authors: Norton, A. A.; Duvall, T. L.; Schou, J.; Cheung, M. C. M.;
   Scherrer, P. H.
Bibcode: 2016usc..confE..95N
Altcode:
  The form of the point spread function (PSF) derived for HMI is an
  Airy function convolved with a Lorentzian. The parameters are bound
  by observational ground-based testing of the instrument conducted
  prior to launch (Wachter et al., 2012), by full-disk data used to
  evaluate the off-limb behavior of the scattered light, as well as by
  data obtained during the Venus transit. The PSF correction has been
  programmed in both C and cuda C and runs within the JSOC environment
  using either a CPU or GPU. A single full-disk intensity image can
  be deconvolved in less than one second. The PSF is described in more
  detail in Couvidat et al. (2016) and has already been used by Hathaway
  et al. (2015) to forward-model solar-convection spectra, by Krucker et
  al. (2015) to investigate footpoints of off-limb solar flares and by
  Whitney, Criscuoli and Norton (2016) to examine the relations between
  intensity contrast and magnetic field strengths. In this presentation,
  we highlight the changes to umbral darkness, granulation contrast
  and plage field strengths that result from stray light correction. A
  twenty-four hour period of scattered-light corrected HMI data from
  2010.08.03, including the isolated sunspot NOAA 11092, is currently
  available for anyone. Requests for additional time periods of interest
  are welcome and will be processed by the HMI team.

Title: Observables Processing for the Helioseismic and Magnetic
    Imager Instrument on the Solar Dynamics Observatory
Authors: Couvidat, S.; Schou, J.; Hoeksema, J. T.; Bogart, R. S.;
   Bush, R. I.; Duvall, T. L.; Liu, Y.; Norton, A. A.; Scherrer, P. H.
Bibcode: 2016SoPh..291.1887C
Altcode: 2016SoPh..tmp..120C; 2016arXiv160602368C
  NASA's Solar Dynamics Observatory (SDO) spacecraft was launched
  11 February 2010 with three instruments onboard, including the
  Helioseismic and Magnetic Imager (HMI). After commissioning, HMI
  began normal operations on 1 May 2010 and has subsequently observed
  the Sun's entire visible disk almost continuously. HMI collects
  sequences of polarized filtergrams taken at a fixed cadence with two
  4096 ×4096 cameras, from which are computed arcsecond-resolution maps
  of photospheric observables that include line-of-sight velocity and
  magnetic field, continuum intensity, line width, line depth, and the
  Stokes polarization parameters [I ,Q ,U ,V ]. Two processing pipelines
  have been implemented at the SDO Joint Science Operations Center (JSOC)
  at Stanford University to compute these observables from calibrated
  Level-1 filtergrams, one that computes line-of-sight quantities every
  45 seconds and the other, primarily for the vector magnetic field, that
  computes averages on a 720-second cadence. Corrections are made for
  static and temporally changing CCD characteristics, bad pixels, image
  alignment and distortion, polarization irregularities, filter-element
  uncertainty and nonuniformity, as well as Sun-spacecraft velocity. We
  detail the functioning of these two pipelines, explain known issues
  affecting the measurements of the resulting physical quantities,
  and describe how regular updates to the instrument calibration impact
  them. We also describe how the scheme for computing the observables
  is optimized for actual HMI observations. Initial calibration of
  HMI was performed on the ground using a variety of light sources and
  calibration sequences. During the five years of the SDO prime mission,
  regular calibration sequences have been taken on orbit to improve and
  regularly update the instrument calibration, and to monitor changes
  in the HMI instrument. This has resulted in several changes in the
  observables processing that are detailed here. The instrument more
  than satisfies all of the original specifications for data quality and
  continuity. The procedures described here still have significant room
  for improvement. The most significant remaining systematic errors are
  associated with the spacecraft orbital velocity.

Title: Nominal Values for Selected Solar and Planetary Quantities:
    IAU 2015 Resolution B3
Authors: Prša, Andrej; Harmanec, Petr; Torres, Guillermo; Mamajek,
   Eric; Asplund, Martin; Capitaine, Nicole; Christensen-Dalsgaard,
   Jørgen; Depagne, Éric; Haberreiter, Margit; Hekker, Saskia; Hilton,
   James; Kopp, Greg; Kostov, Veselin; Kurtz, Donald W.; Laskar, Jacques;
   Mason, Brian D.; Milone, Eugene F.; Montgomery, Michele; Richards,
   Mercedes; Schmutz, Werner; Schou, Jesper; Stewart, Susan G.
Bibcode: 2016AJ....152...41P
Altcode: 2016arXiv160509788P
  In this brief communication we provide the rationale for and the
  outcome of the International Astronomical Union (IAU) resolution
  vote at the XXIXth General Assembly in Honolulu, Hawaii, in 2015,
  on recommended nominal conversion constants for selected solar and
  planetary properties. The problem addressed by the resolution is a lack
  of established conversion constants between solar and planetary values
  and SI units: a missing standard has caused a proliferation of solar
  values (e.g., solar radius, solar irradiance, solar luminosity, solar
  effective temperature, and solar mass parameter) in the literature,
  with cited solar values typically based on best estimates at the time
  of paper writing. As precision of observations increases, a set of
  consistent values becomes increasingly important. To address this, an
  IAU Working Group on Nominal Units for Stellar and Planetary Astronomy
  formed in 2011, uniting experts from the solar, stellar, planetary,
  exoplanetary, and fundamental astronomy, as well as from general
  standards fields to converge on optimal values for nominal conversion
  constants. The effort resulted in the IAU 2015 Resolution B3, passed at
  the IAU General Assembly by a large majority. The resolution recommends
  the use of nominal solar and planetary values, which are by definition
  exact and are expressed in SI units. These nominal values should be
  understood as conversion factors only, not as the true solar/planetary
  properties or current best estimates. Authors and journal editors are
  urged to join in using the standard values set forth by this resolution
  in future work and publications to help minimize further confusion.

Title: The shrinking Sun: A systematic error in local correlation
    tracking of solar granulation
Authors: Löptien, B.; Birch, A. C.; Duvall, T. L.; Gizon, L.;
   Schou, J.
Bibcode: 2016A&A...590A.130L
Altcode: 2016arXiv160404469L
  Context. Local correlation tracking of granulation (LCT) is an important
  method for measuring horizontal flows in the photosphere. This method
  exhibits a systematic error that looks like a flow converging toward
  disk center, which is also known as the shrinking-Sun effect. <BR
  /> Aims: We aim to study the nature of the shrinking-Sun effect for
  continuum intensity data and to derive a simple model that can explain
  its origin. <BR /> Methods: We derived LCT flow maps by running the
  LCT code Fourier Local Correlation Tracking (FLCT) on tracked and
  remapped continuum intensity maps provided by the Helioseismic and
  Magnetic Imager (HMI) onboard the Solar Dynamics Observatory (SDO). We
  also computed flow maps from synthetic continuum images generated from
  STAGGER code simulations of solar surface convection. We investigated
  the origin of the shrinking-Sun effect by generating an average
  granule from synthetic data from the simulations. <BR /> Results: The
  LCT flow maps derived from the HMI data and the simulations exhibit
  a shrinking-Sun effect of comparable magnitude. The origin of this
  effect is related to the apparent asymmetry of granulation originating
  from radiative transfer effects when observing with a viewing angle
  inclined from vertical. This causes, in combination with the expansion
  of the granules, an apparent motion toward disk center.

Title: On HMI's Mod-L Sequence: Test and Evaluation
Authors: Liu, Yang; Baldner, Charles; Bogart, R. S.; Bush, R.;
   Couvidat, S.; Duvall, Thomas L.; Hoeksema, Jon Todd; Norton, Aimee Ann;
   Scherrer, Philip H.; Schou, Jesper
Bibcode: 2016SPD....47.0810L
Altcode:
  HMI Mod-L sequence can produce full Stokes parameters at a cadence of 90
  seconds by combining filtergrams from both cameras, the front camera and
  the side camera. Within the 90-second, the front camera takes two sets
  of Left and Right Circular Polarizations (LCP and RCP) at 6 wavelengths;
  the side camera takes one set of Linear Polarizations (I+/-Q and I+/-U)
  at 6 wavelengths. By combining two cameras, one can obtain full Stokes
  parameters of [I,Q,U,V] at 6 wavelengths in 90 seconds. In norminal
  Mod-C sequence that HMI currently uses, the front camera takes LCP and
  RCP at a cadence of 45 seconds, while the side camera takes observation
  of the full Stokes at a cadence of 135 seconds. Mod-L should be
  better than Mod-C for providing vector magnetic field data because
  (1) Mod-L increases cadence of full Stokes observation, which leads
  to higher temporal resolution of vector magnetic field measurement;
  (2) decreases noise in vector magnetic field data because it uses
  more filtergrams to produce [I,Q,U,V]. There are two potential issues
  in Mod-L that need to be addressed: (1) scaling intensity of the two
  cameras’ filtergrams; and (2) if current polarization calibration
  model, which is built for each camera separately, works for the combined
  data from both cameras. This presentation will address these questions,
  and further place a discussion here.

Title: The Processing of Observables Made by the HMI Instrument on SDO
Authors: Hoeksema, Jon Todd; Schou, Jesper; Couvidat, Sebastien;
   Bogart, Richard S.; Bush, Rock; Duvall, Thomas L.; Liu, Yang; Norton,
   Aimee Ann; Scherrer, Philip H.
Bibcode: 2016SPD....47.0808H
Altcode:
  The Helioseismic and Magnetic Imager (HMI) acquires sequences of
  polarized filtergrams of the Sun from which observable quantities
  are computed. The observables include five line-of-sight quantities -
  magnetic field, velocity, continuum intensity, line depth, and line
  width - as well as Stokes polarization parameters. The process of
  turning a set of filtergrams into calibrated measurements is quite
  involved. Since May 2010 the streams of data from HMI’s two cameras
  have been treated separately. The frame list for the Doppler camera
  repeats every 45 seconds and the images are combined to determine
  the line-of-sight observables. The Vector camera sequence measures
  additional polarizations and so requires 135s; images from ten sequences
  are combined every 720s to determine the four Stokes polarization
  parameters at each of six wavelengths, as well as the LoS observables. A
  variety of calibration corrections are made to the Level-1 filtergrams
  to account for distortion, image motion and alignment, polarization,
  wavelength and intensity irregularities, camera issues, solar rotation,
  and other effects. Residual random variations in the final observables
  are consistent with photon noise levels, but systematic errors remain
  that have not been fully corrected. Of particular concern are those
  associated with the velocity of the instrument relative to the Sun
  due to the geosynchronous orbit of the Solar Dynamics Observatory
  (SDO) spacecraft. This presentation describes the creation of the
  observables, characterizes the residual errors, and indicates plans
  for future improvements - including correction for the instrument point
  spread function. All HMI data are available at http://jsoc.stanford.edu.

Title: Data compression for local correlation tracking of solar
    granulation
Authors: Löptien, B.; Birch, A. C.; Duvall, T. L.; Gizon, L.;
   Schou, J.
Bibcode: 2016A&A...587A...9L
Altcode: 2015arXiv151203243L
  Context. Several upcoming and proposed space missions, such as
  Solar Orbiter, will be limited in telemetry and thus require data
  compression. <BR /> Aims: We test the impact of data compression on
  local correlation tracking (LCT) of time series of continuum intensity
  images. We evaluate the effect of several lossy compression methods
  (quantization, JPEG compression, and a reduced number of continuum
  images) on measurements of solar differential rotation with LCT. <BR
  /> Methods: We applied the different compression methods to tracked
  and remapped continuum intensity maps obtained by the Helioseismic
  and Magnetic Imager (HMI) on board the Solar Dynamics Observatory. We
  derived 2D vector velocities using the local correlation tracking code
  Fourier Local Correlation Tracking (FLCT) and determined the additional
  bias and noise introduced by compression to differential rotation. <BR
  /> Results: We find that probing differential rotation with LCT is
  very robust to lossy data compression when using quantization. Our
  results are severely affected by systematic errors of the LCT method
  and the HMI instrument. The sensitivity of LCT to systematic errors
  is a concern for Solar Orbiter.

Title: Asteroseismic inversions for radial differential rotation of
Sun-like stars: ensemble fits
Authors: Schunker, H.; Schou, J.; Ball, W. H.; Nielsen, M. B.;
   Gizon, L.
Bibcode: 2016A&A...586A..79S
Altcode: 2015arXiv151207169S
  Context. Radial differential rotation is an important parameter
  for stellar dynamo theory and for understanding angular momentum
  transport. <BR /> Aims: We investigate the potential of using a large
  number of similar stars simultaneously to constrain their average radial
  differential rotation gradient: we call this "ensemble fitting". <BR
  /> Methods: We use a range of stellar models along the main sequence,
  each with a synthetic rotation profile. The rotation profiles are step
  functions with a step of ΔΩ = -0.35 μHz, which is located at the base
  of the convection zone. These models are used to compute the rotational
  splittings of the p modes and to model their uncertainties. We then
  fit an ensemble of stars to infer the average ΔΩ. <BR /> Results: All
  the uncertainties on the inferred ΔΩ for individual stars are of the
  order 1 μHz. Using 15 stellar models in an ensemble fit, we show that
  the uncertainty on the average ΔΩ is reduced to less than the input
  ΔΩ, which allows us to constrain the sign of the radial differential
  rotation. We show that a solar-like ΔΩ ≈ 30 nHz can be constrained
  by an ensemble fit of thousands of main-sequence stars. Observing the
  number of stars required to successfully exploit the ensemble fitting
  method will be possible with future asteroseismology missions, such
  as PLATO. We demonstrate the potential of ensemble fitting by showing
  that any systematic differences in the average ΔΩ between F, G,
  and K-type stars larger than 100 nHz could be detected.

Title: Asteroseismic inversions for radial differential rotation of
Sun-like stars: Sensitivity to uncertainties
Authors: Schunker, H.; Schou, J.; Ball, W. H.
Bibcode: 2016A&A...586A..24S
Altcode: 2015arXiv151108365S
  <BR /> Aims: We quantify the effect of observational spectroscopic
  and asteroseismic uncertainties on regularised least squares (RLS)
  inversions for the radial differential rotation of Sun-like and subgiant
  stars. <BR /> Methods: We first solved the forward problem to model
  rotational splittings plus the observed uncertainties for models
  of a Sun-like star, HD 52265, and a subgiant star, KIC 7341231. We
  randomly perturbed the parameters of the stellar models within the
  uncertainties of the spectroscopic and asteroseismic constraints and
  used these perturbed stellar models to compute rotational splittings. We
  experimented with three rotation profiles: solid body rotation, a step
  function, and a smooth rotation profile decreasing with radius. We
  then solved the inverse problem to infer the radial differential
  rotation profile using a RLS inversion and kernels from the best-fit
  stellar model. We also compared RLS, optimally localised average (OLA)
  and direct functional fitting inversion techniques. <BR /> Results:
  We found that the inversions for Sun-like stars with solar-like radial
  differential rotation profiles are insensitive to the uncertainties
  in the stellar models. The uncertainties in the splittings dominate
  the uncertainties in the inversions and solid body rotation is not
  excluded. We found that when the rotation rate below the convection
  zone is increased to six times that of the surface rotation rate the
  inferred rotation profile excluded solid body rotation. We showed
  that when we reduced the uncertainties in the splittings by a factor
  of about 100, the inversion is sensitive to the uncertainties in the
  stellar model. With the current observational uncertainties, we found
  that inversions of subgiant stars are sensitive to the uncertainties
  in the stellar model. <BR /> Conclusions: Our findings suggest that
  inversions for the radial differential rotation of subgiant stars would
  benefit from more tightly constrained stellar models. We conclude that
  current observational uncertainties make it difficult to infer radially
  resolved features of the rotation profile in a Sun-like star using
  inversions with regularisation. In Sun-like stars, the insensitivity
  of the inversions to stellar model uncertainties suggests that it
  may be possible to perform ensemble inversions for the average radial
  differential rotation of many stars with a range of stellar types to
  better constrain the inversions.

Title: Solar Dynamics, Rotation, Convection and Overshoot
Authors: Hanasoge, S.; Miesch, M. S.; Roth, M.; Schou, J.; Schüssler,
   M.; Thompson, M. J.
Bibcode: 2015SSRv..196...79H
Altcode: 2015SSRv..tmp...24H; 2015arXiv150308539H
  We discuss recent observational, theoretical and modeling progress
  made in understanding the Sun's internal dynamics, including its
  rotation, meridional flow, convection and overshoot. Over the past
  few decades, substantial theoretical and observational effort has
  gone into appreciating these aspects of solar dynamics. A review of
  these observations, related helioseismic methodology and inference and
  computational results in relation to these problems is undertaken here.

Title: Helioseismology with Solar Orbiter
Authors: Löptien, Björn; Birch, Aaron C.; Gizon, Laurent; Schou,
   Jesper; Appourchaux, Thierry; Blanco Rodríguez, Julián; Cally,
   Paul S.; Dominguez-Tagle, Carlos; Gandorfer, Achim; Hill, Frank;
   Hirzberger, Johann; Scherrer, Philip H.; Solanki, Sami K.
Bibcode: 2015SSRv..196..251L
Altcode: 2014arXiv1406.5435L; 2014SSRv..tmp...31L
  The Solar Orbiter mission, to be launched in July 2017, will
  carry a suite of remote sensing and in-situ instruments, including
  the Polarimetric and Helioseismic Imager (PHI). PHI will deliver
  high-cadence images of the Sun in intensity and Doppler velocity
  suitable for carrying out novel helioseismic studies. The orbit of
  the Solar Orbiter spacecraft will reach a solar latitude of up to
  21<SUP>∘</SUP> (up to 34<SUP>∘</SUP> by the end of the extended
  mission) and thus will enable the first local helioseismology studies of
  the polar regions. Here we consider an array of science objectives to be
  addressed by helioseismology within the baseline telemetry allocation
  (51 Gbit per orbit, current baseline) and within the science observing
  windows (baseline 3×10 days per orbit). A particularly important
  objective is the measurement of large-scale flows at high latitudes
  (rotation and meridional flow), which are largely unknown but play an
  important role in flux transport dynamos. For both helioseismology
  and feature tracking methods convection is a source of noise in
  the measurement of longitudinally averaged large-scale flows, which
  decreases as T <SUP>-1/2</SUP> where T is the total duration of the
  observations. Therefore, the detection of small amplitude signals (e.g.,
  meridional circulation, flows in the deep solar interior) requires long
  observation times. As an example, one hundred days of observations at
  lower spatial resolution would provide a noise level of about three m/s
  on the meridional flow at 80<SUP>∘</SUP> latitude. Longer time-series
  are also needed to study temporal variations with the solar cycle. The
  full range of Earth-Sun-spacecraft angles provided by the orbit will
  enable helioseismology from two vantage points by combining PHI with
  another instrument: stereoscopic helioseismology will allow the study
  of the deep solar interior and a better understanding of the physics
  of solar oscillations in both quiet Sun and sunspots. We have used a
  model of the PHI instrument to study its performance for helioseismology
  applications. As input we used a 6 hr time-series of realistic solar
  magneto-convection simulation (Stagger code) and the SPINOR radiative
  transfer code to synthesize the observables. The simulated power
  spectra of solar oscillations show that the instrument is suitable for
  helioseismology. In particular, the specified point spread function,
  image jitter, and photon noise are no obstacle to a successful mission.

Title: Improved Helioseismic Analysis of Medium-ℓ Data from the
    Michelson Doppler Imager
Authors: Larson, Timothy P.; Schou, Jesper
Bibcode: 2015SoPh..290.3221L
Altcode: 2015SoPh..tmp..175L; 2015arXiv151105217L
  We present a comprehensive study of one method for measuring various
  parameters of global modes of oscillation of the Sun. Using velocity
  data taken by the Michelson Doppler Imager (MDI), we analyze spherical
  harmonic degrees ℓ ≤300 . Both current and historical methodologies
  are explained, and the various differences between the two are
  investigated to determine their effects on global-mode parameters
  and systematic errors in the analysis. These differences include
  a number of geometric corrections made during spherical harmonic
  decomposition; updated routines for generating window functions,
  detrending time series, and filling gaps; and consideration of physical
  effects such as mode-profile asymmetry, horizontal displacement at
  the solar surface, and distortion of eigenfunctions by differential
  rotation. We apply these changes one by one to three years of data, and
  then reanalyze the entire MDI mission applying all of them, using both
  the original 72-day long time series and 360-day long time series. We
  find significant changes in mode parameters, both as a result of the
  various changes to the processing, as well as between the 72-day and
  360-day analyses. We find reduced residuals of inversions for internal
  rotation, but seeming artifacts remain, such as the peak in the rotation
  rate near the surface at high latitudes. An annual periodicity in the
  f -mode frequencies is also investigated.

Title: IAU 2015 Resolution B2 on Recommended Zero Points for the
    Absolute and Apparent Bolometric Magnitude Scales
Authors: Mamajek, E. E.; Torres, G.; Prsa, A.; Harmanec, P.;
   Asplund, M.; Bennett, P. D.; Capitaine, N.; Christensen-Dalsgaard,
   J.; Depagne, E.; Folkner, W. M.; Haberreiter, M.; Hekker, S.; Hilton,
   J. L.; Kostov, V.; Kurtz, D. W.; Laskar, J.; Mason, B. D.; Milone,
   E. F.; Montgomery, M. M.; Richards, M. T.; Schou, J.; Stewart, S. G.
Bibcode: 2015arXiv151006262M
Altcode:
  The XXIXth IAU General Assembly in Honolulu adopted IAU 2015 Resolution
  B2 on recommended zero points for the absolute and apparent bolometric
  magnitude scales. The resolution was proposed by the IAU Inter-Division
  A-G Working Group on Nominal Units for Stellar and Planetary
  Astronomy after consulting with a broad spectrum of researchers from
  the astronomical community. Resolution B2 resolves the long-standing
  absence of an internationally-adopted zero point for the absolute and
  apparent bolometric magnitude scales. Resolution B2 defines the zero
  point of the absolute bolometric magnitude scale such that a radiation
  source with $M_{\rm Bol}$ = 0 has luminosity L$_{\circ}$ = 3.0128e28
  W. The zero point of the apparent bolometric magnitude scale ($m_{\rm
  Bol}$ = 0) corresponds to irradiance $f_{\circ}$ = 2.518021002e-8
  W/m$^2$. The zero points were chosen so that the nominal solar
  luminosity (3.828e26 W) adopted by IAU 2015 Resolution B3 corresponds
  approximately to $M_{\rm Bol}$(Sun) = 4.74, the value most commonly
  adopted in recent literature. The nominal total solar irradiance (1361
  W/m$^2$) adopted in IAU 2015 Resolution B3 corresponds approximately to
  apparent bolometric magnitude $m_{\rm bol}$(Sun) = -26.832. Implicit
  in the IAU 2015 Resolution B2 definition of the apparent bolometric
  magnitude scale is an exact definition for the parsec (648000/$\pi$ au)
  based on the IAU 2012 Resolution B2 definition of the astronomical unit.

Title: IAU 2015 Resolution B3 on Recommended Nominal Conversion
    Constants for Selected Solar and Planetary Properties
Authors: Mamajek, E. E.; Prsa, A.; Torres, G.; Harmanec, P.;
   Asplund, M.; Bennett, P. D.; Capitaine, N.; Christensen-Dalsgaard,
   J.; Depagne, E.; Folkner, W. M.; Haberreiter, M.; Hekker, S.; Hilton,
   J. L.; Kostov, V.; Kurtz, D. W.; Laskar, J.; Mason, B. D.; Milone,
   E. F.; Montgomery, M. M.; Richards, M. T.; Schou, J.; Stewart, S. G.
Bibcode: 2015arXiv151007674M
Altcode:
  Astronomers commonly quote the properties of celestial objects in
  units of parameters for the Sun, Jupiter, or the Earth. The resolution
  presented here was proposed by the IAU Inter-Division Working Group
  on Nominal Units for Stellar and Planetary Astronomy and passed by the
  XXIXth IAU General Assembly in Honolulu. IAU 2015 Resolution B3 adopts
  a set of nominal solar, terrestrial, and jovian conversion constants
  for stellar and (exo)planetary astronomy which are defined to be
  exact SI values. While the nominal constants are based on current best
  estimates (CBEs; which have uncertainties, are not secularly constant,
  and are updated regularly using new observations), they should be
  interpreted as standard values and not as CBEs. IAU 2015 Resolution
  B3 adopts five solar conversion constants (nominal solar radius,
  nominal total solar irradiance, nominal solar luminosity, nominal
  solar effective temperature, and nominal solar mass parameter) and six
  planetary conversion constants (nominal terrestrial equatorial radius,
  nominal terrestrial polar radius, nominal jovian equatorial radius,
  nominal jovian polar radius, nominal terrestrial mass parameter,
  and nominal jovian mass parameter).

Title: Effects of granulation on the visibility of solar oscillations
Authors: Schou, J.
Bibcode: 2015A&A...580L..11S
Altcode: 2015arXiv150708856S
  Context. The interaction of solar oscillations with near surface
  convection is poorly understood. These interactions are likely the
  cause of several problems in helio- and astero-seismology, including the
  so-called surface effect and apparently unphysical travel time shifts
  as a function of center to limb distance. There is thus a clear need
  for further theoretical understanding and observational tests. <BR
  /> Aims: The aim is to determine how the observed modes are affected
  by the convection. <BR /> Methods: I used HMI velocity and intensity
  images to construct k-ω diagrams showing how the oscillation amplitude
  and phase depend on the local granulation intensity. <BR /> Results:
  There is a clear and significant dependence of the observed properties
  of the oscillations on the local convection state.

Title: A Method for the Estimation of p-Mode Parameters from Averaged
    Solar Oscillation Power Spectra
Authors: Reiter, J.; Rhodes, E. J., Jr.; Kosovichev, A. G.; Schou,
   J.; Scherrer, P. H.; Larson, T. P.
Bibcode: 2015ApJ...803...92R
Altcode: 2015arXiv150407493R
  A new fitting methodology is presented that is equally well suited for
  the estimation of low-, medium-, and high-degree mode parameters from
  m-averaged solar oscillation power spectra of widely differing spectral
  resolution. This method, which we call the “Windowed, MuLTiple-Peak,
  averaged-spectrum” or WMLTP Method, constructs a theoretical profile
  by convolving the weighted sum of the profiles of the modes appearing
  in the fitting box with the power spectrum of the window function of
  the observing run, using weights from a leakage matrix that takes into
  account observational and physical effects, such as the distortion of
  modes by solar latitudinal differential rotation. We demonstrate that
  the WMLTP Method makes substantial improvements in the inferences of
  the properties of the solar oscillations in comparison with a previous
  method, which employed a single profile to represent each spectral
  peak. We also present an inversion for the internal solar structure,
  which is based upon 6366 modes that we computed using the WMLTP method
  on the 66 day 2010 Solar and Heliospheric Observatory/MDI Dynamics
  Run. To improve both the numerical stability and reliability of the
  inversion, we developed a new procedure for the identification and
  correction of outliers in a frequency dataset. We present evidence
  for a pronounced departure of the sound speed in the outer half of the
  solar convection zone and in the subsurface shear layer from the radial
  sound speed profile contained in Model S of Christensen-Dalsgaard and
  his collaborators that existed in the rising phase of Solar Cycle 24
  during mid-2010.

Title: Temporal evolution of the solar torsional oscillation and
    implications for cycle 25
Authors: Hill, Frank; Howe, Rachel; Komm, Rudolf; Schou, Jesper;
   Thompson, Michael; Larson, Timothy
Bibcode: 2015TESS....110502H
Altcode:
  The zonal flow known as the torsional oscillation has been observed
  on the Sun’s surface since 1980 and in its interior since 1995. It
  has two branches that migrate during the solar cycle, with one moving
  towards the equator and the other towards the poles. The rate at which
  these branches migrate in latitude is tightly correlated with the
  timing of the solar cycle, as seen during the long minimum between
  cycles 23 and 24. The poleward branch generally becomes visible 10
  to 12 years before the appearance of the magnetic activity associated
  with the corresponding sunspot cycle as it did for the current cycle
  24. However, the poleward flow for cycle 25, which was expected to
  appear in 2008-2010, was not observed. Subsequent analysis showed
  that it is a very weak flow, and is masked by an apparent change
  in the background solar differential rotation rate. We will present
  the latest observations of the zonal flow as determined from global
  helioseismology, and will discuss the implications for the strength
  and timing of cycle 25.

Title: Image compression in local helioseismology
Authors: Löptien, B.; Birch, A. C.; Gizon, L.; Schou, J.
Bibcode: 2014A&A...571A..42L
Altcode: 2014arXiv1409.4176L
  Context. Several upcoming helioseismology space missions are
  very limited in telemetry and will have to perform extensive data
  compression. This requires the development of new methods of data
  compression. <BR /> Aims: We give an overview of the influence of lossy
  data compression on local helioseismology. We investigate the effects
  of several lossy compression methods (quantization, JPEG compression,
  and smoothing and subsampling) on power spectra and time-distance
  measurements of supergranulation flows at disk center. <BR /> Methods:
  We applied different compression methods to tracked and remapped
  Dopplergrams obtained by the Helioseismic and Magnetic Imager onboard
  the Solar Dynamics Observatory. We determined the signal-to-noise
  ratio of the travel times computed from the compressed data as a
  function of the compression efficiency. <BR /> Results: The basic
  helioseismic measurements that we consider are very robust to lossy
  data compression. Even if only the sign of the velocity is used,
  time-distance helioseismology is still possible. We achieve the
  best results by applying JPEG compression on spatially subsampled
  data. However, our conclusions are only valid for supergranulation
  flows at disk center and may not be valid for all helioseismology
  applications.

Title: The PLATO 2.0 mission
Authors: Rauer, H.; Catala, C.; Aerts, C.; Appourchaux, T.; Benz,
   W.; Brandeker, A.; Christensen-Dalsgaard, J.; Deleuil, M.; Gizon,
   L.; Goupil, M. -J.; Güdel, M.; Janot-Pacheco, E.; Mas-Hesse,
   M.; Pagano, I.; Piotto, G.; Pollacco, D.; Santos, Ċ.; Smith, A.;
   Suárez, J. -C.; Szabó, R.; Udry, S.; Adibekyan, V.; Alibert, Y.;
   Almenara, J. -M.; Amaro-Seoane, P.; Eiff, M. Ammler-von; Asplund, M.;
   Antonello, E.; Barnes, S.; Baudin, F.; Belkacem, K.; Bergemann, M.;
   Bihain, G.; Birch, A. C.; Bonfils, X.; Boisse, I.; Bonomo, A. S.;
   Borsa, F.; Brandão, I. M.; Brocato, E.; Brun, S.; Burleigh, M.;
   Burston, R.; Cabrera, J.; Cassisi, S.; Chaplin, W.; Charpinet, S.;
   Chiappini, C.; Church, R. P.; Csizmadia, Sz.; Cunha, M.; Damasso, M.;
   Davies, M. B.; Deeg, H. J.; Díaz, R. F.; Dreizler, S.; Dreyer, C.;
   Eggenberger, P.; Ehrenreich, D.; Eigmüller, P.; Erikson, A.; Farmer,
   R.; Feltzing, S.; de Oliveira Fialho, F.; Figueira, P.; Forveille,
   T.; Fridlund, M.; García, R. A.; Giommi, P.; Giuffrida, G.; Godolt,
   M.; Gomes da Silva, J.; Granzer, T.; Grenfell, J. L.; Grotsch-Noels,
   A.; Günther, E.; Haswell, C. A.; Hatzes, A. P.; Hébrard, G.; Hekker,
   S.; Helled, R.; Heng, K.; Jenkins, J. M.; Johansen, A.; Khodachenko,
   M. L.; Kislyakova, K. G.; Kley, W.; Kolb, U.; Krivova, N.; Kupka, F.;
   Lammer, H.; Lanza, A. F.; Lebreton, Y.; Magrin, D.; Marcos-Arenal,
   P.; Marrese, P. M.; Marques, J. P.; Martins, J.; Mathis, S.; Mathur,
   S.; Messina, S.; Miglio, A.; Montalban, J.; Montalto, M.; Monteiro,
   M. J. P. F. G.; Moradi, H.; Moravveji, E.; Mordasini, C.; Morel, T.;
   Mortier, A.; Nascimbeni, V.; Nelson, R. P.; Nielsen, M. B.; Noack,
   L.; Norton, A. J.; Ofir, A.; Oshagh, M.; Ouazzani, R. -M.; Pápics,
   P.; Parro, V. C.; Petit, P.; Plez, B.; Poretti, E.; Quirrenbach, A.;
   Ragazzoni, R.; Raimondo, G.; Rainer, M.; Reese, D. R.; Redmer, R.;
   Reffert, S.; Rojas-Ayala, B.; Roxburgh, I. W.; Salmon, S.; Santerne,
   A.; Schneider, J.; Schou, J.; Schuh, S.; Schunker, H.; Silva-Valio,
   A.; Silvotti, R.; Skillen, I.; Snellen, I.; Sohl, F.; Sousa, S. G.;
   Sozzetti, A.; Stello, D.; Strassmeier, K. G.; Švanda, M.; Szabó,
   Gy. M.; Tkachenko, A.; Valencia, D.; Van Grootel, V.; Vauclair,
   S. D.; Ventura, P.; Wagner, F. W.; Walton, N. A.; Weingrill, J.;
   Werner, S. C.; Wheatley, P. J.; Zwintz, K.
Bibcode: 2014ExA....38..249R
Altcode: 2014ExA...tmp...41R; 2013arXiv1310.0696R
  PLATO 2.0 has recently been selected for ESA's M3 launch opportunity
  (2022/24). Providing accurate key planet parameters (radius, mass,
  density and age) in statistical numbers, it addresses fundamental
  questions such as: How do planetary systems form and evolve? Are there
  other systems with planets like ours, including potentially habitable
  planets? The PLATO 2.0 instrument consists of 34 small aperture
  telescopes (32 with 25 s readout cadence and 2 with 2.5 s candence)
  providing a wide field-of-view (2232 deg <SUP>2</SUP>) and a large
  photometric magnitude range (4-16 mag). It focusses on bright (4-11
  mag) stars in wide fields to detect and characterize planets down to
  Earth-size by photometric transits, whose masses can then be determined
  by ground-based radial-velocity follow-up measurements. Asteroseismology
  will be performed for these bright stars to obtain highly accurate
  stellar parameters, including masses and ages. The combination of
  bright targets and asteroseismology results in high accuracy for
  the bulk planet parameters: 2 %, 4-10 % and 10 % for planet radii,
  masses and ages, respectively. The planned baseline observing strategy
  includes two long pointings (2-3 years) to detect and bulk characterize
  planets reaching into the habitable zone (HZ) of solar-like stars
  and an additional step-and-stare phase to cover in total about 50 %
  of the sky. PLATO 2.0 will observe up to 1,000,000 stars and detect
  and characterize hundreds of small planets, and thousands of planets
  in the Neptune to gas giant regime out to the HZ. It will therefore
  provide the first large-scale catalogue of bulk characterized planets
  with accurate radii, masses, mean densities and ages. This catalogue
  will include terrestrial planets at intermediate orbital distances,
  where surface temperatures are moderate. Coverage of this parameter
  range with statistical numbers of bulk characterized planets is unique
  to PLATO 2.0. The PLATO 2.0 catalogue allows us to e.g.: - complete
  our knowledge of planet diversity for low-mass objects, - correlate the
  planet mean density-orbital distance distribution with predictions from
  planet formation theories,- constrain the influence of planet migration
  and scattering on the architecture of multiple systems, and - specify
  how planet and system parameters change with host star characteristics,
  such as type, metallicity and age. The catalogue will allow us to study
  planets and planetary systems at different evolutionary phases. It
  will further provide a census for small, low-mass planets. This will
  serve to identify objects which retained their primordial hydrogen
  atmosphere and in general the typical characteristics of planets
  in such low-mass, low-density range. Planets detected by PLATO 2.0
  will orbit bright stars and many of them will be targets for future
  atmosphere spectroscopy exploring their atmosphere. Furthermore,
  the mission has the potential to detect exomoons, planetary rings,
  binary and Trojan planets. The planetary science possible with PLATO
  2.0 is complemented by its impact on stellar and galactic science via
  asteroseismology as well as light curves of all kinds of variable stars,
  together with observations of stellar clusters of different ages. This
  will allow us to improve stellar models and study stellar activity. A
  large number of well-known ages from red giant stars will probe the
  structure and evolution of our Galaxy. Asteroseismic ages of bright
  stars for different phases of stellar evolution allow calibrating
  stellar age-rotation relationships. Together with the results of ESA's
  Gaia mission, the results of PLATO 2.0 will provide a huge legacy to
  planetary, stellar and galactic science.

Title: The radial gradient of the near-surface shear layer of the Sun
Authors: Barekat, A.; Schou, J.; Gizon, L.
Bibcode: 2014A&A...570L..12B
Altcode: 2014arXiv1410.3162B
  Context. Helioseismology has provided unprecedented information about
  the internal rotation of the Sun. One of the important achievements was
  the discovery of two radial shear layers: one near the bottom of the
  convection zone (the tachocline) and one near the surface. These shear
  layers may be important ingredients for explaining the magnetic cycle of
  the Sun. <BR /> Aims: We measure the logarithmic radial gradient of the
  rotation rate (dlnΩ/dlnr) near the surface of the Sun using 15 years of
  f mode rotational frequency splittings from the Michelson Doppler Imager
  (MDI) and four years of data from the Helioseismic and Magnetic Imager
  (HMI). <BR /> Methods: We model the angular velocity of the Sun in the
  upper ~10 Mm as changing linearly with depth and use a multiplicative
  optimally localized averaging inversion to infer the gradient of the
  rotation rate as a function of latitude. <BR /> Results: Both the MDI
  and HMI data show that dlnΩ/dlnr is close to -1 from the equator
  to 60° latitude and stays negative up to 75° latitude. However,
  the value of the gradient is different for MDI and HMI for latitudes
  above 60°. Additionally, there is a significant difference between
  the value of dlnΩ/dlnr using an older and recently reprocessed MDI
  data for latitudes above 30°. <BR /> Conclusions: We could reliably
  infer the value of dlnΩ/dlnr up to 60°, but not above this latitude,
  which will hopefully constrain theories of the near-surface shear
  layer and dynamo. Furthermore, the recently reprocessed MDI splitting
  data are more reliable than the older versions which contained clear
  systematic errors in the high degree f modes.

Title: The Helioseismic and Magnetic Imager (HMI) Vector Magnetic
Field Pipeline: Overview and Performance
Authors: Hoeksema, J. Todd; Liu, Yang; Hayashi, Keiji; Sun, Xudong;
   Schou, Jesper; Couvidat, Sebastien; Norton, Aimee; Bobra, Monica;
   Centeno, Rebecca; Leka, K. D.; Barnes, Graham; Turmon, Michael
Bibcode: 2014SoPh..289.3483H
Altcode: 2014SoPh..tmp...57H; 2014arXiv1404.1881H
  The Helioseismic and Magnetic Imager (HMI) began near-continuous
  full-disk solar measurements on 1 May 2010 from the Solar Dynamics
  Observatory (SDO). An automated processing pipeline keeps pace
  with observations to produce observable quantities, including the
  photospheric vector magnetic field, from sequences of filtergrams. The
  basic vector-field frame list cadence is 135 seconds, but to reduce
  noise the filtergrams are combined to derive data products every 720
  seconds. The primary 720 s observables were released in mid-2010,
  including Stokes polarization parameters measured at six wavelengths,
  as well as intensity, Doppler velocity, and the line-of-sight magnetic
  field. More advanced products, including the full vector magnetic field,
  are now available. Automatically identified HMI Active Region Patches
  (HARPs) track the location and shape of magnetic regions throughout
  their lifetime.

Title: The Helioseismic and Magnetic Imager (HMI) Vector Magnetic
Field Pipeline: Optimization of the Spectral Line Inversion Code
Authors: Centeno, R.; Schou, J.; Hayashi, K.; Norton, A.; Hoeksema,
   J. T.; Liu, Y.; Leka, K. D.; Barnes, G.
Bibcode: 2014SoPh..289.3531C
Altcode: 2014SoPh..tmp...44C; 2014arXiv1403.3677C
  The Very Fast Inversion of the Stokes Vector (VFISV) is a
  Milne-Eddington spectral line inversion code used to determine the
  magnetic and thermodynamic parameters of the solar photosphere from
  observations of the Stokes vector in the 6173 Å Fe I line by the
  Helioseismic and Magnetic Imager (HMI) onboard the Solar Dynamics
  Observatory (SDO). We report on the modifications made to the original
  VFISV inversion code in order to optimize its operation within
  the HMI data pipeline and provide the smoothest solution in active
  regions. The changes either sped up the computation or reduced the
  frequency with which the algorithm failed to converge to a satisfactory
  solution. Additionally, coding bugs which were detected and fixed in
  the original VFISV release are reported here.

Title: Rotational splitting as a function of mode frequency for six
    Sun-like stars
Authors: Nielsen, M. B.; Gizon, L.; Schunker, H.; Schou, J.
Bibcode: 2014A&A...568L..12N
Altcode: 2014arXiv1408.4307N
  Asteroseismology offers the prospect of constraining differential
  rotation in Sun-like stars. Here we have identified six high
  signal-to-noise main-sequence Sun-like stars in the Kepler field,
  which all have visible signs of rotational splitting of their p-mode
  frequencies. For each star, we extract the rotational frequency
  splitting and inclination angle from separate mode sets (adjacent modes
  with l = 2, 0, and 1) spanning the p-mode envelope. We use a Markov
  chain Monte Carlo method to obtain the best fit and errors associated
  with each parameter. We are able to make independent measurements of
  rotational splittings of ~8 radial orders for each star. For all six
  stars, the measured splittings are consistent with uniform rotation,
  allowing us to exclude large radial differential rotation. This work
  opens the possibility of constraining internal rotation of Sun-like
  stars. <P />Table 2 is only available at the CDS via anonymous ftp to <A
  href="http://cdsarc.u-strasbg.fr">http://cdsarc.u-strasbg.fr</A>
  (ftp://130.79.128.5) or via <A
  href="http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/568/L12">http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/568/L12</A>

Title: VizieR Online Data Catalog: Rotational frequency splitting
    in Sun-like stars (Nielsen+, 2014)
Authors: Nielsen, M. B.; Gizon, L.; Schunker, H.; Schou, J.
Bibcode: 2014yCat..35689012N
Altcode:
  We used short-cadence (~58s) white light observations from the NASA
  Kepler mission from March 2009 until the end of the mission in early
  2013. The data were obtained from the Mikulski Archive for Space
  Telescopes. <P />We fit the power spectrum with a model consisting
  of a constant noise level, two frequency-dependent Harvey-like noise
  terms (see Eq. (1) in Aigrain et al. 2004A&amp;A...414.1139A), in
  addition to the individual oscillation modes. We model these as a
  sum of Lorentzian profiles as per Eq. (10) in Handberg &amp; Campante
  (2011A&amp;A...527A..56H), each consisting of mode power, frequency,
  and linewidth. <P />(2 data files).

Title: Helioseismic and Magnetic Imager Observations of Linear
    Polarization from a Loop Prominence System
Authors: Saint-Hilaire, Pascal; Schou, Jesper; Martinez Oliveros, Juan
   Carlos; Hudson, Hugh S.; Krucker, Sam; Bain, Hazel; Couvidat, Sebastien
Bibcode: 2014AAS...22412311S
Altcode:
  White-light observations by the Solar Dynamics Observatory's
  Helioseismic and Magnetic Imager of a loop-prominence system occurring
  in the aftermath of an X-class flare on 2013 May 13 near the eastern
  solar limb show a linearly polarized component, reaching up to 20%
  at an altitude of 33 Mm, about the maximal amount expected if the
  emission were due solely to Thomson scattering of photospheric light
  by the coronal material. The mass associated with the polarized
  component was 8.2x10^14 g. At 15 Mm altitude, the brightest part of
  the loop was 3(+/-0.5)% linearly polarized, only about 20% of that
  expected from pure Thomson scattering, indicating the presence of an
  additional unpolarized component at wavelengths near Fe I (617.33 nm),
  probably thermal emission. We estimated the free electron density of
  the white-light loop system to possibly be as high as 1.8x10^12 cm^-3.

Title: Observations of Linear Polarization in a Solar Coronal Loop
    Prominence System Observed near 6173 Å
Authors: Saint-Hilaire, Pascal; Schou, Jesper; Martínez Oliveros,
   Juan-Carlos; Hudson, Hugh S.; Krucker, Säm; Bain, Hazel; Couvidat,
   Sébastien
Bibcode: 2014ApJ...786L..19S
Altcode: 2014arXiv1402.7016S
  White-light observations by the Solar Dynamics Observatory's
  Helioseismic and Magnetic Imager of a loop-prominence system occurring
  in the aftermath of an X-class flare on 2013 May 13 near the eastern
  solar limb show a linearly polarized component, reaching up to ~20%
  at an altitude of ~33 Mm, about the maximum amount expected if the
  emission were due solely to Thomson scattering of photospheric light by
  the coronal material. The mass associated with the polarized component
  was 8.2 × 10<SUP>14</SUP> g. At 15 Mm altitude, the brightest part
  of the loop was 3(±0.5)% linearly polarized, only about 20% of that
  expected from pure Thomson scattering, indicating the presence of an
  additional unpolarized component at wavelengths near Fe I (617.33
  nm). We estimate the free electron density of the white-light loop
  system to possibly be as high as 1.8 × 10<SUP>12</SUP> cm<SUP>-3</SUP>.

