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Author name code: pesnell
ADS astronomy entries on 2022-09-14
author:"Pesnell, William Dean" 

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Title: Two New Methods for Counting and Tracking the Evolution of
    Polar Faculae
Authors: Hovis-Afflerbach, B.; Pesnell, W. Dean
2022SoPh..297...48H    Altcode: 2022arXiv220410863H
  Polar faculae are the footpoints of magnetic-field lines near the Sun's
  poles that are seen as bright regions along the edges of granules. The
  time variation in the number of polar faculae has been shown to
  correlate with the strength of the polar magnetic field and to be a
  predictor of the subsequent solar cycle. Due to the small size and
  transient nature of these features, combined with different techniques
  and observational factors, previous counts of polar faculae differ
  in magnitude. Further, there were no scalable techniques to measure
  the statistical properties of the faculae, such as the variation
  of the facular lifetime with time or solar activity. Using data
  from the Helioseismic and Magnetic Imager (HMI) onboard the Solar
  Dynamics Observatory (SDO), we present two new methods for tracking
  faculae and measuring their properties. In the first, we calculate
  the pixel-by-pixel standard deviation of the HMI continuum intensity
  images over one day, visualizing the faculae as streaks. The lifetime
  of the facula is found by dividing the angular length of the streaks
  by the latitude-dependent rotation rate. We apply this method to the
  more visible pole each day for a week every six months, from September
  2010 to March 2021. Combining all of the measured facular lifetimes
  provides a statistical distribution with a mean of 6.0 hours, a FWHM
  of 5.4 hours, and a skew towards longer lifetimes, with some faculae
  lasting up to 1 day. In the second method, we overlay images of the
  progressive standard deviation with the HMI magnetogram to show the
  close relationship between the facular candidates and the magnetic
  field. The results of this method allow us to distinguish between
  motion due to the Sun's rotation and "proper motion" due to faculae
  moving across the Sun's surface, confirming that faculae participate
  in convective motions at the poles. Counts of polar faculae using both
  methods agree with previous counts in their variation with the solar
  cycle and the polar magnetic field. These methods can be extended to
  automate the identification and measurement of other properties of
  polar faculae, which would allow for daily measurements of all faculae
  since SDO began operation in 2010.

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Title: Comparing the Sun Watcher Using Active Pixel System Detector
    and Image Processing Instrument to the Atmosphere Imaging Assembly
    Instrument Through Measurements of Polar Coronal Holes
Authors: Kirk, Michael S. F.; Pesnell, W. Dean; Arge, C. Nickolos;
   West, Matthew J.; Attié, Raphael
2022SoPh..297...42K    Altcode:
  The PRoject for OnBoard Autonomy 2/Sun Watcher using Active pixel
  system detector and image Processing (PROBA2/SWAP) instrument images
  the full-disk extreme ultraviolet (EUV) Sun using a complementary
  metal-oxide semiconductor active-pixel sensor (CMOS-APS) detector
  with a filter centered on a 174 Å passband at a cadence of one to two
  minutes. In contrast, the Atmosphere Imaging Assembly (AIA) instrument
  onboard the Solar Dynamics Observatory (SDO) has a passband filter
  centered on 171 Å and uses a charge-coupled device (CCD) detector
  to make full-disk observations of the EUV corona. The images that
  these two telescope designs produce are visually quite similar in
  active regions, coronal loops, and the quiet corona. This work takes a
  deeper look at the stability of the most difficult coronal features to
  capture in an image: polar coronal holes. Polar coronal holes are the
  longest-lived features on the Sun and are critical to understand the
  global state of the solar corona, but because of an oblique viewing
  angle, obstruction due to the coronal plasma scale height and lack of
  ground-truth magnetic-field measurements make reliable segmentation
  of polar holes difficult. We use perimeter tracing to make consistent
  measurements of a polar-hole's perimeter and area in both SWAP 174
  Å and AIA 171 Å images. The generated time series of coronal-hole
  parameters rarely agree with each other. Direct comparison of polar-hole
  measurements generated by these two imagers allows us to simultaneously
  analyze the physical properties of polar coronal holes and to identify
  systematic differences between the two different instruments.

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Title: Properties of Polar Faculae
Authors: Pesnell, William; Hovis-Afflerbach, Beryl; Wampler, Paul
2021AGUFMSH34D..03P    Altcode:
  Polar Faculae (PFe) are bright points at the edges of granules that
  illuminate where magnetic field lines intersect the solar surface
  near the Suns poles. We previously reported the average PF lifetime
  determined from the Helioseismic and Magnetic Imager (HMI) on Solar
  Dynamics Observatory (SDO) is 6.0 2.7 hours. We also showed that
  the number of PFe in Solar Cycle 24 is correlated with the strength
  of the polar magnetic field and anti-correlated with the sunspot
  number. Those correlations had been known before but, as with any
  solar activity variable, the time dependence is more complicated than
  a linear correlation. We report on our continuing analysis of HMI PF
  data, extending the time coverage of the number of PFe and measuring
  the magnetic field associated with a sample of those PFe. We will map
  the proper motion of those PF that appear to move in latitude. This
  proper motion confirms that faculae participate in convective motions
  at the poles. By measuring the presence, trajectory, and magnetic field
  strength of a large sample of faculae, we can better understand polar
  faculae and therefore the polar magnetic field and its evolution,
  as well as conditions and convective motions at the poles. These
  observations will help design space missions to observe the solar
  polar regions.