Title: Seismic constraints on the radial dependence of the internal
    rotation profiles of six Kepler subgiants and young red giants
Authors: Deheuvels, S.; Doğan, G.; Goupil, M. J.; Appourchaux, T.;
   Benomar, O.; Bruntt, H.; Campante, T. L.; Casagrande, L.; Ceillier,
   T.; Davies, G. R.; De Cat, P.; Fu, J. N.; García, R. A.; Lobel,
   A.; Mosser, B.; Reese, D. R.; Regulo, C.; Schou, J.; Stahn, T.;
   Thygesen, A. O.; Yang, X. H.; Chaplin, W. J.; Christensen-Dalsgaard,
   J.; Eggenberger, P.; Gizon, L.; Mathis, S.; Molenda-Żakowicz, J.;
   Pinsonneault, M.
Bibcode: 2014A&A...564A..27D
Altcode: 2014arXiv1401.3096D
  Context. We still do not understand which physical mechanisms are
  responsible for the transport of angular momentum inside stars. The
  recent detection of mixed modes that contain the clear signature of
  rotation in the spectra of Kepler subgiants and red giants gives us
  the opportunity to make progress on this question. <BR /> Aims: Our
  aim is to probe the radial dependence of the rotation profiles for a
  sample of Kepler targets. For this purpose, subgiants and early red
  giants are particularly interesting targets because their rotational
  splittings are more sensitive to the rotation outside the deeper core
  than is the case for their more evolved counterparts. <BR /> Methods:
  We first extracted the rotational splittings and frequencies of the
  modes for six young Kepler red giants. We then performed a seismic
  modeling of these stars using the evolutionary codes Cesam2k and
  astec. By using the observed splittings and the rotational kernels
  of the optimal models, we inverted the internal rotation profiles
  of the six stars. <BR /> Results: We obtain estimates of the core
  rotation rates for these stars, and upper limits to the rotation in
  their convective envelope. We show that the rotation contrast between
  the core and the envelope increases during the subgiant branch. Our
  results also suggest that the core of subgiants spins up with time,
  while their envelope spins down. For two of the stars, we show that a
  discontinuous rotation profile with a deep discontinuity reproduces
  the observed splittings significantly better than a smooth rotation
  profile. Interestingly, the depths that are found to be most probable
  for the discontinuities roughly coincide with the location of the
  H-burning shell, which separates the layers that contract from those
  that expand. <BR /> Conclusions: We characterized the differential
  rotation pattern of six young giants with a range of metallicities, and
  with both radiative and convective cores on the main sequence. This will
  bring observational constraints to the scenarios of angular momentum
  transport in stars. Moreover, if the existence of sharp gradients in
  the rotation profiles of young red giants is confirmed, it is expected
  to help in distinguishing between the physical processes that could
  transport angular momentum in the subgiant and red giant branches. <P
  />Appendices and Tables 3-9 are available in electronic form at <A
  href="http://www.aanda.org/10.1051/0004-6361/201322779/olm">http://www.aanda.org</A>

Title: On the information content of stellar spectra
Authors: Schou, Jesper
Bibcode: 2014IAUS..301..481S
Altcode: 2013arXiv1309.7871S
  With the increasing quality of asteroseismic observations it is
  important to minimize the random and systematic errors in mode
  parameter estimates. To this end it is important to understand how
  the oscillations relate to the directly observed quantities, such as
  intensities and spectra, and to derived quantities, such as Doppler
  velocity. Here I list some of the effects we need to take into account
  and show an example of the impact of some of them.

Title: Precise and accurate interpolated stellar oscillation
    frequencies on the main sequence
Authors: Ball, Warrick H.; Schou, Jesper; Gizon, Laurent; Marques,
   João P. C.
Bibcode: 2014IAUS..301..379B
Altcode: 2013arXiv1309.3044B
  High-quality data from space-based observatories present an opportunity
  to fit stellar models to observations of individually-identified
  oscillation frequencies, not just the large and small frequency
  separations. But such fits require the evaluation of a large number of
  accurate stellar models, which remains expensive. Here, we show that
  global-mode oscillation frequencies interpolated in a grid of stellar
  models are precise and accurate, at least in the neighbourhood of a
  solar model.

Title: Chromospheric and Coronal Observations of Solar Flares with
    the Helioseismic and Magnetic Imager
Authors: Martínez Oliveros, Juan-Carlos; Krucker, Säm; Hudson, Hugh
   S.; Saint-Hilaire, Pascal; Bain, Hazel; Lindsey, Charles; Bogart,
   Rick; Couvidat, Sebastien; Scherrer, Phil; Schou, Jesper
Bibcode: 2014ApJ...780L..28M
Altcode: 2013arXiv1311.7412M
  We report observations of white-light ejecta in the low corona, for
  two X-class flares on 2013 May 13, using data from the Helioseismic
  and Magnetic Imager (HMI) of the Solar Dynamics Observatory. At least
  two distinct kinds of sources appeared (chromospheric and coronal),
  in the early and later phases of flare development, in addition to
  the white-light footpoint sources commonly observed in the lower
  atmosphere. The gradual emissions have a clear identification
  with the classical loop-prominence system, but are brighter than
  expected and possibly seen here in the continuum rather than line
  emission. We find the HMI flux exceeds the radio/X-ray interpolation
  of the bremsstrahlung produced in the flare soft X-ray sources by at
  least one order of magnitude. This implies the participation of cooler
  sources that can produce free-bound continua and possibly line emission
  detectable by HMI. One of the early sources dynamically resembles
  "coronal rain", appearing at a maximum apparent height and moving
  toward the photosphere at an apparent constant projected speed of 134
  ± 8 km s<SUP>-1</SUP>. Not much literature exists on the detection of
  optical continuum sources above the limb of the Sun by non-coronagraphic
  instruments and these observations have potential implications for our
  basic understanding of flare development, since visible observations
  can in principle provide high spatial and temporal resolution.

Title: Characterization of High-Degree Modes using MDI, HMI and
    GONG Data
Authors: Korzennik, S. G.; Eff-Darwich, A.; Larson, T. P.;
   Rabello-Soares, M. C.; Schou, J.
Bibcode: 2013ASPC..478..173K
Altcode:
  We present the first characterization of high-degree modes (i.e.,
  ℓ up to 900 or 1000), using three instruments and three epochs
  corresponding to the 2001, 2002 and 2010 MDI Dynamics runs. For 2001,
  we analyzed MDI full-disk Dopplergrams, while for 2002, we analyzed
  MDI and GONG full-disk Dopplergrams, and for 2012 we analyzed
  MDI, GONG and HMI full-disk Dopplergrams. These Dopplergrams were
  spatially decomposed up to ℓ = 900 or 1000, and power spectra for
  all degrees and all azimuthal orders were computed using a high-order
  multi-taper, power spectrum estimator. These spectra were then fitted
  for all degrees and all azimuthal orders, above ℓ = 100, and for all
  orders with substantial amplitude. Fitting at high degrees generates
  ridge characteristics, characteristics that do not correspond to
  the underlying mode characteristics. We used a sophisticated forward
  modeling to recover the best possible estimate of the underlying mode
  characteristics (mode frequencies, as well as linewidths, amplitudes
  and asymmetries). We present the first attempt to apply this method to
  three instruments and three epochs. The derived sets of corrected mode
  characteristics (frequencies, line widths, asymmetries and amplitudes)
  are presented and compared.

Title: Comparing the Internal Structure of the Sun During the Cycle
    23 and Cycle 24 Minima
Authors: Basu, S.; Broomhall, A. -M.; Chaplin, W. J.; Elsworth, Y.;
   Davies, G. R.; Schou, J.; Larson, T. P.
Bibcode: 2013ASPC..478..161B
Altcode:
  The Birmingham Solar-Oscillations Network (BiSON) has been collecting
  helioseismic data for the last three solar cycles. We use these data to
  determine whether the internal properties of the Sun during the minimum
  preceding cycle 24 was different compared to that preceding cycle 23.

Title: The Torsional Oscillation and the Timing of the Solar Cycle:
    Is it Maximum Yet?
Authors: Howe, R.; Christensen-Dalsgaard, J.; Hill, F.; Komm, R.;
   Larson, T. P.; Schou, J.; Thompson, M. J.
Bibcode: 2013ASPC..478..303H
Altcode:
  After the late start to Cycle 24 there are some indications that
  activity may have peaked as early as late 2011 and that the polar-field
  reversal has already occurred in the North. We use helioseismic
  measurements of the migrating zonal flow pattern known as the torsional
  oscillation to estimate the length of the solar cycle, and find that
  it has held steady at about 12.3 years since late 2009, which would
  point to solar maximum in 2013 as expected.

Title: Observing Open Clusters with a Sequence of Ages with Kepler
Authors: Guzik, Joyce A.; Bradley, Paul A.; Szabo, Robert; Molnar,
   Laszlo; Pigulski, Andrzej; Zwintz, Konstanze; Ngeow, Chow-Choong;
   Schou, Jesper; Handler, Gerald
Bibcode: 2013arXiv1310.0772G
Altcode:
  We propose to observe with Kepler an age sequence of nearby uncrowded
  open clusters. The current Kepler field contains very few (only 4)
  somewhat distant and/or old clusters. Nearby open clusters are already
  well characterized from ground- and many space-based observations. Our
  proposal focuses on mid and upper main-sequence variables (main sequence
  and pre-main sequence gamma Dor or delta Scuti stars, SPB/beta Cep
  stars, Cepheids, or yellow supergiants), having periods of hours to
  days accessible by longer cadence observations. Asteroseismology for
  these objects to date is limited by the number of modes observable
  from the ground, difficulty in obtaining spectroscopic or photometric
  mode ID for the fainter targets that have been observed by Kepler,
  uncertainties in interior and initial abundances, especially for stars
  with abundance anomalies, uncertainties in distance/luminosity, and lack
  of knowledge of prior evolution history. The additional constraints
  of common age, distance and initial abundances in clusters will place
  these variables in their evolutionary context, and help unlock some of
  the science and reduce uncertainties for understanding star formation
  and stellar evolution.

Title: Global-Oscillation Eigenfunction Measurements of Solar
    Meridional Flow
Authors: Woodard, M.; Schou, J.; Birch, A. C.; Larson, T. P.
Bibcode: 2013SoPh..287..129W
Altcode: 2012SoPh..tmp..179W
  We describe and apply a new helioseismic method for measuring solar
  subsurface axisymmetric meridional and zonal flow. The method is
  based on a theoretical model of the response of global-oscillation
  eigenfunctions to the flow velocity and uses cross spectra of the
  time-varying coefficients in the spherical-harmonic expansion of
  the photospheric Doppler-velocity field. Eigenfunction changes
  modify the leakage matrix, which describes the sensitivity of the
  spherical-harmonic coefficients to the global-oscillation modes. The
  form of the leakage matrix in turn affects the theoretically expected
  spherical-harmonic cross spectra. Estimates of internal meridional and
  zonal flow were obtained by fitting the theoretical flow-dependent cross
  spectra to spherical-harmonic cross spectra computed from approximately
  500 days of full-disk Dopplergrams from the Helioseismic and Magnetic
  Imager (HMI) on the SDO spacecraft. The zonal-flow measurements,
  parameterized in the form of "a" coefficients, substantially agree
  with measurements obtained from conventional global-mode-frequency
  analysis. The meridional-flow estimates, in the form of depth-weighted
  averages of the flow velocity, are similar to estimates obtained from
  earlier analyses, for oscillation modes that penetrate the outermost
  one-third of the convection zone. For more deeply penetrating modes,
  the inferred flow velocity increases significantly with penetration
  depth, indicating the need for either a modification of the simple
  conveyor-belt picture of meridional flow or improvement in the
  cross-spectral model.

Title: Kepler White Paper: Asteroseismology of Solar-Like Oscillators
    in a 2-Wheel Mission
Authors: Chaplin, W. J; Kjeldsen, H.; Christensen-Dalsgaard, J.;
   Gilliland, R. L.; Kawaler, S. D.; Basu, S.; De Ridder, J.; Huber, D.;
   Arentoft, T.; Schou, J.; Garcia, R. A.; Metcalfe, T. S.; Brogaard, K.;
   Campante, T. L.; Elsworth, Y.; Miglio, A.; Appourchaux, T.; Bedding,
   T. R.; Hekker, S.; Houdek, G.; Karoff, C.; Molenda-Zakowicz, J.;
   Monteiro, M. J. P. F. G.; Silva Aguirre, V.; Stello, D.; Ball, W.;
   Beck, P. G.; Birch, A. C.; Buzasi, D. L.; Casagrande, L.; Cellier,
   T.; Corsaro, E.; Creevey, O. L.; Davies, G. R.; Deheuvels, S.; Dogan,
   G.; Gizon, L.; Grundahl, F.; Guzik, J.; Handberg, R.; Jimenez, A.;
   Kallinger, T.; Lund, M. N.; Lundkvist, M.; Mathis, S.; Mathur, S.;
   Mazumdar, A.; Mosser, B.; Neiner, C.; Nielsen, M. B.; Palle, P. L.;
   Pinsonneault, M. H.; Salabert, D.; Serenelli, A. M.; Shunker, H.;
   White, T. R.
Bibcode: 2013arXiv1309.0702C
Altcode:
  We comment on the potential for continuing asteroseismology of
  solar-type and red-giant stars in a 2-wheel Kepler Mission. Our main
  conclusion is that by targeting stars in the ecliptic it should be
  possible to perform high-quality asteroseismology, as long as favorable
  scenarios for 2-wheel pointing performance are met. Targeting the
  ecliptic would potentially facilitate unique science that was not
  possible in the nominal Mission, notably from the study of clusters
  that are significantly brighter than those in the Kepler field. Our
  conclusions are based on predictions of 2-wheel observations made by
  a space photometry simulator, with information provided by the Kepler
  Project used as input to describe the degraded pointing scenarios. We
  find that elevated levels of frequency-dependent noise, consistent with
  the above scenarios, would have a significant negative impact on our
  ability to continue asteroseismic studies of solar-like oscillators in
  the Kepler field. However, the situation may be much more optimistic
  for observations in the ecliptic, provided that pointing resets of the
  spacecraft during regular desaturations of the two functioning reaction
  wheels are accurate at the &lt; 1 arcsec level. This would make it
  possible to apply a post-hoc analysis that would recover most of the
  lost photometric precision. Without this post-hoc correction---and the
  accurate re-pointing it requires---the performance would probably be
  as poor as in the Kepler-field case. Critical to our conclusions for
  both fields is the assumed level of pointing noise (in the short-term
  jitter and the longer-term drift). We suggest that further tests will
  be needed to clarify our results once more detail and data on the
  expected pointing performance becomes available, and we offer our
  assistance in this work.

Title: The Kepler-SEP Mission: Harvesting the South Ecliptic Pole
    large-amplitude variables with Kepler
Authors: Szabó, R.; Molnár, L.; Kołaczkowski, Z.; Moskalik, P.;
   Ivezić, Ž.; Udalski, A.; Szabados, L.; Kuehn, C.; Smolec, R.;
   Pigulski, A.; Bedding, T.; Ngeow, C. C.; Guzik, J. A.; Ostrowski,
   J.; De Cat, P.; Antoci, V.; Borkovits, T.; Soszyński, I.; Poleski,
   R.; Kozłowski, Sz.; Pietrukowicz, P.; Skowron, J.; Szczygieł, D.;
   Wyrzykowski, Ł.; Szymański, M.; Pietrzyński, G.; Ulaczyk, K.;
   Plachy, E.; Schou, J.; Evans, N. R.; Kopaczki, G.
Bibcode: 2013arXiv1309.0741S
Altcode:
  As a response to the white paper call, we propose to turn Kepler
  to the South Ecliptic Pole (SEP) and observe thousands of large
  amplitude variables for years with high cadence in the frame of
  the Kepler-SEP Mission. The degraded pointing stability will still
  allow observing these stars with reasonable (probably better
  than mmag) accuracy. Long-term continuous monitoring already
  proved to be extremely helpful to investigate several areas of
  stellar astrophysics. Space-based missions opened a new window to
  the dynamics of pulsation in several class of pulsating variable
  stars and facilitated detailed studies of eclipsing binaries. The
  main aim of this mission is to better understand the fascinating
  dynamics behind various stellar pulsational phenomena (resonances,
  mode coupling, chaos, mode selection) and interior physics (turbulent
  convection, opacities). This will also improve the applicability of
  these astrophysical tools for distance measurements, population and
  stellar evolution studies. We investigated the pragmatic details of
  such a mission and found a number of advantages: minimal reprogramming
  of the flight software, a favorable field of view, access to both
  galactic and LMC objects. However, the main advantage of the SEP
  field comes from the large sample of well classified targets, mainly
  through OGLE. Synergies and significant overlap (spatial, temporal
  and in brightness) with both ground- (OGLE, LSST) and space-based
  missions (GAIA, TESS) will greatly enhance the scientific value of
  the Kepler-SEP mission. GAIA will allow full characterization of the
  distance indicators. TESS will continuously monitor this field for at
  least one year, and together with the proposed mission provide long time
  series that cannot be obtained by other means. If Kepler-SEP program is
  successful, there is a possibility to place one of the so-called LSST
  "deep-drilling" fields in this region.

Title: Accurate Characterization of High-degree Modes Using MDI
    Observations
Authors: Korzennik, S. G.; Rabello-Soares, M. C.; Schou, J.; Larson,
   T. P.
Bibcode: 2013ApJ...772...87K
Altcode:
  We present the first accurate characterization of high-degree modes,
  derived using the best Michelson Doppler Imager (MDI) full-disk
  full-resolution data set available. A 90 day long time series of
  full-disk 2 arcsec pixel<SUP>-1</SUP> resolution Dopplergrams was
  acquired in 2001, thanks to the high rate telemetry provided by the
  Deep Space Network. These Dopplergrams were spatially decomposed using
  our best estimate of the image scale and the known components of MDI's
  image distortion. A multi-taper power spectrum estimator was used to
  generate power spectra for all degrees and all azimuthal orders, up to
  l = 1000. We used a large number of tapers to reduce the realization
  noise, since at high degrees the individual modes blend into ridges and
  thus there is no reason to preserve a high spectral resolution. These
  power spectra were fitted for all degrees and all azimuthal orders,
  between l = 100 and l = 1000, and for all the orders with substantial
  amplitude. This fitting generated in excess of 5.2 × 10<SUP>6</SUP>
  individual estimates of ridge frequencies, line widths, amplitudes,
  and asymmetries (singlets), corresponding to some 5700 multiplets
  (l, n). Fitting at high degrees generates ridge characteristics,
  characteristics that do not correspond to the underlying mode
  characteristics. We used a sophisticated forward modeling to recover
  the best possible estimate of the underlying mode characteristics (mode
  frequencies, as well as line widths, amplitudes, and asymmetries). We
  describe in detail this modeling and its validation. The modeling has
  been extensively reviewed and refined, by including an iterative process
  to improve its input parameters to better match the observations. Also,
  the contribution of the leakage matrix on the accuracy of the
  procedure has been carefully assessed. We present the derived set of
  corrected mode characteristics, which includes not only frequencies,
  but line widths, asymmetries, and amplitudes. We present and discuss
  their uncertainties and the precision of the ridge-to-mode correction
  schemes, through a detailed assessment of the sensitivity of the model
  to its input set. The precision of the ridge-to-mode correction is
  indicative of any possible residual systematic biases in the inferred
  mode characteristics. In our conclusions, we address how to further
  improve these estimates, and the implications for other data sets,
  like GONG+ and HMI.

Title: How much more can sunspots tell us about the solar dynamo?
Authors: Norton, Aimee A.; Jones, Eric H.; Liu, Y.; Hayashi, K.;
   Hoeksema, J. T.; Schou, Jesper
Bibcode: 2013IAUS..294...25N
Altcode:
  Sunspot observations inspired solar dynamo theory and continue
  to do so. Simply counting them established the sunspot cycle
  and its period. Latitudinal distributions introduced the tough
  constraint that the source of sunspots moves equator-ward as the
  cycle progresses. Observations of Hale's polarity law mandated
  hemispheric asymmetry. How much more can sunspots tell us about
  the solar dynamo? We draw attention to a few outstanding questions
  raised by inherent sunspot properties. Namely, how to explain sunspot
  rotation rates, the incoherence of follower spots, the longitudinal
  spacing of sunspot groups, and brightness trends within a given sunspot
  cycle. After reviewing the first several topics, we then present new
  results on the brightness of sunspots in Cycle 24 as observed with
  the Helioseismic Magnetic Imager (HMI). We compare these results
  to the sunspot brightness observed in Cycle 23 with the Michelson
  Doppler Imager (MDI). Next, we compare the minimum intensities of five
  sunspots simultaneously observed by the Hinode Solar Optical Telescope
  Spectropolarimeter (SOT-SP) and HMI to verify that the minimum
  brightness of sunspot umbrae correlates well to the maximum field
  strength. We then examine 90 and 52 sunspots in the north and south
  hemisphere, respectively, from 2010 - 2012. Finally, we conclude that
  the average maximum field strengths of umbra 40 Carrington Rotations
  into Cycle 24 are 2690 Gauss, virtually indistinguishable from the
  2660 Gauss value observed at a similar time in Cycle 23 with MDI.

Title: Accurate characterization of high-degree modes using MDI data
Authors: Korzennik, S. G.; Rabello-Soares, M. C.; Schou, J.; Larson, T.
Bibcode: 2013JPhCS.440a2016K
Altcode: 2012arXiv1209.6414K
  We present the first accurate characterization of high-degree modes
  (i.e., l up to 1000), using the best MDI full-disk full-resolution
  data set available (90-day long time series, acquired in
  2001). The Dopplergrams were spatially decomposed using our best
  estimate of the image scale and the known components of MDI's image
  distortion. Multi-tapered power spectra were fitted for all degrees
  and all azimuthal orders, between l = 100 and l = 1000, and for all
  orders with substantial amplitude. Fitting at high degrees generates
  ridge characteristics, characteristics that do not correspond to the
  underlying mode characteristics. We used a sophisticated forward
  modeling to recover the best possible estimate of the underlying
  mode characteristics. We have derived a final set of corrected mode
  characteristics (frequencies, line widths, asymmetries and amplitudes)
  and their uncertainties.

Title: The High-latitude Branch of the Solar Torsional Oscillation
    in the Rising Phase of Cycle 24
Authors: Howe, R.; Christensen-Dalsgaard, J.; Hill, F.; Komm, R.;
   Larson, T. P.; Rempel, M.; Schou, J.; Thompson, M. J.
Bibcode: 2013ApJ...767L..20H
Altcode:
  We use global heliseismic data from the Global Oscillation Network
  Group, the Michelson Doppler Imager on board the Solar and Heliospheric
  Observatory, and the Helioseismic and Magnetic Imager on board the Solar
  Dynamics Observatory, to examine the behavior, during the rising phase
  of Solar Cycle 24, of the migrating zonal flow pattern known as the
  torsional oscillation. Although the high-latitude part of the pattern
  appears to be absent in the new cycle when the flows are derived by
  subtracting a mean across a full solar cycle, it can be seen if we
  subtract the mean over a shorter period in the rising phase of each
  cycle, and these two mean rotation profiles differ significantly
  at high latitudes. This indicates that the underlying high-latitude
  rotation has changed; we speculate that this is in response to weaker
  polar fields, as suggested by a recent model.

Title: Stray Light Correction for HMI Data
Authors: Norton, A. A.; Duvall, T.; Schou, J.; Cheung, M.
Bibcode: 2013enss.confE..95N
Altcode:
  Our goal is to find a deconvolution routine that can remove scattered
  light in sunspot umbrae without introducing extraneous power in high
  spatial frequencies in helioseismology analysis of the same data. Using
  ground-based calibration data, a third-order polynomial fit was obtained
  for the instrumental modulation transfer function (MTF). Images of the
  solar limb and the limb and disk of Venus during its transit were used
  to model stray light. An Airy function and a Lorentzian are used in
  combination to model the instrumental point spread function (PSF) for
  HMI which is made to be positive definite everywhere and zero above
  the ideal optical Nyquist frequency. Deconvolution was carried out
  using a Lucy-Richardson algorithm on a graphics processing unit. The
  deconvolved image is then compared to the original to determine the
  extent of introduced Gibb's phenomenon (ringing) and how the power
  changes as a function of spatial frequency.

Title: Using Distortion of Global Mode Eigenfunctions to Estimate
    Large Scale Flows
Authors: Schou, J.; Woodard, M. F.; Baldner, C. S.; Larson, T. P.
Bibcode: 2013enss.confE.103S
Altcode:
  The accurate measurement of large scale flows, such as differential
  rotation and meridional flow, throughout the solar interior is important
  for understanding the solar interior and the processes relevant for
  the solar dynamo. Ordinarily normal modes would be expected to give
  more accurate measurement of large scale flows than local helioseismic
  techniques. Unfortunately, mode frequencies are not sensitive to the
  meridional flow and so traditional methods do not work. Here we describe
  our progress on using the distortion of the eigenfunctions to measure
  flows. In particular on identifying the source of the large systematic
  errors previously reported and determining the effect of light travel
  time, center to limb phase variations and other physical effects.

Title: Femtosecond-laser ablation dynamics of dielectrics: basics
    and applications for thin films
Authors: Balling, P.; Schou, J.
Bibcode: 2013RPPh...76c6502B
Altcode:
  Laser ablation of dielectrics by ultrashort laser pulses is
  reviewed. The basic interaction between ultrashort light pulses and
  the dielectric material is described, and different approaches to the
  modeling of the femtosecond ablation dynamics are reviewed. Material
  excitation by ultrashort laser pulses is induced by a combination
  of strong-field excitation (multi-photon and tunnel excitation),
  collisional excitation (potentially leading to an avalanche process),
  and absorption in the plasma consisting of the electrons excited to
  the conduction band. It is discussed how these excitation processes
  can be described by various rate-equation models in combination with
  different descriptions of the excited electrons. The optical properties
  of the highly excited dielectric undergo a rapid change during the
  laser pulse, which must be included in a detailed modeling of the
  excitations. The material ejected from the dielectric following the
  femtosecond-laser excitation can potentially be used for thin-film
  deposition. The deposition rate is typically much smaller than that
  for nanosecond lasers, but film production by femtosecond lasers
  does possess several attractive features. First, the strong-field
  excitation makes it possible to produce films of materials that are
  transparent to the laser light. Second, the highly localized excitation
  reduces the emission of larger material particulates. Third, lasers
  with ultrashort pulses are shown to be particularly useful tools for
  the production of nanocluster films. The important question of the
  film stoichiometry relative to that of the target will be thoroughly
  discussed in relation to the films reported in the literature.

Title: Comparison Between Line-Of-Sight Observables And
Milne-Eddington Inversion Results From HMI: 24- And 12-hour Period
    Oscillations
Authors: Couvidat, Sebastien; Liu, Yang; Scherrer, Philip H.; Schou,
   Jesper; HMI Team
Bibcode: 2013enss.confE..84C
Altcode:
  Oscillations with 12 and 24 hour periods are visible in sunspots
  on line-of-sight (LOS) observables and, to a lesser extent, on
  Milne-Eddington (ME) inversion results from the SDO/HMI instrument.Such
  oscillations are artifacts produced by the LOS algorithm and ME
  inversion procedure, and are not of solar origin. For instance, the LOS
  algorithm depends on an Fe I line profile and on HMI filter transmission
  profiles to convert the HMI intensities into Doppler velocities and LOS
  magnetic-field strengths: one of the issues we encountered is that in
  the presence of strong fields the Fe I profile used is inappropriate
  and results in errors in the left and right circular polarization
  velocity estimates. Here we present some properties of these 12-
  and 24-hour period oscillations, and we discuss their origin and the
  possibility of improving the LOS algorithm and ME inversion procedure
  to reduce their amplitudes.

Title: Progress in Near-Surface Flow Determinations: Minimizing
    Systematics
Authors: Baldner, Charles S.; Basu, Sarbani; Bogart, Richard S.;
   Schou, Jesper
Bibcode: 2013enss.confE.116B
Altcode:
  One of the key achievements in helioseismology has been the measurement
  of sub-surface dynamics. Measurements of both differential rotation
  and meridional circulation exist from multiple instruments for more
  than one and a half solar cycles. The precision of flow determinations
  from various helioseismic techniques has been found to be greater than
  their accuracy. Flows have been found to depend on the disk position
  of the measurements, and some inconsistencies between measurements
  from different instruments have also been found. In this work, we
  report progress in understanding and correcting for these systematic
  errors, and present the latest ring diagram determinations of shallow
  subsurface flows with HMI/SDO data.

Title: Three 2012 Transits of Venus: From Earth, Jupiter, and Saturn
Authors: Pasachoff, Jay M.; Schneider, G.; Babcock, B. A.; Lu, M.;
   Edelman, E.; Reardon, K.; Widemann, T.; Tanga, P.; Dantowitz, R.;
   Silverstone, M. D.; Ehrenreich, D.; Vidal-Madjar, A.; Nicholson,
   P. D.; Willson, R. C.; Kopp, G. A.; Yurchyshyn, V. B.; Sterling,
   A. C.; Scherrer, P. H.; Schou, J.; Golub, L.; McCauley, P.; Reeves, K.
Bibcode: 2013AAS...22131506P
Altcode:
  We observed the 2012 June 6/5 transit seen from Earth (E/ToV),
  simultaneously with Venus Express and several other spacecraft
  not only to study the Cytherean atmosphere but also to provide an
  exoplanet-transit analog. From Haleakala, the whole transit was visible
  in coronal skies; among our instruments was one of the world-wide Venus
  Twilight Experiment's nine coronagraphs. Venus's atmosphere became
  visible before first contact. SacPeak/IBIS provided high-resolution
  images at Hα/carbon-dioxide. Big Bear's NST also provided
  high-resolution observations of the Cytherean atmosphere and black-drop
  evolution. Our liaison with UH's Mees Solar Observatory scientists
  provided magneto-optical imaging at calcium and potassium. Solar
  Dynamics Observatory's AIA and HMI, and the Solar Optical Telescope
  (SOT) and X-ray Telescope (XRT) on Hinode, and total-solar-irradiance
  measurements with ACRIMSAT and SORCE/TIM, were used to observe the
  event as an exoplanet-transit analog. On September 20, we imaged
  Jupiter for 14 Hubble Space Telescope orbits, centered on a 10-hour
  ToV visible from Jupiter (J/ToV), as an exoplanet-transit analog in
  our own solar system, using Jupiter as an integrating sphere. Imaging
  was good, although much work remains to determine if we can detect
  the expected 0.01% solar irradiance decrease at Jupiter and the even
  slighter differential effect between our violet and near-infrared
  filters caused by Venus's atmosphere. We also give a first report on our
  currently planned December 21 Cassini UVIS observations of a transit of
  Venus from Saturn (S/ToV). Our E/ToV expedition was sponsored by the
  Committee for Research and Exploration/National Geographic Society;
  supplemented: NASA/AAS's Small Research Grant Program. We thank Rob
  Ratkowski, Stan Truitt, Rob Lucas, Aram Friedman, and Eric Pilger
  '82 at Haleakala, and Joseph Gangestad '06 at Big Bear for assistance,
  and Lockheed Martin Solar and Astrophysics Lab and Hinode science and
  operations teams for support for coordinated observations with NASA
  satellites. Our J/ToV observations were based on observations made
  with HST, operated by AURA, Inc., under NASA contract NAS 5-26555;
  these observations are associated with program #13067.

Title: Erratum: "On the Determination of Michelson
    Doppler Imager High-degree Mode Frequencies" <A
    href="/abs/2004ApJ...602..481K">(2004, ApJ, 602, 481)</A>
Authors: Korzennik, S. G.; Rabello-Soares, M. C.; Schou, J.
Bibcode: 2012ApJ...760..156K
Altcode:
  No abstract at ADS

Title: Effects of Asymmetric Flows in Solar Convection on Oscillation
    Modes
Authors: Baldner, Charles S.; Schou, Jesper
Bibcode: 2012ApJ...760L...1B
Altcode: 2012arXiv1210.1583B
  Many helioseismic measurements suffer from substantial systematic
  errors. A particularly frustrating one is that time-distance
  measurements suffer from a large center to limb effect which looks
  very similar to the finite light travel time, except that the magnitude
  depends on the observable used and can have the opposite sign. This has
  frustrated attempts to determine the deep meridional flow in the solar
  convection zone, with Zhao et al. applying an ad hoc correction with
  little physical basis to correct the data. In this Letter, we propose
  that part of this effect can be explained by the highly asymmetrical
  nature of the solar granulation which results in what appears to the
  oscillation modes as a net radial flow, thereby imparting a phase shift
  on the modes as a function of observing height and thus heliocentric
  angle.

Title: The 2012 Transit of Venus for Cytherean Atmospheric Studies
    and as an Exoplanet Analog
Authors: Pasachoff, Jay M.; Schneider, G.; Babcock, B. A.; Lu, M.;
   Reardon, K. P.; Widemann, T.; Tanga, P.; Dantowitz, R.; Willson,
   R.; Kopp, G.; Yurchyshyn, V.; Sterling, A.; Scherrer, P.; Schou, J.;
   Golub, L.; Reeves, K.
Bibcode: 2012DPS....4450806P
Altcode:
  We worked to assemble as complete a dataset as possible for the
  Cytherean atmosphere in collaboration with Venus Express in situ
  and to provide an analog of spectral and total irradiance exoplanet
  measurements. From Haleakala, the whole transit was visible in
  coronal skies; our B images showed the evolution of the visibility
  of Venus's atmosphere and of the black-drop effect, as part of the
  Venus Twilight Experiment's 9 coronagraphs distributed worldwide
  with BVRI. We imaged the Cytherean atmosphere over two minutes before
  first contact, with subarcsecond resolution, with the coronagraph and
  a separate refractor. The IBIS imaging spectrometer at Sacramento
  Peak Observatory at H-alpha and carbon-dioxide also provided us
  high-resolution imaging. The NST of Big Bear Solar Observatory
  also provided high-resolution vacuum observations of the Cytherean
  atmosphere and black drop evolution. Our liaison with UH's Mees Solar
  Observatory scientists provided magneto-optical imaging at calcium
  and potassium. Spaceborne observations included the Solar Dynamics
  Observatory's AIA and HMI, and the Solar Optical Telescope (SOT)
  and X-ray Telescope (XRT) on Hinode, and total-solar-irradiance
  measurements with ACRIMSAT and SORCE/TIM, to characterize the
  event as an exoplanet-transit analog. Our expedition was sponsored
  by the Committee for Research and Exploration/National Geographic
  Society. Some of the funds for the carbon-dioxide filter for IBIS were
  provided by NASA through AAS's Small Research Grant Program. We thank
  Rob Lucas, Aram Friedman, and Eric Pilger '82 for assistance with
  Haleakala observing, Rob Ratkowski of Haleakala Amateur Astronomers
  for assistance with equipment and with the site, Stan Truitt for the
  loan of his Paramount ME, and Steve Bisque/Software Bisque for TheSky
  X controller. We thank Joseph Gangestad '06 of Aerospace Corp., a
  veteran of our 2004 expedition, for assistance at Big Bear. We thank
  the Lockheed Martin Solar and Astrophysics Laboratory and Hinode
  science and operations teams for planning and support.

Title: A Determination of High-degree Mode Parameters Based on
    MDI Observations
Authors: Korzennik, S. G.; Rabello-Soares, M. C.; Schou, J.; Larson,
   T. P.
Bibcode: 2012ASPC..462..189K
Altcode:
  We present the best to date determination of high-degree mode
  parameters obtained from a ninety day long time series of full-disk
  full-resolution Michelson Doppler Imager (MDI) Dopplergrams. These
  Dopplergrams were decomposed using our best estimate of the image
  scale and the known components of MDI's image distortion. The
  spherical harmonic decomposition was carried out up to ℓ=1000,
  and a high-order sine multi-taper power spectrum estimator was used
  to generate power spectra. These power spectra were fitted for all
  degrees and all azimuthal orders, for 100 ≤ ℓ ≤ 1000, and
  for all radial orders with substantial amplitude, generating some
  6 × 10<SUP>6</SUP> estimates of ridge frequencies, line-widths,
  amplitudes and asymmetries. We used a sophisticated forward modeling
  of the mode to ridge blending, to recover the best possible estimate
  of the underlying mode characteristics.

Title: Helioseismic Measurements of the Torsional Oscillation
Authors: Schou, J.; Howe, R.; Larson, T. P.
Bibcode: 2012ASPC..462..352S
Altcode:
  The zonal flows known as the torsional oscillation have by now been
  observed for more than 15 years using observations from the Michelson
  Doppler Imager (MDI) and Global Oscillation Network Group (GONG). Even
  with this limited set of data it is clear that there are significant
  differences between the cycles, as also evidenced by the prolonged
  recent solar minimum. Here we discuss some of these differences and
  their significance. In particular we discuss the slower development of
  the current solar cycle and the lack of a polar branch in the torsional
  oscillation. We will also compare results from MDI and the Helioseismic
  Magnetic Imager (HMI) and discuss the prospects for generating longer
  consistent sets of observations.

Title: Seismic Evidence for a Rapidly Rotating Core in a
    Lower-giant-branch Star Observed with Kepler
Authors: Deheuvels, S.; García, R. A.; Chaplin, W. J.; Basu, S.;
   Antia, H. M.; Appourchaux, T.; Benomar, O.; Davies, G. R.; Elsworth,
   Y.; Gizon, L.; Goupil, M. J.; Reese, D. R.; Regulo, C.; Schou, J.;
   Stahn, T.; Casagrande, L.; Christensen-Dalsgaard, J.; Fischer, D.;
   Hekker, S.; Kjeldsen, H.; Mathur, S.; Mosser, B.; Pinsonneault, M.;
   Valenti, J.; Christiansen, J. L.; Kinemuchi, K.; Mullally, F.
Bibcode: 2012ApJ...756...19D
Altcode: 2012arXiv1206.3312D
  Rotation is expected to have an important influence on the structure
  and the evolution of stars. However, the mechanisms of angular momentum
  transport in stars remain theoretically uncertain and very complex to
  take into account in stellar models. To achieve a better understanding
  of these processes, we desperately need observational constraints on the
  internal rotation of stars, which until very recently was restricted to
  the Sun. In this paper, we report the detection of mixed modes—i.e.,
  modes that behave both as g modes in the core and as p modes in
  the envelope—in the spectrum of the early red giant KIC 7341231,
  which was observed during one year with the Kepler spacecraft. By
  performing an analysis of the oscillation spectrum of the star, we
  show that its non-radial modes are clearly split by stellar rotation
  and we are able to determine precisely the rotational splittings of
  18 modes. We then find a stellar model that reproduces very well the
  observed atmospheric and seismic properties of the star. We use this
  model to perform inversions of the internal rotation profile of the
  star, which enables us to show that the core of the star is rotating at
  least five times faster than the envelope. This will shed new light on
  the processes of transport of angular momentum in stars. In particular,
  this result can be used to place constraints on the angular momentum
  coupling between the core and the envelope of early red giants, which
  could help us discriminate between the theories that have been proposed
  over the last few decades.

Title: Comparison of Line-of-Sight Magnetograms Taken by the Solar
    Dynamics Observatory/Helioseismic and Magnetic Imager and Solar and
    Heliospheric Observatory/Michelson Doppler Imager
Authors: Liu, Y.; Hoeksema, J. T.; Scherrer, P. H.; Schou, J.;
   Couvidat, S.; Bush, R. I.; Duvall, T. L.; Hayashi, K.; Sun, X.;
   Zhao, X.
Bibcode: 2012SoPh..279..295L
Altcode: 2012SoPh..tmp...75L
  We compare line-of-sight magnetograms from the Helioseismic and
  Magnetic Imager (HMI) onboard the Solar Dynamics Observatory (SDO) and
  the Michelson Doppler Imager (MDI) onboard the Solar and Heliospheric
  Observatory (SOHO). The line-of-sight magnetic signal inferred from
  the calibrated MDI data is greater than that derived from the HMI data
  by a factor of 1.40. This factor varies somewhat with center-to-limb
  distance. An upper bound to the random noise for the 1'' resolution
  HMI 720-second magnetograms is 6.3 Mx cm<SUP>−2</SUP>, and 10.2 Mx
  cm<SUP>−2</SUP> for the 45-second magnetograms. Virtually no p-mode
  leakage is seen in the HMI magnetograms, but it is significant in
  the MDI magnetograms. 12-hour and 24-hour periodicities are detected
  in strong fields in the HMI magnetograms. The newly calibrated
  MDI full-disk magnetograms have been corrected for the zero-point
  offset and underestimation of the flux density. The noise is 26.4 Mx
  cm<SUP>−2</SUP> for the MDI one-minute full-disk magnetograms and
  16.2 Mx cm<SUP>−2</SUP> for the five-minute full-disk magnetograms
  observed with four-arcsecond resolution. The variation of the noise over
  the Sun's disk found in MDI magnetograms is likely due to the different
  optical distortions in the left- and right-circular analyzers, which
  allows the granulation and p-mode to leak in as noise. Saturation
  sometimes seen in sunspot umbrae in MDI magnetograms is caused by
  the low intensity and the limitation of the onboard computation. The
  noise in the HMI and MDI line-of-sight magnetic-field synoptic charts
  appears to be fairly uniform over the entire map. The noise is 2.3 Mx
  cm<SUP>−2</SUP> for HMI charts and 5.0 Mx cm<SUP>−2</SUP> for MDI
  charts. No evident periodicity is found in the HMI synoptic charts.

Title: The Height of a White-light Flare and Its Hard X-Ray Sources
Authors: Martínez Oliveros, Juan-Carlos; Hudson, Hugh S.; Hurford,
   Gordon J.; Krucker, Säm; Lin, R. P.; Lindsey, Charles; Couvidat,
   Sebastien; Schou, Jesper; Thompson, W. T.
Bibcode: 2012ApJ...753L..26M
Altcode: 2012arXiv1206.0497M
  We describe observations of a white-light (WL) flare
  (SOL2011-02-24T07:35:00, M3.5) close to the limb of the Sun, from which
  we obtain estimates of the heights of the optical continuum sources and
  those of the associated hard X-ray (HXR) sources. For this purpose, we
  use HXR images from the Reuven Ramaty High Energy Spectroscopic Imager
  and optical images at 6173 Å from the Solar Dynamics Observatory. We
  find that the centroids of the impulsive-phase emissions in WL and HXRs
  (30-80 keV) match closely in central distance (angular displacement
  from Sun center), within uncertainties of order 0farcs2. This directly
  implies a common source height for these radiations, strengthening the
  connection between visible flare continuum formation and the accelerated
  electrons. We also estimate the absolute heights of these emissions
  as vertical distances from Sun center. Such a direct estimation has
  not been done previously, to our knowledge. Using a simultaneous 195
  Å image from the Solar-Terrestrial RElations Observatory spacecraft
  to identify the heliographic coordinates of the flare footpoints,
  we determine mean heights above the photosphere (as normally defined;
  τ = 1 at 5000 Å) of 305 ± 170 km and 195 ± 70 km, respectively, for
  the centroids of the HXR and WL footpoint sources of the flare. These
  heights are unexpectedly low in the atmosphere, and are consistent
  with the expected locations of τ = 1 for the 6173 Å and the ~40 keV
  photons observed, respectively.

Title: Meridional Circulation From Normal Mode Analysis
Authors: Schou, Jesper; Woodard, M. F.; Larson, T. P.
Bibcode: 2012AAS...22020505S
Altcode:
  We have recently been able to make significant progress in the
  determining the solar meridional flow from the perturbations it causes
  to the eigenfunctions of normal modes. In this poster we will describe
  some of our recent progress and show that it will likely be possible to
  determine the flow over a substantial part of the solar interior with
  a precision sufficient <P />to address important questions. However,
  we also see what appears to be significant systematic errors and will
  describe our efforts at understanding those.

Title: Line-of-Sight Observables Algorithms for the Helioseismic
    and Magnetic Imager (HMI) Instrument Tested with Interferometric
    Bidimensional Spectrometer (IBIS) Observations
Authors: Couvidat, Sébastien; Rajaguru, S. P.; Wachter, Richard;
   Sankarasubramanian, K.; Schou, Jesper; Scherrer, Philip H.
Bibcode: 2012SoPh..278..217C
Altcode:
  The Helioseismic and Magnetic Imager (HMI) instrument onboard the
  Solar Dynamics Observatory produces line-of-sight (LOS) observables
  (Doppler velocity, magnetic-field strength, Fe I line width, line
  depth, and continuum intensity) as well as vector magnetic-field maps
  at the solar surface. The accuracy of LOS observables is dependent
  on the algorithm used to translate a sequence of HMI filtergrams into
  the corresponding observables. Using one hour of high-cadence imaging
  spectropolarimetric observations of a sunspot in the Fe I line at 6173
  Å through the Interferometric Bidimensional Spectrometer installed
  at the Dunn Solar Telescope, and the Milne-Eddington inversion of the
  corresponding Stokes vectors, we test the accuracy of the observables
  algorithm currently implemented in the HMI data-analysis pipeline:
  the MDI-like algorithm. In an attempt to improve the accuracy of
  HMI observables, we also compare this algorithm to others that may be
  implemented in the future: a least-squares fit with a Gaussian profile,
  a least-squares fit with a Voigt profile, and the use of second Fourier
  coefficients in the MDI-like algorithm.

Title: Viewing Geometry, Line Height-of-Formation, and Helioseismic
    Measurements
Authors: Baldner, Charles; Parchevsky, K.; Schou, J.; Larson, T.;
   Couvidat, S.
Bibcode: 2012AAS...22020506B
Altcode:
  Helioseismic mode parameters or travel times are commonly measured by
  observing an absorption line in the solar atmosphere and determining
  the line-of-sight velocity by means of the Doppler effect. Helioseismic
  measurements are thus susceptible to a number of systematic errors
  associated with the details of the line formation and wave propagation
  in the atmosphere. Observing at different heights in the atmosphere
  introduce errors through fairly simple geometric effects. In addition,
  mode amplitudes and eigenfunction may change with height. More complex
  potential sources of error include the fact that not all waves are
  purely evanescent, the effects of convection, the acoustic source
  depth and distribution, and non-adiabaticity. In this work, we report
  progress in characterizing the effects on helioseismic measurements
  by the differing height-of-formation across the disk. We consider the
  effects of height-of-formation on global mode parameters, ring diagram
  parameters, and time-distance travel time measurements.

Title: Latest Results on the Torsional Oscillation and Solar Cycle 25
Authors: Hill, Frank; Howe, R.; Schou, J.; Thompson, M.; Larson, T.;
   Komm, R.
Bibcode: 2012AAS...22012302H
Altcode:
  The Torsional Oscillation in the Sun is a zonal (East-West) flow
  that is slightly faster than the background differential rotation
  profile. The location of this flow slowly migrates in latitude over
  a period of several years. There are two branches of the flow: an
  equatorward branch that underlies the active regions, and a poleward
  branch. The timing of the equatorward migration is correlated with the
  timing of the solar cycle such that the activity for a cycle appears
  when the center of the flow reaches latitude 25 degrees. In addition,
  the poleward branch appears about 12 years prior to the activity for
  a cycle. Thus we should have observed the onset of Cycle 25 in 2008,
  but did not. This poster will update the observations to 2012, and
  present a new analysis that shows that the Cycle 25 flow appeared
  in 2010, but was hidden by a change in the background differential
  rotation profile. These results suggest that the next minimum will be
  two years longer than average, and that Cycle 25 will begin in 2022.

Title: Using HMI To Study Photospheric Footpoint Motions In X-class
    Flares
Authors: Desai, Priyamvada; Bogart, R.; Couvidat, S.; Schou, J.
Bibcode: 2012AAS...22020418D
Altcode:
  Recent investigations of flare-related changes in the photospheric <P
  />absorption line (FeI 617.3 nm) profile of solar flares of varying
  X-ray <P />classes, observed using the Helioseismic and Magnetic
  Imager (HMI) <P />aboard the Solar Dynamic Observatory (SD0),
  has indicated that a large <P />percentage of them show distinct
  continuum enhancement, along with a marked decrease in line-depth
  (Desai,et al,submitted). <P />Some of the X-class flares also showed a
  reversal in the line profile, from absorption into emission during the
  peak of the flare. We investigate the temporal and spatial variations
  in the velocity of the photospheric foot point motions and track the
  evolution of the flares of some of these X-class <P />flares.

Title: Direct Measurement Of The Height Of A White-light Flare
Authors: Hudson, Hugh S.; Martinez-Oliveros, J.; Krucker, S.; Hurford,
   G.; Thompson, W.; Schou, J.; Couvidat, S.; Lindsey, C.
Bibcode: 2012AAS...22020441H
Altcode:
  We have used RHESSI and HMI observations to observe hard X-ray and
  white-light continuum sources of the limb flare SOL2011-02-24, and
  find the source centroids to coincide within errors of about 0.2 arc s,
  with the conclusion that the emissions form at the same height in the
  atmosphere. This greatly strengthens the known association between
  non-thermal electrons and white-light continuum formation. We also
  use STEREO observations to find the heliographic coordinates of the
  flare. This determines the projected height of the photosphere directly
  below the flare emissions. With this information, the RHESSI metrology
  determines the absolute height of the sources to be remarkably low
  in the solar atmosphere: the two footpoints have comparable heights,
  which we estimate at about 290 +- 138 km above the photosphere. This
  location lies significantly below the visible-light limb height,
  estimated at 500 km by Brown &amp; Christensen-Dalsgaard (1998), and
  the height of optical depth unity to Thomson scattering, estimated
  at a higher altitude. The results are not consistent with any current
  models of these processes.

Title: Two Years of Global Analysis with HMI
Authors: Larson, Timothy P.; Schou, J.
Bibcode: 2012AAS...22020702L
Altcode:
  With HMI completing over two years of observations in May 2012,
  we have the opportunity to see the beginning of any trends in the
  global mode parameters and rotational inversions. In particular we
  can investigate whether the one-year periodicity seen in the f-mode
  frequencies measured by MDI is present in HMI. Furthermore, HMI gives
  us an opportunity to examine the helioseismic signals for a long span
  of time in observables contemporaneous with velocity, such as intensity
  and line depth, which MDI was unable to provide. The high resolution
  of the HMI instrument also gives us a chance to study in detail how
  the apodization of the images affects the inferred mode parameters,
  since our previous work has shown an as yet not understood systematic
  error relating to the apodization.

Title: A First Look at Magnetic Field Data Products from SDO/HMI
Authors: Liu, Y.; Scherrer, P. H.; Hoeksema, J. T.; Schou, J.; Bai,
   T.; Beck, J. G.; Bobra, M.; Bogart, R. S.; Bush, R. I.; Couvidat,
   S.; Hayashi, K.; Kosovichev, A. G.; Larson, T. P.; Rabello-Soares,
   C.; Sun, X.; Wachter, R.; Zhao, J.; Zhao, X. P.; Duvall, T. L., Jr.;
   DeRosa, M. L.; Schrijver, C. J.; Title, A. M.; Centeno, R.; Tomczyk,
   S.; Borrero, J. M.; Norton, A. A.; Barnes, G.; Crouch, A. D.; Leka,
   K. D.; Abbett, W. P.; Fisher, G. H.; Welsch, B. T.; Muglach, K.;
   Schuck, P. W.; Wiegelmann, T.; Turmon, M.; Linker, J. A.; Mikić,
   Z.; Riley, P.; Wu, S. T.
Bibcode: 2012ASPC..455..337L
Altcode:
  The Helioseismic and Magnetic Imager (HMI; Scherrer &amp; Schou 2011)
  is one of the three instruments aboard the Solar Dynamics Observatory
  (SDO) that was launched on February 11, 2010 from Cape Canaveral,
  Florida. The instrument began to acquire science data on March 24. The
  regular operations started on May 1. HMI measures the Doppler velocity
  and line-of-sight magnetic field in the photosphere at a cadence of
  45 seconds, and the vector magnetic field at a 135-second cadence,
  with a 4096× 4096 pixels full disk coverage. The vector magnetic
  field data is usually averaged over 720 seconds to suppress the p-modes
  and increase the signal-to-noise ratio. The spatial sampling is about
  0".5 per pixel. HMI observes the Fe i 6173 Å absorption line, which
  has a Landé factor of 2.5. These data are further used to produce
  higher level data products through the pipeline at the HMI-AIA Joint
  Science Operations Center (JSOC) - Science Data Processing (Scherrer et
  al. 2011) at Stanford University. In this paper, we briefly describe the
  data products, and demonstrate the performance of the HMI instrument. We
  conclude that the HMI is working extremely well.

Title: Wavelength Dependence of the Helioseismic and Magnetic Imager
    (HMI) Instrument onboard the Solar Dynamics Observatory (SDO)
Authors: Couvidat, Sébastien; Schou, Jesper; Shine, Richard A.;
   Bush, Rock I.; Miles, John W.; Scherrer, Philip H.; Rairden, Richard L.
Bibcode: 2012SoPh..275..285C
Altcode: 2011SoPh..tmp..150C; 2011SoPh..tmp..219C; 2011SoPh..tmp...33C;
   2011SoPh..tmp..110C
  The Helioseismic and Magnetic Imager (HMI) instrument will produce
  Doppler-velocity and vector-magnetic-field maps of the solar surface,
  whose accuracy is dependent on a thorough knowledge of the transmission
  profiles of the components of the HMI optical-filter system. Here we
  present a series of wavelength-dependence calibration tests, performed
  on the instrument from 2005 onwards, to obtain these profiles. We
  obtained the transmittances as a function of wavelength for the tunable
  and non-tunable filter elements, as well as the variation of these
  transmittances with temperature and the angle of incidence of rays of
  light. We also established the presence of fringe patterns produced by
  interferences inside the blocking filter and the front window, as well
  as a change in transmitted intensity with the tuning position. This
  thorough characterization of the HMI-filter system confirmed the very
  high quality of the instrument, and showed that its properties are
  well within the required specifications to produce superior data with
  high spatial and temporal resolution.

Title: Image Quality of the Helioseismic and Magnetic Imager (HMI)
    Onboard the Solar Dynamics Observatory (SDO)
Authors: Wachter, R.; Schou, J.; Rabello-Soares, M. C.; Miles, J. W.;
   Duvall, T. L.; Bush, R. I.
Bibcode: 2012SoPh..275..261W
Altcode: 2011SoPh..tmp..100W; 2011SoPh..tmp...19W; 2011SoPh..tmp..148W;
   2011SoPh..tmp..217W
  We describe the imaging quality of the Helioseismic and Magnetic Imager
  (HMI) onboard the Solar Dynamics Observatory (SDO) as measured during
  the ground calibration of the instrument. We describe the calibration
  techniques and report our results for the final configuration of
  HMI. We present the distortion, modulation transfer function, stray
  light, image shifts introduced by moving parts of the instrument,
  best focus, field curvature, and the relative alignment of the two
  cameras. We investigate the gain and linearity of the cameras, and
  present the measured flat field.

Title: Polarization Calibration of the Helioseismic and Magnetic
    Imager (HMI) onboard the Solar Dynamics Observatory (SDO)
Authors: Schou, J.; Borrero, J. M.; Norton, A. A.; Tomczyk, S.;
   Elmore, D.; Card, G. L.
Bibcode: 2012SoPh..275..327S
Altcode:
  As part of the overall ground-based calibration of the Helioseismic
  and Magnetic Imager (HMI) instrument an extensive set of polarimetric
  calibrations were performed. This paper describes the polarimetric
  design of the instrument, the test setup, the polarimetric model,
  the tests performed, and some results. It is demonstrated that HMI
  achieves an accuracy of 1% or better on the crosstalks between Q,
  U, and V and that our model can reproduce the intensities in our
  calibration sequences to about 0.4%. The amount of depolarization
  is negligible when the instrument is operated as intended which,
  combined with the flexibility of the polarimeter design, means that
  the polarimetric efficiency is excellent.

Title: Design and Ground Calibration of the Helioseismic and Magnetic
    Imager (HMI) Instrument on the Solar Dynamics Observatory (SDO)
Authors: Schou, J.; Scherrer, P. H.; Bush, R. I.; Wachter, R.;
   Couvidat, S.; Rabello-Soares, M. C.; Bogart, R. S.; Hoeksema, J. T.;
   Liu, Y.; Duvall, T. L.; Akin, D. J.; Allard, B. A.; Miles, J. W.;
   Rairden, R.; Shine, R. A.; Tarbell, T. D.; Title, A. M.; Wolfson,
   C. J.; Elmore, D. F.; Norton, A. A.; Tomczyk, S.
Bibcode: 2012SoPh..275..229S
Altcode:
  The Helioseismic and Magnetic Imager (HMI) investigation (Solar
  Phys. doi:10.1007/s11207-011-9834-2, 2011) will study the solar
  interior using helioseismic techniques as well as the magnetic field
  near the solar surface. The HMI instrument is part of the Solar
  Dynamics Observatory (SDO) that was launched on 11 February 2010. The
  instrument is designed to measure the Doppler shift, intensity, and
  vector magnetic field at the solar photosphere using the 6173 Å Fe I
  absorption line. The instrument consists of a front-window filter, a
  telescope, a set of waveplates for polarimetry, an image-stabilization
  system, a blocking filter, a five-stage Lyot filter with one tunable
  element, two wide-field tunable Michelson interferometers, a pair
  of 4096<SUP>2</SUP> pixel cameras with independent shutters, and
  associated electronics. Each camera takes a full-disk image roughly
  every 3.75 seconds giving an overall cadence of 45 seconds for the
  Doppler, intensity, and line-of-sight magnetic-field measurements
  and a slower cadence for the full vector magnetic field. This article
  describes the design of the HMI instrument and provides an overview of
  the pre-launch calibration efforts. Overviews of the investigation,
  details of the calibrations, data handling, and the science analysis
  are provided in accompanying articles.

Title: The Helioseismic and Magnetic Imager (HMI) Investigation for
    the Solar Dynamics Observatory (SDO)
Authors: Scherrer, P. H.; Schou, J.; Bush, R. I.; Kosovichev, A. G.;
   Bogart, R. S.; Hoeksema, J. T.; Liu, Y.; Duvall, T. L.; Zhao, J.;
   Title, A. M.; Schrijver, C. J.; Tarbell, T. D.; Tomczyk, S.
Bibcode: 2012SoPh..275..207S
Altcode:
  The Helioseismic and Magnetic Imager (HMI) instrument and investigation
  as a part of the NASA Solar Dynamics Observatory (SDO) is designed
  to study convection-zone dynamics and the solar dynamo, the origin
  and evolution of sunspots, active regions, and complexes of activity,
  the sources and drivers of solar magnetic activity and disturbances,
  links between the internal processes and dynamics of the corona and
  heliosphere, and precursors of solar disturbances for space-weather
  forecasts. A brief overview of the instrument, investigation objectives,
  and standard data products is presented.

Title: HMI vector magnetic field products: the long-awaited release
    has come! Now what?
Authors: Centeno, R.; Barnes, G.; Borrero, J.; Couvidat, S. P.;
   Hayashi, K.; Hoeksema, J. T.; Leka, K. D.; Liu, Y.; Schou, J.; Schuck,
   P. W.; Sun, X.; Tomczyk, S.
Bibcode: 2011AGUFMSH31A1985C
Altcode:
  HMI vector magnetic field test products will be released, alongside
  with the corresponding documentation, soon after the submission of this
  abstract. These data represent a stage of the project at which the HMI
  vector team has a large degree of confidence in the results. However,
  longer-term research topics on how to improve certain aspects of the
  data pipeline in general -and the spectral line inversion code in
  particular- are being pursued as we get valuable input from the user
  community. I will give a brief summary of the characteristics of the
  released inversion data products and an update of where we stand now.

Title: Sunspot Groups Simultaneously Observed with HMI and MDI
Authors: Norton, A. A.; Schou, J.; Liu, Y.; Hoeksema, J. T.
Bibcode: 2011sdmi.confE..42N
Altcode:
  Simultaneous data from HMI and MDI is analyzed for active regions 11084
  and 11087. We showcase the improved quality of HMI 45-second magnetogram
  data over MDI magnetogram data due to higher spectral and spatial
  sampling as well as better optical alignment and a magnetically more
  sensitive spectral line. Specifically, HMI magnetogram data contains
  less leakage of p-mode signal, umbrae do not show saturation at low
  intensities, and HMI flux values are consistent with vector data. We
  show comparisons of magnetic time series and power spectra observed
  by HMI and MDI for sunspot, plage and quiet-Sun.

Title: VFISV: Very Fast Inversion of the Stokes Vector for the
    Helioseismic and Magnetic Imager
Authors: Borrero, J. M.; Tomczyk, S.; Kubo, M.; Socas-Navarro, H.;
   Schou, J.; Couvidat, S.; Bogart, R.
Bibcode: 2011SoPh..273..267B
Altcode: 2009arXiv0901.2702B
  In this paper we describe in detail the implementation and main
  properties of a new inversion code for the polarized radiative transfer
  equation (VFISV: Very Fast Inversion of the Stokes Vector). VFISV will
  routinely analyze pipeline data from the Helioseismic and Magnetic
  Imager (HMI) on-board of the Solar Dynamics Observatory (SDO). It
  will provide full-disk maps (4096×4096 pixels) of the magnetic field
  vector on the Solar Photosphere every ten minutes. For this reason
  VFISV is optimized to achieve an inversion speed that will allow
  it to invert sixteen million pixels every ten minutes with a modest
  number (approx. 50) of CPUs. Here we focus on describing a number of
  important details, simplifications and tweaks that have allowed us to
  significantly speed up the inversion process. We also give details on
  tests performed with data from the spectropolarimeter on-board of the
  Hinode spacecraft.

Title: Earth-Affecting Solar Causes Observatory (EASCO): a mission
    at the Sun-Earth L5
Authors: Gopalswamy, Nat; Davila, Joseph M.; Auchère, Frédéric;
   Schou, Jesper; Korendyke, Clarence M.; Shih, Albert; Johnston, Janet
   C.; MacDowall, Robert J.; Maksimovic, Milan; Sittler, Edward; Szabo,
   Adam; Wesenberg, Richard; Vennerstrom, Suzanne; Heber, Bernd
Bibcode: 2011SPIE.8148E..0ZG
Altcode: 2011SPIE.8148E..30G; 2011arXiv1109.2929G
  Coronal mass ejections (CMEs) and corotating interaction regions
  (CIRs) as well as their source regions are important because of
  their space weather consequences. The current understanding of CMEs
  primarily comes from the Solar and Heliospheric Observatory (SOHO)
  and the Solar Terrestrial Relations Observatory (STEREO) missions,
  but these missions lacked some key measurements: STEREO did not have a
  magnetograph; SOHO did not have in-situ magnetometer. SOHO and other
  imagers such as the Solar Mass Ejection Imager (SMEI) located on the
  Sun-Earth line are also not well-suited to measure Earth-directed
  CMEs. The Earth-Affecting Solar Causes Observatory (EASCO) is a
  proposed mission to be located at the Sun-Earth L5 that overcomes
  these deficiencies. The mission concept was recently studied at the
  Mission Design Laboratory (MDL), NASA Goddard Space Flight Center,
  to see how the mission can be implemented. The study found that the
  scientific payload (seven remote-sensing and three in-situ instruments)
  can be readily accommodated and can be launched using an intermediate
  size vehicle; a hybrid propulsion system consisting of a Xenon ion
  thruster and hydrazine has been found to be adequate to place the
  payload at L5. Following a 2-year transfer time, a 4-year operation
  is considered around the next solar maximum in 2025.

Title: Photospheric signatures of Solar Flares
Authors: Desai, P.; Bogart, R.; Couvidat, S.; Schou, J.
Bibcode: 2011sdmi.confE..32D
Altcode:
  White Light flares (WLF's) are enjoying a renewed interest in the
  solar commmunity since the recent detections of white light continuum
  emission of solar flares with TRACE (Hudson et.al, 2006; Fletcher
  et.al, 2007) and HINODE(Wang, H., 2009). The Helioseismic and Magnetic
  Imager (HMI) on the Solar Dynamic Observatory (SDO) produces a nearly
  continuous stream of full disc images of the sun in a set of six
  narrow wavelength bands around the FeI photospheric absorption line
  at 6173 Angstrom with filtergrams made at a cadence of one every 1.85
  seconds. Preliminary analysis shows that the photospheric signature of
  Xray flares of sufficient intensity (Martinez Oliveros,J.C. et al, 2011)
  can be readily detected in the HMI data. Motivated by this finding,
  we have analyzed the HMI observables (in particular the Line Depth
  and Continuum Intensity) and the corresponding line core intensity
  during recent GOES M and X class flares (e.g. M6.6 on 2/13/2011,
  X2.2 on 2/15/2011, X6.9 on 8/9/11).

Title: Comparing Leakage Matrices
Authors: Larson, T. P.; Schou, J.; Korzennik, S. G.
Bibcode: 2011sdmi.confE..44L
Altcode:
  The standard leakage matrix for global mode helioseismology is
  calculated assuming a value of zero for the P-angle, B-angle, and CCD
  offsets, and value of 1 AU for the observer distance. Since image center
  is not constant we vary this parameter so see what effect is has on the
  leaks and explore the possibility of using a leakage matrix averaged
  over pixel offsets. Since the B-angle and observer distance vary in
  a known way with time, we recompute the leakage matrix for realistic
  values of these parameters and repeat the fits to find out how the mode
  parameters are affected. Since previous studies have indicated certain
  systematic errors are associated with the apodization, we also compute
  leakage matrices for different apodizations, repeat the spherical
  harmonic decomposition with those apodizations, and fit these to see
  the effect on mode parameters. Lastly, we compare the leakage matrix
  computed at Stanford with a completely independent calculation in order
  to both verify our results and discover the source of any discrepancy.

Title: Measuring Meridional Flow Using Global Modes
Authors: Schou, J.; Woodard, M. F.; Birch, A. C.; Larson, T. P.
Bibcode: 2011sdmi.confE..71S
Altcode:
  In the past the meridional flow has been determined near the photosphere
  by direct observations and below the solar surface using local
  helioseismic methods. To first order normal mode frequencies are not
  sensitive to the meridional flow, and so they are not useful for this
  purpose. However, the eigenfunctions are sensitive to the meridional
  flow to first order. Here we describe our progress on a project to
  measure the eigenfunction perturbations and infer the meridional flow
  with depth.

Title: A determination of high degree mode parameters based on
    MDI observations
Authors: Korzennik, S. G.; Rabello-Soares, M. C.; Schou, J.; Larson, T.
Bibcode: 2011sdmi.confE..88K
Altcode:
  We present the best to date determination of high degree mode parameters
  obtained from the longest full-disk high-resolution data set available
  over the 13 years of MDI operations. A ninety day long time series
  of full-disk two arc-second per pixel resolution dopplergrams were
  acquired in 2001, thanks to the high rate telemetry provided by the
  deep space network. These dopplergrams were decomposed using our best
  estimate of the image scale and the known components of MDI's image
  distortion. The spherical harmonics decomposition was carried out up
  to l=1000, and a sine multi-taper power spectrum estimator was used
  to generate power spectra for all degrees and all azimuthal orders up
  to l=1000. We used a large number of tapers to reduce the realization
  noise. Since at high degrees the individual modes blend into ridges,
  there is no reason to preserve a high spectral resolution. These
  power spectra were fitted for all degrees and all azimuthal orders,
  between l=100 and l=1000, and for all orders with substantial amplitude,
  generating in excess of 6 million individual estimate of frequencies,
  line-widths amplitudes and asymmetries, corresponding to some 6,000
  singlets. Fitting at high degrees generates characteristics of the
  blended ridges, characteristics that do not correspond to the underlying
  mode characteristics. We used a sophisticated forward modeling of the
  mode to ridge blending to recover the best possible estimate of the
  underlying mode characteristics for the mode frequency, as well as the
  line-width, amplitude and asymmetry. We describe this modeling, as it
  has been recently fine tuned, and the iterative process used to refine
  its input parameters. Finally not only did we generate corrected mode
  characteristics and their uncertainties, but we computed the sensitivity
  of the model to its input set to best estimate the precision of the
  ridge to mode correction itself. This was carried out to assess the
  magnitude of any residual systematic errors in the final estimates of
  the mode characteristics.

Title: Temporal changes in the frequencies of the solar p-mode
    oscillations during solar cycle 23
Authors: Rhodes, E. J.; Reiter, J.; Schou, J.; Larson, T.; Scherrer,
   P.; Brooks, J.; McFaddin, P.; Miller, B.; Rodriguez, J.; Yoo, J.
Bibcode: 2011IAUS..273..389R
Altcode:
  We present a study of the temporal changes in the sensitivities of the
  frequencies of the solar p-mode oscillations to corresponding changes in
  the levels of solar activity during Solar Cycle 23. From MDI and GONG++
  full-disk Dopplergram three-day time series obtained between 1996 and
  2008 we have computed a total of 221 sets of m-averaged power spectra
  for spherical harmonic degrees ranging up to 1000. We have then fit
  these 284 sets of m-averaged power spectra using our WMLTP fitting
  code and both symmetric Lorentzian profiles for the peaks as well as
  the asymmetric profile of Nigam and Kosovichev to obtain 568 tables
  of p-mode parameters. We then inter-compared these 568 tables, and
  we performed linear regression analyses of the differences in p-mode
  frequencies, widths, amplitudes, and asymmetries as functions of the
  differences in as many as ten different solar activity indices. From the
  linear regression analyses that we performed on the frequency difference
  data sets, we have discovered a new signature of the frequency shifts
  of the p-modes. Specifically, we have discovered that the temporal
  shifts of the solar oscillation frequencies are positively correlated
  with the changes in solar activity below a limiting frequency. They
  then become anti-correlated with the changes in activity for a range of
  frequencies before once again becoming positively-correlated with the
  activity changes at very high frequencies. We have also discovered
  that the two frequencies where the sensitivities of the temporal
  frequency shifts change sign also change in phase with the average
  level of solar activity.

Title: Transient Artifacts in SDO/HMI Flare Observations
Authors: Martinez Oliveros, Juan Carlos; Lindsey, C.; Hudson, H.;
   Schou, J.; Couvidat, S.
Bibcode: 2011SPD....42.2123M
Altcode: 2011BAAS..43S.2123M
  The Helioseismic and Magnetic Imager (HMI) on SDO provides a new
  tool for the systematic observation of white-light flares, including
  Doppler and magnetic information as well as continuum. In our initial
  analysis of the highly impulsive gamma-ray flare SOL2010-06-12T00:57
  (Martinez-Oliveros et al. 2011), we detected an apparently artifactual
  blue shift in the two footpoint sources. We have now deployed the PASCAL
  algorithm for the same flare as viewed in GONG++ data. This algorithm
  makes it possible to obtain much better photometry (plus Doppler and
  magnetic measurements) from the ground-based data. Using GONG++ we
  have demonstrated the artifactual nature of the apparent blueshift,
  finding instead weak redshifts at the foopoints. We discuss the flare
  physics associated with these observations and describe the use of
  PASCAL (with GONG++ or other ground-based data) as a complement to
  the systematic SDO data.

Title: A Comparison Of Solar High-degree p-mode Parameters From HMI
    And MDI
Authors: Rabello-Soares, M. Cristina; Bogart, R.; Korzennik, S.;
   Larson, T.; Reiter, J.; Rhodes, E.; Schou, J.
Bibcode: 2011SPD....42.1606R
Altcode: 2011BAAS..43S.1606R
  Solar acoustic modes have been successfully used to make inferences
  about the solar interior. The comparison of independent contemporaneous
  data sets is important to test the reliability of our inferences. Here
  we compare helioseismic data from the Michelson Doppler Imager (MDI)
  on board SOHO with Helioseismic and Magnetic Imager (HMI) on board SDO
  using spherical harmonic decomposition and ring-diagram analysis. We
  will focus on the analysis of high-degree modes. They propagate through
  the outer layers of the Sun giving valuable information about this
  region. This interesting region is the seat of the near-surface shear
  layer, where the excitation and damping mechanisms are believed to be
  concentrated and where the effects of the equation of state are felt
  most strongly.

Title: The Height of White-light Flare Continuum Formation
Authors: Martinez Oliveros, J.; Hudson, Hugh; Krucker, S.; Schou,
   J.; Couvidat, S.
Bibcode: 2011SPD....42.2211M
Altcode: 2011BAAS..43S.2211M
  White-light continuum and hard X-ray emission in flares have strong
  correlations in time and in horizontal position, but at present we do
  not have a clear idea about their height structures. On 24 February
  2011 a white-light flare (SOL2011-02-24T07:35) was observed on the
  east limb, simultaneously by the Helioseismic Magnetic Imager (HMI)
  on the Solar Dynamics Observatory (SDO), and by the Reuven Ramaty
  High Energy Solar Spectroscopic Imager (RHESSI). This observation
  gives us the opportunity to determine the heights of these emissions
  directly, limited only by the limb references for the two spacecraft,
  with almost no projection undertainty. HMI obtained clear images in
  the pseudo-continuum around 6173A, and RHESSI obtained hard X-ray
  images. For both data sets, the precision of centroid determination
  is of order 0.1 arc s. We believe that the position of the white-light
  limb, as a local reference, can also be understood at a corresponding
  level of accuracy for the two data sets. We report the results of
  this analysis and discuss our findings in terms of present models of
  particle acceleration and energy transport in the impulsive phase.

Title: Extending Global Helioseismic Measurements From MDI to HMI
Authors: Schou, Jesper; Larson, T. P.
Bibcode: 2011SPD....42.1605S
Altcode: 2011BAAS..43S.1605S
  With the end of regular observations using MDI the question arises if
  we can provide good continuity between MDI and HMI. In particular MDI
  has shown intriguing differences in the torsional oscillation between
  the two most recent 11-year solar cycles. In this poster we will discuss
  some of the instrumental differences as well as examine the differences
  in global mode parameters and inferred quantities between the two
  during the period of overlap of MDI and HMI observations. <P />This
  work is supported by NASA contract NAS5-02139 to Stanford University.

Title: Medium-l Global Helioseismology with MWO Dopplergrams
Authors: Larson, Timothy P.; Schou, J.; Rhodes, E. J.; Spinella, A.;
   Irish, S.
Bibcode: 2011SPD....42.1609L
Altcode: 2011BAAS..43S.1609L
  The 60-foot solar tower at Mount Wilson Observatory took high resolution
  dopplergrams at a cadence of one minute between the summers of 1988 and
  2006. Because this instrument overlaps with GONG and MDI, it provides
  a unique opportunity to extend the inferences of those two projects
  backwards in time to solar cycle 22. Furthermore, access to the MWO data
  has been facilitated by its ingestion at the Joint Science Operations
  Center (JSOC) at Stanford. For this initial study we choose for our
  analysis a single summer in which MDI was also operating. By running
  the MWO data through the same processing pipeline and comparing with
  the results from MDI, we are able to determine how accurately the two
  datasets can be combined. In future we will be able to use the MWO
  data to compare the torsional oscillation during solar cycles 22 and 23.

Title: Large-scale Zonal Flows During the Solar Minimum -- Where Is
    Cycle 25?
Authors: Hill, Frank; Howe, R.; Komm, R.; Christensen-Dalsgaard, J.;
   Larson, T. P.; Schou, J.; Thompson, M. J.
Bibcode: 2011SPD....42.1610H
Altcode: 2011BAAS..43S.1610H
  The so-called torsional oscillation is a pattern of migrating zonal flow
  bands that move from mid-latitudes towards the equator and poles as the
  magnetic cycle progresses. Helioseismology allows us to probe these
  flows below the solar surface. The prolonged solar minimum following
  Cycle 23 was accompanied by a delay of 1.5 to 2 years in the migration
  of bands of faster rotation towards the equator. During the rising phase
  of Cycle 24, while the lower-level bands match those seen in the rising
  phase of Cycle 23, the rotation rate at middle and higher latitudes
  remains slower than it was at the corresponding phase in earlier cycles,
  perhaps reflecting the weakness of the polar fields. In addition,
  there is no evidence of the poleward flow associated with Cycle 25. We
  will present the latest results based on nearly sixteen years of global
  helioseismic observations from GONG and MDI, with recent results from
  HMI, and discuss the implications for the development of Cycle 25.

Title: HMI: First Results
Authors: Centeno, R.; Tomczyk, S.; Borrero, J. M.; Couvidat,
   S. Hayashi, K.; Hoeksema, T.; Liu, Y.; Schou, J.
Bibcode: 2011ASPC..437..147C
Altcode: 2010arXiv1012.3796C
  The Helioseismic and Magnetic Imager (HMI) has just started producing
  data that will help determine what the sources and mechanisms of
  variability in the Sun's interior are. The instrument measures the
  Doppler shift and the polarization of the Fe I 6173 Å line, on the
  entire solar disk at a relatively-high cadence, in order to study
  the oscillations and the evolution of the full vector magnetic field
  of the solar Photosphere. After the data are properly calibrated,
  they are given to a Milne-Eddington inversion code (VFISV, Borrero et
  al. 2010) whose purpose is to infer certain aspects of the physical
  conditions in the Sun's Photosphere, such as the full 3-D topology
  of the magnetic field and the line-of-sight velocity at the solar
  surface. We will briefly describe the characteristics of the inversion
  code, its advantages and limitations -both in the context of the model
  atmosphere and the actual nature of the data-, and other aspects of its
  performance on such a remarkable data load. Also, a cross-comparison
  with near-simultaneous maps from the Spectro-Polarimeter (SP) onboard
  Hinode will be made.

Title: Imaging Spectroscopy of a White-Light Solar Flare
Authors: Martínez Oliveros, J. C.; Couvidat, S.; Schou, J.; Krucker,
   S.; Lindsey, C.; Hudson, H. S.; Scherrer, P.
Bibcode: 2011SoPh..269..269M
Altcode: 2011SoPh..tmp....7M; 2010arXiv1012.0344M
  We report observations of a white-light solar flare
  (SOL2010-06-12T00:57, M2.0) observed by the Helioseismic Magnetic
  Imager (HMI) on the Solar Dynamics Observatory (SDO) and the Reuven
  Ramaty High Energy Solar Spectroscopic Imager (RHESSI). The HMI data
  give us the first space-based high-resolution imaging spectroscopy
  of a white-light flare, including continuum, Doppler, and magnetic
  signatures for the photospheric Fe I line at 6173.34 Å and its
  neighboring continuum. In the impulsive phase of the flare, a bright
  white-light kernel appears in each of the two magnetic footpoints. When
  the flare occurred, the spectral coverage of the HMI filtergrams (six
  equidistant samples spanning ±172 mÅ around nominal line center)
  encompassed the line core and the blue continuum sufficiently far from
  the core to eliminate significant Doppler crosstalk in the latter, which
  is otherwise a possibility for the extreme conditions in a white-light
  flare. RHESSI obtained complete hard X-ray and γ-ray spectra (this
  was the first γ-ray flare of Cycle 24). The Fe I line appears to be
  shifted to the blue during the flare but does not go into emission; the
  contrast is nearly constant across the line profile. We did not detect
  a seismic wave from this event. The HMI data suggest stepwise changes
  of the line-of-sight magnetic field in the white-light footpoints.

Title: First Global Rotation Inversions of HMI Data
Authors: Howe, R.; Larson, T. P.; Schou, J.; Hill, F.; Komm, R.;
   Christensen-Dalsgaard, J.; Thompson, M. J.
Bibcode: 2011JPhCS.271a2061H
Altcode:
  We present the first 2-dimensional global rotational inversions of
  medium-degree p-mode data from the Helioseismic and Magnetic Imager,
  and compare the results with inversions of Michelson Doppler Imager
  data for the same time period. The inferred rotation profiles show
  good agreement between the two instruments.

Title: The torsional oscillation and the new solar cycle
Authors: Howe, R.; Hill, F.; Komm, R.; Christensen-Dalsgaard, J.;
   Larson, T. P.; Schou, J.; Thompson, M. J.; Ulrich, R.
Bibcode: 2011JPhCS.271a2074H
Altcode:
  We present updated observations of the pattern of migrating solar
  zonal flows known as the torsional oscillation, covering 15 years of
  helioseismic measurements with GONG and MDI and 30 years of surface
  Doppler observations from Mount Wilson. We compare the behavior of the
  flows during the extended solar minimum following Cycle 23 with that in
  earlier minima. We demonstrate that the timing of the migration of the
  zonal flow belts may be of some use in predicting the start of the new
  cycle. We also note that the behavior of the high-latitude part of the
  pattern currently differs from that seen early in the previous cycle,
  with the high-latitude poleward-migrating branch still not established.

Title: Rotation-rate variations at the tachocline: An update
Authors: Howe, R.; Komm, R.; Hill, F.; Christensen-Dalsgaard, J.;
   Larson, T. P.; Schou, J.; Thompson, M. J.; Toomre, J.
Bibcode: 2011JPhCS.271a2075H
Altcode:
  After 15 years of GONG and MDI observations of the solar interior
  rotation, we revisit the issue of variations in the rotation rate near
  the base of the convection zone. The 1.3-year period seen in the first
  few years of the observations disappeared after 2000 and has still
  not returned. On the other hand, the agreement between GONG and MDI
  observations suggests that variations seen in this region have some
  solar origin, whether a true rotation-rate change or possibly mere
  stochastic variation; we present a numerical experiment supporting
  this contention.

Title: HMI global helioseismology data analysis pipeline
Authors: Larson, Tim; Schou, Jesper
Bibcode: 2011JPhCS.271a2062L
Altcode:
  The HMI global helioseismology data analysis pipeline is based largely
  on the MDI medium-l program. All of the modules that ran in the SOI
  Science Support Center have been ported for use in the SDO Joint Science
  Operations Center (JSOC) and given greater functionality. Many errors
  and approximations which are present in the standard MDI pipeline
  have been corrected and improvements have been added. Scripts have
  been written to automate the submission of compute jobs to our local
  cluster; it is now possible to go from dopplergrams to mode parameters
  with the push of a button. JSOC dataseries have been created to
  hold all intermediate data products, timeseries, window functions,
  and mode parameters. Here we discuss the operation of the pipeline,
  the structure of the data it generates, and access to the same.

Title: Temporal changes in the frequencies and widths of the solar
    p-mode oscillations
Authors: Rhodes, E. J., Jr.; Reiter, J.; Schou, J.; Larson, T.;
   Scherrer, P.; Brooks, J.; McFaddin, P.; Miller, B.; Rodriguez, J.;
   Yoo, J.
Bibcode: 2011JPhCS.271a2029R
Altcode:
  We present a study of the temporal changes in the sensitivities of the
  frequencies and widths of the solar p-mode oscillations to corresponding
  changes in the levels of solar activity during Solar Cycle 23. From MDI
  and GONG++ full-disk Dopplergram three-day time series obtained between
  1996 and 2008 we have computed a total of 221 sets of m-averaged power
  spectra for spherical harmonic degrees ranging up to 1000. We have then
  fit these 221 sets of m-averaged power spectra using our WMLTP fitting
  code and both symmetric Lorentzian profiles for the peaks as well as
  the asymmetric profile of Nigam and Kosovichev to obtain 442 tables
  of p-mode parameters. We then inter-compared these 442 tables which
  comprise in excess of 5.3 million p-mode parameters, and we performed
  linear regression analyses of the differences in p-mode frequencies
  and widths as functions of the differences in as many as ten different
  solar activity indices. From these linear regression analyses we have
  discovered new signatures of the frequency shifts of the p-modes and
  a similar, but slightly different, signature of the temporal shifts
  in the widths of the oscillations.

Title: Wavelike Properties of Supergranulation
Authors: Lee, S.; Beck, J. G.; Schou, J.; Stanford Solar Observatories
   Group
Bibcode: 2010AGUFMSH11A1606L
Altcode:
  Supergranulation has been a long studied feature of solar
  convection. While the cellular pattern and horizontal outflows are
  consistent with a convective phenomenon, the details of supergranulation
  indicate that it can not be explained by a simple convective model. One
  such aspect is its apparent super-rotation. Supergranulation appears to
  rotate a few percent faster than the solar surface plasma. Some have
  theorized that this super-rotation can be explained by a wave like
  component in the supergranulation signal. Here, we present research
  that cumulates into the discovery of two distinct components of the
  supergranulation rotation rate using dopplergrams obtained from the
  HMI instrument aboard the Solar Dynamics Observatory.

Title: A Precise Asteroseismic Age and Radius for the Evolved Sun-like
    Star KIC 11026764
Authors: Metcalfe, T. S.; Monteiro, M. J. P. F. G.; Thompson, M. J.;
   Molenda-Żakowicz, J.; Appourchaux, T.; Chaplin, W. J.; Doǧan, G.;
   Eggenberger, P.; Bedding, T. R.; Bruntt, H.; Creevey, O. L.; Quirion,
   P. -O.; Stello, D.; Bonanno, A.; Silva Aguirre, V.; Basu, S.; Esch,
   L.; Gai, N.; Di Mauro, M. P.; Kosovichev, A. G.; Kitiashvili, I. N.;
   Suárez, J. C.; Moya, A.; Piau, L.; García, R. A.; Marques, J. P.;
   Frasca, A.; Biazzo, K.; Sousa, S. G.; Dreizler, S.; Bazot, M.; Karoff,
   C.; Frandsen, S.; Wilson, P. A.; Brown, T. M.; Christensen-Dalsgaard,
   J.; Gilliland, R. L.; Kjeldsen, H.; Campante, T. L.; Fletcher, S. T.;
   Handberg, R.; Régulo, C.; Salabert, D.; Schou, J.; Verner, G. A.;
   Ballot, J.; Broomhall, A. -M.; Elsworth, Y.; Hekker, S.; Huber, D.;
   Mathur, S.; New, R.; Roxburgh, I. W.; Sato, K. H.; White, T. R.;
   Borucki, W. J.; Koch, D. G.; Jenkins, J. M.
Bibcode: 2010ApJ...723.1583M
Altcode: 2010arXiv1010.4329M
  The primary science goal of the Kepler Mission is to provide
  a census of exoplanets in the solar neighborhood, including the
  identification and characterization of habitable Earth-like planets. The
  asteroseismic capabilities of the mission are being used to determine
  precise radii and ages for the target stars from their solar-like
  oscillations. Chaplin et al. published observations of three bright
  G-type stars, which were monitored during the first 33.5 days of science
  operations. One of these stars, the subgiant KIC 11026764, exhibits a
  characteristic pattern of oscillation frequencies suggesting that it
  has evolved significantly. We have derived asteroseismic estimates of
  the properties of KIC 11026764 from Kepler photometry combined with
  ground-based spectroscopic data. We present the results of detailed
  modeling for this star, employing a variety of independent codes and
  analyses that attempt to match the asteroseismic and spectroscopic
  constraints simultaneously. We determine both the radius and the age
  of KIC 11026764 with a precision near 1%, and an accuracy near 2%
  for the radius and 15% for the age. Continued observations of this
  star promise to reveal additional oscillation frequencies that will
  further improve the determination of its fundamental properties.

Title: HMI Global Helioseismology Data Analysis Pipeline
Authors: Larson, Timothy P.; Schou, J.
Bibcode: 2010AAS...21640205L
Altcode: 2010BAAS...41..873L
  The HMI global helioseismology data analysis pipeline is based largely
  on the MDI medium-l program. All of the modules that ran in the SOI
  Science Support Center have been ported for use in the SDO Joint Science
  Operations Center (JSOC) and given greater functionality. Many errors
  and approximations which are present in the standard MDI pipeline
  have been corrected and improvements have been added. Scripts have
  been written to automate the submission of compute jobs to our local
  cluster; it is now possible to go from dopplergrams to mode parameters
  with the push of a button. JSOC dataseries have been created to hold
  all intermediate data products, timeseries, window functions, and mode
  parameters. In this poster we discuss the operation of the pipeline,
  the structure of the data it generates, and access to the same. This
  work has been supported by NASA contract NAS5-02139.

Title: First Data From the Helioseismic and Magnetic Imager
Authors: Schou, Jesper; HMI Team
Bibcode: 2010AAS...21630801S
Altcode:
  With the successful launch of the Solar Dynamics Observatory on
  February 11, 2010 and the HMI commissioning activities scheduled
  to be completed, we expect to be producing science quality data by
  the time of this meeting. In this talk we will start by describing
  some of the results from the commissioning activities and show how
  the measured performance compares to that expected. <P />I will also
  show a selection of science data including Dopplergrams, Line-of-Sight
  magnetograms and vector magnetograms. This work was supported by NASA
  through contract NAS5-02139 to Stanford University.

Title: Improving Leakage Matrix Calculation
Authors: Larson, Timothy P.; Schou, J.
Bibcode: 2010AAS...21640010L
Altcode: 2010BAAS...41..856L
  Previous work has revealed discrepancies between the analysis of MDI
  full disk data and medium-l data from the same time period. Most
  notably, the full disk analysis lacks some systematic errors
  and generally results in better fits to the data. One of the
  differences between the two analyses is the leakage matrix used in
  the peakbagging. In this poster we discuss the effect of such things
  as proper pixel integration, higher resolution spherical harmonics,
  improved interpolation in the remapping, and various point spread
  functions on the leakage matrix itself and the resulting mode
  parameters. This work has been supported by NASA contract NAS5-02139.

Title: The Asteroseismic Potential of Kepler: First Results for
    Solar-Type Stars
Authors: Chaplin, W. J.; Appourchaux, T.; Elsworth, Y.; García,
   R. A.; Houdek, G.; Karoff, C.; Metcalfe, T. S.; Molenda-Żakowicz,
   J.; Monteiro, M. J. P. F. G.; Thompson, M. J.; Brown, T. M.;
   Christensen-Dalsgaard, J.; Gilliland, R. L.; Kjeldsen, H.; Borucki,
   W. J.; Koch, D.; Jenkins, J. M.; Ballot, J.; Basu, S.; Bazot, M.;
   Bedding, T. R.; Benomar, O.; Bonanno, A.; Brandão, I. M.; Bruntt,
   H.; Campante, T. L.; Creevey, O. L.; Di Mauro, M. P.; Doǧan,
   G.; Dreizler, S.; Eggenberger, P.; Esch, L.; Fletcher, S. T.;
   Frandsen, S.; Gai, N.; Gaulme, P.; Handberg, R.; Hekker, S.; Howe,
   R.; Huber, D.; Korzennik, S. G.; Lebrun, J. C.; Leccia, S.; Martic,
   M.; Mathur, S.; Mosser, B.; New, R.; Quirion, P. -O.; Régulo, C.;
   Roxburgh, I. W.; Salabert, D.; Schou, J.; Sousa, S. G.; Stello, D.;
   Verner, G. A.; Arentoft, T.; Barban, C.; Belkacem, K.; Benatti, S.;
   Biazzo, K.; Boumier, P.; Bradley, P. A.; Broomhall, A. -M.; Buzasi,
   D. L.; Claudi, R. U.; Cunha, M. S.; D'Antona, F.; Deheuvels, S.;
   Derekas, A.; García Hernández, A.; Giampapa, M. S.; Goupil, M. J.;
   Gruberbauer, M.; Guzik, J. A.; Hale, S. J.; Ireland, M. J.; Kiss,
   L. L.; Kitiashvili, I. N.; Kolenberg, K.; Korhonen, H.; Kosovichev,
   A. G.; Kupka, F.; Lebreton, Y.; Leroy, B.; Ludwig, H. -G.; Mathis, S.;
   Michel, E.; Miglio, A.; Montalbán, J.; Moya, A.; Noels, A.; Noyes,
   R. W.; Pallé, P. L.; Piau, L.; Preston, H. L.; Roca Cortés, T.;
   Roth, M.; Sato, K. H.; Schmitt, J.; Serenelli, A. M.; Silva Aguirre,
   V.; Stevens, I. R.; Suárez, J. C.; Suran, M. D.; Trampedach, R.;
   Turck-Chièze, S.; Uytterhoeven, K.; Ventura, R.; Wilson, P. A.
Bibcode: 2010ApJ...713L.169C
Altcode: 2010arXiv1001.0506C
  We present preliminary asteroseismic results from Kepler on three G-type
  stars. The observations, made at one-minute cadence during the first
  33.5 days of science operations, reveal high signal-to-noise solar-like
  oscillation spectra in all three stars: about 20 modes of oscillation
  may be clearly distinguished in each star. We discuss the appearance of
  the oscillation spectra, use the frequencies and frequency separations
  to provide first results on the radii, masses, and ages of the stars,
  and comment in the light of these results on prospects for inference
  on other solar-type stars that Kepler will observe.

Title: Toward Eliminating Systematic Errors in Intermediate-Degree
    p-Mode Measurements
Authors: Vorontsov, S. V.; Jefferies, S. M.; Giebink, C.; Schou, J.
Bibcode: 2009ASPC..416..301V
Altcode:
  We report new measurements of p-mode frequency splittings from Michelson
  Doppler Imager (MDI) in which systematic errors, previously seen,
  appear to have been eliminated. We identify neglect of the effects
  of mode coupling by differential rotation as a major source of the
  systematic errors.

Title: The internal dynamics and magnetism of the sun -- the
    perspective from global helioseismology (Invited)
Authors: Howe, R.; Hill, F.; Komm, R.; Christensen-Dalsgaard, J.;
   Schou, J.; Thompson, M. J.
Bibcode: 2009AGUFMSH11B..04H
Altcode:
  Helioseismology allows us to probe the interior dynamics of the
  Sun. Observations over the past three decades reveal the interior
  rotation profile, with a near-surface shear layer, differential
  rotation throughout the convection zone, a strong shear layer -- the
  tachocline -- at the base of the convection zone, and approximately
  uniform rotation in the radiative interior. Since the mid 1990's,
  continuous observations from the Global Oscillations Network Group and
  the Michelson Doppler Imager have allowed the study of subtle temporal
  variations in the rotation within the convection zone. The so-called
  "torsional oscillation" pattern of migrating zonal flows accompanying
  the surface activity migration during the solar cycle has been shown to
  penetrate deep within the convection zone. During the current extended
  solar minimum, the flow bands can be seen to migrate more slowly towards
  the equator than was seen in the previous minimum. There have also been
  (still unconfirmed) findings of shorter-term variations in the rotation
  rate close to the tachocline during the early years of the previous
  solar cycle. This review will describe the important results and give
  an update on the most recent observations of the interior dynamics as
  we await the rise of solar cycle 24.

Title: Variations in Global Mode Analysis
Authors: Larson, T.; Schou, J.
Bibcode: 2009ASPC..416..311L
Altcode:
  As with any data analysis, the standard Michelson Doppler Imager (MDI)
  medium-l analysis pipeline is based on approximations and somewhat
  arbitrary choices in the processing. It is furthermore known that the
  results of the standard analysis contain systematic errors, most notably
  a bump in the normalized residuals of the a-coefficients around 3.4 mHz,
  an annual variation in f-mode frequencies, and possibly a polar jet in
  the rotation inversions. Our previous work has explored how these errors
  are affected by making various corrections to the analysis. In this
  article we extend our study to include a comparison of the results of
  full disk data to those of the binned data we have previously used. We
  go on to explore how several choices made in the analysis, such as
  the amount of zero padding and the width of the fitting interval,
  affect the mode parameters and the magnitude of the systematic errors.

Title: The Torsional Oscillation and the Solar Minimum
Authors: Howe, R.; Hill, F.; Komm, R.; Christensen-Dalsgaard, J.;
   Schou, J.; Thompson, M. J.
Bibcode: 2009AGUFM.U34A..03H
Altcode:
  The so-called torsional oscillation is a pattern of zonal flow bands,
  detected at the solar surface by direct Doppler measurements and within
  the convection zone by helioseismic measurements such as those carried
  out by the Global Oscillations Network Group and the Michelson Doppler
  Imager, that migrates from mid-latitudes towards the equator and poles
  with each solar cycle. In the current minimum the low-latitude branch
  of the pattern can be seen to have taken at least a year longer to
  migrate towards the equator than was the case in the previous minimum. A
  flow configuration matching that of the previous minimum was reached
  during 2008, and by early 2009 the fast-rotating belt associated with
  the new cycle had reached the latitude at which the onset of activity
  was seen in Cycle 23, but magnetic activity has remained low. We will
  present the most recent results and consider the implications for the
  new solar cycle.

Title: The Torsional Oscillation and the Solar Cycle: Is it Minimum
    Yet?
Authors: Howe, R.; Komm, R.; Hill, F.; Larson, T.; Schou, J.; Thompson,
   M. J.; Ulrich, R. K.
Bibcode: 2009ASPC..416..269H
Altcode:
  The torsional oscillation pattern of migrating zonal flows is related to
  the solar activity cycle. In the approach to solar minimum, we compare
  the current flow profile with that seen at the previous minimum, using
  Global Oscillation Network Group (GONG) and Michelson Doppler Imager
  (MDI) data as well as Mount Wilson Doppler observations that reach
  further back in time. Will the flow pattern at the upcoming minimum
  match that for the previous one?

Title: Inferring Small-Scale Flatfields from Solar Rotation
Authors: Wachter, R.; Schou, J.
Bibcode: 2009SoPh..258..331W
Altcode:
  We present a method to infer small-scale flatfields for imaging solar
  instruments using only regular-observation intensity images with a
  fixed field of view. The method is related to the flatfielding method
  developed by Kuhn, Lin, and Loranz (Publ. Astron. Soc. Pac. 103,
  1097 - 1108, 1991), but does not require image offsets. Instead, it
  takes advantage of the fact that the solar image is changing in the CCD
  reference frame due to solar rotation. We apply the method to data sets
  of MDI filtergrams and compare the results to flat fields derived with
  other methods. Finally, we discuss the planned implementation of this
  method in the data processing for Helioseismic and Magnetic Imager on
  the Solar Dynamics Observatory.

Title: A Note on the Torsional Oscillation at Solar Minimum
Authors: Howe, R.; Christensen-Dalsgaard, J.; Hill, F.; Komm, R.;
   Schou, J.; Thompson, M. J.
Bibcode: 2009ApJ...701L..87H
Altcode: 2009arXiv0907.2965H
  We examine the evolution of the zonal flow pattern in the upper solar
  convection zone during the current extended solar minimum, and compare
  it with that during the previous minimum. The results suggest that
  a configuration matching that at the previous minimum was reached
  during 2008, but that the flow band corresponding to the new cycle has
  been moving more slowly toward the equator than was observed in the
  previous cycle, resulting in a gradual increase in the apparent length
  of the cycle during the 2007-2008 period. The current position of the
  lower-latitude fast-rotating belt corresponds to that seen around the
  onset of activity in the previous cycle.

Title: Large Scale Flows From Eigenfunction Fitting
Authors: Schou, Jesper; Woodard, M. F.; Birch, A. C.
Bibcode: 2009SPD....40.0705S
Altcode:
  It is well known that the eigenfunctions, as well as the
  eigenfrequencies, of normal modes are perturbed by flows and other
  asphericities. In the case of meridional flows, it is known that
  while the perturbations to the frequencies are second order, the
  eigenfunctions are perturbed at first order in the strength of the
  meridional flow. This leads to the question of whether one might be
  able to measure meridional flows using the observed eigenfunction
  perturbations. Here we discuss how well we expect to be able to do
  this and show some preliminary analysis of MDI data.

Title: Exploring Data Discrepancies in Global Mode Analysis
Authors: Larson, Timothy P.; Schou, J.
Bibcode: 2009SPD....40.0717L
Altcode:
  The MDI instrument produces both full resolution and binned
  Dopplergrams. Although one might expect the analysis of these two
  data products to give the same results in the medium-l range, in
  fact significant differences are observed, depending on both spatial
  resolution and image apodization. This can clearly be seen in raw
  mode parameters such as amplitude as well as in inversions of mode
  frequencies. Furthermore, the difference seems to vary from year to
  year. In this poster we shall examine the first 13 dynamics runs taken
  by MDI and try to account for these discrepancies.

Title: The HMI Magnetic Field Pipeline
Authors: Hoeksema, Jon Todd; Liu, Y.; Schou, J.; Scherrer, P.; HMI
   Science Team
Bibcode: 2009SPD....40.1701H
Altcode:
  The Helioseismic and Magnetic Imager (HMI) will provide frequent
  full-disk magnetic field data after launch of the Solar Dynamics
  Observatory (SDO), currently scheduled for fall 2009. 16 megapixel
  line-of-sight magnetograms (Blos) will be recorded every 45 seconds. A
  full set of polarized filtergrams needed to determine the vector
  magnetic field requires 90 seconds. Quick-look data will be available
  within a few minutes of observation. Quick-look space weather and
  browse products must have identified users, and the list currently
  includes full disk magnetograms, feature identification and movies,
  12-minute disambiguated vector fields in active region patches,
  time evolution of AR indices, synoptic synchronic frames, potential
  and MHD model results, and 1 AU predictions. A more complete set of
  definitive science data products will be offered about a day later and
  come in three types. "Pipeline” products, such as full disk vector
  magnetograms, will be computed for all data on an appropriate cadence. A
  larger menu of "On Demand” products, such as Non-Linear Force Free
  Field snapshots of an evolving active region, will be produced whenever
  a user wants them. Less commonly needed "On Request” products that
  require significant project resources, such as a high resolution MHD
  simulation of the global corona, will be created subject to availability
  of resources. Further information can be found at the SDO Joint Science
  Operations Center web page, jsoc.stanford.edu

Title: Asteroseismology: The Next Frontier in Stellar Astrophysics
Authors: Giampapa, Mark S.; Aerts, Conny; Bedding, Tim; Bonanno,
   Alfio; Brown, Timothy M.; Christensen-Dalsgaard, Jorgen; Dominik,
   Martin; Ge, Jian; Gilliland, Ronald L.; Harvey, J. W.; Hill, Frank;
   Kawaler, Steven D.; Kjeldsen, Hans; Kurtz, D. W.; Marcy, Geoffrey W.;
   Matthews, Jaymie M.; Monteiro, Mario Joao P. F. G.; Schou, Jesper
Bibcode: 2009astro2010S..91G
Altcode:
  No abstract at ADS

Title: Improvements in global mode analysis
Authors: Larson, T. P.; Schou, J.
Bibcode: 2008JPhCS.118a2083L
Altcode:
  As with any data analysis, the standard MDI medium-l analysis pipeline
  is based on several approximations. Physical effects such as line
  asymmetry, horizontal displacement at the solar surface, and distortion
  of eigenfunctions have been ignored, as well as cubic distortion in the
  optics and instrumental errors in the plate scale and orientation of
  the CCD. Furthermore, we see several systematic errors in the results
  of the analysis, most notably an annual variation in f-mode frequencies
  and a bump in the normalized residuals of the a-coefficients around
  3.4 mHz, which may relate to polar jets in the inversions. We have
  reprocessed several years of data applying the above corrections, and
  made improvements in the pipeline algorithm itself by recomputing the
  locations of bad data points and using updated routines for detrending
  and gapfilling. Along the way the pipeline has been almost entirely
  automated. Here we discuss the resulting changes in mode parameters
  and their effect on the magnitude of systematic errors.

Title: High degree modes &amp; instrumental effects
Authors: Korzennik, S. G.; Rabello-Soares, M. C.; Schou, J.
Bibcode: 2008JPhCS.118a2027K
Altcode:
  Full-disk observations taken with the Michelson Doppler Imager (MDI)
  on board the Solar and Heliospheric Observatory (SOHO) spacecraft, or
  the upgraded Global Oscillations Network Group (GONG) instruments, have
  enough spatial resolution to resolve modes up to ι = 1000 if not ι =
  1500. The inclusion of such high-degree modes (i.e., ι &lt;= 1000)
  improves dramatically inferences near the surface. Unfortunately,
  observational and instrumental effects cause the characterization
  of high degree modes to be quite complicated. <P />Indeed, the
  characteristics of the solar acoustic spectrum are such that, for a
  given order, mode lifetimes get shorter and spatial leaks get closer
  in frequency as the degree of a mode increases. A direct consequence
  of this property is that individual modes are resolved only at low
  and intermediate degrees. At high degrees the individual modes blend
  into ridges and the power distribution of the ridge defines the
  ridge central frequency, masking the underlying mode frequency. An
  accurate model of the amplitude of the peaks that contribute to the
  ridge power distribution is needed to recover the underlying mode
  frequency from fitting the ridge. <P />We present a detailed discussion
  of the modeling of the ridge power distribution, and the contribution
  of the various observational and instrumental effects on the spatial
  leakage, in the context of the MDI instrument. We have constructed a
  physically motivated model (rather than an ad hoc correction scheme)
  that results in a methodology that can produce unbiased estimates of
  high-degree modes. This requires that the instrumental characteristics
  are well understood, a task that has turned out to pose a major
  challenge. <P />We also present our latest results, where most of the
  known instrumental and observational effects that affect specifically
  high-degree modes were removed. These new results allow us to focus
  our attention on changes with solar activity. <P />Finally, we present
  variations of mode frequencies resulting from solar activity over
  most of solar cycle 23. We present the correlation of medium and high
  degree modes with different solar indices. Our results confirm that
  the frequency shift scaled by the relative mode inertia is a function
  of frequency alone and follows a simple power law.

Title: Analysis of MDI High-Degree Mode Frequencies and their
    Rotational Splittings
Authors: Rabello-Soares, M. C.; Korzennik, S. G.; Schou, J.
Bibcode: 2008SoPh..251..197R
Altcode: 2008arXiv0808.2838R; 2008SoPh..tmp..133R
  We present a detailed analysis of solar acoustic mode frequencies and
  their rotational splittings for modes with degree up to 900. They were
  obtained by applying spherical harmonic decomposition to full-disk
  solar images observed by the Michelson Doppler Imager onboard the
  Solar and Heliospheric Observatory spacecraft. Global helioseismology
  analysis of high-degree modes is complicated by the fact that the
  individual modes cannot be isolated, which has limited so far the use
  of high-degree data for structure inversion of the near-surface layers
  (r&gt;0.97R<SUB>⊙</SUB>). In this work, we took great care to recover
  the actual mode characteristics using a physically motivated model
  which included a complete leakage matrix. We included in our analysis
  the following instrumental characteristics: the correct instantaneous
  image scale, the radial and non-radial image distortions, the effective
  position angle of the solar rotation axis, and a correction to the
  Carrington elements. We also present variations of the mode frequencies
  caused by the solar activity cycle. We have analyzed seven observational
  periods from 1999 to 2005 and correlated their frequency shift with four
  different solar indices. The frequency shift scaled by the relative mode
  inertia is a function of frequency alone and follows a simple power law,
  where the exponent obtained for the p modes is twice the value obtained
  for the f modes. The different solar indices present the same result.

Title: Analysis of MDI high-degree solar-p mode parameters
Authors: Rabello-Soares, M.; Korzennik, S.; Schou, J.
Bibcode: 2008AGUSMSP21A..03R
Altcode:
  We present a detailed analysis of solar acoustic mode parameters for
  modes with degree up to 900. They were obtained by applying spherical
  harmonic decomposition to full-disk solar images observed by the
  Michelson Doppler Imager (MDI) on board the Solar and Heliospheric
  Observatory (SOHO) spacecraft. We have analyzed seven observational
  periods (2-3 months long) from 1999 to 2005. A physically motivated
  model including a complete leakage matrix was used to recover the
  actual high-degree mode characteristics.

Title: Helioseismic and Magnetic Imager Calibration and Expected
    Performance
Authors: Schou, J.; Team, H.
Bibcode: 2008AGUSMSP51B..14S
Altcode:
  The HMI instrument was delivered in November 2007 and has been
  integrated onto the SDO spacecraft with launch planned for December
  2008. During the integration and testing of the instrument an extensive
  series of calibrations were performed. Here we describe some of the
  calibrations performed and show selected results. We will also discuss
  remaining efforts, such as on-orbit calibrations as well as describe the
  expected performance of the instrument. The HMI project is supported
  by the National Aeronautics and Space Administration under contract
  NAS5-02139 to Stanford University.

Title: Views of the Solar Torsional Oscillation
Authors: Howe, R.; Komm, R. W.; Hill, F.; Schou, J.; Thompson, M. J.
Bibcode: 2008AGUSMSP41A..05H
Altcode:
  The pattern of zonal flows migrating towards the equator over the
  solar cycle, known as the torsional oscillation, is well established
  from both helioseismology and surface Doppler measurements. However,
  the exact appearance of the pattern will vary depending on the form of
  the overall rotation profile that has been subtracted, even when the
  data cover a full eleven-year cycle. Here we compare the appearance
  of the flow pattern when applying several different methods to the
  MDI and GONG data for Solar Cycle 23.

Title: Variations of the solar acoustic high-degree mode frequencies
    over solar cycle 23
Authors: Rabello-Soares, M. C.; Korzennik, Sylvain G.; Schou, J.
Bibcode: 2008AdSpR..41..861R
Altcode: 2007arXiv0712.3608R
  Using full-disk observations obtained with the Michelson Doppler Imager
  (MDI) on board the Solar and Heliospheric Observatory (SOHO) spacecraft,
  we present variations of the solar acoustic mode frequencies caused by
  the solar activity cycle. High-degree (100 &lt; ℓ &lt; 900) solar
  acoustic modes were analyzed using global helioseismology analysis
  techniques over most of solar cycle 23. We followed the methodology
  described in details in [Korzennik, S.G., Rabello-Soares, M.C., Schou,
  J. On the determination of Michelson Doppler Imager high-degree mode
  frequencies. ApJ 602, 481 515, 2004] to infer unbiased estimates
  of high-degree mode parameters ([see also Rabello-Soares, M.C.,
  Korzennik, S.G., Schou, J. High-degree mode frequencies: changes
  with solar cycle. ESA SP-624, 2006]). We have removed most of the
  known instrumental and observational effects that affect specifically
  high-degree modes. We show that the high-degree changes are in good
  agreement with the medium-degree results, except for years when the
  instrument was highly defocused. We analyzed and discuss the effect
  of defocusing on high-degree estimation. Our results for high-degree
  modes confirm that the frequency shift scaled by the relative mode
  inertia is a function of frequency and it is independent of degree.

Title: Solar Cycle Changes Over 11 Years of Medium-Degree Helioseismic
    Observations
Authors: Howe, Rachel; Komm, R. W.; Hill, F.; Christensen-Dalsgaard,
   J.; Schou, J.; Thompson, M. J.
Bibcode: 2007AAS...210.2218H
Altcode: 2007BAAS...39..127H
  The Global Oscillations Network Group (GONG) has now completed, and
  the Michelson Doppler Imager (MDI) aboard SOHO will soon complete,
  a full eleven years of continuous observations of the medium-degree
  solar oscillations. This enables us to follow changes in the acoustic
  mode parameters and interior dynamics over a full solar cycle. We
  present results from observations of convection-zone dynamics, in
  which the torsional oscillation pattern seen at the surface can be
  followed throughout most of the bulk of the convection zone, and also
  changes in the frequency, lifetime and amplitude of the modes which
  can be shown to be closely related in space and time to the migrating
  pattern of surface activity. <P />This work utilizes data obtained by
  the Global Oscillation Network Group (GONG) program, managed by the
  National Solar Observatory, which is operated by AURA, Inc. under a
  cooperative agreement with the National Science Foundation. SOHO is
  a mission of international cooperation between ESA and NASA.

Title: Helioseismic and Magnetic Imager Calibration Status
Authors: Schou, Jesper; HMI Calibration Team
Bibcode: 2007AAS...210.2416S
Altcode: 2007BAAS...39..131S
  The HMI instrument is planned to be delivered shortly and launched
  in August 2008. During the integration and testing of the instrument
  we have performed an extensive series of calibrations. <P />In this
  poster we will start with a brief summary of the instrument status. <P
  />We will then describe the calibrations performed so far including
  some of the results. <P />Finally we will describe what remains to be
  done, including on-orbit calibrations, and how well we expect to be
  able to calibrate the final data. <P />The HMI project is supported
  by the National Aeronautics and Space Administration under contract
  NAS5-02139 to Stanford University.

Title: Reduction of Systematic Errors in Global Mode Analysis
Authors: Larson, Timothy P.; Schou, J.
Bibcode: 2007AAS...210.2202L
Altcode: 2007BAAS...39..124L
  In spite of the unprecedented success of the MDI Medium-l program, the
  global mode analysis pipeline is known to contain errors. Physical
  effects such as line assymmetry, horizontal displacement at the
  solar surface, and distortion of eigenfunctions have been ignored, as
  well as a wide array of instrumental effects. Additionally, certain
  improvements in the pipeline algorithm itself are possible, most
  notably in the gap-filling of time series. Perhaps unsurprisingly,
  some features of the results seem to be the effect of systematic
  errors. The most remarkable of these features are an annual variation
  in f-mode frequency changes, a bump in the normalized residuals of the
  a-coefficients around 3.4mHz, and polar jets in the inversions. In
  this poster we discuss the application of a variety of corrections
  to the analysis, the resulting changes in the mode parameters, and
  the effect on the magnitude of systematic errors. We also describe
  new software tools that been created to simplify and generalize the
  pipeline, making it of greater utility to anyone interested in global
  mode analysis. <P />This work has been funded by NASA.

Title: High-degree Mode Frequencies Using Global Helioseismology
    Analysis Of MDI Observations And Their Variation With Solar Cycle.
Authors: Rabello-Soares, M. Cristina; Korzennik, S. G.; Schou, J.
Bibcode: 2007AAS...210.2215R
Altcode: 2007BAAS...39..126R
  Using full-disk observations obtained with the Michelson Doppler
  Imager (MDI) on board the Solar and Heliospheric Observatory (SOHO)
  spacecraft, we present solar acoustic mode frequencies and their
  rotational splitting coefficients for modes with degree up to 900
  determined using global helioseismology analysis. Most of the known
  instrumental and observational effects that affect specifically the
  high-degree modes have been removed. <P />The structural and dynamical
  properties of the near-surface layers of the Sun was analyzed through
  the study of: (a) the difference between the observed and theoretical
  frequencies; and (b) the solar rotation at different latitudes estimated
  using a simple analytical method. <P />We also present variations of
  the mode frequencies resulting from solar activity over most of solar
  cycle 23. We have studied the correlation of medium and high degree
  modes with four different solar indices. Our results confirm that the
  frequency shift scaled by the relative mode inertia is a function of
  frequency alone and follows a simple power law.

Title: Magnetic Field Vector Retrieval With the Helioseismic and
    Magnetic Imager
Authors: Borrero, J. M.; Tomczyk, S.; Norton, A.; Darnell, T.; Schou,
   J.; Scherrer, P.; Bush, R.; Liu, Y.
Bibcode: 2007SoPh..240..177B
Altcode: 2006astro.ph.11565B
  We investigate the accuracy to which we can retrieve the solar
  photospheric magnetic field vector using the Helioseismic and Magnetic
  Imager (HMI) that will fly onboard of the Solar Dynamics Observatory by
  inverting simulated HMI profiles. The simulated profiles realistically
  take into account the effects of the photon noise, limited spectral
  resolution, instrumental polarization modulation, solar p modes, and
  temporal averaging. The accuracy of the determination of the magnetic
  field vector is studied by considering the different operational modes
  of the instrument.

Title: Temporal variations in solar rotation at the bottom of the
convection zone: The current status
Authors: Howe, R.; Christensen-Dalsgaard, J.; Hill, F.; Komm, R.;
   Schou, J.; Thompson, M. J.; Toomre, J.
Bibcode: 2007AdSpR..40..915H
Altcode:
  We present the most recent results on the short-period variations
  in the solar rotation rate near the base of the convection zone. The
  1.3-year period which was reported in the early years of solar cycle 23
  appears not to persist after 2001, but there are hints of fluctuations
  at a different period during the declining phase of the cycle.

Title: Spectral Line Selection for HMI
Authors: Norton, A. A.; Pietarila Graham, J. D.; Ulrich, R. K.;
   Schou, J.; Tomczyk, S.; Liu, Y.; Lites, B. W.; López Ariste, A.;
   Bush, R. I.; Socas-Navarro, H.; Scherrer, P. H.
Bibcode: 2006ASPC..358..193N
Altcode:
  We present information on two spectral lines, Fe I 6173 Å and Ni I 6768
  Å, that were candidates for use in the Helioseismic and Magnetic Imager
  (HMI) instrument. Both Fe I and Ni I profiles have clean continuum and
  no blends that threaten performance. The higher Landé factor of Fe
  I means its operational velocity range in regions of strong magnetic
  field is smaller than for Ne I. Fe I performs better than Ni I for
  vector magnetic field retrieval. Inversion results show that Fe I
  consistently determines field strength and flux more accurately than
  the Ni I line. Inversions show inclination and azimuthal errors are
  recovered to ≈2° above 600 Mx/cm<SUP>2</SUP> for Fe I and above
  1000 Mx/cm<SUP>2</SUP> for Ni I. The Fe I line was recommended, and
  ultimately chosen, for use in HMI.

Title: Magnetic Field Vector Retrieval with HMI
Authors: Borrero, J. M.; Tomczyk, S.; Norton, A. A.; Darnell, T.;
   Schou, J.; Scherrer, P.; Bush, R. I.; Lui, Y.
Bibcode: 2006ASPC..358..144B
Altcode:
  The Helioseismic and Magnetic Imager (HMI), on board the Solar Dynamics
  Observatory (SDO), will begin data acquisition in 2008. It will provide
  the first full-disk, high temporal cadence observations of the full
  Stokes vector with a 0.5 arcsec pixel size. This will allow for a
  continuous monitoring of the Solar magnetic-field vector. HMI data will
  advance our understanding of the small- and large-scale magnetic field
  evolution, its relation to the solar and global dynamic processes,
  coronal field extrapolations, flux emergence, magnetic helicity, and
  the nature of the polar magnetic fields. We summarize HMI's expected
  operation modes, focusing on the polarization cross-talk induced
  by the solar oscillations, and how this affects the magnetic-field
  vector determination.

Title: Spectral Line Selection for HMI: A Comparison of Fe I 6173
    Å and Ni I 6768 Å
Authors: Norton, A. A.; Graham, J. Pietarila; Ulrich, R. K.; Schou,
   J.; Tomczyk, S.; Liu, Y.; Lites, B. W.; Ariste, A. López; Bush,
   R. I.; Socas-Navarro, H.; Scherrer, P. H.
Bibcode: 2006SoPh..239...69N
Altcode: 2006SoPh..tmp...88N; 2006astro.ph..8124N
  We present a study of two spectral lines, Fe I 6173 Å and Ni I 6768 Å,
  that were candidates to be used in the Helioseismic and Magnetic Imager
  (HMI) for observing Doppler velocity and the vector magnetic field. The
  line profiles were studied using the Mt. Wilson Observatory, the
  Advanced Stokes Polarimeter and the Kitt Peak-McMath Pierce telescope
  and one-meter Fourier transform spectrometer atlas. Both Fe I and Ni
  I profiles have clean continua and no blends that threaten instrument
  performance. The Fe I line is 2% deeper, 15% narrower, and has a 6%
  smaller equivalent width than the Ni I line. The potential of each
  spectral line to recover pre-assigned solar conditions is tested
  using a least-squares minimization technique to fit Milne-Eddington
  models to tens of thousands of line profiles that have been sampled
  at five spectral positions across the line. Overall, the Fe I line
  has a better performance than the Ni I line for vector-magnetic-field
  retrieval. Specifically, the Fe I line is able to determine field
  strength, longitudinal and transverse flux four times more accurately
  than the Ni I line in active regions. Inclination and azimuthal angles
  can be recovered to ≈2<SUP>°</SUP> above 600 Mx cm<SUP>−2</SUP>
  for Fe I and above 1000 Mx cm<SUP>−2</SUP> for Ni I. Therefore, the
  Fe I line better determines the magnetic-field orientation in plage,
  whereas both lines provide good orientation determination in penumbrae
  and umbrae. We selected the Fe I spectral line for use in HMI due to
  its better performance for magnetic diagnostics while not sacrificing
  velocity information. The one exception to the better performance of the
  Fe I line arises when high field strengths combine with high velocities
  to move the spectral line beyond the effective sampling range. The
  higher g<SUB>eff</SUB> of Fe I means that its useful range of velocity
  values in regions of strong magnetic field is smaller than Ni I.

Title: High-degree mode frequencies: changes with solar cycle
Authors: Rabello-Soares, M. C.; Korzennik, S. G.; Schou, J.
Bibcode: 2006ESASP.624E..71R
Altcode: 2006soho...18E..71R
  No abstract at ADS

Title: Frequency, splitting, linewidth and amplitude estimates of
low-l p modes of alpha Cen A: analysis of WIRE photometry
Authors: Fletcher, S. T.; Chaplin, W. J.; Elsworth, Y.; Schou, J.;
   Buzasi, D.
Bibcode: 2006ESASP.624E..27F
Altcode: 2006soho...18E..27F
  No abstract at ADS

Title: Solar Convection Zone Dynamics: How Sensitive Are Inversions
    to Subtle Dynamo Features?
Authors: Howe, R.; Rempel, M.; Christensen-Dalsgaard, J.; Hill, F.;
   Komm, R.; Larsen, R. M.; Schou, J.; Thompson, M. J.
Bibcode: 2006ApJ...649.1155H
Altcode:
  The nearly 10 year span of medium-degree helioseismic data from the
  Global Oscillation Network Group and the Michelson Doppler Imager has
  allowed us to study the evolving flows in the solar convection zone
  over most of solar cycle 23. Using two independent two-dimensional
  rotation inversion techniques and extensive studies of the resolution
  using artificial data from different assumed flow profiles, including
  those generated from sample mean field dynamo models, we attempt to
  assess the reality of certain features seen in the inferred rotation
  profiles. Our results suggest that the findings from observations of
  a substantial depth dependence of the phase of the zonal flow pattern
  in the low latitudes, and the penetration of the flows deep into the
  convection zone, are likely to be real rather than artifacts of the
  inversion process.

Title: Solar rotation and zonal flows from Mount Wilson 60 ft
    tower data
Authors: Howe, R.; Bogart, R.; Christensen-Dalsgaard, J.; Rhodes,
   E. J., Jr.; Rose, P.; Schou, J.
Bibcode: 2006ESASP.624E..56H
Altcode: 2006soho...18E..56H
  No abstract at ADS

Title: Line Shape Changes and Doppler Measurements in Solar Active
    Regions. I. A Method for Correcting Dopplergrams from SOHO MDI
Authors: Wachter, R.; Schou, J.; Sankarasubramanian, K.
Bibcode: 2006ApJ...648.1256W
Altcode:
  We present a method to correct MDI high-resolution Dopplergrams
  in active regions for systematic observational errors due to the
  spectral line shape changes. We use a measurement campaign with the
  Advanced Stokes Polarimeter to investigate the influence of line shape
  changes in active regions on MDI Dopplergram calibration. An estimate
  of the width of the Ni I λ6768 absorption line used by MDI to measure
  velocity provides a linear correction to the standard calibration. This
  correction can be largely explained by the Zeeman broadening of the
  absorption line.

Title: Computational Acoustics in Spherical Geometry: Steps toward
    Validating Helioseismology
Authors: Hanasoge, S. M.; Larsen, R. M.; Duvall, T. L., Jr.; De Rosa,
   M. L.; Hurlburt, N. E.; Schou, J.; Roth, M.; Christensen-Dalsgaard,
   J.; Lele, S. K.
Bibcode: 2006ApJ...648.1268H
Altcode:
  Throughout the past decade, detailed helioseismic analyses of
  observations of solar surface oscillations have led to advances in our
  knowledge of the structure and dynamics of the solar interior. Such
  analyses involve the decomposition of time series of the observed
  surface oscillation pattern into its constituent wave modes, followed
  by inversion procedures that yield inferences of properties of the
  solar interior. While this inverse problem has been a major focus in
  recent years, the corresponding forward problem has received much less
  attention. We aim to rectify this situation by taking the first steps
  toward validating and determining the efficacy of the helioseismic
  measurement procedure. The goal of this effort is to design a means
  to perform differential studies of various effects such as flows and
  thermal perturbations on helioseismic observables such as resonant
  frequencies, travel-time shifts, etc. Here we describe our first
  efforts to simulate wave propagation within a spherical shell,
  which extends from 0.2 to about 1.0004 R<SUB>solar</SUB> (where
  R<SUB>solar</SUB> is the radius of the Sun) and which possesses a
  solar-like stratification. We consider a model containing no flows
  that will serve as a reference model for later studies. We discuss the
  computational procedure, some difficulties encountered in a simulation
  of this kind, and the means to overcome them. We also present techniques
  used to validate the simulation.

Title: Frequency, splitting, linewidth and amplitude estimates
of low-ℓ p modes of α Cen A: analysis of Wide-Field Infrared
    Explorer photometry
Authors: Fletcher, S. T.; Chaplin, W. J.; Elsworth, Y.; Schou, J.;
   Buzasi, D.
Bibcode: 2006MNRAS.371..935F
Altcode: 2006astro.ph..7172F; 2006MNRAS.tmp..824F
  We present results of fitting the 50-d time series of photometry of α
  Cen A taken by the Wide-Field Infrared Explorer (WIRE) satellite in
  1999. Both power spectrum and autocovariance function (ACF) fitting
  techniques were used in an attempt to determine mode frequencies,
  rotational splittings, lifetimes and amplitudes of low-l p modes. In
  all, using both techniques, we managed to fit 18 modes (seven l = 0,
  eight l = 1 and three l = 2) with frequencies determined to within
  1-2 μHz. These estimates are shown to be 0.6 +/- 0.3 μHz lower, on
  average, than the frequencies determined from two other more recent
  studies, which used data gathered about 19 months after the WIRE
  observations. This could be indicative of an activity cycle, although
  due to the large uncertainty, more data would be needed to confirm
  this. <P />Over a range of 1700-2650 μHz, we were also able to use
  the ACF fitting to determine an average lifetime of 3.9 +/- 1.4 d,
  and an average rotational splitting of 0.54 +/- 0.22 μHz, which is
  the first ever reliable estimate of this parameter. In contrast to
  the ACF, the power spectrum fitting was shown to return significantly
  biased results for these parameters.

Title: The determination of global high-degree solar p-mode
parameters: challenges and new results
Authors: Rabello-Soares, M. C.; Korzennik, S. G.; Schou, J.
Bibcode: 2006IAUJD..17E...7R
Altcode:
  We review the challenges of estimating unbiased mode parameters for
  global high-degree solar acoustic modes (100 &lt; ℓ &lt; 1000), with
  emphasis on the importance of knowing the instrumental characteristics
  and how they affect mode parameters determination. We present new
  estimates of the global high-degree mode parameters resulting from
  incorporating our best knowledge of the MDI instrument on board SOHO
  and we also present their dependence with the solar cycle.

Title: Helioseismic and Magnetic Imager Calibration Status
Authors: Schou, Jesper; HMI Team
Bibcode: 2006SPD....37.0606S
Altcode: 2006BAAS...38..226S
  The Helioseismic and Magnetic Imager (HMI) instrument, which is due to
  be launched in August 2008 as part of the Solar Dynamics Observatory
  spacecraft, is now nearly assembled and most of the ground based
  calibrations have been performed.In this poster we will briefly
  summarize the status of the instrument, describe the ground based
  calibration efforts and outline the calibration efforts planned after
  launch.Based on the calibration results we will also briefly discuss
  the quality of the data expected from the instrument after launch.This
  work is supported by the National Aeronautics and Space Administration
  through contract NAS5-02139.

Title: Changes Of The Solar Acoustic High-degree Mode Frequencies
    Over The Solar Cycle
Authors: Korzennik, Sylvain G.; Rabello-Soares, M. C.; Schou, J.
Bibcode: 2006SPD....37.0508K
Altcode: 2006BAAS...38..224K
  Using full-disk observations obtained with the Michelson Doppler
  Imager (MDI) on board the Solar and Heliospheric Observatory (SOHO)
  spacecraft, we present frequency and frequency splitting variations
  of high-degree (100 &lt; l &lt; 1000) solar acoustic modes over the
  solar cycle using global helioseismology analysis techniques. Since we
  analyzed high-degree modes, we focus on properties of the near-surface
  solar region. We have corrected for most of the known instrumental
  effects that affect the characterization of high-degree modes using
  the methodology described in Korzennik et al. (2004) as to estimate
  unbiased high-degree mode frequencies.

Title: Large-Scale Zonal Flows Near the Solar Surface
Authors: Howe, R.; Komm, R.; Hill, F.; Ulrich, R.; Haber, D. A.;
   Hindman, B. W.; Schou, J.; Thompson, M. J.
Bibcode: 2006SoPh..235....1H
Altcode:
  Migrating bands of weak, zonal flow, associated with the activity
  bands in the solar cycle, have been observed at the solar surface for
  some time. More recently, these flows have been probed deep within the
  convection zone using global helioseismology and examined in more detail
  close to the surface with the techniques of local helioseismology. We
  compare the near-surface results from global and local helioseismology
  using data from the Michelson Doppler Imager and the Global Oscillation
  Network Group with surface Doppler velocity measurements from the Mount
  Wilson 150-foot tower and find that the results are in reasonable
  agreement, with some explicable differences in detail. All of the
  data sets show zones of faster rotation approaching the equator from
  mid-latitudes during the solar cycle, with a variation at any given
  location that can be approximately, but not completely, described by a
  single sinusoid and an amplitude that does not drop off steeply below
  the surface.

Title: Variations of the solar acoustic high-degree mode parameters
    over solar cycle 23
Authors: Rabello-Soares, M. C.; Korzennik, S. G.; Schou, J.
Bibcode: 2006cosp...36.2668R
Altcode: 2006cosp.meet.2668R
  The structural and dynamical properties of the Sun as well as the
  excitation and damping of the solar acoustic modes change with the solar
  cycle The first two manifest themselves as changes in the acoustic mode
  frequencies and frequency splittings While the last two are observed
  as changes in the mode amplitudes and lifetimes Using full-disk
  observations obtained with the Michelson Doppler Imager MDI on board
  the Solar and Heliospheric Observatory SOHO spacecraft we present
  the amplitude width frequency and frequency splitting variations of
  high-degree 100 l 1000 solar acoustic modes over most of solar cycle
  23 using global helioseismology analysis techniques By looking at
  high-degree modes we focus on the properties of the near-surface solar
  region Following the methodology described in detail in Korzennik
  et al 2004 we have removed the known instrumental and observational
  effects that affect specifically high-degree modes as well as possible
  to infer unbiased estimates of high-degree mode parameters

Title: Solar Convection-Zone Dynamics, 1995-2004
Authors: Howe, R.; Christensen-Dalsgaard, J.; Hill, F.; Komm, R.;
   Schou, J.; Thompson, M. J.
Bibcode: 2005ApJ...634.1405H
Altcode:
  The nine-year span of medium-degree helioseismic data from the Global
  Oscillation Network Group (GONG) and the Michelson Doppler Imager (MDI)
  allows us to study the evolving zonal flows in the solar convection
  zone over the rising phase, maximum, and early declining phase
  of solar cycle 23. Using two independent two-dimensional rotation
  inversion techniques, we investigate the depth profile of the flow
  pattern known as the torsional oscillation. The observations suggest
  that the flows penetrate deep within the convection zone-perhaps to
  its base-even at low latitudes, and that the phase of the pattern is
  approximately constant along lines of constant rotation rather than
  lines of constant latitude.

Title: How Sensitive are Rotation Inversions to Subtle Features of
    the Dynamo?
Authors: Howe, R.; Rempel, M.; Christensen-Dalsgaard, J.; Schou, J.;
   Thompson, M. J.; Komm, R.; Hill, F.
Bibcode: 2005ASPC..346...99H
Altcode:
  Global rotation inversions can probe the pattern of zonal flows
  well into the convection zone. In this paper, we test the ability
  of the inversions to constrain the predictions of dynamo models. A
  flux-transport dynamo model, including a mean-field theory of
  differential rotation and allowing for feedback of the Lorentz force
  on differential rotation and meridional flow, was used to produce a
  22-year cycle of simulated rotation profiles. These were then subjected
  to simulated inversions with realistic mode sets and errors, in order
  to test how well the subtle subsurface features of the input profile
  could be recovered. The preliminary results are quite encouraging.

Title: Global, Local and Surface Measurements of Large-Scale Zonal
    Flows Near the Solar Surface
Authors: Howe, R.; Komm, R. W.; Haber, D. A.; Hindman, B. W.; Ulrich,
   R. K.; Schou, J.; Thompson, M. J.; Hill, F.
Bibcode: 2005AGUSMSP32A..03H
Altcode:
  Migrating bands of weak zonal flow, associated with the activity
  bands in the solar cycle, have been observed at the solar surface
  for some time. More recently, these flows have been probed deep
  within the convection zone using global helioseismology, and
  examined in more detail close to the surface with the techniques of
  local helioseismology. We compare the results from global and local
  helioseismology using data from the Michelson Doppler Imager and the
  GONG network and also Doppler measurements from Mount Wilson, and find
  that the results are in reasonable agreement, with some explicable
  differences in detail. This was work was supported by the National
  Science Foundation and NASA.

Title: Designing Data Services for the SDO AIA/HMI Joint Science
    Operations Center
Authors: Larsen, R. M.; Bogart, R. S.; Scherrer, P. H.; Schou, J.;
   Tian, K. Q.
Bibcode: 2005AGUSMSH51B..04L
Altcode:
  The Joint Science Operations Center (JSOC) is designed to provide data
  capture, archive, analysis, and distribution functions for both the
  Helioseismic and Magnetic Imager and the Atmospheric Imaging Array
  on the Solar Dynamics Observatory. These instruments are notable
  for the large quantity of raw data they will generate, more than
  doubling the total volume of all existing solar data in the first few
  months alone. In addition, the JSOC will be required to handle a larger
  component of higher-level data products than most previous missions. The
  fundamental concept of the JSOC architecture is that the metadata and
  bulk image data are stored separately, not being combined until the time
  of use or export. This enables all metadata to be rapidly accessible
  through a relational database. It permits flexible organization of the
  data into virtual data sets or series, and the use of an abstracted
  syntax, such as a URL, for data description and querying. Furthermore,
  data organization details dictated by the requirements of efficient mass
  storage can be hidden from the user. Multiple classes of access to the
  processing and data are envisioned, ranging from production pipeline
  modules generating standard mission products to workstation users
  analyzing self-contained data products exported from the archive. The
  JSOC design provides a rich set of primitives upon which VSO-like
  services can be built, and should allow us to provide a unified view
  of the data and data services to all classes of users.

Title: New Steps Towards the Unbiased Characterization of High-Degree
    Mode Frequencies
Authors: Rabello-Soares, M. C.; Korzennik, S. G.; Schou, J.
Bibcode: 2005AGUSMSP11B..08R
Altcode:
  Bias in the characterization of high-degree mode frequency results
  from the blending of individual modes into ridges as mode lifetimes get
  shorter and spatial leaks get closer in frequency at high degrees. To
  recover the actual underlying mode frequency from fitting the ridge,
  an accurate model of the amplitude of the peaks that contribute to the
  ridge power distribution is crucial. Such a model requires that the
  instrumental characteristics be very well understood and very precisely
  measured. We here present new results from our continuing effort to
  estimate unbiased high-degree mode frequencies using full-disk data
  from the Michelson Doppler Imager (MDI) on the Solar and Heliospheric
  Observatory (SOHO). The methodology is based on the extensive analysis
  presented in Korzennik et al (2004) - and will in turn be beneficial
  to MDI, GONG and eventually HMI. The key improvement on our previous
  work is the re-decomposition of the images onto spherical harmonic
  component. This new spatial decomposition incorporates specific MDI
  instrumental characteristics, like a more accurate plate scale, our
  best model of the image distortion, the image orientation, etc... These
  instrumental effects were introduced one at a time and their effect
  carefully compared to the predictions of our model. As expected, by
  including these corrections in the spatial decomposition, the residual
  corrections that must be applied to the ridge frequency are reduced,
  leading to a less biased frequency estimation.

Title: Systematic errors in Dopplergrams of active regions
Authors: Wachter, R.; Schou, J.; Kosovichev, A. G.; Rajaguru, P.
Bibcode: 2005AGUSMSP13A..07W
Altcode:
  Dopplergrams of magnetic regions are used in time-distance
  helioseismology and for the investigation of oscillations in
  sunspots. MDI Dopplergrams are produced onboard SOHO by measuring four
  filtergrams which are sensitive to intensity fluctuations in the wings
  of the Ni i absorption line at 6768 Å. The line of sight velocity
  is inferred from a lookup table which is based on the shape of the
  line in the quiet sun. In magnetic regions, however, the line shape
  changes drastically and molecular absorption lines appear close to the
  line's wavelength. This problem is equally relevant for the upcoming
  Helioseismic and Magnetic Imager (HMI) which measures velocities based
  on the same principles as MDI, using however a different absorption
  line (Fe i at 6173 Å). Based on high spectral resolution images of
  magnetic regions obtained by the ASP (Advanced Stokes Polarimeter)
  instrument we show that the MDI Doppler velocities are systematically
  underestimated in magnetic regions. We discuss possibilities to correct
  the velocity measurements in magnetic regions using intensity and
  magnetic field data.

Title: The non-detection of oscillations in Procyon by MOST: Is it
    really a surprise?
Authors: Bedding, T. R.; Kjeldsen, H.; Bouchy, F.; Bruntt, H.; Butler,
   R. P.; Buzasi, D. L.; Christensen-Dalsgaard, J.; Frandsen, S.; Lebrun,
   J. -C.; Martić, M.; Schou, J.
Bibcode: 2005A&A...432L..43B
Altcode: 2005astro.ph..1662B
  We argue that the non-detection of oscillations in Procyon by the
  MOST satellite reported by [CITE] is fully consistent with published
  ground-based velocity observations of this star. We also examine the
  claims that the MOST observations represent the best photometric
  precision so far reported in the literature by about an order of
  magnitude and are the most sensitive data set for asteroseismology
  available for any star other than the Sun. These statements are
  not correct, with the most notable exceptions being observations
  of oscillations in α Cen A that are far superior. We further
  disagree that the hump of excess power seen repeatedly from velocity
  observations of Procyon can be explained as an artefact caused by
  gaps in the data. The MOST observations failed to reveal oscillations
  clearly because their noise level is too high, possibly from scattered
  Earthlight in the instrument. We did find an excess of strong peaks in
  the MOST amplitude spectrum that is inconsistent with a simple noise
  source such as granulation, and may perhaps indicate oscillations at
  roughly the expected level.

Title: Helio- and Asteroseismic Analysis Methods
Authors: Schou, Jesper
Bibcode: 2005HiA....13..415S
Altcode:
  Over the last few decades increasingly sophisticated analysis algorithms
  have been developed in helioseismology. In this talk I will describe
  some of these methods with an emphasis on those most relevant to the
  study of oscillations in other stars and some of the relevant lessons
  learned. I will then go on to discuss some of the properties of stellar
  oscillations which distinguish them from solar oscillations and how
  to address those in the analysis. Finally I will speculate on what we
  may learn from the stellar oscillations.

Title: How Sensitive are Rotation Inversions to Subtle Features of
    the Dynamo?
Authors: Howe, R.; Rempel, M.; Christensen-Dalsgaard, J.; Hill, F.;
   Komm, R. W.; Schou, J.; Thompson, M. J.
Bibcode: 2004ESASP.559..468H
Altcode: 2004soho...14..468H
  No abstract at ADS

Title: The Current Status of Analyzing High-Degree Modes
Authors: Reiter, J.; Rhodes, E. J., Jr.; Kosovichev, A. G.; Schou, J.
Bibcode: 2004ESASP.559...61R
Altcode: 2004soho...14...61R
  No abstract at ADS

Title: The Phase of the Torsional Oscillation Pattern
Authors: Howe, R.; Komm, R. W.; Hill, F.; Christensen-Dalsgaard, J.;
   Schou, J.; Thompson, M. J.
Bibcode: 2004ESASP.559..476H
Altcode: 2004soho...14..476H
  No abstract at ADS

Title: Low Frequency Modes
Authors: Schou, J.
Bibcode: 2004ESASP.559..134S
Altcode: 2004soho...14..134S
  No abstract at ADS

Title: Convection-Zone Dynamics from GONG and MDI, 1995-2004
Authors: Howe, R.; Komm, R. W.; Hill, F.; Christensen-Dalsgaard, J.;
   Haber, D. A.; Schou, J.; Thompson, M. J.
Bibcode: 2004ESASP.559..472H
Altcode: 2004soho...14..472H
  No abstract at ADS

Title: On the Determination of Michelson Doppler Imager High-Degree
    Mode Frequencies
Authors: Korzennik, S. G.; Rabello-Soares, M. C.; Schou, J.
Bibcode: 2004ApJ...602..481K
Altcode: 2002astro.ph..7371K
  The characteristics of the solar acoustic spectrum are such that mode
  lifetimes get shorter and spatial leaks get closer in frequency as
  the degree of a mode increases for a given order. A direct consequence
  of this property is that individual p-modes are resolved only at low
  and intermediate degrees and that at high degrees individual modes
  blend into ridges. Once modes have blended into ridges, the power
  distribution of the ridge defines the ridge central frequency, and it
  will mask the true underlying mode frequency. An accurate model of the
  amplitude of the peaks that contribute to the ridge power distribution
  is needed to recover the underlying mode frequency from fitting the
  ridge. We present the results of fitting high-degree power ridges
  (up to l=900) computed from several 2-3 month long time series of
  full-disk observations taken with the Michelson Doppler Imager (MDI) on
  board the Solar and Heliospheric Observatory between 1996 and 1999. We
  also present a detailed discussion of the modeling of the ridge power
  distribution, and the contribution of the various observational
  and instrumental effects on the spatial leakage, in the context
  of the MDI instrument. We have constructed a physically motivated
  model (rather than some ad hoc correction scheme) that we believe
  results in a methodology that can produce an unbiased determination
  of high-degree modes once the instrumental characteristics are well
  understood. Finally, we present preliminary estimates of changes in
  high-degree mode parameters with epoch and thus solar activity level and
  discuss their significance. These estimates are preliminary because they
  rely on a simple-if not simplistic-ridge-to-mode correction scheme to
  account for errors in the plate scale used for the spherical harmonic
  decomposition. Such a correction scheme produced residual systematics
  that, as we show, are not always constant with time. These cannot be
  properly corrected without reprocessing the data back to the level of
  the spherical harmonic decomposition.

Title: SOHO MDI CCD performance
Authors: Schou, J.
Bibcode: 2004ESASP.538..411S
Altcode: 2004sshp.conf..411S
  The Michelson Doppler Imager (MDI) instrument on the Solar and
  Heliospheric Observatory (SOHO) spacecraft is designed to study
  solar oscillations. While MDI was not designed for high photometric
  accuracy, I will describe how MDI data can be used to estimate the
  photometric stability of a CCD camera in a space environment and show
  that the system appears to be stable, at the relevant time-scales,
  to a level well beyond that required for both planet finding and
  asteroseismology. I will also present a simple minded analysis of
  various types of radiation induced damage. Given the similarity of the
  orbits (L1 for SOHO versus L2 for Eddington) some of these measurements
  may be useful for the design of Eddington.

Title: Wavelike Properties of Solar Supergranulation Detected in
    Doppler Shift Data
Authors: Schou, J.
Bibcode: 2003ApJ...596L.259S
Altcode:
  Recently, Gizon, Duvall, &amp; Schou suggested that supergranulation has
  a wavelike component. In this Letter, I show that the same phenomenon
  can be observed using surface Doppler shift data, thereby confirming
  their observations, which were made using a helioseismic time-distance
  technique. In addition to confirming those results, I show that the
  wave motion is predominantly longitudinal (the fluid displacement is
  in the direction of propagation), and I am able to extend the results
  for the rotation and the meridional flow beyond +/-70° latitude. The
  meridional flow results, which extend further than previous helioseismic
  measurements, appear to show no sign of a second cell.

Title: A Comparison of Solar p-Mode Parameters from MDI and GONG:
    Mode Frequencies and Structure Inversions
Authors: Basu, S.; Christensen-Dalsgaard, J.; Howe, R.; Schou, J.;
   Thompson, M. J.; Hill, F.; Komm, R.
Bibcode: 2003ApJ...591..432B
Altcode:
  Helioseismic analysis of solar global oscillations allows investigation
  of the internal structure of the Sun. One important test of the
  reliability of the inferences from helioseismology is that the
  results from independent sets of contemporaneous data are consistent
  with one another. Here we compare mode frequencies from the Global
  Oscillation Network Group and Michelson Doppler Imager on board SOHO
  and resulting inversion results on the Sun's internal structure. The
  average relative differences between the data sets are typically less
  than 1×10<SUP>-5</SUP>, substantially smaller than the formal errors in
  the differences; however, in some cases the frequency differences show
  a systematic behavior that might nonetheless influence the inversion
  results. We find that the differences in frequencies are not a result
  of instrumental effects but are almost entirely related to the data
  pipeline software. Inversion of the frequencies shows that their
  differences do not result in any significant effects on the resulting
  inferences on solar structure. We have also experimented with fitting
  asymmetric profiles to the oscillation power spectra and find that,
  compared with the symmetric fits, this causes no significant change
  in the inversion results.

Title: The LoHCo Project. 1 -- Comparison of Ring-Diagram Local
    Helioseismology on GONG++, MDI and Mt. Wilson Data Sets
Authors: Bogart, R. S.; Schou, J.; Basu, S.; Bolding, J.; Hill, F.;
   Howe, R.; Komm, R. W.; Leibacher, J. W.; Toner, C. G.; Corbard, T.;
   Haber, D. A.; Hindman, B. W.; Toomre, J.; Rhodes, E. J.; Rose, P. J.;
   LoHCo Project Team
Bibcode: 2003SPD....34.0804B
Altcode: 2003BAAS...35..822B
  Full deployment of the GONG+ enhanced observing network in October
  2001 and implementation of ring-diagram helioseismology in the
  GONG++ analysis pipeline this year has enabled us to make a detailed
  intercomparison of results obtained through multiple paths, from
  observation through each of the analysis steps. Such comparisons
  can provide a certain degree of validation of the implementations
  of the analysis procedures, hints of systematic errors, and better
  characterization of the observations, possibly leading to improved
  calibrations. The Local Helioseismology Comparison (LoHCo) Project
  has been established to provide standards for intercomparison of
  results obtained with different local helioseismic analysis techniques
  applied to the available observational data sources. We present here
  a detailed comparison of ring-diagram determinations of localized
  sub-surface flows and frequency shifts obtained from both MDI and
  GONG in common observing intervals during Carrington Rotation 1988
  (2002/3/30 -- 2002/4/26), using both the MDI and the GONG analysis
  pipelines. We also present preliminary results of similar analyses of
  data obtained by the Mt. Wilson MOF during the same times. <P />This
  work is partially supported by grants from NASA and NSF.

Title: Time Variations of Meridional and Zonal Flows
Authors: Schou, J.
Bibcode: 2003SPD....34.2603S
Altcode: 2003BAAS...35Q.854S
  The so-called torsional oscillation, which manifests itself as
  bands of faster and slower rotation on top of the large-scale
  differential rotation, is well known. Initially it was discovered
  in surface Doppler shift observations, but it has since been seen
  using a variety of helioseismic techniques and in the rotation rate
  of the supergranulation. In this talk I will start by describing
  some of these measurements and show how it has been possible to
  detect the torsional oscillations to a significant depth. I will
  also discuss some of the other variations which have been detected in
  the solar rotation, in particular the 1.3 year oscillation near the
  solar tachocline. Finally I will discuss recent measurements of the
  meridional flow and its variations and what we may be able to learn in
  the near future. <P />This work was supported by NASA Grant NAG5-10483
  to Stanford University.

Title: Optimal Masks for Solar g-Mode Detection
Authors: Wachter, R.; Schou, J.; Kosovichev, A. G.; Scherrer, P. H.
Bibcode: 2003ApJ...588.1199W
Altcode:
  The detection of gravity (g) modes of solar oscillations is important
  for probing the physical conditions in the Sun's energy-generating
  core. We have developed a new method of spatial masks optimized to
  reveal solar g-modes of angular degree l=1-3 and applied it to Michelson
  Doppler Imager data in the frequency range of 50-500 μHz. These
  masks take into account the horizontal component of g-mode velocity
  eigenfunctions and the variations in the level of noise across the
  solar disk and adjust for the time-dependent mode projection properties
  caused by the inclination of the Sun's axis of rotation. They allow us
  to optimize the signal-to-noise ratio in the oscillation power spectra
  for potential g-modes of various angular order and degree. The peaks
  in the resulting spectra are analyzed in terms of their instrumental
  origin, long-term stability, and correspondence to the theoretically
  predicted g-mode spectrum. As a consequence of failing to detect
  any g-mode candidates, new upper limits for the surface amplitude of
  g-modes are obtained. The lowest upper limits in the range of 5-6 mm
  s<SUP>-1</SUP> are found for sectorial g-modes (l=m). These limits
  are an order of magnitude higher than the theoretical prediction of
  Kumar et al. in 1996.

Title: Supergranular waves observed using MDI surface Doppler
    shift data
Authors: Schou, Jesper
Bibcode: 2003ESASP.517..381S
Altcode: 2003soho...12..381S
  Recently Gizon, Duvall and Schou (2002) suggested that supergranulation
  has a wave-like component. Here I show that the phenomenon can also be
  observed using surface Doppler shift data and extend their results. I
  also show results for rotation and meridional flows beyond ±70°
  latitude inferred using the supergranular waves and look for temporal
  variations in the various properties.

Title: On the characterization of high-degree modes: a lesson from MDI
Authors: Korzennik, Sylvain G.; Rabello-Soares, Cristina; Schou, Jesper
Bibcode: 2003ESASP.517..145K
Altcode: 2003soho...12..145K
  High degree power ridges (up to l = 900) were computed and fitted for
  several two to three-month-long time-series of full-disk observations
  taken with the Michelson Doppler Imager (MDI) on-board the Solar and
  Heliospheric Observatory between 1996 and 1999. A detailed discussion
  of the modeling of the ridge power distribution, and the contribution
  of the various observational and instrumental effects on the spatial
  leakage, in the context of the MDI instrument, are presented. The result
  of this work is a better understanding of the problems associated with
  the characterization of high degree modes. We present the instrumental
  and observational requirements needed to achieve a determination of high
  degree mode frequencies whose residual systematic errors associated
  with the accuracy of the ridge to mode correction scheme are smaller
  than the uncertainty of the fitting itself.

Title: High-degree p-modes and the sun's evolving surface
Authors: Rhodes, E. J., Jr.; Reiter, J.; Schou, J.
Bibcode: 2003ESASP.517..173R
Altcode: 2003soho...12..173R
  Two of the most glaring problems in contemporary helioseismology are
  the limited availability of high-degree p-mode frequencies for use in
  inversions of solar internal structure and the lack of high-degree
  frequency splitting coefficients for use in inversions of solar
  internal dynamics. A third major problem is the lack of a consensus
  regarding the mechanism underlying the temporal shifts of the p-mode
  frequencies. The lack of high-degree frequencies and the lack of similar
  high-degree frequency splittings have occurred because of the inherent
  difficulties in measuring such frequencies and frequency splittings in
  high-degree power spectra without the inclusion of numerous systematic
  errors. We will first point out the importance of high-degree p-modes to
  helioseismic inversions. Next, we will describe recent progress we have
  made in estimating high-degree frequencies, including the use of both
  asymmetric and symmetric profiles in our fits. We will then demonstrate
  that the inclusion of corrections for the eigenfunction distortion
  due to latitudinal differential rotation removes long-standing
  discontinuities in the high-degree frequency splittings. We will go
  on to describe our recent efforts of increasing the sensitivity of the
  p-mode frequencies to changing levels of solar activity through the use
  of observing runs which are as short as three days in duration. Finally,
  we will also describe planned efforts at verifying recent discoveries in
  solar internal dynamics through the reduction and analysis of full-disk
  Dopplergrams obtained during Solar Cycle 22 prior to the beginning of
  the GONG and MDI projects. Taken together, the recent improvements
  in the estimation of high-degree frequencies, frequency splittings,
  and the availability of useful data from Solar Cycle 22 indicate that
  a renaissance in global helioseismology is now at hand.

Title: Transient oscillations near the solar tachocline
Authors: Toomre, Juri; Christensen-Dalsgaard, Jorgen; Hill, Frank;
   Howe, Rachel; Komm, Rudolf W.; Schou, Jesper; Thompson, Michael J.
Bibcode: 2003ESASP.517..409T
Altcode: 2003soho...12..409T
  We report on further developments in the 1.3-yr quasi-periodic
  oscillations reported by Howe et al. (2000). These are small (6 to 8
  nHz peak-to-peak) oscillations in the inferred rotation rate near the
  bottom of the convection zone and in the outer part of the radiative
  interior. The oscillations are strongest and most coherent at about a
  fractional radius of 0.72 in the equatorial region. Further monitoring
  of the oscillations near the equator shows that they continued for a
  period after the end of the data analyzed by Howe et al., but appear to
  have now diminished in amplitude. This is reminiscent of the transient
  behavior of similar (1.3 to 1.4 yr) periodicities in solar-wind and
  geomagnetic datasets previously reported. We speculate that the near
  tachocline oscillation is associated with the rising phase of the
  solar cycle. We discuss tests performed to eliminate various possible
  explanations of the oscillations due to systematic errors in the data
  and in their analyses.

Title: erratum: Wave-like properties of solar supergranulation
Authors: Gizon, L.; Duvall, T. L.; Schou, J.
Bibcode: 2003Natur.421..764G
Altcode:
  No abstract at ADS

Title: Accurate measurements of SOI/MDI high-degree frequencies and
    frequency splittings
Authors: Reiter, J.; Kosovichev, A. G.; Rhodes, E. J., Jr.; Schou, J.
Bibcode: 2003ESASP.517..369R
Altcode: 2003soho...12..369R
  We present accurate measurements of high-degree p-mode frequencies
  and frequency splittings obtained from the Full-Disk Program of
  the Michelson Doppler Imager (MDI) experiment onboard the Solar
  and Heliospheric Observatory (SOHO). The frequencies and frequency
  splittings are computed from unaveraged zonal, tesseral, and sectoral
  power spectra using a new fitting method of Reiter et al. (2002)
  based upon a maximum-likelihood fitting approach. In this method,
  both the spectral power distribution and contributions of the
  various observational and instrumental effects to the spatial leakage
  matrices are modelled accurately. We demonstrate that one of the most
  long-standing problems in high-degree helioseismology, viz. the jumps
  in the frequency splitting coefficients, can be solved by taking into
  account the distortion of the leakage matrix by the solar differential
  rotation. The results of inversion of the initial frequency set
  determined using this new method in the range of angular degree l =
  45-300 show a substantially better resolution of the subsurface layers
  compared to the previous studies with l below 220.

Title: Helio- and Asteroseismic Analysis Methods
Authors: Schou, Jesper
Bibcode: 2003IAUJD..12E..34S
Altcode:
  Over the last few decades increasingly sophisticated analysis algorithms
  have been developed in helioseismology. In this talk I will describe
  some of these methods with an emphasis on those most relevant to the
  study of oscillations in other stars and some of the relevant lessons
  learned. I will then go on to discuss some of the properties of stellar
  oscillations which distinguish them from solar oscillations and how
  to address those in the analysis. Finally I will speculate on what we
  may learn from the stellar oscillations.

Title: Wave-like properties of solar supergranulation
Authors: Gizon, L.; Duvall, T. L.; Schou, J.
Bibcode: 2003Natur.421...43G
Altcode: 2002astro.ph..8343G
  Supergranulation on the surface of the Sun is a pattern of horizontal
  outflows, outlined by a network of small magnetic features, with a
  distinct scale of 30 million metres and an apparent lifetime of one
  day. It is generally believed that supergranulation corresponds to
  a preferred `cellular' scale of thermal convection; rising magnetic
  fields are dragged by the outflows and concentrated into `ropes' at
  the `cell' boundaries. But as the convection zone is highly turbulent
  and stratified, numerical modelling has proved to be difficult and
  the dynamics remain poorly understood. Moreover, there is as yet no
  explanation for the observation that the pattern appears to rotate
  faster around the Sun than the magnetic features. Here we report
  observations showing that supergranulation undergoes oscillations and
  supports waves with periods of 6-9 days. The waves are predominantly
  prograde, which explains the apparent super-rotation of the pattern. The
  rotation of the plasma through which the pattern propagates is
  consistent with the motion of the magnetic network.

Title: Helioseismic data analysis
Authors: Schou, Jesper
Bibcode: 2003safd.book..247S
Altcode:
  The last decade has seen an impressive improvement in the quality and
  quantity of helioseismic data. While much of the progress has come
  from a new generation of instruments, such as GONG and MDI, data
  analysis has also played a major role. In this review I will start
  with a brief discussion of how the basic analysis of helioseismic
  data is done. I will then discuss some of the data analysis problems,
  their influence on our inferences about the Sun and speculate on what
  improvements may be expected in the near future. Finally I will show
  a selection of recent results.

Title: Vector Magnetic Field Measurement Capabiliity of the
    Helioseismic and Magnetic Imager on SDO
Authors: Bush, R.; Scherrer, P.; Schou, J.; Liu, Y.; Tomczyk, S.;
   Graham, J.; Norton, A.
Bibcode: 2002AGUFMSH52A0464B
Altcode:
  The Helioseismic and Magnetic Imager (HMI) instrument has been selected
  as part of the payload complement of the Solar Dynamics Observatory
  Spacecraft. In this poster we describe the observing technique for
  measuring solar vector magnetic fields. The expected performance of
  the HMI instrument will be discussed including results of modeling
  the observing lines and instrument.

Title: Solar Supergranulation Waves Detected in Surface Doppler Shift
Authors: Schou, J.
Bibcode: 2002astro.ph..8387S
Altcode:
  Recently Gizon, Duvall and Schou (2002) suggested that supergranulation
  has a wave-like component. In this paper I show that the same phenomenon
  can be observed using surface Doppler shift data, thereby confirming
  their observations. I am also able to measure the dispersion relation to
  lower wavenumbers and to extend the results for rotation and meridional
  flows beyond +/-70 degrees latitude.

Title: A new method for measuring frequencies and splittings of
    high-degree modes
Authors: Reiter, Johann; Rhodes, E. J., Jr.; Kosovichev, A. G.; Schou,
   J.; Scherrer, P. H.
Bibcode: 2002ESASP.508...91R
Altcode: 2002soho...11...91R
  A novel peak-bagging method is presented that operates by fitting a
  theoretical profile (symmetric or asymmetric) to the separate peaks of
  each multiplet within each unaveraged power spectrum. This new approach
  allows a separate frequency, width, and amplitude to be obtained for
  each m value at each value of l, n. Hence, the frequency splittings
  due to solar rotation for each multiplet can be measured directly. We
  present some of our initial results obtained with this new method
  in the range 45 &lt;= l &lt;= 300, ν &lt;= 7 mHz when applied to
  data from the Michelson Doppler Imager (MDI) onboard the Solar and
  Heliospheric Observatory (SOHO). Also discussed are some instrumental
  and methodological problems of high-degree mode measurements.

Title: Effect of line asymmetry on determination of high-degree
    mode frequencies
Authors: Reiter, Johann; Rhodes, E. J., Jr.; Kosovichev, A. G.; Schou,
   J.; Scherrer, P. H.
Bibcode: 2002ESASP.508...87R
Altcode: 2002soho...11...87R
  Accurate measurements of frequencies of high-degree p-modes are
  important for diagnostics of the structure and dynamics of the
  upper convective boundary layer, and understanding the nature of
  the solar-cycle variations detected in low- and medium-degree mode
  frequencies. Neglecting line asymmetry in the peak-bagging approach
  may lead to systematic errors in the determination of the mode
  characteristics and, hence, may affect the results of inversions. Here
  we demonstrate how the p-mode frequencies are systematically changed in
  the range of l &lt;= 1000, ν &lt;= 7mHz when line asymmetry is taken
  into account in the fitting of the spectral power peaks. The results
  reported are based upon spectra that were created from observations
  obtained from the MDI Full-Disk Program during the 1996 SOHO/MDI
  Dynamics Run.

Title: Solar Cycle Variability of High-Frequency and High-Degree
    p-Mode Oscillation Frequencies
Authors: Rhodes, E. J.; Reiter, J.; Schou, J.
Bibcode: 2002AAS...200.0420R
Altcode: 2002BAAS...34..949R
  Most studies of the solar cycle dependence of the frequencies of the
  p-mode oscillations have employed only the low- and intermediate-degree
  modes having ν &lt;=4500μ Hz. Most of these past studies have also
  employed lengthy observing runs covering two or more solar rotations. In
  this poster we will present measurements of the frequencies of both
  the high-ν and high-l oscillations which we have obtained during
  widely-varying levels of solar activity over the past 13 years. In
  contrast to the case of the lower-ν p-modes, the frequencies of the
  higher-ν modes are anti-correlated with solar activity. Furthermore,
  these frequencies can be estimated reliably from runs which are as
  short as only a few days. Using such brief time series, we have been
  able to obtain frequencies which show a higher sensitivity to changing
  levels of activity than has been the case in the past. This higher
  sensitivity gives us the expectation that such frequency shifts will
  provide tighter constraints upon future estimates of their origin.

Title: Solar g modes?
Authors: Schou, Jesper
Bibcode: 2002ESASP.508...99S
Altcode: 2002soho...11...99S
  Due to the importance g modes for understanding the solar interior,
  the search for them has been going on for decades, so far without any
  definite detections. Mostly the search has been done at low degrees,
  both for physical reasons and because these modes can be detected by the
  very stable instruments which observe in integrated sunlight. However,
  instead of searching for such g modes, I use MDI observations to follow
  the f-mode and low order p-mode ridges towards lower degrees. It was
  estimated (Schou, 1998) that at least half a solar cycle of data would
  be required to detect these modes down to the first avoided crossing
  with the g modes. The necessary observations are now available and I
  will make such an attempt. I will also estimate mode parameters such
  as frequencies, amplitudes and linewidths, the knowledge of which may
  improve our inference regarding the deep solar interior and enable
  better predictions for the amplitude of g modes.

Title: Solar internal rotation as seen from SOHO MIDI data
Authors: Vorontsov, S. V.; Christensen-Dalsgaard, J.; Schou, J.;
   Strakhov, V. N.; Thompson, M. J.
Bibcode: 2002ESASP.508..111V
Altcode: 2002soho...11..111V
  We report results of inverting the rotational splittings of solar
  p-mode frequencies measured from the MDI data, using an adaptive
  regularization technique as described by Strakhov &amp; Vorontsov
  (2001). We analyse the spatial and temporal structure of the variations
  in the internal rotation, which constitute the 11-yr solar torsional
  oscillations. We employ all the data collected over half a solar cycle
  to analyse further the time-independent component of the differential
  rotation, particularly focusing on the solar tachocline region. We
  address systematic errors in the rotational splitting measurements,
  as indicated by the inversion residuals, which appear to restrict the
  accuracy of the current helioseismic measurements.

Title: Solar cycle variability of high-frequency and high-degree
    p-mode oscillation frequencies
Authors: Rhodes, E. J., Jr.; Reiter, J.; Schou, J.
Bibcode: 2002ESASP.508...37R
Altcode: 2002soho...11...37R
  Most studies of the solar cycle dependence of the frequencies of the
  p-mode oscillations have employed only the low- and intermediate-degree
  modes having ν &lt;= 4500 μHz. Most of these past studies have
  also employed lengthy observing runs covering two or more solar
  rotations. In this paper we will present measurements of the frequencies
  of both the high-ν and high-l oscillations which we have obtained
  at widely-varying levels of solar activity over the past 13 years. In
  contrast to the case of the lower-ν p-modes, the frequencies of the
  higher-ν modes are anti-correlated with solar activity. Furthermore,
  these frequencies can be estimated reliably from runs which are as
  short as only a few days. Using such brief time series, we have been
  able to obtain frequencies which show a higher sensitivity to changing
  levels of activity than has been the case in the past. This higher
  sensitivity gives us the expectation that such frequency shifts will
  provide tighter constraints upon future estimates of their origin.

Title: Optimal masks for g-mode detection in MIDI velocity data
Authors: Wachter, R.; Schou, J.; Kosovichev, A.; Scherrer, P. H.
Bibcode: 2002ESASP.508..115W
Altcode: 2002soho...11..115W
  We are applying spatial masks to MDI velocity data that are optimized
  for revealing g-modes in the frequency range 50 through 500 μHz. These
  masks take into account the horizontal component of g-mode velocity
  eigenfunctions as well as the time dependent mode projection properties
  due to the changing solar B angle, and the varying noise level across
  the solar disk. The solar noise, which is likely to be caused by
  supergranulation in this frequency range is assumed to be uniformly
  distributed over the solar surface, consisting of a dominant horizontal
  component and a small radial component. The resulting time series are
  examined for possible g-mode candidates and new upper limits for the
  surface amplitude of g-modes are obtained.

Title: Optimal masks for g-mode detection in MDI velocity data
Authors: Wachter, R.; Schou, J.; Kosovichev, A.; Scherrer, P. H.;
   Phoebus Team
Bibcode: 2002AAS...200.0412W
Altcode: 2002BAAS...34..645W
  We are applying spatial masks for MDI velocity data that are optimized
  for revealing g-modes in the frequency range 50 through 500 μ
  Hz. These masks take into account the horizontal component of g-mode
  velocity eigenfunctions as well as the time dependent mode projection
  properties due to the changing solar B angle, and the varying noise
  level across the solar disk. The solar noise, which is likely to be
  caused by supergranulation in this frequency range is assumed to be
  uniformly distributed over the solar surface, consisting of a dominant
  horizontal component and a smaller radial component. The optimal masks
  are applied to the image and the resulting time series are examined
  for possible g-mode candidates. Because no mode peak has been detected,
  firm upper limits for the surface visibility of individual low degree
  modes can be given.

Title: Reduction of Systematic Errors in MDI Measurements
Authors: Schou, J.; Bogart, R. S.
Bibcode: 2002AAS...200.0411S
Altcode: 2002BAAS...34..645S
  Several types of imperfections have been identified in the MDI
  instrument and it has become clear that the resulting systematic
  errors in the results limit our ability to make inferences about the
  Sun. In this poster we will start by describing some of these problems
  and how we have succeeded in quantifying them. We will then apply the
  corresponding corrections to MDI data and show how various results are
  improved. In particular we show the improvements to normal mode and
  ring-diagram results and discuss how this will improve our inferences
  about the Sun. The MDI project is supported by NASA grant NAG5-10483
  to Stanford University.

Title: Helioseismic Measurement of Solar Torsional Oscillations
Authors: Vorontsov, S. V.; Christensen-Dalsgaard, J.; Schou, J.;
   Strakhov, V. N.; Thompson, M. J.
Bibcode: 2002Sci...296..101V
Altcode:
  Bands of slower and faster rotation, the so-called torsional
  oscillations, are observed at the Sun's surface to migrate in latitude
  over the 11-year solar cycle. Here, we report on the temporal variations
  of the Sun's internal rotation from solar p-mode frequencies obtained
  over nearly 6 years by the Michelson Doppler Imager (MDI) instrument
  on board the Solar and Heliospheric Observatory (SOHO) satellite. The
  entire solar convective envelope appears to be involved in the torsional
  oscillations, with phase propagating poleward and equatorward from
  midlatitudes at all depths throughout the convective envelope.

Title: A Comparison of Solar p-Mode Parameters from the Michelson
Doppler Imager and the Global Oscillation Network Group: Splitting
    Coefficients and Rotation Inversions
Authors: Schou, J.; Howe, R.; Basu, S.; Christensen-Dalsgaard, J.;
   Corbard, T.; Hill, F.; Komm, R.; Larsen, R. M.; Rabello-Soares, M. C.;
   Thompson, M. J.
Bibcode: 2002ApJ...567.1234S
Altcode:
  Using contemporaneous helioseismic data from the Global Oscillation
  Network Group (GONG) and Michelson Doppler Imager (MDI) onboard SOHO,
  we compare frequency-splitting data and resulting inversions about the
  Sun's internal rotation. Helioseismology has been very successful in
  making detailed and subtle inferences about the solar interior. But
  there are some significant differences between inversion results
  obtained from the MDI and GONG projects. It is important for making
  robust inferences about the solar interior that these differences are
  located and their causes eliminated. By applying the different analysis
  pipelines developed by the projects not only to their own data but
  also to the data from the other project, we conclude that the most
  significant differences arise not from the observations themselves
  but from the different frequency estimation analyses used by the
  projects. We find that the GONG pipeline results in substantially fewer
  fitted modes in certain regions. The most serious systematic differences
  in the results, with regard to rotation, appear to be an anomaly in
  the MDI odd-order splitting coefficients around a frequency of 3.5 mHz
  and an underestimation of the low-degree rotational splittings in the
  GONG algorithm.

Title: Asteroseismology of the roAp Star α Cir Using the WIRE
    Star Camera
Authors: Buzasi, D. L.; Kreidl, T. J.; Schou, J.; Preston, H. L.;
   Laher, R.; Catanzarite, J.; Conrow, T.
Bibcode: 2001AAS...19913311B
Altcode: 2001BAAS...33.1501B
  Using the camera on board the WIRE spacecraft, we observed α Cir
  from 18 August through 29 September 2000. α Cir is the brightest
  roAp star in the sky. Previous observers have detected a single
  oscillation mode at 2442 μ Hz, split by the rotational frequency,
  though Kurtz et al. (1994) reported the marginal detection of four
  low-amplitude secondary frequencies. Our time series has considerably
  improved signal-to-noise compared with past attempts. However, though
  we do directly detect the rotation of α Cir, we see no sign of the
  secondary frequencies reported earlier.

Title: Solar-cycle variation of the sound-speed asphericity from
    GONG and MDI data 1995-2000
Authors: Antia, H. M.; Basu, S.; Hill, F.; Howe, R.; Komm, R. W.;
   Schou, J.
Bibcode: 2001MNRAS.327.1029A
Altcode: 2001astro.ph..9326A
  We study the variation of the frequency splitting coefficients
  describing the solar asphericity in both GONG and MDI data, and
  use these data to investigate temporal sound-speed variations as a
  function of both depth and latitude during the period 1995-2000 and a
  little beyond. The temporal variations in even splitting coefficients
  are found to be correlated to the corresponding component of magnetic
  flux at the solar surface. We confirm that the sound-speed variations
  associated with the surface magnetic field are superficial. Temporally
  averaged results show a significant excess in sound speed around
  r=0.92R<SUB>solar</SUB> and latitude of 60°.

Title: Observed and Predicted Ratios of the Horizontal and Vertical
    Components of the Solar p-Mode Velocity Eigenfunctions
Authors: Rhodes, Edward J., Jr.; Reiter, Johann; Schou, Jesper;
   Kosovichev, Alexander G.; Scherrer, Philip H.
Bibcode: 2001ApJ...561.1127R
Altcode:
  We present evidence that the observed ratios of the horizontal
  and vertical components of the solar intermediate-degree p-mode
  velocity eigenfunctions closely match theoretical predictions of
  these ratios. This evidence comes from estimates of the observed
  eigenfunction component ratios that were obtained from the fitting
  of the p-mode oscillation peaks in low- and intermediate-degree
  (l&lt;=200) m-averaged power spectra computed from two different
  60.75 day time series of Global Oscillation Network Group (GONG)
  project Dopplergrams obtained in late 1996 and early 1998. These fits
  were carried out using a peak-fitting method in which we fitted each
  observed p-mode multiplet with a model profile that included both the
  target mode and its six nearest spatial sidelobes and which incorporated
  the effects of the incomplete observational time series through the
  convolution of the fitted profiles with the temporal window functions,
  which were computed using the two actual GONG observing histories. The
  fitted profile also included the effects of the spatial leakage of
  the modes of differing degrees into the target spectrum through the
  use of different sets of m-averaged spatial leakage matrices. In
  order to study the sensitivity of the estimated component ratios to
  the details of the computation of the m-averaged power spectra and of
  the image-masking schemes employed by the GONG project, we generated
  a total of 22 different sets of modal fits. We found that the best
  agreement between the predicted and inferred ratios came from the use
  of unweighted averaged power spectra that were computed using so-called
  n-averaged frequency-splitting coefficients, which had been computed
  by cross-correlating the 2l+1 zonal, tesseral, and sectoral power
  spectra at each l over a wide range of frequencies. This comparison
  yielded a total of 1906 pairs of predicted c<SUB>t,theory</SUB> and
  fitted c<SUB>t,fit</SUB> eigenfunction component ratios. A linear
  regression analysis of these pairs of ratios resulted in the following
  regression equation: c<SUB>t,fit</SUB>=(0.0088+/-0.0013)+(0.9940+/-
  0.0044)c<SUB>t,theory</SUB>. The resulting correlation coefficient
  was 0.9817. This agreement between the predicted and inferred ratios
  suggests that the predicted ratios should be used in the fitting of
  high-degree power spectra where the ratios cannot be inferred because
  of the blending together of individual modal peaks into broad ridges
  of power.

Title: Does the Sun Shrink with Increasing Magnetic Activity?
Authors: Dziembowski, W. A.; Goode, P. R.; Schou, J.
Bibcode: 2001ApJ...553..897D
Altcode: 2001astro.ph..1473D
  We have analyzed the full set of Solar and Heliospheric Observatory
  (SOHO) Michelson Doppler Imager (MDI) f- and p-mode oscillation
  frequencies from 1996 to date in a search for evidence of solar radius
  evolution during the rising phase of the current activity cycle. Just
  as Antia et al. in 2000, we find that a significant fraction of the
  f-mode frequency changes scale with frequency and that if these are
  interpreted in terms of a radius change, it implies a shrinking Sun. Our
  inferred rate of shrinkage is about 1.5 km yr<SUP>-1</SUP>, which is
  somewhat smaller than found by Antia et al. We argue that this rate
  does not refer to the surface but, rather, to a layer extending roughly
  from 4 to 8 Mm beneath the visible surface. The rate of shrinking may
  be accounted for by an increasing radial component of the rms random
  magnetic field at a rate that depends on its radial distribution. If
  it were uniform, the required field would be ~7 kG. However, if it
  were inwardly increasing, then a 1 kG field at 8 Mm would suffice. To
  assess contribution to the solar radius change arising above 4 Mm, we
  analyzed the p-mode data. The evolution of the p-mode frequencies may be
  explained by a magnetic field growing with activity. Our finding here
  is very similar to that of Goldreich et al. (1991). If the change were
  isotropic, then a 0.2 kG increase, from activity minimum to maximum,
  is required at the photosphere, which would grow to about 1 kG at
  1 Mm. If only the radial component of the field were to increase,
  then the requirement for the photospheric field increase is reduced
  to a modest 60-90 G. A relative decrease in temperature of the order
  of 10<SUP>-3</SUP> in the subphotospheric layers, or an equivalent
  decrease in the turbulent energy, would have a similar effect to the
  required inward growth of magnetic field change. The implications
  of the near-surface magnetic field changes depend on the anisotropy
  of the random magnetic field. If the field change is predominantly
  radial, then we infer an additional shrinking at a rate between 1.1
  and 1.3 km yr<SUP>-1</SUP> at the photosphere. If, on the other hand,
  the increase is isotropic, we find a competing expansion at a rate of
  2.3 km yr<SUP>-1</SUP>. In any case, variations in the Sun's radius
  in the activity cycle are at the level of 10<SUP>-5</SUP> or less and,
  hence, have a negligible contribution to the irradiance variations.

Title: An Investigation of Systematic Errors in MDI Mode Parameters
Authors: Schou, J.; Rabello-Soares, M. C.
Bibcode: 2001AGUSM..SP31A24S
Altcode:
  As described at this meeting by Howe et al., there are significant
  differences between the p- and f-mode parameters fitted by the MDI
  and GONG projects. Some of these problems seem to originate in the
  MDI data and/or the analysis methods which has been used for most of
  the MDI data analysis. Also subtle, but highly suspicious, features
  are seen internally in the MDI data. In this poster we will examine
  some of the possible explanations for these problems. In particular we
  will examine the effects of the optical distortions in MDI and those
  of the errors in some of the geometric parameters used for describing
  the raw images. We will also examine some of the approximations made
  in the analysis and see what effects they may have.

Title: High Resolution Analysis of the Upper Convection Zone
Authors: Basu, S.; Bogart, R. S.; Schou, J.; Antia, H. M.
Bibcode: 2001AGUSM..SP31A02B
Altcode:
  Plane-wave (ring-diagram) analysis of high-degree modes in data from the
  SOI/MDI instrument on SOHO have enabled us us to determine the structure
  and dynamics of about 0.1 solar radius below the photosphere, and study
  how these quantities change with time. The bulk of the work done so far
  has utilized full-disc data for which the analysis has the ability to
  resolve structures with a scale of about 180 Mm. Additional data with
  three times the spatial resolution over a small portion of the disc
  are available for shorter durations at various times. Here we report
  on details of various trends which not resolved by full-disc data.

Title: Comparing Global Solar Rotation Results from MDI and GONG
Authors: Howe, R.; Komm, R. W.; Hill, F.; Christensen-Dalsgaard, J.;
   Schou, J.; Thompson, M. J.; Corbard, T.
Bibcode: 2001AGUSM..SP31A14H
Altcode:
  The GONG (Global Oscillations Network Group) project and the Solar
  Oscillations Investigation (SOI) using the Michelson Doppler Imager
  (MDI) instrument aboard the SOHO spacecraft have jointly accumulated
  more than five years of data on medium-degree solar p-modes, including
  nearly four years of contemporaneous observations. The inferences of
  interior solar rotation from the two projects are broadly consistent
  and show similar temporal variations, but there are also significant
  systematic differences. We report here on the results of an ongoing
  attempt to cross-compare the results and analysis techniques of the
  two projects. Three 108-day periods, at low, medium and high solar
  activity epochs, have been analysed, with both MDI and GONG analysis
  being applied to each data set, and the results are compared.

Title: Variations in Rotation Rate Within the Solar Convection Zone
    From GONG and MDI 1995-2000
Authors: Howe, R.; Christensen-Dalsgaard, J.; Hill, F.; Komm, R. W.;
   Schou, J.; Thompson, M. J.; Toomre, J.
Bibcode: 2001AGUSM..SP31A15H
Altcode:
  Helioseismic measurements with the Michelson Doppler Imager (MDI)
  instrument aboard SOHO, and complementary measurements from the Global
  Oscillation Network Group (GONG) project, are revealing changes deep
  within the Sun as the solar cycle progresses. We will present the
  latest results based on recent data from both experiments, including
  flows in the upper part of the convection zone and variations in the
  rotation rate near its base.

Title: Challenges in High-Degree Helioseismology
Authors: Rhodes, E. J.; Reiter, J.; Schou, J.; Kosovichev, A. G.;
   Scherrer, P. H.
Bibcode: 2001AGUSM..SP21C06R
Altcode:
  Some of the most exciting results that the field of helioseismology
  has provided in recent years have come from numerical inversions of
  different properties of the solar p-mode oscillations. Such inversions
  have been primarily of three types: 1) structural inversions which
  have employed tables of the frequencies of various p-modes and
  their associated uncertainties to infer different thermodynamic
  properties of the solar interior as functions of radius and latitude,
  2) rotational inversions which have employed tables of the frequency
  splittings of the modes of different azimuthal order to measure the
  internal angular velocity as functions of radius and latitude, and 3)
  horizontal flow inversions which have employed sets of frequencies
  of the rings that are observed in three-dimensional power spectra to
  infer sub-photospheric horizontal flow vectors as functions of depth,
  latitude and longitude. Unfortunately, the vast majority of such
  inversions have only included frequencies or frequency splittings
  of the low- and the intermediate-degree oscillations. Furthermore,
  the horizontal flow inversions have been somewhat limited by the
  difficulties in accurately fitting the rings of the higher-degree
  power spectra. These limitations have prevented helioseismologists from
  accurately inferring the sound speed, density, adiabatic gradient, and
  helium abundance in the outermost three to four percent (by radius)
  of the solar interior. In addition, the absence of high-l frequency
  splittings from most past rotational inversions has limited the
  accuracy with which we have been able to estimate the angular velocity
  of the solar surface layers. These limitations have mainly come about
  because for l&gt;= 200 the individual modal peaks blend together into
  broad ridges of power. Fitting such ridges requires knowledge of the
  amount of power which leaks into the sidelobes that are adjacent to
  the true spectral peaks. Such leakage information requires detailed
  knowledge of the spatial behavior of each different intrument, of
  the ratio of horizontal and vertical components of the solar p-mode
  eigenfunctions, and of the temporal window function of each dataset. In
  this presentation we will demonstrate the high-l frequencies which we
  have obtained from a new fitting technique which employs m-averaged
  power spectra, temporal window functions, and spatial leakage matrices
  to fit each mode or ridge with a total of seven peaks. We will also
  demonstrate that we have obtained evidence from the fitting of GONG
  power spectra that the true ratios of the eigenfunction components
  match the theoretical predictions of these ratios. Finally, we will
  also demonstrate that cross-correlations of the peaks and ridges in
  the 2l+1 individual spectra at each l result in systematic jumps in the
  frequency-splitting coefficients for l&gt;=200 due to the blending of
  the peaks into ridges. We will point out that, unless some method can
  be found which overcomes these detrimental effects of peak-blending,
  we will not be able to provide measures of the latitudinal behavior
  of the solar angular velocity close to the photosphere which will
  be independent of the horizontal flow mesurements obtained with the
  so-called ``ring and trumpet'' technique.

Title: Supergranulation rotation
Authors: Schou, Jesper; Beck, John G.
Bibcode: 2001ESASP.464..677S
Altcode: 2001soho...10..677S
  Simple convection models estimate the depth of supergranulation at
  approximately 15,000 km which suggests that supergranules should rotate
  at the rate of the plasma in the outer 2% of the Sun by radius. Previous
  measurements (Snodgrass &amp; Ulrich, 1990; Beck &amp; Schou, 2000)
  found that supergranules rotate significantly faster than this, with
  a size-dependent rotation rate. We expand on previous work and show
  that the torsional oscillation signal seen in the supergranules tracks
  that obtained for normal modes. We also find that the amplitudes and
  lifetimes of the supergranulation are size dependent.

Title: Inversion for the solar internal rotation with an adaptive
    regularization technique
Authors: Vorontsov, S. V.; Christensen-Dalsgaard, J.; Schou, J.;
   Strakhov, V. N.; Thompson, M. J.
Bibcode: 2001ESASP.464..559V
Altcode: 2001soho...10..559V
  We report the first preliminary results of applying the adaptive
  regularization technique (Strakhov and Vorontsov 2000) to the inversion
  for the solar internal rotation. The 360d SOHO MDI data set with 18-th
  degree fit to the rotational splittings is used in the 1.5-D and 2-D
  inversions, and we used the 72d data sets (Schou 1999) to trace the
  possible variations with solar activity.

Title: How correlated are f-mode frequencies with solar activity?
Authors: Antia, H. M.; Basu, Sarbani; Pintar, J.; Schou, Jesper
Bibcode: 2001ESASP.464...27A
Altcode: 2001soho...10...27A
  Temporal variations of solar f-mode frequencies are studied using data
  from the Global Oscillation Network Group (GONG) and the Michelson
  Doppler Imager (MDI) covering the period from 1995 to 2000. The
  frequencies show an increase with activity. There appears to be
  one component in the time varying part of the frequencies which is
  correlated with the solar activity indices. Superposed on this is an
  oscillatory variation with a period of 1 year, whose origin is not
  clear. The amplitudes of both the oscillatory and non-oscillatory
  component increases with the degree (and hence frequency) of the mode.

Title: Studying asphericity in the solar sound speed from MDI and
    GONG data
Authors: Antia, H. M.; Basu, S.; Hill, F.; Howe, R.; Komm, R. W.;
   Schou, J.
Bibcode: 2001ESASP.464...45A
Altcode: 2001soho...10...45A
  We study the variation of the frequency splitting coefficients
  describing the solar asphericity in both GONG and MDI data, and
  use these data to investigate temporal sound-speed variations as a
  function of both depth and latitude during the period 1995-2000. The
  temporal variations in even splitting coefficients are found to
  be correlated with the corresponding component of magnetic flux at
  the solar surface. The sound-speed variations associated with the
  surface magnetic field appear to be superficial. Temporally averaged
  results show a significant excess in sound speed around r = 0.92
  R<SUB>solar</SUB> and latitude of 60°.

Title: Comparing mode frequencies from MDI and GONG
Authors: Howe, R.; Hill, F.; Basu, S.; Christensen-Dalsgaard, J.;
   Komm, R. W.; Munk Larsen, R.; Roth, M.; Schou, J.; Thompson, M. J.;
   Toomre, J.
Bibcode: 2001ESASP.464..137H
Altcode: 2001soho...10..137H
  We present results of analyses of MDI and GONG time series covering
  the same time intervals, and using both the MDI and GONG peakbagging
  algorithms. We discuss some of the likely causes of differences between
  the inferred frequencies and frequency splittings. In addition, we
  consider the effect of these differences on the results of inversions
  for the solar internal rotation and sound speed.

Title: Solar cycle changes in convection zone dynamics from MDI and
    GONG 1995 - 2000
Authors: Howe, R.; Christensen-Dalsgaard, J.; Hill, F.; Komm, R. W.;
   Munk Larsen, R.; Schou, J.; Thompson, M. J.; Toomre, J.
Bibcode: 2001ESASP.464...19H
Altcode: 2001soho...10...19H
  The combined GONG and MDI medium-degree helioseismic data sets now cover
  just over 5 years and allow us to probe the changing dynamics of the
  convection zone in unprecedented detail. Here we present the latest
  results from both projects, showing the evolution of the migrating
  zonal flows close to the surface and also changes close to and below
  the base of the convection zone.

Title: Spatially-resolved Analysis of the the Upper Covnection Zone
Authors: Bogart, R. S.; Schou, J.; Basu, S.; Haber, D. A.; Hill, F.;
   Antia, H. M.
Bibcode: 2001IAUS..203..183B
Altcode:
  Plane-wave (ring-diagram) analysis of high-degree modes in data from the
  SOI/MDI instrument on SOHO permits us to determine spatial and temporal
  variations of the structure and dynamics of the upper convection zone,
  to a depth of about 0.1 solar radius below the photosphere. The spatial
  resolution achieved with full-disc data is at least 15 heliographic
  degrees (180 Mm), and the temporal resolution is of order 1 day. Data
  useful for such analysis cover at least two full Carrington rotations
  in each year since 1996. Additional data with three times the spatial
  resolution over a small portion of the disc are available for shorter
  durations at various times. Analyses of the full-disc data from the
  earlier years have already revealed systematic patterns in the global
  meridional flow and flows associated with active regions during the
  early phase of the solar cycle. Here we report on variations and trends
  seen in the flows as the activity level of the cycle approaches maximum.

Title: The determination of MDI high-degree mode frequencies
Authors: Rabello-Soares, M. C.; Korzennik, S. G.; Schou, J.
Bibcode: 2001ESASP.464..129R
Altcode: 2001soho...10..129R
  As mode lifetimes get shorter and spatial leaks get closer in frequency,
  individual p-modes can only be resolved up to some degree l (around
  150). At higher degrees, individual modes blend into ridges and
  the power distribution of the ridge masks the true underlying mode
  frequency. To recover the underlying mode frequency from fitting the
  ridge, an accurate model of the amplitude of the peaks that contribute
  to the ridge power distribution is needed. Using full-disk data from the
  Michelson Doppler Imager data on the Solar and Heliospheric Observatory,
  we present and discuss the differences between the observations and
  the spatial leakage calculation (including the horizontal component)
  and estimate the horizontal-to-vertical displacement ratio for
  medium-degree modes using sectoral modes for different observational
  periods. We show how time variations in the instrument calibration
  affect the spatial leakage and discuss their importance in the spatial
  leakage calculation. By constructing a physically motivated model
  (rather than some ad hoc correction scheme) can we hope to produce an
  unbiased determination of the high-degree modes in the near future.

Title: Observations of p-modes in α Cen
Authors: Schou, Jesper; Buzasi, Derek L.
Bibcode: 2001ESASP.464..391S
Altcode: 2001soho...10..391S
  We present the results of an analysis of a 50 day time-series of
  photometry of α Cen taken by the WIRE spacecraft. We see evidence of
  p-modes similar to those observed in the Sun and present the results
  obtained. We also discuss some of the implications of the measurements
  and what can be observed in other stars.

Title: Interior Solar-Cycle Changes Detected by Helioseismology
Authors: Howe, R.; Hill, F.; Komm, R. W.; Christensen-Dalsgaard, J.;
   Munk Larsen, R.; Schou, J.; Thompson, M. J.; Toomre, J.
Bibcode: 2001IAUS..203...40H
Altcode:
  Helioseismic measurements with the MDI instrument aboard SOHO,
  and complementary measurements from the GONG network, are revealing
  changes deep within the Sun as the solar cycle progresses. We will
  present results based on recent data from both experiments, including
  variations in the rotation rate deep inside the convection zone.

Title: On the signature of the solar activity at the base of the
    convective envelope
Authors: Monteiro, M. J. P. F. G.; Christensen-Dalsgaard, J.; Schou,
   J.; Thompson, M. J.
Bibcode: 2001ESASP.464..535M
Altcode: 2001soho...10..535M
  A we approach the solar maximum for the current cycle it is timely to
  establish what helioseismology can tell us about the internal changes
  the Sun undergoes as the cycle progresses. In this work we use SOI-MDI
  data in order to identify changes occurring to the stratification of
  the Sun at the base of the convective envelope. Both changes with
  time (averaged over colatitude) and changes over time at different
  colatitudes are addressed. These are discussed in terms of the changes
  in the properties of the convection at the base of the envelope in
  the region where the tachocline is present. Those variations could
  be attributed to the interaction between convection, rotation and
  magnetic fields, which must be intrinsically time-dependent phenomena,
  possibly correlated with the observed changes occurring over the cycle
  in the envelope up to the surface.

Title: A New Class of Solar Oscillation Measurements
Authors: Schou, J.
Bibcode: 2001IAUS..203...21S
Altcode:
  Over the last few years the quality and quantity of basic helioseismic
  data have increased dramatically as instruments such as MDI on the
  SOHO spacecraft and the GONG network have become operational. While the
  data from these new instruments have led to a significant increase in
  our ability to make inferences about the solar interior, it has become
  apparent that the current analysis techniques are limiting our ability
  to fully utilize these data. The high signal to noise ratio of these
  data means that subtle details of the spectra, which were ignored in
  earlier analysis, have to be properly modeled, both to extract all
  the available information and to eliminate systematic errors. These
  details include both solar effects and instrumental limitations and
  artifacts. In this talk I will describe some recent results, some of
  the problems involved in the analysis of normal modes and what progress
  we may be able to make once we understand these problems better.

Title: Observations of p-modes in α Cen
Authors: Schou, J.; Buzasi, D. L.
Bibcode: 2000AAS...197.4604S
Altcode: 2000BAAS...32.1477S
  We present results of an analysis of time-series of photometry of α
  Cen taken by the WIRE spacecraft in 1999 and 2000. We see evidence of
  p-modes similar to those observed in the Sun and we present some of the
  results obtained. We also discuss how the observed properties of the
  modes relate to those expected and what can be observed in other stars.

Title: Irradiation induced decomposition of the surface of icy
    satellites and generation of oxidizing atmospheres
Authors: Baragiola, R. A.; Bahr, D. A.; Schou, J.; Shi, M.; Vidal,
   R. A.
Bibcode: 2000DPS....32.3408B
Altcode: 2000BAAS...32.1056B
  Past studies of sputtering of water ice, related to the question
  of magnetospheric effects on icy satellites, have concluded that
  desorption of intact water molecules dominates at low temperatures
  (below ~ 100 K) and that emission of H<SUB>2</SUB>, and O<SUB>2</SUB>
  become important at higher temperatures. The temperature dependence of
  sputtering was predicted to change with the magnitude of the energy
  deposition at the surface. However, our new results show that the
  temperature dependence of the total sputtering yields for ions and
  Lyman-alpha photons scales with energy deposition over five orders
  of magnitude, against predictions. With new, absolute measurements of
  the sputtered ejecta produced by 100 keV protons, we have discovered
  that O and OH are primary species, even at low temperatures. This
  surprising finding will require revision of models for sputter
  generation of atmospheres. The presence of radicals imply strongly
  oxidizing atmospheres, which in turn has implications on the state of
  the surface of the satellites: formation of hydrogen peroxide from ice
  and oxidation of non-ice components. Work supported by NASA-Office of
  Space Research and Cassini mission, and by NSF-Astronomy Div.

Title: Signatures of the Rise of Cycle 23
Authors: Dziembowski, W. A.; Goode, P. R.; Kosovichev, A. G.; Schou, J.
Bibcode: 2000ApJ...537.1026D
Altcode:
  During the rise of Cycle 23, we have found a sizable, systematic
  evolution of the Solar and Heliospheric Observatory/Michelson Doppler
  Imager solar oscillation frequencies implying significant changes in the
  spherically symmetric structure of the Sun's outer layers as well as in
  its asphericity up to a P<SUB>18</SUB> Legendre distortion. We conducted
  a search for corresponding asymmetries in Ca II K data from Big Bear
  Solar Observatory. We found tight temporal and angular correlations of
  the respective asphericities up through P<SUB>10</SUB>. This result
  emphasizes the role of the magnetic field in producing the frequency
  changes. We carried out inversions of the frequency differences and
  the splitting coefficients assuming that the source of the evolving
  changes is a varying stochastic magnetic field. With respect to the
  most recent activity minimum, we detected a significant perturbation in
  the spherical part at a depth of 25-100 Mm, which may be interpreted
  as being a result of a magnetic perturbation, &lt;B<SUP>2</SUP>&gt;,
  of about (60KG)<SUP>2</SUP> and/or a relative temperature perturbation
  of about 1.2×10<SUP>-4</SUP>. Larger, although less statistically
  significant, perturbations of the interior structure were found in
  the aspherical distortion.

Title: Studying Asphericity in the Solar Sound Speed from MDI and
    GONG Data 1995-1999
Authors: Schou, J.; Antia, H. M.; Basu, S.; Howe, R.; Hill, F.; Komm,
   R. W.
Bibcode: 2000SPD....31.0111S
Altcode: 2000BAAS...32..803S
  We study the variation of the frequency splitting coefficients
  describing the solar asphericity in both GONG and MDI data, and use
  these data to investigate temporal sound-speed variations as a function
  of both depth and latitude during the period 1995--99. We confirm that
  the sound-speed variations associated with the surface magnetic field
  are superficial.

Title: Solar-Cycle Changes in Convection-Zone Dynamics from SOI and
    GONG Data
Authors: Howe, R.; Christensen-Dalsgaard, J.; Hill, F.; Komm, R. W.;
   Larsen, R. M.; Schou, J.; Thompson, M. J.; Toomre, J.
Bibcode: 2000SPD....31.0113H
Altcode: 2000BAAS...32..803H
  The combined GONG and MDI medium-degree helioseismic data sets now cover
  more than 4.5 years and allow us to probe the changing dynamics of the
  convection zone in unprecedented detail. Here we present the latest
  results from both projects, showing the evolution of the migrating zonal
  flows close to the surface and also changes close to and below the base
  of the convection zone. This work utilizes data obtained by the Global
  Oscillation Network Group (GONG) project, managed by the National Solar
  Observatory, a Division of the National Optical Astronomy Observatories,
  which is operated by AURA, Inc. under a cooperative agreement with the
  National Science Foundation. SOHO is a joint project of ESA and NASA.

Title: Seismology of the Sun and Other Stars
Authors: Schou, J.
Bibcode: 2000SPD....31.0501S
Altcode: 2000BAAS...32..836S
  The last several years have seen impressive improvements in our
  knowledge of the structure and dynamics of the solar interior. In
  particular we have started seeing signs of temporal variations extending
  to significant depths, in addition to the well known near surface
  changes. Given these improvements it is natural to ask what we might
  learn from future observations of global modes. Are there fundamental
  questions we can expect to answer with the extended operations of
  MDI and GONG? Are there other questions for which we will require
  significantly different observations, such as observations of the
  whole Sun or other ways of detecting the oscillations? In this talk I
  will briefly review some of the recent observations and try to answer
  some of these questions. Given that answering some of the fundamental
  questions may not be feasible using solar oscillations, it is natural
  to ask whether some of them might be answered by observing oscillations
  in other stars. What might we learn from the asteroseismology missions
  currently proposed or under development and what may be possible in
  the more distant future using missions such as SISP, currently in
  the Sun-Earth Connection Roadmap. The SOI--MDI project is supported
  by NASA grant NAG5-3077 to Stanford University. SOHO is a mission of
  international cooperation between ESA and NASA.

Title: US Mission of Opportunity on MONS
Authors: Schou, J.; Scherrer, P. H.; Bogart, R. S.;
   Christensen-Dalsgaard, J.; Kjeldsen, H.; Buzasi, D. L.
Bibcode: 2000mons.proc..123S
Altcode:
  The Measuring Oscillations in Nearby Stars (MONS) Survey Telescope
  (MONS-ST) is a Mission of Opportunity that will study the interior
  of a large number of stars using stellar oscillations. MONS-ST will
  provide additional hardware and/or extend the lifetime of the Danish
  MONS micro satellite, which has been selected for flight in 2003. The
  additional hardware provided by MONS-ST will enhance the MONS mission
  by increasing the number of stars observable and extending the lifetime
  of the mission. A Guest Investigator program, allowing a number of
  scientists to propose targets and analyze data, will be part of the
  mission.

Title: Deeply Penetrating Banded Zonal Flows in the Solar Convection
    Zone
Authors: Howe, R.; Christensen-Dalsgaard, J.; Hill, F.; Komm, R. W.;
   Larsen, R. M.; Schou, J.; Thompson, M. J.; Toomre, J.
Bibcode: 2000ApJ...533L.163H
Altcode: 2000astro.ph..3121H
  Helioseismic observations have detected small temporal variations
  of the rotation rate below the solar surface that correspond to the
  so-called ``torsional oscillations'' known from Doppler measurements of
  the surface. These appear as bands of slower- and faster-than-average
  rotation moving equatorward. Here we establish, using complementary
  helioseismic observations over 4 yr from the GONG network and from
  the MDI instrument on board SOHO, that the banded flows are not
  merely a near-surface phenomenon: rather, they extend downward at
  least 60 Mm (some 8% of the total solar radius) and thus are evident
  over a significant fraction of the nearly 200 Mm depth of the solar
  convection zone.

Title: Supergranulation rotation
Authors: Beck, John G.; Schou, Jesper
Bibcode: 2000SoPh..193..333B
Altcode:
  Simple convection models estimate the depth of supergranulation at
  approximately 7500 km which suggests that supergranules would rotate
  at the rate of the plasma in the outer 1% of the solar radius. The
  supergranulation rotation obtained from MDI dopplergrams shows that
  supergranules rotate faster than the outer 5% of the convection
  zone and show zonal flows matching results from inversions of f-mode
  splittings. Additionally, the rotation rate depends on the size scale
  of the features.

Title: Does the tachocline show solar cycle related changes?
Authors: Basu, Sarbani; Schou, Jesper
Bibcode: 2000SoPh..192..481B
Altcode:
  The tachocline at the base of the convection zone is generally believed
  to be the seat of the solar dynamo. Here we investigate whether the
  tachocline shows any detectable change using several 72 day time-series
  of the Michelson Doppler Imager (MDI) Medium-l data. We do not find
  any clear evidence of change with time.

Title: Time Variability of Rotation in Solar Convection Zone From
    soi-mdi
Authors: Toomre, J.; Christensen-Dalsgaard, J.; Howe, R.; Larsen,
   R. M.; Schou, J.; Thompson, M. J.
Bibcode: 2000SoPh..192..437T
Altcode:
  The variation of rotation in the convection zone over a period of two
  years from mid-1996 is studied using inversions of SOI-MDI data. We
  confirm the existence of near-surface banded zonal flows migrating
  towards the equator from higher latitudes, and reveal that these banded
  flows extend substantially beneath the surface, possibly to depths
  as great as 70 Mm (10% of the solar radius). Our results also reveal
  apparently significant temporal variations in the rotation rate at
  high latitudes and in the vicinity of the tachocline over the period
  of study.

Title: Dynamic Variations at the Base of the Solar Convection Zone
Authors: Howe, R.; Christensen-Dalsgaard, J.; Hill, F.; Komm, R. W.;
   Larsen, R. M.; Schou, J.; Thompson, M. J.; Toomre, J.
Bibcode: 2000Sci...287.2456H
Altcode:
  We have detected changes in the rotation of the sun near the base of
  its convective envelope, including a prominent variation with a period
  of 1.3 years at low latitudes. Such helioseismic probing of the deep
  solar interior has been enabled by nearly continuous observation of
  its oscillation modes with two complementary experiments. Inversion of
  the global-mode frequency splittings reveals that the largest temporal
  changes in the angular velocity Ω are of the order of 6 nanohertz
  and occur above and below the tachocline that separates the sun's
  differentially rotating convection zone (outer 30% by radius) from
  the nearly uniformly rotating deeper radiative interior beneath. Such
  changes are most pronounced near the equator and at high latitudes and
  are a substantial fraction of the average 30-nanohertz difference in Ω
  with radius across the tachocline at the equator. The results indicate
  variations of rotation close to the presumed site of the solar dynamo,
  which may generate the 22-year cycles of magnetic activity.

Title: Helioseismic detection of temporal variations of solar rotation
    rate near the base of the convection zone
Authors: Howe, R.; Christensen-Dalsgaard, J.; Hill, F.; Komm, R. W.;
   Larsen, R. M.; Schou, J.; Thompson, M. J.; Toomre, J.
Bibcode: 1999AAS...19510702H
Altcode: 1999BAAS...31R1530H
  The differential rotation of the Sun and its ability to generate
  large-scale magnetic fields through cyclic dynamo action appear to be
  intimately linked. It is now commonly thought that the global dynamo
  behavior responsible for the emergence of active regions is derived
  from strong organized toroidal magnetic fields generated by rotational
  shear in a thin region (the tachocline) at the base of the convection
  zone. The magnetic field could well have a feedback effect on the fluid
  motions in the region. We are thus motivated to use helioseismology
  to look for changes in rotation profiles near the tachocline as the
  Sun's magnetic cycle progresses. This approach has become possible
  using frequency-splitting data for p- and f-mode oscillations derived
  over four years (from May 1995 to Sept 1999) of full-disk Doppler
  observations from the ground-based Global Oscillation Network Group
  (GONG) project and from the Michelson Doppler Imager (MDI) experiment
  aboard the SOHO spacecraft. Inversions using two different methods of
  the splittings from these two independent data sets reveal systematic
  variations of the rotation rate close to the base of the convection
  zone, with different behavior at low and high latitudes. Notable
  are variations of order 6 nHz in rotation rates near the equator,
  to be compared with the radial angular velocity contrast across the
  tachocline of about 30 nHz. These exhibit several nearly repetitive
  changes with a period of about 1.2-1.4 years and appear to be real
  changes in the deep convection zone and tachocline rotation rates that
  need to be followed as the solar cycle progresses. The GONG project is
  managed by the National Solar Observatory, a Division of the National
  Optical Astronomy Observatories, which is operated by AURA, Inc. under
  a cooperative agreement with the National Science Foundation. SOHO is
  a joint project of ESA and NASA.

Title: Helioseismic Constraints on the Structure of the Solar
    Tachocline
Authors: Charbonneau, P.; Christensen-Dalsgaard, J.; Henning, R.;
   Larsen, R. M.; Schou, J.; Thompson, M. J.; Tomczyk, S.
Bibcode: 1999ApJ...527..445C
Altcode:
  This paper presents a series of helioseismic inversions aimed at
  determining with the highest possible confidence and accuracy the
  structure of the rotational shear layer (the tachocline) located
  beneath the base of the solar convective envelope. We are particularly
  interested in identifying features of the inversions that are robust
  properties of the data, in the sense of not being overly influenced
  by the choice of analysis methods. Toward this aim we carry out
  two types of two-dimensional linear inversions, namely Regularized
  Least-Squares (RLS) and Subtractive Optimally Localized Averages
  (SOLA), the latter formulated in terms of either the rotation rate or
  its radial gradient. We also perform nonlinear parametric least-squares
  fits using a genetic algorithm-based forward modeling technique. The
  sensitivity of each method is thoroughly tested on synthetic data. The
  three methods are then used on the LOWL 2 yr frequency-splitting
  data set. The tachocline is found to have an equatorial thickness
  of w/R<SUB>solar</SUB>=0.039+/-0.013 and equatorial central radius
  r<SUB>c</SUB>/R<SUB>solar</SUB>=0.693+/-0.002. All three techniques
  also indicate that the tachocline is prolate, with a difference in
  central radius Δr<SUB>c</SUB>/R<SUB>solar</SUB>~=0.024+/-0.004 between
  latitude 60° and the equator. Assuming uncorrelated and normally
  distributed errors, a strictly spherical tachocline can be rejected
  at the 99% confidence level. No statistically significant variation
  in tachocline thickness with latitude is found. Implications of these
  results for hydrodynamical and magnetohydrodynamical models of the
  solar tachocline are discussed.

Title: Stellar and Planetary Explorer (SPEX)
Authors: Schou, J.; Bogart, R. S.; Bush, R. I.; Hoeksema, J. T.;
   Scherrer, P. H.; Brown, T. M.; Buzasi, D. L.; Horner, S. D.; Korzennik,
   S. G.
Bibcode: 1999AAS...195.8808S
Altcode: 1999BAAS...31.1506S
  The Stellar and Planetary Explorer (SPEX) mission will search for
  terrestrial inner planets around Sun-like (FGK, main sequence) stars
  using photometric techniques as well as provide very long time series
  for asteroseismology. If every Sun-like star had a planetary system
  similar to ours, the proposed instrumentation would detect at least
  100 terrestrial planets similar to the Earth or Venus and be able to
  provide statistics on their diameters and orbital periods. SPEX will
  accomplish this by continuously observing a large number of field stars
  to detect planetary transits. The instrument consists of a fast Schmidt
  camera with a mosaic of large CCD detectors. SPEX will observe a field
  near the galactic plane from a geosynchronous orbit for a minimum of 3
  years. The very long asteroseismic time series will allow inferences
  on the interiors of more than 100 Sun-like stars with a variety of
  masses and ages. This will allow us to substantially refine stellar
  model calculations and in particular improve on the age estimates of
  stars. This in turn is of considerable interest for the understanding
  of the evolution of our galaxy and the universe as a whole. SPEX will
  also provide new data for stellar activity and will be able to detect
  the reflected light from large inner planets, such as those detected
  using ground based Doppler velocity searches.

Title: Migration of Zonal Flows Detected Using Michelson Doppler
    Imager F-Mode Frequency Splittings
Authors: Schou, J.
Bibcode: 1999ApJ...523L.181S
Altcode:
  The small-scale zonal flows in the outer part of the solar convection
  zone were recently detected by Kosovichev &amp; Schou using f-mode
  frequency splittings. Results from five 72 day time series (Schou
  et al.) show a slight drift of the pattern toward the equator in a
  manner similar to that seen in the so-called torsional oscillation
  observed using surface Doppler shift measurements. Here I describe
  results using 12 72 day time series of the Michelson Doppler Imager
  medium-l data. These results show a clear drift of the pattern toward
  the equator. Also, the near-surface rotation rate close to the solar
  poles is observed to be slower than expected from an extrapolation
  from lower latitudes and to be changing with time.

Title: Rotation of the solar core from BiSON and LOWL frequency
    observations
Authors: Chaplin, W. J.; Christensen-Dalsgaard, J.; Elsworth, Y.;
   Howe, R.; Isaak, G. R.; Larsen, R. M.; New, R.; Schou, J.; Thompson,
   M. J.; Tomczyk, S.
Bibcode: 1999MNRAS.308..405C
Altcode:
  Determination of the rotation of the solar core requires very accurate
  data on splittings for the low-degree modes which penetrate to the core,
  as well as for modes of higher degree to suppress the contributions
  from the rest of the Sun to the splittings of the low-degree modes. Here
  we combine low-degree data based on 32 months of observations with the
  BiSON network and data from the LOWL instrument. The data are analysed
  with a technique that specifically aims at obtaining an inference of
  rotation that is localized to the core. Our analysis provides what we
  believe is the most stringent constraint to date on the rotation of
  the deep solar interior.

Title: Supergranules and Photospheric Motions Near the Solar Poles
Authors: Bogart, R. S.; Beck, J. G.; Bush, R. I.; Schou, J.
Bibcode: 1999AAS...194.9303B
Altcode: 1999BAAS...31Q.989B
  Since the SOHO launch in 1995, there have been seven opportunities for
  the Michelson Doppler Imager (MDI) to provide continuous Dopplergrams
  of the solar poles over extended intervals of time. Because of the
  nearly constant and uniform focus of the MDI images over small regions
  it is possible to resolve and track supergranules across the pole at
  these times. Seismic analysis of global modes from the MDI data has
  previously hinted at the possibility of a polar vortex in the upper
  convection zone. We report here on the first analysis of polar surface
  motions inferred from MDI data covering a total of about 2000 hours
  during five polar observing windows, including two full months around
  the south polar apparition of 1998. Research supported by SOI-MDI NASA
  grant NAG5-3077 at Stanford University.

Title: Solar Internal Rotation as Measured by the SOHO SOI/MDI
    Full-Disk Program
Authors: Rhodes, E. J., Jr.; Reiter, J.; Kosovichev, A. G.; Schou,
   J.; Scherrer, P. H.
Bibcode: 1999AAS...194.5602R
Altcode: 1999BAAS...31..911R
  We present estimates of the solar internal angular velocity obtained
  from p-mode frequency splittings computed from observations of the
  SOHO SOI/MDI Experiment's Full-Disk Program. Specifically, a time
  series of full-disk Dopplergrams which was obtained during the 61-day
  long 1996 Dynamics Run of the SOI/MDI Experiment were converted into
  time series of spherical harmonic coeffificients for degrees ranging
  up to 1000. These time series of spherical harmonic coefficients
  were then converted into 1001 sets of zonal, sectoral, and tesseral
  power spectra. Estimates of the rotationally-induced p-mode frequency
  splittings for every degree between 1 and 1000 were then obtained from
  these sets of power spectra through a cross-correlation of the 2l+1
  spectra within each set. Because this cross-correlation was carried
  out between the frequency limits of 1800 to 4800 mu Hz for each set
  of spectra, the resulting splitting coefficients were effectively
  averaged over the radial order, n, at each degree. Due to the blending
  of individual p-mode spectral peaks for degrees above 200, the raw
  frequency splitting coefficients for all degrees between 200 and 1000
  had to be corrected before an inversion could be performed. We will
  describe the method we adopted for correcting the raw splittings and
  we will present both the raw and corrected splitting coefficients. We
  will also present a two-dimensional inversion of the corrected
  coefficients. Finally, we will also demonstrate how the inclusion of
  the high-degree splittings allows us to obtain better estimates of the
  solar internal angular velocity in the shallow sub-photospheric part
  of the solar convection zone than have been possible in past studies
  which included only the splittings of the low- and intermediate-degree
  p-modes.

Title: The SOI-MDI Dynamics Program: Observing the Solar Cycle
Authors: Bush, R. I.; Beck, J. G.; Bogart, R. S.; Hoeksema, J. T.;
   Kosovichev, A. G.; Scherrer, P. H.; Schou, J.; Sommers, J.; Duvall,
   T. L.
Bibcode: 1999AAS...194.9205B
Altcode: 1999BAAS...31..987B
  The Michelson Doppler Imager instrument on the SOHO spacecraft has been
  observing the Sun over the last three years. The MDI Dynamics Program
  provides nearly continuous full disk Doppler measurements of the solar
  photosphere with 4 arc-second resolution for periods of 60 to 90 days
  each year. Three of these Dynamics periods have been completed: 23 May
  to 24 July 1996, 13 April to 14 July 1997, 9 January to 10 April 1998. A
  fourth Dynamics observing period began on 13 March and is scheduled to
  continue through mid July. These observations provide a unique view
  of the evolution of the Sun in the early part of the solar cycle,
  both from interior flows deduced by helioseimic analysis and changes
  in large scale surface motion. Details of the Dynamics programs will
  be presented along with an overview of current results. This research
  is supported by the SOI-MDI NASA grant NAG5-3077 at Stanford University.

Title: Daily Variations and Average Structure of Solar Shear Flows
    Deduced from Helioseismic Dense-Pack Samplings of Ring Diagrams
Authors: Haber, D. A.; Hindman, B. W.; Toomre, J.; Bogart, R. S.;
   Schou, J.; Hill, F.
Bibcode: 1999AAS...194.5611H
Altcode: 1999BAAS...31..913H
  We report on the daily variations and average behavior of large-scale
  flows in the upper convection zone as determined by ring-diagram
  helioseismic analysis applied to SOI-MDI full-disk velocity data from
  the 1996 and 1998 Dynamics Campaigns. We have tracked many small regions
  of 15 degrees diameter whose centers are spaced 7.5 degrees apart in
  latitude and longitude, creating a mosaic of tiles that oversample
  the spatial domain. The tiles cover the solar disk out to a distance
  of 52.5 degrees from disk center. An individual dense-pack mosaic
  is prepared by tracking each of 189 regions for 1664 minutes (27.7
  hrs). Successive mosaics are prepared every 15 degrees in Carrington
  longitude, roughly once every 1633 minutes. Such mosaics now cover
  more than two full Carrington rotations in 1996 and one rotation in
  1998. This is the best spatial and temporal coverage of any ring-diagram
  study carried out to date. The longitudinally averaged meridional flow
  varies with latitude but remains relatively constant with depth below
  the upper shear layer at 2 Mm down to a depth of about 16 Mm. The
  averaged zonal flow increases with depth within this same layer and
  agrees well with the rotation rates found from global modes. However
  with the high-degree wave field data from this analysis we are better
  able to resolve that shear layer within the upper convection zone. We
  see bands of faster averaged zonal flow near 30 degrees latitude both
  in the northern and southern hemisphere that are present at all depths
  studied. We also present movies of the daily variations in the flows
  within this dense pack for given depths that show the evolution of
  the complex velocity field. This research was supported by NASA grants
  NAG5-3077 and NAG5-7996, and NSF grant AST-9417337.

Title: Zonal Flows from the MDI Medium-l Data
Authors: Schou, J.
Bibcode: 1999AAS...194.5612S
Altcode: 1999BAAS...31..913S
  The small scale zonal flows in the outer part of the solar convection
  zone were recently detected by Kosovichev &amp; Schou (1997) using
  f-mode frequency splittings. Results from five 72 day time-series
  (Schou et al. 1998) showed a slight drift of the pattern towards the
  equator in a manner similar to that seen in the so-called torsional
  oscillation observed using surface Doppler shift measurements. Here
  I describe results using several 72 day time-series of MDI Medium-l
  data. These results show a clear drift of the pattern towards the
  equator and that the near surface polar rotation rate appears to
  change with time. This research is supported by the SOI-MDI NASA grant
  NAG5-3077 at Stanford University.

Title: A New Technique for Inversion of Helioseismic Data
Authors: Larsen, R. M.; Kosovichev, A. G.; Schou, J.
Bibcode: 1999AAS...194.5604L
Altcode: 1999BAAS...31..912L
  Inversions of rotational frequency splittings derived from helioseismic
  data obtained by the MDI instrument and the GONG network have given a
  detailed picture of the differential rotation in the convection zone
  (Schou et al. 1998). However, features associated with sharp gradients
  of the rotation rate such as jets, near surface shear layers (torsional
  oscillations) as well as the transition layer to the radiative interior
  (the "tachocline") are usually not well resolved. This is due to the
  smoothing applied by traditional inversion methods such as Regularized
  Least Squares (RLS) and Optimally Localized Averages (OLA). In this work
  we show how a generalized version of the method proposed by Thompson
  (1990) can used be to study these features by inverting directly
  for the radial or latitudinal derivative of the rotation rate. This
  research is supported by the SOI-MDI NASA grant NAG5-3077 at Stanford
  University. References: G.I. Marchuk, Methods of Numerical Mathematics,
  New York, Springer-Verlag, 1975. Schou, J. et al., 1998, Astrophys J.,
  505, 390. Thompson, M. J., 1990, Sol. Phys., 125, 1.

Title: Time-Variability of the Inferred Rotation in the Upper
    Convection Zone
Authors: Toomre, J.; Christensen-Dalsgaard, J.; Howe, R.; Larsen,
   R. M.; Schou, J.; Thompson, M. J.
Bibcode: 1999soho....9E..87T
Altcode:
  We present results of inverting for the rotation of the upper convection
  zone, using frequency splittings derived from successive 72-day time
  series of SOI-MDI observations. Schou (1999; also Schou et al. 1998)
  has studied the evolution of the pattern of small-scale zonal flows
  in the near-surface layers using f-mode splittings and has found that
  this flow pattern migrates equatorward in a manner similar to that seen
  in the so-called torsional oscillation observed in surface Doppler
  measurements. In the present work we look at the time variability
  of the rotation at greater depth, in the upper convection zone, by
  inverting both f- and p-mode splittings. The evolution of the flow is
  less regular than is seen at the surface, but we do observe apparently
  significant variations in the inferred flow pattern, on latitudinal
  scales similar to those seen at the surface. In particular, in the
  subsurface shear layer we see intriguing variations, with the first
  year's data showing apparent emergence of zonal flows of some 10-15
  m/s amplitude at around 20 degrees latitude.

Title: Supergranule Rotation: Too Fast For Convective Cells?
Authors: Beck, J. G.; Schou, J.
Bibcode: 1999soho....9E..40B
Altcode:
  Supergranulation has been long suspected of being a convective
  phenomenon. Conventional wisdom regarding convection suggests that
  the depth of supergranulation is approximately one half of its width,
  or 25,000 km. If supergranules are confined to the outer 25,000 km of
  the convective zone, they should rotate at a rate consistent with that
  range of depths. However, measurements suggest that supergranules rotate
  faster than the plasma at any depth within the convection zone. We
  will present supergranulation rotation measurements from improved data
  and compare with the results of rotation inversions to determine the
  anchor depth of supergranules and discuss the implications for models
  of convection. This research is supported by NASA grant NAG5-3077 at
  Stanford University.

Title: Does the Tachocline Show Solar Cycle Related Changes?
Authors: Basu, Sarbani; Schou, Jesper
Bibcode: 1999soho....9E..36B
Altcode:
  The tachocline at the base of the convection zone is generally believed
  to be the seat of the solar dynamo. Here we investigate whether the
  tachocline shows any detectable change using several 72 day time-series
  of MDI Medium-l data.

Title: Changes in High-Degree Oscillation Frequencies from 1996 to
    1999 Determined from Ring-Diagram Analysis
Authors: Bogart, R. S.; Schou, J.; Haber, D. A.; Hindman, B. W.;
   Toomre, J.; Hill, F.
Bibcode: 1999soho....9E..45B
Altcode:
  Ring-diagram analysis has traditionally been used primarily as a
  diagnostic for large-scale flows in the upper convection zone. It
  also yields values for the unperturbed (rest) frequencies of the
  local high-degree p-mode oscillations. These frequencies, positioned
  predominantly in a regime where ridge-fitting of traditional
  global modes is difficult, possess information about the average
  near-surface temperature profile in the region being analyzed. As
  the solar magnetic activity level increased from 1996 through 1999,
  we might expect these frequencies to have changed correspondingly. We
  present spatially and temporally averaged rest frequencies determined
  from ring-diagram analysis of full-disk Doppler data for selected
  intervals from each of the four annual SOI Dynamics campaigns covering
  the rise in solar activity from 1996 through 1999. These analyses are
  performed on a `dense-pack' mosaic of tracked tiles that oversample
  the spatial domain with a resolution of 15 heliographic degrees (180
  Mm). Tiles are individually tracked over time spans of 1664 minutes
  (27.7 hr), so a given physical region on the Sun is sampled from 7 to
  15 times depending on its latitude as it rotates across the visible
  hemisphere. We discuss the frequency changes seen for comparable areas
  on the disc over the years analyzed. This research is supported by
  NASA grant NAG5-3077 at Stanford University.

Title: Changes in the Near Surface Rotation Rate Observed by MDI
Authors: Schou, J.
Bibcode: 1999soho....9E..80S
Altcode:
  Observations of solar f modes have shown that the small scale zonal
  flows in the outer part of the solar convection zone vary with time in
  a manner similar to that seen in surface Doppler shift measurements
  of the so-called torsional oscillation. Using normal modes to study
  these flows should allow their depth dependence to be determined which
  could be an important clue for understanding their origin. Here I will
  describe the results of using p and f modes to determine the depth and
  time dependence of these flows. I will also examine the evolution of
  the near polar rotation rate. This research is supported by NASA grant
  NAG5-3077 at Stanford University.

Title: Helioseismic Studies of the Solar Tachocline
Authors: Larsen, R. M.; Kosovichev, A. G.; Schou, J.
Bibcode: 1999soho....9E..69L
Altcode:
  Accurate determinations of the depth and width of the solar tachocline
  provide important observational constraints on theoretical models of
  solar convection and the solar dynamo, which drives the Sun's magnetic
  field. We present the tachocline parameters obtained from inversions
  of frequency splittings from MDI, GONG and LOWL and compare this with
  previously published results. Finally we invert frequency splittings
  for individual GONG months and a number of 72 days sets from MDI, in
  order to see if any variation can be seen in the tachocline parameters
  with the solar cycle. Briefly, our method consists in inverting
  the frequency splittings directly for the radial derivative of the
  solar rotation rate using a full 2D SOLA technique. Subsequently the
  radial derivative of a parametric model of the rotation profile in
  the tachocline is convolved with the averaging kernels from the SOLA
  inversion, and the parameters in the models are adjusted to obtain a
  chi-squared fit of the model to the inversion result. This research
  is supported by NASA grant NAG5-3077 at Stanford University.

Title: Solar Shear Flows Deduced From Helioseismic Dense-Pack
    Samplings of Ring Diagrams
Authors: Haber, D. A.; Hindman, B. W.; Toomre, J.; Bogart, R. S.;
   Schou, J.; Hill, F.
Bibcode: 1999soho....9E..62H
Altcode:
  Large-scale flows in the upper convection zone can be inferred
  by ring-diagram helioseismic analysis, permitting the study of
  both their daily variations and their longer temporal means. We use
  selected full-disk SOI-MDI velocity data from the 1996, 1997, and 1998
  Dynamics campaigns. We have tracked sets of regions (each 15 degrees
  in diameter and spaced 7.5 degrees apart in latitude and longitude),
  creating a `dense-pack' mosaic of such tiles that oversamples the
  spatial domain. The tiles cover the solar disc to a distance of up to
  52.5 degrees from center. A single dense-pack mosaic is prepared by
  tracking each of 189 regions for 1664 minutes (27.7 hrs). Such mosaics
  now cover more than two full Carrington rotations in 1996 and one-third
  of a rotation each in both 1997 and 1998. This is the best spatial and
  temporal coverage of any ring-diagram study carried out to date. We
  are able to compare the mean flows determined over 9-day averages
  for data from the different SOI-MDI Dynamics campaigns, as well as
  examine the daily flow maps, allowing us to study possible changes
  in the convection during the rising magnetic activity of the current
  solar cycle. We also present movies of the daily variations in the
  flows within this dense pack for given depths that show the evolution
  of the complex velocity field. The longitudinally-averaged meridional
  flow varies with latitude but remains relatively constant with depth
  below the upper shear layer at 2 Mm down to a depth of about 16 Mm. The
  averaged zonal flow increases with depth within this same layer and
  agrees well with the rotation rates found from global modes. However,
  with the high-degree wave-field data from this analysis we are better
  able to resolve the shear layer within the upper convection zone. We
  see bands of faster and slower average zonal flows in both hemispheres;
  these are present at all depths studied.

Title: Solar Cycle Onset Seen in SOHO Michelson Doppler Imager
    Seismic Data
Authors: Dziembowski, W. A.; Goode, P. R.; di Mauro, M. P.; Kosovichev,
   A. G.; Schou, J.
Bibcode: 1998ApJ...509..456D
Altcode:
  We have analyzed time changes in centroid frequencies and multiplet
  frequency splittings of solar oscillations determined with the Michelson
  Doppler Imager instrument (MDI) on SOHO. The data were divided into
  five consecutive 72 day sets covering the period from 1996 May 1
  through 1997 April 25. We have detected a significant trend in the
  a<SUB>4</SUB> and a<SUB>6</SUB> frequency splitting coefficients,
  which reflects a decrease in the P<SUB>4</SUB> distortion (described by
  the fourth-degree Legendre polynomial of colatitude) and an increase
  in the P<SUB>6</SUB> distortion. The rise of the latter distortion
  seems to coincide precisely with the rise in the number of new cycle
  sunspots. Such sharp and detailed clues to activity onset are new and do
  not exist in splitting data from the rising phase of the last cycle. The
  relative differences among the solar radii inferred from the f-mode
  frequencies from the five sets (at most 6 × 10<SUP>-6</SUP> or 4 km)
  are formally significant, reaching a minimum during the observed period.

Title: Helioseismic Studies of Differential Rotation in the Solar
    Envelope by the Solar Oscillations Investigation Using the Michelson
    Doppler Imager
Authors: Schou, J.; Antia, H. M.; Basu, S.; Bogart, R. S.; Bush,
   R. I.; Chitre, S. M.; Christensen-Dalsgaard, J.; Di Mauro, M. P.;
   Dziembowski, W. A.; Eff-Darwich, A.; Gough, D. O.; Haber, D. A.;
   Hoeksema, J. T.; Howe, R.; Korzennik, S. G.; Kosovichev, A. G.;
   Larsen, R. M.; Pijpers, F. P.; Scherrer, P. H.; Sekii, T.; Tarbell,
   T. D.; Title, A. M.; Thompson, M. J.; Toomre, J.
Bibcode: 1998ApJ...505..390S
Altcode:
  The splitting of the frequencies of the global resonant acoustic modes
  of the Sun by large-scale flows and rotation permits study of the
  variation of angular velocity Ω with both radius and latitude within
  the turbulent convection zone and the deeper radiative interior. The
  nearly uninterrupted Doppler imaging observations, provided by the
  Solar Oscillations Investigation (SOI) using the Michelson Doppler
  Imager (MDI) on the Solar and Heliospheric Observatory (SOHO) spacecraft
  positioned at the L<SUB>1</SUB> Lagrangian point in continuous sunlight,
  yield oscillation power spectra with very high signal-to-noise ratios
  that allow frequency splittings to be determined with exceptional
  accuracy. This paper reports on joint helioseismic analyses of
  solar rotation in the convection zone and in the outer part of the
  radiative core. Inversions have been obtained for a medium-l mode set
  (involving modes of angular degree l extending to about 250) obtained
  from the first 144 day interval of SOI-MDI observations in 1996. Drawing
  inferences about the solar internal rotation from the splitting data
  is a subtle process. By applying more than one inversion technique
  to the data, we get some indication of what are the more robust
  and less robust features of our inversion solutions. Here we have
  used seven different inversion methods. To test the reliability and
  sensitivity of these methods, we have performed a set of controlled
  experiments utilizing artificial data. This gives us some confidence
  in the inferences we can draw from the real solar data. The inversions
  of SOI-MDI data have confirmed that the decrease of Ω with latitude
  seen at the surface extends with little radial variation through much
  of the convection zone, at the base of which is an adjustment layer,
  called the tachocline, leading to nearly uniform rotation deeper
  in the radiative interior. A prominent rotational shearing layer in
  which Ω increases just below the surface is discernible at low to
  mid latitudes. Using the new data, we have also been able to study the
  solar rotation closer to the poles than has been achieved in previous
  investigations. The data have revealed that the angular velocity
  is distinctly lower at high latitudes than the values previously
  extrapolated from measurements at lower latitudes based on surface
  Doppler observations and helioseismology. Furthermore, we have found
  some evidence near latitudes of 75° of a submerged polar jet which
  is rotating more rapidly than its immediate surroundings. Superposed
  on the relatively smooth latitudinal variation in Ω are alternating
  zonal bands of slightly faster and slower rotation, each extending
  some 10° to 15° in latitude. These relatively weak banded flows
  have been followed by inversion to a depth of about 5% of the solar
  radius and appear to coincide with the evolving pattern of ``torsional
  oscillations'' reported from earlier surface Doppler studies.

Title: Flows and Horizontal Displacements from Ring Diagrams
Authors: Schou, J.; Bogart, R. S.
Bibcode: 1998ApJ...504L.131S
Altcode:
  A new algorithm for analyzing ring diagrams from helioseismic data
  is presented. This method is applied to two months of Solar and
  Heliospheric Observatory/Michelson Doppler Imager data from 1996
  May 24 through July 24 to study flows and to measure the ratio of
  the horizontal displacement to the vertical displacement for the
  oscillations. We find that (1) the rotation rate agrees well with
  that measured from global modes, extending the measurements closer to
  the surface; (2) there is a 20 m s<SUP>-1</SUP> poleward meridional
  flow; (3) there are medium-scale velocity features persisting for
  several days; (4) the radial gradient of the near surface rotation
  rate decreases with latitude; and (5) meridional flow decreases with
  depth. The measured horizontal-to-vertical displacement ratio is in
  agreement with that expected from theoretical considerations.

Title: Initial High-Degree p-Mode Frequencies and Rotational Frequency
    Splittings from the SOHO SOI/MDI Experiment
Authors: Rhodes, E. J., Jr.; Reiter, J.; Kosovichev, A. G.; Schou,
   J.; Scherrer, P. H.
Bibcode: 1998AAS...192.1901R
Altcode: 1998BAAS...30..845R
  We present the first high-degree p-mode frequencies and
  rotationally-induced frequency splittings obtained from the Full-Disk
  Program of the SOHO Solar Oscillation Investigation/Michelson
  Doppler Imager experiment. The frequencies and splittings which we
  present here were computed from power spectra obtained during the
  1996 SOI/MDI Dynamics Run. Specifically, a 60.75-day time series of
  full-disk Dopplergrams was converted into sets of zonal, tesseral,
  and sectoral power spectra covering the degree range of 0 through
  1000. Estimates of the n-averaged frequency splittings were computed
  for the frequency range of 1800 to 4800 microhertz at each degree and
  these averaged splitting coefficients were then employed to compute an
  average power spectrum for that degree. From these 1001 average power
  spectra estimates were made of the frequencies, frequency uncertainties,
  widths, peak power densities, and background power densities of a total
  of 13664 separate peaks in the set of 1001 average power spectra. A
  total of 2554 of these peaks were isolated enough in their respective
  spectra to be fit as single p-modes. However, for the remaining 11110
  peaks (mostly those above l =200), the individual p-mode peaks and
  their spatial sidelobes were located so close together in frequency
  that they appeared as ridges rather than as isolated modal peaks in the
  average power spectra. For these p-mode ridges we obtained so-called
  ``ridge-fit'' parameter estimates. Observed asymmetries in the p-mode
  ridge shapes altered the fitted peak frequencies from their ``true''
  values and required that we correct the raw ridge-fit frequencies. Forty
  sets of these power spectra were also processed to yield estimates of
  the rotational splitting coefficients for individual p-mode ridges
  for every 25th degree between l =25 and 1000. For l between 25
  and 175 we will compare these Full-Disk program splittings with the
  previously-published splittings from the 1996 SOI/MDI Medium-l Program
  (Kosovichev et al., Solar Physics, 170, 43-61,1997).

Title: The Rotation of the Solar Core Inferred by Genetic Forward
    Modeling
Authors: Charbonneau, P.; Tomczyk, S.; Schou, J.; Thompson, M. J.
Bibcode: 1998ApJ...496.1015C
Altcode:
  Genetic forward modeling is a genetic algorithm-based modeling technique
  that can be used to perform helioseismic inversions of the Sun's
  internal angular velocity profile. The method can easily accommodate
  constraints such as positivity and monotonicity and readily lends itself
  to the use of robust statistical goodness-of-fit estimators. After
  briefly describing the technique, we ascertain its performance
  by carrying out a series of inversions for artificial splitting
  data generated from a set of synthetic internal rotation profiles
  characterized by various small inward increases in angular velocity in
  the deep solar core (r/R<SUB>⊙</SUB> &lt;= 0.5). These experiments
  indicate that the technique is accurate down to r/R<SUB>⊙</SUB>
  ~= 0.2, and retains useful sensitivity down to r/R<SUB>⊙</SUB> ~=
  0.1. <P />We then use genetic forward modeling in conjunction with the
  LOW degree L (LOWL) 2 year frequency-splitting data set to determine
  the rotation rate in the deep solar core. We perform a large set
  of one-dimensional and 1.5-dimensional inversions using regularized
  least-squares minimization, conventional least-squares minimization
  with a monotonicity constraint (∂Ω/∂r &lt;= 0), and inversions
  using robust statistical estimators. These calculations indicate that
  the solar core rotates very nearly rigidly down to r/R<SUB>⊙</SUB> ~
  0.1. More specifically, on spatial scales &gt;~0.04 R<SUB>⊙</SUB> we
  can rule out inward increases by more than 50% down to r/R<SUB>⊙</SUB>
  = 0.2, and by more than a factor of 2 down to r/R<SUB>⊙</SUB> =
  0.1. Thorough testing of various possible sources of bias associated
  with our technique indicates that these results are robust with respect
  to intrinsic modeling assumptions. Consequences of our results for
  models of the rotational evolution of the Sun and solar-type stars
  are discussed.

Title: Asymmetry in Velocity and Intensity Helioseismic Spectra:
    A Solution to a Long-standing Puzzle
Authors: Nigam, R.; Kosovichev, A. G.; Scherrer, P. H.; Schou, J.
Bibcode: 1998ApJ...495L.115N
Altcode:
  We give an explanation for the opposite sense of asymmetry of the
  solar acoustic mode lines in velocity and intensity oscillation
  power spectra, thereby solving the half-decade-old puzzle of Duvall
  and coworkers. The solution came after comparing the velocity and
  intensity oscillation data of medium angular degree l obtained from the
  Michelson Doppler Imager instrument on board the Solar and Heliospheric
  Observatory with the theoretical power spectra. We conclude that the
  solar noise in the velocity and intensity spectra is made up of two
  components: one is correlated to the source that is responsible for
  driving the solar p-modes, and the other is an additive uncorrelated
  background. The correlated component of the noise affects the line
  profiles. The asymmetry of the intensity spectrum is reversed because
  the correlated component is of a sufficiently large level, while the
  asymmetry of the velocity spectrum remains unreversed because the
  correlated component is smaller. This also explains the high-frequency
  shift between velocity and intensity at and above the acoustic cutoff
  frequency. A composite source consisting of a monopole term (mass term)
  and a dipole term (force due to Reynolds stress) is found to explain
  the observed spectra when it is located in the zone of superadiabatic
  convection at a depth of 75+/-50 km below the photosphere.

Title: Subphotospheric Convective Flows Determined by Ring-Diagram
    Analyses of SOI-MDI Observations
Authors: Haber, D.; Hindman, B.; Toomre, J.; Bogart, R.; Schou, J.;
   Hill, F.
Bibcode: 1998ESASP.418..791H
Altcode: 1998soho....6..791H
  The variation of large-scale velocity flows with depth and location
  on the sun places important constraints on theoretical models of the
  solar convection zone and dynamo. High-degree oscillations can be
  viewed as nearly plane waves that are advected and distorted by the
  underlying flows. By conducting observations over limited regions
  of the solar surface to obtain `ring diagram' power spectra, we can
  deduce spatially-averaged horizontal flows with depth below that
  region. Previous analyses of ring diagrams have already suggested
  the presence of strong shearing flows below the surface. We have
  now implemented a highly efficient technique for determining these
  horizontal flows with depth and report here on a systematic analysis of
  full-disk Doppler velocity data taken continuously with a one-minute
  cadence during portions of the two-month dynamics observing program
  with SOI-MDI in 1996. The square regions examined span about 15-circ,
  and are studied for time intervals each of about 1536 mins (~25 hrs). A
  lattice of such squares is considered: their centers are spaced 15-circ
  apart in longitude and there are seven such regions across the solar
  disk at +20-circ, 0-circ, -20-circ latitude. Another set of regions
  is placed along the central meridian at 10-circ and 15-circ intervals
  in latitude. Properties of the underlying large-scale subphotospheric
  flows and their temporal variations so revealed are presented in detail.

Title: Slow Poles and Shearing Flows from Heliospheric Observations
    with MDI and GONG Spanning a Year
Authors: Schou, J.; Christensen-Dalsgaard, J.; Howe, R.; Larsen,
   R. M.; Thompson, M. J.; Toomre, J.
Bibcode: 1998ESASP.418..845S
Altcode: 1998soho....6..845S
  We invert one year of coeval high-resolution rotational splitting data
  (up to degree l 250) from GONG and SOI-MDI. The first 4 months of
  MDI data uncovered several new features in the rotation of the solar
  convective envelope: surface and subsurface zonal bands corresponding
  to the so-called torsional oscillations, superimposed on the overall
  smooth latitudinal surface rotation; a drop in the near-polar surface
  rotation rate below the rate extrapolated from lower latitudes; and an
  indication of a prograde jet-like feature at high latitudes at a depth
  of about 5 percent of the solar radius. Using the 1 year of data from
  the MDI and GONG instruments, we test the robustness and stationarity of
  these features. As an aid to testing the robustness of our inferences,
  we use two independent inversion methods (2-D regularized least squares
  and SOLA) and apply them to the splitting data obtained from both GONG
  and MDI.

Title: The Comparison of Simultaneous SOI/MDI and Mt. Wilson 60-foot
    Tower Power Spectra and p-Mode Parameters
Authors: Rhodes, E. J., Jr.; Reiter, J.; Kosovichev, A. G.; Schou,
   J.; Scherrer, P. H.; Rose, P. J.; Irish, S.; Jones, A. R.
Bibcode: 1998ESASP.418..311R
Altcode: 1998soho....6..311R
  We present the results of the first detailed comparison between the
  1996 SOHO SOI/MDI Dynamics Run program of full-disk Ni I Dopplergram
  observations and a simultaneous time series of ground-based
  observations obtained in the Na D lines at the 60-Foot Solar Tower
  of the Mt. Wilson Observatory (MWO). Specifically, we will compare
  sets of simultaneously-observed SOHO/MDI and MWO power spectra and
  the high-degree p-mode frequencies, frequency splittings, widths, and
  power densities which we obtained by fitting these two sets of power
  spectra. Beginning on May 23, 1996, the SOI/MDI experiment began its
  first high duty cycle run of 1024x1024 pixel images. this was the
  1996 Dynamics Run. On all but three of the days of this 60.75-day
  time series a second time series of simultaneous 1024x1024 pixel
  full-disk Dopplergrams was obtained at MWO. From these simultaneous MWO
  observations we have computed 601 sets of zonal, tesseral, and sectoral
  power spectra which covered the degree range of 0 to 600. These sets
  of power spectra were then analyzed in two different ways to yield
  both frequencies and frequency splittings. First, estimates of the
  frequency splittings were computed for the frequency range of 1800 to
  4800 microhertz at each degree and these n-averaged splittings were
  employed to compute an average power spectrum for that degree. Estimates
  were then made of the frequencies, frequency uncertainties, widths, peak
  power densities, and background power densities of the set of peaks in
  these 601 average power spectra. As is described in our companion paper
  on the MDI ridge-fit frequency measurements (Rhodes et al.,1998), we
  also had to correct our raw MWO ridge-fit frequencies for the effects
  the merger of individual p-mode peaks and sidelobes into ridges. We
  could also directly compare the frequency dependence of the observed
  power density in both the MDI and MWO power spectra. We have found
  that there is a systematic difference such that the power density in
  the chromospheric-level power spectra from MWO tends to be below that
  of the photosheric-level MDI spectra at low frequencies and to rise
  above the MDI power density as the frequency increases. All but the l
  = 0 MWO power spectra were also processed to yield estimates of the
  rotational splitting coefficients for individual p-mode ridges for
  every degree between l = 4 and 600. We will compare these splittings
  with both the previously-published splittings from the 1996 SOI/MDI
  Medium-l Program (Kosovichev et al., 1997) and with the MDI high-degree
  splittings presented in our companion MDI paper.

Title: Comparison of SOHO-SOI/MDI and GONG Spectra
Authors: Komm, R. W.; Anderson, E.; Hill, F.; Howe, R.; Kosovichev,
   A. G.; Scherrer, P. H.; Schou, J.; Fodor, I.; Stark, P.
Bibcode: 1998ESASP.418..253K
Altcode: 1998soho....6..253K
  We compare solar p-mode parameters, such as central frequency, width,
  and amplitude, derived from GONG and SOHO-SOI/MDI Medium-l Program
  time series obtained during the same time period. With the excellent
  data available now from GONG and SOHO-SOI/MDI, there exist data
  sets long enough to make such a comparison useful. For this study,
  we have chosen time series of three ell values (ell = 30, 65, and 100)
  corresponding to GONG month 16 (Oct 28 -- Dec 2, 1996). For each time
  series, we calculated multitaper power spectra using generalized
  sine tapers to reduce the influence of the gap structure, which is
  different for the two data sets. Then, we applied the GONG peakfitting
  algorithm to the spectra to derive mode parameters and selected `good'
  fits common to both MDI and GONG spectra, according to three selection
  criteria. Preliminary results show that mode frequencies determined
  from MDI spectra are essentially the same as the frequencies from
  GONG spectra and that the difference is, in general, well within one
  formal error bar. The background slope at frequencies above 5mHz is
  different between MDI and GONG spectra depending on ell. At present,
  we are analyzing 3-month time series of ell = 0 to ell = 150. We intend
  to present the results of the on-going comparison.

Title: Initial SOI/MDI High-Degree Frequencies and Frequency
    Splittings
Authors: Rhodes, E. J., Jr.; Reiter, J.; Kosovichev, A. G.; Schou,
   J.; Scherrer, P. H.
Bibcode: 1998ESASP.418...73R
Altcode: 1998soho....6...73R
  We present the first high-degree p-mode frequencies and frequency
  splittings obtained from the Full-Disk Program of the SOHO Solar
  Oscillation Investigation/Michelson Doppler Imager experiment. The
  frequencies and splittings which we present here were computed
  from power spectra obtained during the 1996 SOI/MDI Dynamics
  Run. Specifically, a time series of full-disk Dopplergrams, which
  began on May 23, 1996, and which covered 87480 minutes (60.75 days),
  was converted into sets of zonal, tesseral, and sectoral power spectra
  covering the degree range of 0 through 1000. These sets of power spectra
  were then analyzed in two different ways to yield both frequencies and
  frequency splittings. First, estimates of the frequency splittings
  were computed for the frequency range of 1800 to 4800 microhertz at
  each degree and these n-averaged splittings were employed to compute an
  average power spectrum for that degree. Estimates were then made of the
  frequencies, frequency uncertainties, widths, peak power densities,
  and background power densities of a total of 13664 separate peaks
  in these 1001 average power spectra. A total of 2554 of these peaks
  were isolated enough in their respective spectra to be fit as single
  p-modes. However, for the remaining 11110 peaks (mostly those above l
  = 200), the individual p-mode peaks and their spatial sidelobes were
  located so close together in frequency that they appeared as ridges
  rather than as isolated modal peaks in the average power spectra. For
  these cases we were forced to employ a wider fitting range for our
  frequency-estimation code and in so doing we obtained so-called
  ``ridge-fit'' parameter estimates. Due to a degree-dependence in
  the measured velocity power density, the observed p-mode ridges were
  asymmetric in shape. These asymmetries in the p-mode ridge shapes,
  which are in addition to the intinsic asymmetries caused by the
  excitation mechanism of the p-modes themselves, alter the fitted peak
  frequencies from their ``true'' values. For this reason, we had to
  develop a mechanism which we then used to correct the raw ridge-fit
  frequencies. Forty sets of these power spectra were also processed to
  yield estimates of the rotational splitting coefficients for individual
  p-mode ridges for every 25th degree between l = 25 and 1000. For l
  between 25 and 175 we will compare these Full-Disk program splittings
  with the previously-published splittings from the 1996 SOI/MDI Medium-l
  Program (Kosovichev et al., Solar Physics, 170, 43-61,1997).

Title: The Stellar and Planetary Explorer (SPEX) Mission
Authors: Schou, J.; Scherrer, P. H.; Brown, T. M.; Frandsen, S.;
   Horner, S. D.; Korzennik, S. G.; Noyes, R. W.; Tarbell, T. D.; Title,
   A. M.; Walker, A. B. C., II; Weiss, W. W.; Bogart, R. S.; Bush, R. I.;
   Christensen-Dalsgaard, J.; Hoeksema, J. T.; Jones, A.; Kjeldsen, H.
Bibcode: 1998ESASP.418..401S
Altcode: 1998soho....6..401S
  The Stellar and Planetary Explorer (SPEX) is a mission designed
  to search for terrestrial sized planets around sun-like stars using
  precise photometry. The planets will be detected by searching for the
  decrease in brightness associated with transits of the planets in front
  of their parent stars. One of the secondary scientific objective of
  SPEX is to do asteroseismology on a number of sun-like stars. SPEX
  is designed as a secondary payload on a commercial communications
  satellite and will have a design life time of three years. We will
  provide an overview of the SPEX scientific objectives and design,
  with particular emphasis on the prospects for doing asteroseismology.

Title: Solar Internal Rotation
Authors: Schou, J.; SOE Internal Rotation Team
Bibcode: 1998IAUS..185..141S
Altcode:
  With the flood of high quality helioseismic data from the instruments
  on the SOHO spacecraft (MDI/VIRGO/GOLF) and ground based instruments
  (eg. GONG and LOWL) we have been able to get increasingly detailed
  information on the rotation and other large scale flows in the solar
  interior. In this talk I will discuss some of the highlights of what
  we have learned so far and what we may expect to learn in the near
  future. Among the recent advances have been tighter constraints on the
  tachocline at the bottom of the convection zone, detection of details in
  the surface rotation rate similar to the torsional oscillations found
  in the surface Doppler shift and helioseismic evidence for meridional
  flows. The MDI project is supported by NASA contract NAG5-3077 at
  Stanford University.

Title: Solar Asymmetries from SOHO/MDI Splitting Data
Authors: Goode, P. R.; Dziembowski, W. A.; DiMauro, M. P.; Kosovichev,
   A. G.; Schou, J.
Bibcode: 1998ESASP.418..887G
Altcode: 1998soho....6..887G
  No abstract at ADS

Title: How Low Can We Get: The Quest for Ever Lower Frequencies
Authors: Schou, J.
Bibcode: 1998ESASP.418..341S
Altcode: 1998soho....6..341S
  Almost since the dawn of helioseismology observers have tried to push
  the low frequency limit of the observed modes down. Why is that? In
  this poster I will ramble about the importance of these modes to our
  inferences about the Sun. How much would it help to push the limit
  down by another couple of hundred muHz? Do we have to see g-modes
  in order to make a significant difference? Using nearly two years of
  MDI data, devious analysis techniques and a bit of imagination I will
  see how far down medium-degree modes can be observed. I will try to
  determine what the noise sources are and what one might be able to do
  to decrease their effect. What have we learned from the low frequency
  modes we have seen so far? The f-mode observations have allowed us to
  determine the acoustic radius of the Sun. Also low frequency modes have
  made it possible to probe the so-called torsional oscillations. I will
  present some recent results from these and other areas. Finally I will
  speculate on the possibility of getting even lower in frequency. How
  much does longer observations help? Would seeing the back side of the
  Sun help? Are different analysis techniques needed? Are we ever going
  to see g-modes?

Title: Improved SOLA Inversions of MDI Data
Authors: Larsen, R. M.; Christensen-Dalsgaard, J.; Kosovichev, A. G.;
   Schou, J.
Bibcode: 1998ESASP.418..813L
Altcode: 1998soho....6..813L
  We present a new version of 2d-SOLA, where the target functions have
  been modified to match the behavior of the mode kernels near the
  rotation axis and to minimize near-surface contributions. Inversion
  of artificial data show that these modifications significantly improve
  the effective resolution near the pole, which allows us to assess the
  reliability of the high-latitude features seen by other inversion
  methods. Most importantly, our new inversions seem to confirm the
  detection of a submerged polar jet previously seen in the 2d-RLS
  inversions reported by Schou et al. 1998. A test of the robustness of
  the improved method is carried out by inverting artificial data from
  the MDI Hare and Hounds exercise. We analyze the averaging kernels and
  error propagation of the method, and also describe the error-correlation
  between different points in the solution, the latter being a potential
  source of spurious features in the solutions as pointed out by Howe
  and Thompson, 1996. So far, helioseismic datasets given in the form of
  a-coefficients have been inverted under the assumption that the errors
  in different a-coefficients are uncorrelated. The MDI peak-bagging
  procedure, however, does produce estimates of the error-correlation
  between a-coefficients within the same multiplet. Here we investigate
  the effect of including this knowledge in the inversions.

Title: Tests of Convective Frequency Effects with SOI/MDI High-Degree
    Data
Authors: Rosenthal, C. S.; Christensen-Dalsgaard, J.; Kosovichev,
   A. G.; Nordlund, A. A.; Reiter, J.; Rhodes, E. J., Jr.; Schou, J.;
   Stein, R. F.; Trampedach, R.
Bibcode: 1998ESASP.418..521R
Altcode: 1998astro.ph..7066R; 1998soho....6..521R
  Advances in hydrodynamical simulations have provided new insight into
  the effects of convection on the frequencies of solar oscillations. As
  more accurate observations become available, this may lead to an
  improved understanding of the dynamics of convection and the interaction
  between convection and pulsation (Rosenthal et al. 1999). Recent
  high-resolution observations from the SOI/MDI instrument on the
  SOHO spacecraft have provided the so-far most-detailed observations
  of high-degree modes of solar oscillations, which are particularly
  sensitive to the near-surface properties of the Sun. Here we present
  preliminary results of a comparison between these observations and
  frequencies computed for models based on realistic simulations of
  near-surface convection. Such comparisons may be expected to help
  in identifying the causes for the remaining differences between the
  observed frequencies and those of solar models.

Title: Spherical and aspherical structure of the sun: First year of
    SOHO/MDI observations
Authors: Kosovichev, A. G.; Schou, J.; Scherrer, P. H.; Goode, P. H.;
   Dziembowski, W. A.; Rhodes, E. J., Jr.; SOI Structure Inversion Team
Bibcode: 1998IAUS..185..157K
Altcode:
  We report the results of one year of continuous observations of the
  Sun's internal structure using data from the Medium-l Program of
  the Michelson Doppler Imager (MDI) on board SOHO. The data provide
  continuous coverage of p modes of angular degree l from 0 to 250,
  and the f mode from l=100 to 250. The striking stability of solar
  Dopplergrams measured by MDI, without an intervening atmosphere,
  substantially decreases the noise in the solar oscillations power
  spectrum compared with ground-based observations. This permits
  detection of lower amplitude oscillations, extending the range and
  precision of measured normal mode frequencies. We present new inversion
  results for the radial and latitudinal seismic solar structures with
  particular attention to zonal asphericity inferred with the high
  angular resolution from the data. Using f-mode frequency splitting
  we estimate the large-scale structure of the subsurface magnetic
  fields. The variations of the solar structure observed during the
  first year of MDI observations are also discussed.

Title: Observations of Medium- and High-Degree Modes: Methods and
    Sand-Traps
Authors: Schou, J.
Bibcode: 1998ESASP.418...47S
Altcode: 1998soho....6...47S
  The spectrum of solar oscillations is often divided into low-, medium-
  and high-degree (l) modes. Low-degree modes are those observable in
  integrated sunlight, medium-degree modes are those for which the modes
  with the same order (n) but adjacent l can be separated in a frequency
  spectrum and high-degree modes are those for which the modes blend
  together to form ridges. The medium-degree modes are those for which
  most parameter estimates exist. Indeed, most of our knowledge of the
  solar interior has been derived from observations of medium-degree
  p- and f-mode frequencies and splittings. While much effort has been
  spent on measuring the medium-degree mode parameters it is clear that
  significant systematic errors remain and that further analysis is needed
  to resolve those. I will discuss some of the methods used for observing
  and analyzing medium-degree modes and describe some of the systematic
  errors seen. It is likely that most of the errors come from the analysis
  methods and the approximations they make. I will describe the general
  idea behind some of the methods and try to identify some of the likely
  causes for the systematic errors. For high-degree modes ridges are
  formed and the instrumental problems become more important. Significant
  progress has been made recently in the analysis of the high-degree
  spectra. I will describe some of the problems encountered, summarize
  the recent results and discuss what remains to be done.

Title: Solar Asymmetries from SOHO/MDI Splitting Data
Authors: Dziembowski, W. A.; Goode, P. R.; Di Mauro, M. P.; Kosovichev,
   A. G.; Schou, J.
Bibcode: 1998ESASP.418..887D
Altcode: 1998soho....6..887D
  Systematic changes in p-mode frequencies through the solar cycle
  have been discovered during the previous high activity phase. Most
  significant changes were found in the even-a coefficients of
  the fine structure in the oscillation spectra (Kuhn, 1988;
  and Libbrecht and Woodard, 1990). We analyzed time changes in
  frequencies determined with the SOHO/MDI instrument. The data were
  divided into five 72-day sets covering (1) 5/1/96-7/11/96, (2)
  7/12/96-9/21/96, (3) 9/22/96-12/2/96, (4) 12/3/96-2/12/97, and (5)
  2/13/97-4/25/97. The splitting coefficients a<SUB>k</SUB> are defined by
  nuv<SUB>los</SUB>ell,n,m-bar nu<SUB>ell,n</SUB> = sum<SUB>{k = 1}</SUB>
  a<SUB>k</SUB> {cal P}<SUB>k</SUB><SUP>ell</SUP>(m), where {cal P} are
  are orthogonal polynomials (see Ritzwoller and Lavely 1991 and Schou,
  et al. 1994). We analyzed behavior of the even order coefficients,
  a<SUB>2k</SUB>, which arise from the respective, P<SUB>2k</SUB>
  (cos θ), distortion of the Sun's structure. We found a significant
  trend in behavior of the a<SUB>4</SUB> and a<SUB>6</SUB> coefficients,
  which reflects a decrease of the P<SUB>4</SUB> and an increase of the
  P<SUB>6</SUB> distortions. This trend is the same as seen in the BBSO
  data (Libbrecht and Woodard, 1990) between 1986 and 1988 i.e. at the
  onset of the previous activity phase. The trend in a<SUB>2</SUB> is
  not so apparent. The centroid frequencies, bar nu<SUB>ell,n</SUB>, as
  already reported by Kosovichev et al. (1998), exhibit small nonmonotonic
  variations. The relative differences in solar radius inferred from the
  f-mode frequencies in the five sets (at most 5 times 10<SUP>-6</SUP>)
  are formally significant, but again there is no trend.

Title: The SOI-MDI High-Latitude Jet: the Evidence For and Against
Authors: Howe, R.; Antia, H.; Basu, S.; Christensen-Dalsgaard, J.;
   Korzennik, S. G.; Schou, J.; Thompson, M. J.
Bibcode: 1998ESASP.418..803H
Altcode: 1998soho....6..803H
  The apparent detection of a prograde jet at latitude 75-circ and at a
  radius of about 0.95R<SUB>odot</SUB> in some inversions of rotation data
  from SOI--MDI (Schou et al., 1998) has excited considerable interest,
  but whether the jet really exists in the solar interior is certainly not
  yet firmly established. The detection of the feature is sensitive both
  to the inversion techniques used and to the methods of mode parameter
  estimation used to generate the input data. In particular, the feature
  is much more apparent in Regularized Least-Squares inversions than
  in inversions using an Optimally Localized Average approach, and is
  not detected at all in the present GONG data when analysed with the
  GONG peakfinding algorithm, or indeed in SOI data when analysed with
  the GONG algorithm. Therefore in this poster we examine critically
  the current evidence for the source and existence of this jet in the
  light of forward and inverse analyses.

Title: Probing the Internal Structure of the Sun with the SOHO
    Michelson Doppler Imager
Authors: Kosovichev, A. G.; Nigam, R.; Scherrer, P. H.; Schou, J.;
   Reiter, J.; Rhodes, E. J., Jr.; Toutain, T.
Bibcode: 1997AAS...191.7311K
Altcode: 1997BAAS...29R1322K
  The inference of the thermodynamic structure of the Sun from the
  observed properties of the solar normal modes of oscillation is a
  principal goal of helioseismology. We report the results of the first
  year of continuous observations of the Sun's internal structure using
  data from the Medium-l Program of the Michelson Doppler Imager (MDI)
  on board ESA/NASA spacecraft SOHO. The data provide continuous coverage
  of the acoustic (p) modes of angular degree l from 0 to 250, and the
  fundamental (f) mode of the Sun from l=100 to 250. During two 2-month
  intervals, the high-degree modes, up to l=1000, have been observed. The
  great stability of solar Dopplergrams measured by MDI permits detection
  of lower amplitude oscillations, extending the range and precision of
  measured normal mode frequencies, and thus substantially increasing
  the resolution and precision of helioseismic inversions. We present
  new inversion results for the radial and latitudinal seismic solar
  structures with particular attention to the transition region between
  the radiative and convection zones and to the energy-generating core. We
  discuss evidence for convective overshoot at the base of the convection
  zone, and the significance of deviations in the core structure from
  the standard evolutionary model. Comparing the f-mode frequencies
  with the corresponding frequencies of the standard solar models, we
  argue that the apparent photospheric solar radius (695.99 Mm) used to
  calibrate the models should be reduced by approximately 0.3 Mm. The
  discrepancy between the `seismic' and apparent photospheric radii is
  not explained by the known systematic errors in the helioseismic and
  photospheric measurements. If confirmed, this discrepancy represents
  a new interesting challenge to theories of solar convection and solar
  modeling. Using f-mode frequency splitting we estimate the large-scale
  structure of the subsurface magnetic fields. The variations of the solar
  oscillation frequencies during the first year of MDI observations are
  also discussed.

Title: Solar internal sound speed as inferred from combined BiSON
    and LOWL oscillation frequencies
Authors: Basu, Sarbani; Christensen-Dalsgaard, J.; Chaplin, W. J.;
   Elsworth, Y.; Isaak, G. R.; New, R.; Schou, J.; Thompson, M. J.;
   Tomczyk, S.
Bibcode: 1997MNRAS.292..243B
Altcode: 1997astro.ph..2105B
  Observations of the Sun with the LOWL instrument provide a homogeneous
  set of solar p-mode frequencies from low to intermediate degree that
  allow one to determine the structure of much of the solar interior
  avoiding systematic errors that are introduced when different data sets
  are combined, i.e., principally the effects of solar cycle changes on
  the frequencies. Unfortunately, the LOWL data set contains very few of
  the lowest-degree modes, which are essential for determining reliably
  the structure of the solar core - in addition, these lowest-degree data
  have fairly large associated uncertainties. However, observations made
  by the Birmingham Solar-Oscillations Network (BiSON) in integrated
  sunlight provide high-accuracy measurements of a large number of
  low-degree modes. In this paper we demonstrate that the low-degree mode
  set of the LOWL data can be successfully combined with the more accurate
  BiSON data, provided the observations are contemporaneous for those
  frequencies where the solar cycle induced effects are important. We
  show that this leads to a factor of 2 decrease in the error on the
  inferred sound speed in the solar core. We find that the solar sound
  speed is higher than in solar models for r&lt;0.2Rsolar. The density
  of the solar core is, however, lower than that in solar models.

Title: Rotation and Zonal Flows in the Solar Envelope from the
    SOHO/MDI Observations
Authors: Scherrer, P. H.; Schou, J.; Bogart, R. S.; Bush, R. I.;
   Hoeksema, J. T.; Kosovichev, A. G.; Antia, H. M.; Chitre, S. M.;
   Christensen-Dalsgaard, J.; Larsen, R. M.; Pijpers, F. P.; Eff-Darwich,
   A.; Korzennik, S. G.; Gough, D. O.; Sekii, T.; Howe, R.; Tarbell,
   T.; Title, A. M.; Thompson, M. J.; Toomre, J.
Bibcode: 1997AAS...191.7310S
Altcode: 1997BAAS...29.1322S
  We report on the latest inferences concerning solar differential
  rotation that have been drawn from the helioseismic data that are now
  available from the Solar Oscillations Investigation (SOI) using the
  Michelson Doppler Imager (MDI) on the Solar and Heliospheric Observatory
  (SOHO). That spacecraft is positioned in a halo orbit near the Sun-Earth
  Lagrangian point L_1, in order to obtain continuous Doppler-imaged
  observations of the sun with high spatial fidelity. Doppler velocity,
  intensity and magnetic field images are recorded, based on modulations
  of the 676.8 nm Ni I solar absorption line. The high spatial resolution
  of MDI thereby permits the study of many millions of global resonant
  modes of solar oscillation. Determination and subsequent inversion
  of the frequencies of these modes, including the degeneracy-splitting
  by the rotation of the sun, enables us to infer how the sun's angular
  velocity varies throughout much of the interior. The current MDI data
  are providing substantial refinements to the helioseismic deductions
  that can be made about differential rotation both within the convection
  zone and in its transition to the radiative interior. The shearing
  layer evident in the angular velocity Omega just below the solar
  surface is becoming better defined, as is the adjustment layer or
  tachocline near the base of the convection zone. The MDI data are also
  revealing a prominent decrease in Omega at high latitudes from the
  rotation rate expressed by a simple three-term expansion in latitude
  that was originally deduced from surface Doppler measurements. Further,
  there are indications that a submerged polar vortex involving somewhat
  faster Omega than its surroundings exists at about 75(deg) in latitudes.

Title: Determination of the Sun's Seismic Radius from the SOHO
    Michelson Doppler Imager
Authors: Schou, J.; Kosovichev, A. G.; Goode, P. R.; Dziembowski, W. A.
Bibcode: 1997ApJ...489L.197S
Altcode:
  Dopplergrams from the Michelson Doppler Imager (MDI) instrument on board
  the SOHO spacecraft have been used to accurately measure frequencies of
  the Sun's fundamental (f) mode in the medium angular degree range, l =
  88--250. The comparison of these frequencies with the corresponding
  frequencies of the standard solar models suggests that the apparent
  photospheric solar radius (695.99 Mm) used to calibrate the models
  should be reduced by approximately 0.3 Mm. The precise value of the
  seismologically determined solar radius depends on the description
  of the subsurface layer of superadiabatic convection. The discrepancy
  between the "seismic" and apparent photospheric radii is not explained
  by the known systematic errors in the helioseismic and photospheric
  measurements. If confirmed, this discrepancy represents an interesting
  new challenge to theories of solar convection and solar modeling.

Title: Measurements of Frequencies of Solar Oscillations from the
    MDI Medium-l Program
Authors: Rhodes, E. J., Jr.; Kosovichev, A. G.; Schou, J.; Scherrer,
   P. H.; Reiter, J.
Bibcode: 1997SoPh..175..287R
Altcode:
  Inversions of solar internal structure employ both the frequencies
  and the associated uncertainties of the solar oscillation modes
  as input parameters. In this paper we investigate how systematic
  errors in these input parameters may affect the resulting inferences
  of the sun's internal structure. Such systematic errors are likely
  to arise from inaccuracies in the theoretical models which are used
  to represent the spectral lines in the observational power spectra,
  from line blending, from asymmetries in the profiles of these lines,
  and from other factors. In order to study such systematic effects we
  have employed two different duration observing runs (one of 60 days
  and the second of 144 days) obtained with the Medium-l Program of the
  Michelson Doppler Imager experiment onboard the SOHO spacecraft. This
  observing program provides continuous observations of solar oscillation
  modes having angular degrees, l, ranging from 0 to ∼ 300. For this
  study intermediate- and high-degree p-mode oscillations having degrees
  less than 251 were employed.

Title: Solar internal rotation from LOWL data. A 2D regularized
    least-squares inversion using B-splines.
Authors: Corbard, T.; Berthomieu, G.; Morel, P.; Provost, J.; Schou,
   J.; Tomczyk, S.
Bibcode: 1997A&A...324..298C
Altcode:
  Observations of surface oscillations of the Sun can be analyzed to
  probe the solar interior. We use data obtained by the LOWL instrument
  (LOWL is an abbreviation for low degree with degree denoted by L)
  installed on Mauna Loa, Hawaii, since 1994 to investigate solar
  internal rotation. A 2 Dimensional Regularized Least-Squares (2D RLS)
  inverse method based on an expansion of the solution on B-splines of
  arbitrary order is presented and applied to a 2 year dataset. This
  method insures the regularity of the solution in the center and
  introduces surface constraints. The choice of trade-off parameters in
  the regularization term is discussed using an L-curves analysis and
  we discuss the influence of the choice of the order of derivatives in
  the regularization terms for the description of the deep interior. We
  study the latitudinal resolution of the inversion of a-coefficients
  compared to that of the inversion of individual splittings built from
  these coefficients. Compared to the previous inversion of the first
  three months of LOWL data made by Tomczyk et al. (1995ApJ...448L..57T),
  our solution is extended up to the surface by adding high degree modes
  and constraining the rotation to fit the spectrographic observations
  (Snodgrass, 1984SPh....94...13S). In the radiative zone we obtain
  more rigid rotation and our solution is compatible with a rotation of
  the solar core of the order or smaller than the surface rotation at
  mid latitude.

Title: Helioseismic measure of solar activity-meaning and
    applications.
Authors: Dziembowski, W. A.; Philip, R. Goode; Schou, J.; Tomczyk,
   Steve
Bibcode: 1997A&A...323..231D
Altcode:
  We analyze the antisymmetric part of the fine structure in the LOWL
  data, and find a remarkable agreement with the BBSO data taken during
  the 1986 activity minimum. For both, the P_4_(cosθ) component of the
  Sun's asphericity is dominant. We discuss the importance of measuring
  this part of the fine structure as a global probe of the Sun's varying
  magnetic activity. The asphericity affects oscillation frequencies in
  a way that corrupts any inversion for the radial structure of the deep
  solar interior. The results of inversion of the original and cleansed
  data show that at the current minimal level of solar activity, the
  effect is within the errors. However, this is not true in the case of
  measurements taken in years of high activity. We mimic such measurements
  by adding in appropriate frequency shifts evaluated from 1989 BBSO data.

Title: Detection of Zonal Shear Flows beneath the Sun's Surface from
    f-Mode Frequency Splitting
Authors: Kosovichev, A. G.; Schou, J.
Bibcode: 1997ApJ...482L.207K
Altcode:
  We report on the first successful measure of the zonal variations of
  the Sun's differential rotation (so-called torsional oscillations) by
  helioseismology. Using new helioseismic data from the Michelson Doppler
  Imager on board SOHO, we have detected zonal flow bands with velocity
  variation of 5 m s<SUP>-1</SUP> at a depth of 2-9 Mm beneath the
  surface. The subsurface flow is inferred from rotational splitting of
  frequencies of the fundamental mode of solar oscillations in the range
  of angular degree l from 120 to 250, using a 144 day uninterrupted time
  series of the Sun's Doppler velocities. The structure of the subsurface
  shear flow resembles the pattern of the torsional oscillations observed
  on the surface. Comparing with previous surface measurements, we found
  evidence for migration of the flow bands towards the equator.

Title: On the Importance of Various Sources of Systematic Errors in
    Helioseismic Measurements
Authors: Schou, J.
Bibcode: 1997SPD....28.0205S
Altcode: 1997BAAS...29..893S
  With the increasing precision of helioseismic measurements, the
  importance of systematic errors are increasing too. In this poster
  I will examine the importance of various possible systematic errors
  in the measurements on which some of the recent discoveries in
  helioseismology rely. Among the problems I will examine are the
  effects of the distortion of the p-modes by differential rotation,
  the horizontal displacement and the use of a-coefficients instead of
  individual m splittings. All of these problems could potentially cause
  the frequency splittings to be significantly biased. The research
  presented here was supported by NASA contract NAG5-3077 to MDI at
  Stanford University.

Title: Results from the MDI Instrument
Authors: Schou, J.
Bibcode: 1997AAS...190.0402S
Altcode: 1997BAAS...29..782S
  Using data from the MDI instrument on the SOHO satellite we have been
  able to infer details in the structure and dynamics of the solar
  interior which were not observed before. Here I will discuss some
  of the highlights of what we have learned so far, such as details
  of the near surface rotation rate and the structure and rotation
  rate in the convection zone and below. I will also discuss some of
  the results obtained about the near surface layers using local area
  helioseismology. The MDI project is supported by NASA contract NAG5-3077
  at Stanford University.

Title: Analysis of Velocity and Intensity Helioseismic Spectra
    from SOHO/MDI
Authors: Nigam, R.; Kosovichev, A. G.; Scherrer, P. H.; Schou, J.
Bibcode: 1997SPD....28.0904N
Altcode: 1997BAAS...29..913N
  We give an explanation for the cause of the asymmetry of spectral lines
  of solar oscillation power spectrum. We also explain the cause of the
  opposite sense of asymmetry in velocity and intensity oscillation power
  spectra, thereby resolving a half-decade old puzzle. The motivation for
  the investigation came after comparing the velocity and intensity data
  obtained from the Michelson Doppler Imager (MDI) instrument on board the
  Solar and Heliospheric Observatory (SOHO). The analysis is based on a
  theoretical model of wave excitation with viscous damping in conjunction
  with a spherically symmetric solar model. Neglecting asymmetry can
  lead to systematic errors in the eigenfrequency measurements, which
  in turn leads to errors in inversion. This research was supported by
  NASA grant NAG5-3077 at Stanford University.

Title: Solar Internal Rotation From SOHO and Ground Based
    Helioseismology Experiments
Authors: Schou, J.
Bibcode: 1997SPD....28.0903S
Altcode: 1997BAAS...29..913S
  With the quality of the data from the helioseismology instruments on
  SOHO and from ground based instruments we have begun to see intriguing
  details in the solar rotation rate that could not be detected before. In
  this talk I will briefly discuss some of the highlights of what we
  have learned so far, such as details of the near surface rotation rate,
  the properties of the tachocline at the bottom of the convection zone
  and the rotation of the solar core. The MDI project is supported by
  NASA contract NAG5-3077 at Stanford University.

Title: Performance of the Michelson Doppler Imager Instrument on SOHO
Authors: Scherrer, P.; Bogart, R.; Bush, R.; Duvall, T.; Hoeksema,
   J. T.; Kosovichev, A.; Schou, J.; Morrison, M.; Tarbell, T.; Title, A.
Bibcode: 1997SPD....28.0207S
Altcode: 1997BAAS...29..894S
  Launched on SOHO in December 1995, the MDI instrument took its 10
  millionth filtergram in early April, 1997. The instrument and spacecraft
  have performed admirably since commissioning, providing over a year
  of virtually uninterrupted time series of velocity and intensity
  measurements at moderate resolution, a continuous 60-day time series
  of full disk 4" velocity and line depth maps, monthly 72+ hour time
  series in various observables, a host of daily 8-hour campaigns, and
  full-disk magnetograms every 96 minutes. Another uninterrupted 90-day
  interval of nearly full data recovery is scheduled to be completed in
  mid July. Various scientific results using MDI data are being presented
  at this meeting. About a dozen terabytes of data sets have been created
  and archived and normal pipeline processing is now completed soon after
  retrieving the data, typically less than a month after the observations
  are made. Most of the data products are generally available on the WWW,
  see http://soi.stanford.edu. Selected data are available in near real
  time. The SOI team welcomes collaborations. Routine and extraordinary
  calibrations along with analysis of scientific data sets allow us to
  make good estimates of the noise and understand many of the sources
  of systematic errors in the instrument. In almost every respect the
  instrument performs as well or better than expected before launch,
  the primary limitations being photon noise on the short term and
  fixed or slowly varying offsets on the long term. We have found that
  the Michelsons are somewhat more sensitive to operational temperature
  variations than was expected, adding some additional constraints on
  our observing sequences.

Title: Persistence of Large-Scale Flows Beneath Quiet Sun: Local-Area
    Analysis Using MDI Doppler Data
Authors: Haber, D.; Toomre, J.; Bogart, R.; Schou, J.; Gonzalez, I.;
   Hill, F.
Bibcode: 1997SPD....28.0201H
Altcode: 1997BAAS...29..893H
  Knowing the large-scale flows that occur in the upper convection zone
  is critical to our understanding of the processes that govern the
  solar cycle. Here we apply solar oscillation ring-diagram analysis to
  several small tracked regions on the sun, approximately 15(deg) on a
  side, as they rotate across the solar disk, in order to determine the
  persistence and depth variation of the large-scale flows beneath these
  regions. We use the Doppler velocity images from the Michelson Doppler
  Imager (MDI) instrument aboard the Solar Heliospheric Observatory
  (SOHO) satellite using quiet-sun data taken during the MDI Dynamics
  campaign of 1996. Three regions at different latitudes were extracted
  from full-disk Doppler images of 1024 x 1024 pixels (pixel size ~
  2'' square) with a one-minute temporal cadence. Eight sequential
  1536-minute time intervals were tracked, remapped onto great-circle
  grids, spatially and temporally filtered, and apodized in space and
  time. They were then Fourier transformed in two spatial dimensions
  and time. The resulting power spectra show characteristic rings at
  each frequency slice. Shifts in the center positions of the rings are
  caused by underlying flow fields and can be inverted to map these flows
  with depth. We use several techniques to fit these shifts in order to
  assess the stability of the results.

Title: The Effects of Systematic Errors in the Estimation of p-Mode
    Frequencies on the Inversion of Solar Internal Structure
Authors: Rhodes, E. J., Jr.; Appourchaux, T.; Bachmann, K.; Kosovichev,
   A. G.; Scherrer, P. H.; Schou, J.; Reiter, J.
Bibcode: 1997SPD....28.0901R
Altcode: 1997BAAS...29..913R
  The frequencies and associated uncertainties of the low-, intermdeiate-,
  and high-degree p-mode oscillations are the input quantities for the
  inversion programs which infer the thermodynamic structure of the solar
  interior. In this review we will attempt to demonstrate the different
  possible systematic errors that are currently present in our estimation
  of both the modal frequencies and their uncertainties. We will also
  demonstrate the effects of some of these errors upon the inferred
  radial profile of the solar internal sound speed. Among the different
  possible systematic errors which we will discuss are the effects of:
  1)the asymmetric shapes of the peaks in observational power spectra,
  2)the realization noise which is present in the case of the low-degree
  modes, 3)the different frequency estimation methods used on different
  types of power spectra (i.e., on either tesseral power spectra or
  on m-averaged power spectra), 4) the differences in the frequencies
  which are estimated from velocity- and intensity-based power spectra,
  5) the blending of individual p-modes into so-called "ridges" of
  observed power at both high degrees and high frequencies, and 6) the
  spatial and temporal aliasing which occurs at both high degrees and
  at high frequencies. We will demonstrate these different errors using
  results obtained with the VIRGO and MDI experiments onboard the SOHO
  spacecraft. We will also compare some of these space-based results
  with the results of similar estimates obtained from co-temporaneous
  ground-based observations, such as from the Mt. Wilson 60-Foot Solar
  Tower. We will include the results from different structural inversions
  carried out with different sets of input frequencies and uncertainties
  in order to demonstrate the effects of these different systematic
  errors upon the inverted internal sound speed profile.

Title: Structure and Rotation of the Solar Interior: Initial Results
    from the MDI Medium-L Program
Authors: Kosovichev, A. G.; Schou, J.; Scherrer, P. H.; Bogart, R. S.;
   Bush, R. I.; Hoeksema, J. T.; Aloise, J.; Bacon, L.; Burnette, A.; de
   Forest, C.; Giles, P. M.; Leibrand, K.; Nigam, R.; Rubin, M.; Scott,
   K.; Williams, S. D.; Basu, Sarbani; Christensen-Dalsgaard, J.; Dappen,
   W.; Rhodes, E. J., Jr.; Duvall, T. L., Jr.; Howe, R.; Thompson, M. J.;
   Gough, D. O.; Sekii, T.; Toomre, J.; Tarbell, T. D.; Title, A. M.;
   Mathur, D.; Morrison, M.; Saba, J. L. R.; Wolfson, C. J.; Zayer, I.;
   Milford, P. N.
Bibcode: 1997SoPh..170...43K
Altcode:
  The medium-l program of the Michelson Doppler Imager instrument on board
  SOHO provides continuous observations of oscillation modes of angular
  degree, l, from 0 to ∽ 300. The data for the program are partly
  processed on board because only about 3% of MDI observations can be
  transmitted continuously to the ground. The on-board data processing,
  the main component of which is Gaussian-weighted binning, has been
  optimized to reduce the negative influence of spatial aliasing of the
  high-degree oscillation modes. The data processing is completed in a
  data analysis pipeline at the SOI Stanford Support Center to determine
  the mean multiplet frequencies and splitting coefficients. The initial
  results show that the noise in the medium-l oscillation power spectrum
  is substantially lower than in ground-based measurements. This enables
  us to detect lower amplitude modes and, thus, to extend the range of
  measured mode frequencies. This is important for inferring the Sun's
  internal structure and rotation. The MDI observations also reveal the
  asymmetry of oscillation spectral lines. The line asymmetries agree
  with the theory of mode excitation by acoustic sources localized in the
  upper convective boundary layer. The sound-speed profile inferred from
  the mean frequencies gives evidence for a sharp variation at the edge
  of the energy-generating core. The results also confirm the previous
  finding by the GONG (Gough et al., 1996) that, in a thin layer just
  beneath the convection zone, helium appears to be less abundant than
  predicted by theory. Inverting the multiplet frequency splittings from
  MDI, we detect significant rotational shear in this thin layer. This
  layer is likely to be the place where the solar dynamo operates. In
  order to understand how the Sun works, it is extremely important to
  observe the evolution of this transition layer throughout the 11-year
  activity cycle.

Title: Internal structure and rotation of the Sun: First results
    from MDI data
Authors: Kosovichev, A. G.; Schou, J.; Scherrer, P. H.; Bogart, R. S.;
   Bush, R. I.; Hoeksema, J. T.; Aloise, J.; Bacon, L.; Burnette, A.;
   De Forest, C.; Giles, P. M.; Leibrand, K.; Nigam, R.; Rubin, M.;
   Scott, K.; Williams, S. D.; Basu, Sarbani; Christensen-Dalsgaard,
   J.; Däppen, W.; Rhodes, E. J., Jr.; Duvall, T. L., Jr.; Howe, R.;
   Thompson, M. J.; Gough, D. O.; Sekii, T.; Toomre, J.; Tarbell, T. D.;
   Title, A. M.; Mathur, D.; Morrison, M.; Saba, J. L. R.; Wolfson,
   C. J.; Zayer, I.; Milford, P. N.
Bibcode: 1997IAUS..181..203K
Altcode:
  No abstract at ADS

Title: Time-Distance Helioseismology with the MDI Instrument:
    Initial Results
Authors: Duvall, T. L., Jr.; Kosovichev, A. G.; Scherrer, P. H.;
   Bogart, R. S.; Bush, R. I.; de Forest, C.; Hoeksema, J. T.; Schou,
   J.; Saba, J. L. R.; Tarbell, T. D.; Title, A. M.; Wolfson, C. J.;
   Milford, P. N.
Bibcode: 1997SoPh..170...63D
Altcode:
  In time-distance helioseismology, the travel time of acoustic waves
  is measured between various points on the solar surface. To some
  approximation, the waves can be considered to follow ray paths that
  depend only on a mean solar model, with the curvature of the ray
  paths being caused by the increasing sound speed with depth below the
  surface. The travel time is affected by various inhomogeneities along
  the ray path, including flows, temperature inhomogeneities, and magnetic
  fields. By measuring a large number of times between different locations
  and using an inversion method, it is possible to construct 3-dimensional
  maps of the subsurface inhomogeneities. The SOI/MDI experiment on SOHO
  has several unique capabilities for time-distance helioseismology. The
  great stability of the images observed without benefit of an intervening
  atmosphere is quite striking. It has made it possible for us to detect
  the travel time for separations of points as small as 2.4 Mm in the
  high-resolution mode of MDI (0.6 arc sec pixel<SUP>-1</SUP>). This has
  enabled the detection of the supergranulation flow. Coupled with the
  inversion technique, we can now study the 3-dimensional evolution of
  the flows near the solar surface.

Title: Frequencies of solar oscillations and the seismic structure
    of the Sun from SOHO/MDI.
Authors: Rhodes, E. J., Jr.; Kosovichev, A. G.; Scherrer, P. H.;
   Schou, J.; Reiter, J.
Bibcode: 1997AGAb...13..163R
Altcode:
  No abstract at ADS

Title: New Views of the Sun's Interior from the SOHO/MDI Space
    Experiment
Authors: Scherrer, P. H.; Bogart, R. S.; Bush, R. I.; Hoeksema, J. T.;
   Kosovichev, A. G.; Nigam, R.; Schou, J.; Duvall, T. L., Jr.
Bibcode: 1996AAS...189.1803S
Altcode: 1996BAAS...28.1298S
  The strking stability of solar Dopplergrams measured by the Michelson
  Doppler Imager (MDI) instrument on the SOHO spacecraft, without an
  intervening atmosphere, substantially decreases the noise in the solar
  oscillations power spectrum compared with groundbased observations. This
  permits detection of lower amplitude oscillations, extending the range
  of measured normal mode frequencies. This is important for improving
  resolution and precision of helioseismic inferences about the Sun's
  internal structure and dynamics. The MDI observations also reveal the
  asymmetries of oscillation spectral lines that until now have been
  largely hidden in noise. The line asymmetries agree with a theory of
  excitation of solar oscillations by acoustic sources localized in the
  upper convective boundary layer. High-resolution MDI images make it
  possible to measure the travel time of acoustic waves propagating
  inside the Sun by comparing points on the surface as close as 2.4
  Mm. This is sufficient to detect supergranulation flows beneath the
  surface. Coupled with tomographic inversion techniques, we can now study
  the 3-dimensional evolution of the flows near the photosphere. The
  sound-speed profile inferred from normal modes frequencies shows a
  sharp variation at the edge of the energy-generating core, something
  not accounted for by the standard evolution theory. The analysis also
  confirms recent GONG results suggesting that helium is less abundant
  than theory predicts in a thin layer just beneath the convection
  zone. Inversion of the multiplet frequency splittings shows significant
  rotational shear in this thin layer. This shear flow probably generates
  turbulence that mixes the plasma in the upper radiative zone. This layer
  is likely to be the place where the solar dynamo operates. Continuous
  observation of the evolution of this transition layer during the entire
  11-year activity cycle will be extremely important for understanding
  the mechanisms of solar activity.

Title: Solar structure as revealed by 1 year LOWL data
Authors: Basu, Sarbani; Christensen-Dalsgaard, J.; Schou, J.; Thompson,
   M. J.; Tomczyk, S.
Bibcode: 1996BASI...24..147B
Altcode:
  No abstract at ADS

Title: Results from the LOWL instrument
Authors: Schou, J.; Tomczyk, S.; Thompson, M. J.
Bibcode: 1996BASI...24..375S
Altcode:
  No abstract at ADS

Title: Low-degree frequency splitting measurements and the rotation
    rate of the solar core
Authors: Tomczyk, S.; Schou, J.; Thompson, M. J.
Bibcode: 1996BASI...24..245T
Altcode:
  No abstract at ADS

Title: Measurement of the Rotation Rate in the Deep Solar Interior
Authors: Tomczyk, S.; Schou, J.; Thompson, M. J.
Bibcode: 1996AAS...188.6903T
Altcode: 1996BAAS...28..935T
  We present a measurement of the rotation rate in the interior of the
  Sun based on two years of observations with the LOWL instrument. LOWL
  allows the observation of solar oscillations with degrees from 0
  to 100, thus providing a homogeneous low- and intermediate-degree
  dataset. Significantly, it is able to make spatially resolved
  observations of low degree modes, thereby making it possible to separate
  the different modes within a given multiplet. This reduces the potential
  for systematic errors compared to observations using integrated
  sunlight. We have used observations of the frequency splittings
  of modes with degrees from 1 to 100 to infer the rotation rate in
  the solar interior with some radial resolution and without excessive
  errors. Over most of the interior we have also been able to estimate
  the latitudinal variation of the rotation rate. We confirm earlier
  findings that near the base of the convection zone the solar rotation
  profile undergoes a transition from surface-like differential rotation
  to a rotation rate that is independent of latitude. Additionally,
  we find that below the base of the convection zone our measurement is
  consistent with rigid body rotation at a rate somewhat lower than the
  surface equatorial rate. This measurement provides strong constraints
  on the theories of angular momentum transport in solar-type stars.

Title: Differential Rotation and Dynamics of the Solar Interior
Authors: Thompson, M. J.; Toomre, J.; Anderson, E. R.; Antia, H. M.;
   Berthomieu, G.; Burtonclay, D.; Chitre, S. M.; Christensen-Dalsgaard,
   J.; Corbard, T.; De Rosa, M.; Genovese, C. R.; Gough, D. O.; Haber,
   D. A.; Harvey, J. W.; Hill, F.; Howe, R.; Korzennik, S. G.; Kosovichev,
   A. G.; Leibacher, J. W.; Pijpers, F. P.; Provost, J.; Rhodes, E. J.,
   Jr.; Schou, J.; Sekii, T.; Stark, P. B.; Wilson, P. R.
Bibcode: 1996Sci...272.1300T
Altcode:
  Splitting of the sun's global oscillation frequencies by large-scale
  flows can be used to investigate how rotation varies with radius
  and latitude within the solar interior. The nearly uninterrupted
  observations by the Global Oscillation Network Group (GONG) yield
  oscillation power spectra with high duty cycles and high signal-to-noise
  ratios. Frequency splittings derived from GONG observations confirm
  that the variation of rotation rate with latitude seen at the surface
  carries through much of the convection zone, at the base of which is
  an adjustment layer leading to latitudinally independent rotation at
  greater depths. A distinctive shear layer just below the surface is
  discernible at low to mid-latitudes.

Title: The Shape of Solar Oscillation Eigenfunctions
Authors: Schou, J.
Bibcode: 1996AAS...188.6906S
Altcode: 1996BAAS...28..936S
  Helioseismic images of the Sun have generally been processed
  assuming that their observed surface behavior is given by perfect
  spherical harmonics, although it is well known that this is only
  an approximation. Among the neglected effects are the distortion of
  the modes by differential rotation and the neglect of the transverse
  component of the surface velocity in the reduction. In this poster I
  will discuss these approximations and their possible effects on the
  mode power spectra and the deduced frequencies. While some of the
  effects are rather small others are easily visible in the observed
  power spectra. I will show results of analyzing various datasets to
  look for these effects. While it appears that some of the results are
  as theoretically expected others are more difficult to understand. It
  is the hope that we will be able to obtain more reliable and precise
  mode parameters by taking these effects into account in the analysis of
  data from projects such as SOI/MDI and GONG. This research is supported
  by the SOI-MDI NASA contract NAG5-3077 at Stanford University.

Title: GONG Data: Implications for the Sun's Interior and Near
    Surface Magnetic Field
Authors: Goode, P. R.; Dziembowski, W. A.; Rhodes, E. J., Jr.; Tomczyk,
   S.; Schou, J.; GONG Magnetic Effects Team
Bibcode: 1996AAS...188.5307G
Altcode: 1996BAAS...28..904G
  The solar oscillation spectrum and the fine structure in it from the
  first complete month of GONG data have been used to place a limit
  on the Sun's internal magnetic field. The limit is consistent with
  the magnetic pressure being no more than 1/1000 of the gas pressure
  between the Sun's deep interior and its surface. This conclusion is
  consistent with earlier results. The GONG data are from a time near
  magnetic activity minimum. The effect of the near surface magnetic
  field on the fine structure in the oscillation spectrum reflects
  a perturbation of quadrupole toroidal symmetry. This geometry also
  dominated at the last activity minimum. The meaning of this result is
  discussed. The near surface magnetic perturbation is not spherically
  symmetric. This corrupts the results of inversions designed to probe
  the Sun's deep interior. The solution to this problem is presented.

Title: The Solar Acoustic Spectrum and Eigenmode Parameters
Authors: Hill, F.; Stark, P. B.; Stebbins, R. T.; Anderson, E. R.;
   Antia, H. M.; Brown, T. M.; Duvall, T. L., Jr.; Haber, D. A.;
   Harvey, J. W.; Hathaway, D. H.; Howe, R.; Hubbard, R. P.; Jones,
   H. P.; Kennedy, J. R.; Korzennik, S. G.; Kosovichev, A. G.; Leibacher,
   J. W.; Libbrecht, K. G.; Pintar, J. A.; Rhodes, E. J., Jr.; Schou, J.;
   Thompson, M. J.; Tomczyk, S.; Toner, C. G.; Toussaint, R.; Williams,
   W. E.
Bibcode: 1996Sci...272.1292H
Altcode:
  The Global Oscillation Network Group (GONG) project estimates
  the frequencies, amplitudes, and linewidths of more than 250,000
  acoustic resonances of the sun from data sets lasting 36 days. The
  frequency resolution of a single data set is 0.321 microhertz. For
  frequencies averaged over the azimuthal order m, the median formal
  error is 0.044 microhertz, and the associated median fractional error
  is 1.6 x 10<SUP>-5</SUP>. For a 3-year data set, the fractional error
  is expected to be 3 x 10<SUP>-6</SUP>. The GONG m-averaged frequency
  measurements differ from other helioseismic data sets by 0.03 to 0.08
  microhertz. The differences arise from a combination of systematic
  errors, random errors, and possible changes in solar structure.

Title: Calibration and Performance of the Michelson Doppler Imager
    on SOHO.
Authors: Zayer, I.; Morrison, M.; Tarbell, T. D.; Title, A.; Wolfson,
   C. J.; MDI Engineering Team; Bogart, R. S.; Bush, R. I.; Hoeksema,
   J. T.; Duvall, T.; Sa, L. A. D.; Scherrer, P. H.; Schou, J.
Bibcode: 1996AAS...188.3712Z
Altcode: 1996BAAS...28..879Z
  The Michelson Doppler Imager (MDI) instrument probes the interior
  of the Sun by measuring the photospheric manifestations of solar
  oscillations. MDI was launched in December, 1995, on the Solar and
  Heliospheric Observatory (SOHO) and has been successfully observing the
  Sun since then. The instrument images the Sun on a 1024 x 1024 pixel CCD
  camera through a series of increasingly narrow spectral filters. The
  final elements, a pair of tunable Michelson interferometers, enable
  MDI to record filtergrams with FWHM bandwidth of 94 m Angstroms with
  a resolution of 4 arcseconds over the whole disk. Images can also be
  collected in MDI's higher resolution (1.25 arcsecond) field centered
  about 160 arcseconds north of the equator. An extensive calibration
  program has verified the end-to-end performance of the instrument
  in flight. MDI is working very well; we present the most important
  calibration results and a sample of early science observations. The
  Image Stabilization System (ISS) maintains overall pointing to
  better than ca. 0.01 arcsec, while the ISS' diagnostic mode allows
  us to measure spectrally narrow pointing jitter down to less than
  1 mili-arcsec. We have confirmed the linearity of each CCD pixel to
  lie within 0.5%\ (the FWHM of the distribution is 0.2% ), and have to
  date not detected any contamination on the detector, which is cooled
  to -72 C. The noise in a single Dopplergram is of the order of 20 m/s,
  and initial measurements of transverse velocities are reliable to 100
  m/s. The sensitivity of magnetograms reach 5G in a 10 minute average
  (15G in a single magnetogram). MDI's primary observable, the p-modes
  from full-disk medium-l data, are of very high quality out to l=300
  as seen in the initial l-nu diagram. The SOI-MDI program is supported
  by NASA contract NAG5-3077.

Title: The Sun's Hydrostatic Structure from LOWL Data
Authors: Basu, Sarbani; Christensen-Dalsgaard, J.; Schou, J.; Thompson,
   M. J.; Tomczyk, S.
Bibcode: 1996ApJ...460.1064B
Altcode:
  Recent observations with the LOWL (Low-Degree [l] Oscillations
  Experiment) instrument have for the first time provided a uniform set of
  frequencies that allow detailed inversion for the structure of much of
  the Sun's deep interior. We present the results of inverting the LOWL
  data and compare them with the corresponding results obtained using
  inhomogeneous data sets from more than one instrument. Furthermore,
  improvements in the description of the required physics motivates the
  calculation of new solar models. Thus, we present results of inversions
  of the LOWL data against several reference models using up-to-date
  physics. In models including the gravitational settling of helium, the
  sound speed and density agree with the Sun to within substantially
  better than 1%. We test various modifications to the physics of
  the models in order to see if the remaining small (but significant)
  discrepancy between the Sun and the models can be removed. We find
  that none of the modifications tested can adequately account for the
  remaining discrepancy, though a small increase in helium diffusion
  in the core gives a modest improvement over the standard diffusion
  model. Finally, we find that the seismic data support theoretical
  calculations that indicate that settling of heavier elements has
  reduced the present surface value of Z by about 8% relative to its
  mean interior value.

Title: Inversion for the Velocity Field in the Solar Interior
Authors: Schou, Jesper
Bibcode: 1996imie.conf...48S
Altcode:
  No abstract at ADS

Title: Downflows under sunspots detected by helioseismic tomography
Authors: Duvall, T. L.; D'Silva, S.; Jefferies, S. M.; Harvey, J. W.;
   Schou, J.
Bibcode: 1996Natur.379..235D
Altcode:
  SUNSPOTS are areas of cooler gas and stronger magnetic fields in the
  Sun's photosphere (its 'surface'), but just how they form and are
  maintained has long been a puzzle. It has been proposed<SUP>1</SUP>
  that small vertical magnetic flux tubes, generated deep within the Sun,
  develop downflows around them when they emerge at the surface. The
  downflows bring together a large number of flux tubes in a cluster
  to form a sunspot, which behaves as a single flux bundle as long as
  the downflows bind the flux tubes together. Until now, however,
  it has not been possible to test this model with subsurface
  observations. Here we use the recently developed technique of
  travel-time helioseismology<SUP>2</SUP> to detect the presence of
  strong downflows beneath both sunspots and the bright features known
  as plages. The flows have a velocity of ~2 kms<SUP>-1</SUP>, and they
  persist to a depth of about 2,000 km. The data suggest, however, that
  the vertical magnetic field can be a coherent flux bundle only to a
  depth of ~600 km; below this depth it is possible that the downflows
  hold together a loose collection of flux tubes to maintain the sunspots
  that we see.

Title: Inversion for the Velocity Field in the Solar Interior
Authors: Schou, J.
Bibcode: 1996LNES...63...48S
Altcode:
  No abstract at ADS

Title: The Solar Oscillations Investigation - Michelson Doppler Imager
Authors: Scherrer, P. H.; Bogart, R. S.; Bush, R. I.; Hoeksema, J. T.;
   Kosovichev, A. G.; Schou, J.; Rosenberg, W.; Springer, L.; Tarbell,
   T. D.; Title, A.; Wolfson, C. J.; Zayer, I.; MDI Engineering Team
Bibcode: 1995SoPh..162..129S
Altcode:
  The Solar Oscillations Investigation (SOI) uses the Michelson Doppler
  Imager (MDI) instrument to probe the interior of the Sun by measuring
  the photospheric manifestations of solar oscillations. Characteristics
  of the modes reveal the static and dynamic properties of the
  convection zone and core. Knowledge of these properties will improve
  our understanding of the solar cycle and of stellar evolution. Other
  photospheric observations will contribute to our knowledge of the
  solar magnetic field and surface motions. The investigation consists
  of coordinated efforts by several teams pursuing specific scientific
  objectives.

Title: Results From the LOWL Instrument
Authors: Schou, J.; Tomczyk, S.; Thompson, M. J.
Bibcode: 1995AAS...18710101S
Altcode: 1995BAAS...27.1426S
  In this poster we will present various results from one year of
  observations with the LOWL instrument. The LOWL instrument is designed
  to observe oscillations with degrees l from 0 to about 100 providing a
  homogeneous dataset for inversions. Given the spatial resolution of the
  instrument it is possible to separate different azimuthal orders m even
  for the lowest degree modes, hopefully giving more accurate splittings
  than those determined using integrated sunlight for a similar time
  period. We will show the results of an inversion for the solar rotation
  rate between 0.1R_sun and 0.95R_sun. Given the long duration and the
  large number of terms used to describe the m-dependence of the mode
  frequencies we have been able to obtain very good resolution in both
  the radial direction and in latitude while keeping the statistical
  errors low, thereby obtaining more accurate results than previously
  possible. We will also present results of analyzing different parts of
  the time-series and compare the temporal variations in mode frequencies
  and splittings with variations in the solar activity.

Title: Measurement of the Rotation Rate in the Deep Solar Interior
Authors: Tomczyk, S.; Schou, J.; Thompson, M. J.
Bibcode: 1995ApJ...448L..57T
Altcode:
  We present a measurement of solar internal rotation based
  on observations obtained over 3 months in early 1994 with a new
  instrument called LOWL. This instrument allows for the simultaneous
  observation of low- and intermediate-degree solar oscillations with
  spatial resolution. We have measured the frequency splitting of 673
  multiplets with degrees ranging from 1 to 80 and inverted these to
  derive an estimate of the solar internal rotation profile between 0.2
  and 0.85 R⊙. The accuracy of this measurement ranges from ~1% in the
  outer regions to ~5% at 0.2 R⊙ and thus places better constraints than
  hitherto on the rotation in the deep solar interior. We confirm earlier
  findings that near the base of the convection zone the solar rotation
  profile undergoes a transition from surface-like differential rotation
  to a rotation rate that is independent of latitude. In addition, we
  find that from the base of the convection zone down to 0.2 R⊙ our
  measurement is consistent with rigid body rotation at a rate somewhat
  lower than the surface equatorial rate. The accuracy of our measurement
  in the deep solar interior provides a strong constraint to theories
  of solar and stellar angular momentum transport.

Title: A Measurement of the Rotation Rate in the Deep Solar Interior
Authors: Schou, J.; Tomczyk, S.; Thompson, M. J.
Bibcode: 1995ESASP.376b.275S
Altcode: 1995soho....2..275S; 1995help.confP.275S
  No abstract at ADS

Title: The Sensitivity of Various Mode Sets for Probing Differential
    Rotation Shear Zones
Authors: Christensen-Dalsgaard, J.; Schou, J.; Thompson, M. J.;
   Toomre, J.
Bibcode: 1995ESASP.376b..41C
Altcode: 1995soho....2...41C; 1995help.confP..41C
  The potential of forthcoming datasets from GONG and SOI for resolving
  long-lived azimuthal jets and shearing flows is investigated. The
  authors construct various artificial datasets, containing noise
  resembling that for a one-year observing run. These are then inverted,
  using a 2-D regularized least squares (RLS) inversion. In particular,
  the authors investigate the ability of the RLS method to form
  well-localized averages of the rotation rate, as measured by the
  averaging kernels, using an extensive mode set as well as subsets
  thereof. The authors show that it is possible to keep the noise in
  the solution down to a few nanohertz in much of the solar interior,
  while obtaining very reasonable resolution, for a GONG-like dataset.

Title: Solar Structure Inversion with LOWL Data
Authors: Basu, S.; Christensen-Dalsgaard, J.; Schou, J.; Thompson,
   M. J.; Tomczyk, S.
Bibcode: 1995ESASP.376b..25B
Altcode: 1995help.confP..25B; 1995soho....2...25B
  Presents inversion results for the radial hydrostatic structure of
  the Sun, using six months of oscillation data obtained with the LOWL
  instrument. Using modes with degrees from 0 to 90 and frequencies
  between 1.5 and 3.5 mHz, the authors have inferred the variation with
  depth of the sound speed, density ρ and u = p/ρ (p being pressure)
  from r = 0.05 R<SUB>sun</SUB> to 0.85 R<SUB>sun</SUB>. They find that
  in this region the sound speed in the Sun is within 0.15% of that of a
  model constructed using the MHD equation of state and OPAL opacities
  and incorporating helium diffusion. The density difference between
  Sun and model is less than 0.8%. Given the small error bars on the
  inversion results these small differences are significant, however. The
  solar sound speed appears to be higher than in the model for r &lt;
  0.2 R<SUB>sun</SUB> . The authors speculate that this might indicate
  interesting physics in the inner core.

Title: Constraining Solar Core Rotation with Genetic Forward Modelling
Authors: Tomczyk, S.; Charbonneau, P.; Schou, J.; Thompson, M. J.
Bibcode: 1995ESASP.376b.271T
Altcode: 1995soho....2..271T; 1995help.confP.271T
  No abstract at ADS

Title: Results from the LOWL Instrument
Authors: Schou, J.; Tomczyk, S.; Thompson, M. J.
Bibcode: 1995SPD....26..402S
Altcode: 1995BAAS...27..954S
  No abstract at ADS

Title: Michelson Doppler Imager (MDI) Performance Characteristics
Authors: Zayer, I.; Morrison, M.; Pope, T.; Rosenberg, W.; Tarbell,
   T.; Title, A.; Wolfson, J.; Bogart, R. S.; Hoeksema, J. T.; Milford,
   P.; Scherrer, P. H.; Schou, J.
Bibcode: 1995ASPC...76..456Z
Altcode: 1995gong.conf..456Z
  No abstract at ADS

Title: Optimally Localized Kernels for 2D Helioseismic Inversion
Authors: Christensen-Dalsgaard, J.; Larsen, R. M.; Schou, J.; Thompson,
   M. J.
Bibcode: 1995ASPC...76...70C
Altcode: 1995gong.conf...70C
  No abstract at ADS

Title: Sputtering of water ice surfaces and the production of extended
    neutral atmospheres
Authors: Shi, M.; Baragiola, R. A.; Grosjean, D. E.; Johnson, R. E.;
   Jurac, S.; Schou, J.
Bibcode: 1995JGR...10026387S
Altcode:
  Plasma and UV photon bombardment of an icy object in the outer
  solar system can lead to ejection of atoms and molecules from the
  surface which can, in turn, produce an extended neutral atmosphere. We
  present new laboratory studies of the sputtering of water ice by keV
  ions (H<SUP>+</SUP> through Ne<SUP>+</SUP>) made using a sensitive
  microbalance technique that allows measurements at very low ion
  fluences. These results for the sputtering yield of ice by keV
  O<SUP>+</SUP> ions, the dominant sputtering agents in the Saturnian
  magnetosphere, are much larger than those used previously to model the
  neutral cloud associated with the icy satellites. The data presented
  are used to recalculate previously published sputtering rates for
  the icy satellites of Jupiter and Saturn, and for the E-ring grains
  at Saturn. The new results can account, in part, for the discrepancy
  between the predicted and observed OH cloud near Tethys in Saturn's
  inner magnetosphere. We compare the yields induced by the incident
  ions to the recently measured UV photosputtering yield, and discuss
  possible synergism between UV photon and plasma ion induced erosion.

Title: Some Aspects of Helioseismic Time-Series Analysis
Authors: Schou, J.; Christensen-Dalsgaard, J.; Thompson, M. J.
Bibcode: 1995ASPC...76..528S
Altcode: 1995gong.conf..528S
  No abstract at ADS

Title: Status of the Solar Oscillations Investigation - Michelson
    Doppler Imager
Authors: Scherrer, P. H.; Bogart, R. S.; Bush, R. I.; Hoeksema,
   J. T.; Milford, P.; Schou, J.; Pope, T.; Rosenberg, W.; Springer,
   L.; Tarbell, T.; Title, A.; Wolfson, J.; Zayer, I.
Bibcode: 1995ASPC...76..402S
Altcode: 1995gong.conf..402S
  No abstract at ADS

Title: Preliminary Results from Observations with the LOWL Instrument
Authors: Schou, J.; Tomczyk, S.
Bibcode: 1995ASPC...76..448S
Altcode: 1995gong.conf..448S
  No abstract at ADS

Title: Hunting for Azimuthal Jets and Shearing Flows in the Solar
    Convection Zone
Authors: Christensen-Dalsgaard, J.; Schou, J.; Thompson, M. J.;
   Toomre, J.
Bibcode: 1995ASPC...76..212C
Altcode: 1995gong.conf..212C
  No abstract at ADS

Title: A Measurement of the Rotation Rate in the Deep Solar Interior
Authors: Schou, J.; Tomczyk, S.; Thompson, M. J.
Bibcode: 1994AAS...185.4401S
Altcode: 1994BAAS...26Q1377S
  Measurements of the rotation rate in the deep solar interior using
  helioseismology have given inconsistent results, presumably due to
  problems with the algorithms used for the analysis of spatially
  unresolved observations of the oscillations. Here we present a
  measurement of the rotation rate in the interior of the Sun based
  on observations with a new instrument called LOWL. Unlike earlier
  instruments this instrument allows the observation of oscillations
  with degrees from 0 to ~ 80. In particular it is able to make spatially
  resolved observations of low degree modes, thereby making it possible to
  spatially separate the different modes within a given multiplet. This
  reduces the potential for systematic errors compared to observations
  using integrated sunlight. We have used observations of the frequency
  splittings of modes with degrees from 1 to 80 to infer the rotation rate
  in the solar interior down to ~ 0.2 R_⊙ with some radial resolution
  and without excessive errors. Over part of the range we have also been
  able to estimate the latitudinal variation of the rotation rate. This
  measurement provides strong constraints on the theories of solar and
  stellar angular momentum transport.

Title: Generation of artificial helioseismic time-series.
Authors: Schou, J.; Brown, T. M.
Bibcode: 1994A&AS..107..541S
Altcode:
  We present an outline of an algorithm to generate artificial
  helioseismic time-series, taking into account as much as possible of
  the knowledge we have on solar oscillations. The hope is that it will
  be possible to find the causes of some of the systematic errors in
  analysis algorithms by testing them with such artificial time-series.

Title: On the Rotation Rate in the Solar Convection Zone
Authors: Schou, Jesper; Brown, Timothy M.
Bibcode: 1994ApJ...434..378S
Altcode:
  Recently Gough et al. (1993) have argued that the rotation rate in parts
  of the solar convection zone may be constant on cylinders as predicted
  by models of the convection zone, contrary to the inferences generally
  made from helioseismology. Here we consider models similar to those
  suggested by Gough et al. and show that they are either inconsistent
  with observations made by Fourier Tachometer or require unphysical
  rotation rates in other parts of the Sun. These observations use a more
  detailed model of the effects of the solar rotation on the observed
  frequencies than that used in reducing previous observations. We
  also show the results of an inversion of the Fourier Tachometer
  observations and compare it with an inversion of data similar to that
  used previously. The result of this inversion generally confirms the
  conclusions from previous inversions.

Title: On Comparing Helioseismic Two-dimensional Inversion Methods
Authors: Schou, J.; Christensen-Dalsgaard, J.; Thompson, M. J.
Bibcode: 1994ApJ...433..389S
Altcode:
  We consider inversion techniques for investigating the structure and
  dynamics of the solar interior as functions of radius and latitude. In
  particular, we look at the problem of inferring the radial and
  latitudinal dependence of the Sun's internal rotation, using a fully
  two-dimensional least-squares inversion algorithm. Concepts such as
  averaging kernels, measures of resolution, and trade-off curves, which
  have previously been used in the one-dimensional case, are generalized
  to facilitate a comparison of two-dimensional methods. We investigate
  the weighting given to different modes and discuss the implications of
  this for observational strategies. As an illustration we use a mode
  set whose properties are similar to those expected for data from the
  GONG network.

Title: Generation of artificial helioseismic time-series
Authors: Schou, J.; Brown, T. M.
Bibcode: 1993STIN...9415968S
Altcode:
  We present an outline of an algorithm to generate artificial
  helioseismic time-series, taking into account as much as possible of
  the knowledge we have on solar oscillations. The hope is that it will
  be possible to find the causes of some of the systematic errors in
  analysis algorithms by testing them with such artificial time-series.

Title: Observations of Intermediate Degree Solar Oscillations:
    1989 April--June
Authors: Bachmann, Kurt T.; Schou, Jesper; Brown, Timothy M.
Bibcode: 1993ApJ...412..870B
Altcode:
  Frequencies, splittings, and line widths from 85 d of full disk
  Doppler observations of solar p-modes taken between April 4 and June
  30, 1989 are presented. Comparison of the present mode parameters
  with published Big Bear Solar Observatory (BBSO) results yields good
  agreement in general and is thus a confirmation of their work using an
  independent instrument and set of analysis routines. Average differences
  in p-mode frequencies measured by the two experiments in spring-summer
  1989 are explained as a result of differences in the exact periods of
  data collection during a time of rapidly changing solar activity. It
  is shown that the present a(1) splitting coefficients for p-modes
  with nu/L less than 45 micro-Hz suffer from a significant systematic
  error. Evidence is presented to the effect that a detector distortion
  or alignment problem, not a problem with the power spectra analysis,
  is the most likely explanation of this a(1) anomaly.

Title: Requirements for the Observation of Low-Degree Solar
    Oscillations
Authors: Veitzer, S. A.; Tomczyk, S.; Schou, J.
Bibcode: 1993ASPC...42..465V
Altcode: 1993gong.conf..465V
  No abstract at ADS

Title: Observations of Intermediate Degree Solar Oscillations -
    1989APR-JUN
Authors: Bachmann, K. T.; Schou, J.; Brown, T. M.
Bibcode: 1993ASPC...42..197B
Altcode: 1993gong.conf..197B
  No abstract at ADS

Title: Two-dimensional helioseismic inversions
Authors: Schou, J.; Christensen-Dalsgaard, J.; Thompson, M. J.
Bibcode: 1993ASPC...40...72S
Altcode: 1993IAUCo.137...72S; 1993ist..proc...72S
  No abstract at ADS

Title: On the analysis of helioseismic data
Authors: Schou, Jesper
Bibcode: 1993PhDT.......436S
Altcode:
  No abstract at ADS

Title: Preliminary results from observations with the Fourier
    tachometer.
Authors: Schou, J.; Brown, T. M.; Bachman, K. T.
Bibcode: 1993ASPC...40...90S
Altcode: 1993IAUCo.137...90S; 1993ist..proc...90S
  The authors present preliminary results from an analysis of two ≍3
  month observation runs with the Fourier Tachometer (which was operated
  by HAO and NSO) from 1987 and 1989. The analysis was done with two
  different methods in order to test for systematic errors. It is shown
  that the mode frequencies change in a manner similar to that reported
  by Libbrecht and Woodard. The authors also present results for the
  frequency splittings caused by the solar rotation.

Title: Two-Dimensional Helioseismic Inversions
Authors: Schou, J.; Christensen-Dalsgaard, J.; Thompson, M. J.
Bibcode: 1993ASPC...42..205S
Altcode: 1993gong.conf..205S
  No abstract at ADS

Title: The Resolving Power of Current Helioseismic Inversions for
    the Sun's Internal Rotation
Authors: Schou, J.; Christensen-Dalsgaard, J.; Thompson, M. J.
Bibcode: 1992ApJ...385L..59S
Altcode:
  An inversion of the currently available rotational splitting data
  which is representative of other recent inversions for the sun's
  internal rotation is analyzed. The so-called polar rate is found to be
  an extrapolation from lower latitudes. The basic conclusion that the
  average radial gradient of the rotation rate in the solar convection
  zone is small is corroborated.

Title: On the Analysis of Helioseismic Data
Authors: Schou, J.
Bibcode: 1992PhDT.......380S
Altcode:
  No abstract at ADS

Title: On the Analysis of Helioseismic Time-Series
Authors: Schou, J.; Brown, T. M.
Bibcode: 1991BAAS...23.1390S
Altcode:
  No abstract at ADS

Title: On the 2-Dimensional Rotational Inversion Problem
Authors: Schou, Jesper
Bibcode: 1991LNP...388...93S
Altcode: 1991ctsm.conf...93S
  Inspired by the GONG hound and hare exercise, where 2-dimensional
  inversions are being performed, I have started writing a set of programs
  to do both the forward and inverse problem, in both the 1-dimensional
  case (with possible expansion in latitude and the full 2-dimensional
  case. Some preliminary results of running these programs are presented
  here, together with an outline of the whole package.

Title: An Inversion for the Rotation Rate in the Solar Interior
Authors: Schou, Jesper
Bibcode: 1991LNP...388...81S
Altcode: 1991ctsm.conf...81S
  The results of an inversion of a set of preliminary rotational
  splittings from 1986 and 1988 from Big Bear Solar Observatory are
  presented. The splittings and the results of the inversions for the
  1986 case are essentially identical to those in Christensen-Dalsgaard
  and Schou (1986, and there appear to be no significant differences
  between the two years. The results from both years seem to confirm
  the earlier result that the rotation rate is surface-like and constant
  on radii in the part of the convection zone that is resolved by this
  mode set and independent of both radius and latitude in the radiative
  interior. Since the observations used here only span degrees from 5 -
  60 it has not been possible to perform an inversion for the rotation
  rate inside approximately 0.4R and in the outer part of the convection
  zone, and it is therefore not possible to see whether there is a
  bump in the rotation rate near the surface, as indicated by Hill et
  al. (1988). There are, however, indications that the rotation rate is
  not constant throughout the convection zone.

Title: A comparison of methods for inverting helioseismic data
Authors: Christensen-Dalsgaard, J.; Schou, J.; Thompson, M. J.
Bibcode: 1990MNRAS.242..353C
Altcode:
  Consideration is given to the inversion techniques used to study the
  properties of the solar interior with observed frequencies of solar
  oscillation. Linear inversion schemes for helioseismic problems are
  compared in terms of resolutions and error properties. Measures of the
  error amplification resulting from the inversion and the resolution
  achieved are defined. Although the study includes only inversions for
  a spherically symmetric angular velocity distribution, it is suggested
  that the methods may be used to study kernels for other properties of
  the solar interior.

Title: Differential rotation in the solar interior.
Authors: Christensen-Dalsgaard, J.; Schou, J.
Bibcode: 1988ESASP.286..149C
Altcode: 1988ssls.rept..149C
  The authors present an estimate of the angular velocity in the
  outer half of the Sun, as a function of depth and latitude. This
  was obtained by applying inversion by means of optimally localized
  averages to rotational splitting coefficients observed by Kent
  Libbrecht at BBSO. The results seem to indicate that the surface
  differential rotation persists through the convection zone; beneath
  the convection zone there appears to be a transition, which occurs
  within our resolution width of about 0.1 R, to solid-body rotation. The
  authors were unable to perform the inversion in the core, due to the
  lack of adequate data for modes of low degree.