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Title: Solar Cycle 25 Spits and Sputters, but Fireworks are Predicted
Authors: Pesnell, William
2021AGUFMSH43B..01P    Altcode:
  Solar Cycle 25 has begun its rapid rise to solar maximum. The
  increase in EUV spectral irradiances will cause thermospheric
  densities to increase and create satellite drag. Ham radio operators
  look forward to improved propagation conditions. We have learned much
  about predicting solar activity in Solar Cycle 24, especially with the
  data provided by SDO, STEREO, and other missions and observatories. At
  least 54 predictions of the amplitude of activity in Solar Cycle 25
  have been published. Some of these predictions were made long before
  solar minimum while others are still appearing. As with Solar Cycle 24,
  these predictions depend heavily on statistics and precursors. The next
  step in our attempts to predict solar activity is to produce accurate
  error bars that can be used in simulations of the thermosphere over
  the years of a space mission. An updated prediction of Solar Cycle 25
  using the SODA polar field precursor method will be presented. This
  precursor has accurately predicted the last three cycles. I will also
  comment on the data needed to understand the polar regions of the Sun
  --- the seeds of the next cycle.

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Title: Using Hilbert curves to organize, sample, and sonify solar data
Authors: Pesnell, W. Dean; Ingram-Johnson, Kyle; Addison, Kevin
2021AmJPh..89..943P    Altcode:
  How many ways can we explore the Sun? We have images in many wavelengths
  and squiggly lines of many parameters that we can use to characterize
  the Sun. We know that while the Sun is blindingly bright to the naked
  eye, it also has regions that are dark in some wavelengths of light. All
  of those classifications are based on vision. Hearing is another sense
  that can be used to explore solar data. Some data, such as the sunspot
  number or the extreme ultraviolet spectral irradiance, can be readily
  sonified by converting the data values to musical pitches. Images are
  more difficult. Using a raster scan algorithm to convert a full-disk
  image of the Sun to a stream of pixel values creates variations that
  are dominated by the pattern of moving on and off the limb of the
  Sun. A sonification of such a raster scan will contain discontinuities
  at the limbs that mask the information contained in the image. As
  an alternative, Hilbert curves are continuous space-filling curves
  that map a linear variable onto the two-dimensional coordinates of an
  image. We have investigated using Hilbert curves as a way to sample and
  analyze solar images. Reading the image along a Hilbert curve keeps
  most neighborhoods close together as the resolution (i.e., the order
  of the Hilbert curve) increases. It also removes most of the detector
  size periodicities and may reveal larger-scale features. We present
  several examples of sonified solar data, including sunspot number,
  extreme ultraviolet (EUV) spectral irradiances, an EUV image, and a
  sequence of EUV images during a filament eruption.

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Title: Two new methods for counting and tracking the evolution of
    polar faculae
Authors: Hovis-Afflerbach, B.; Pesnell, W.
2021AAS...23811302H    Altcode:
  Polar Faculae are the unipolar footpoints of field lines near the sun's
  poles and are visible as bright points on the edges of granules. Their
  number has been shown to correlate with the strength of the polar
  magnetic field, and therefore better understanding polar faculae enables
  better understanding of the polar magnetic field and its evolution,
  as well as conditions and convective motions at the poles. We present
  two methods of tracking faculae. In one the standard deviation of HMI
  continuum intensity images is calculated over a day and the facular
  candidates identified by their trails. The other overlays images of
  the progressive standard deviation over the course of the day with
  individual HMI magnetograms to show the close relationship between
  the facular candidates and the magnetic field. We apply this method
  to one pole each day for a week every 6 months, beginning September
  2010. Our results confirm that faculae track regions of unipolar
  magnetic field that match the polarity of the visible pole. We observe
  the motion of the faculae and distinguish between motion due to the
  sun's rotation and "proper motion" due to faculae moving on the sun's
  surface, confirming that faculae participate in convective motions at
  the poles. This method provides a larger daily count of faculae than
  previous studies, allowing for a valid statistical determination of the
  facular lifetime. We show that the lifetime has a mode of 1-3 hours,
  with some faculae lasting up to 10 hours.

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Title: FISHA: the science case for a fast solar imager
Authors: Inglis, A.; Kirk, M.; Attie, R.; Pesnell, W.
2021AAS...23831305I    Altcode:
  The modern era of high-resolution solar EUV imaging at multiple
  wavelengths has unlocked a wealth of scientific discovery. Despite
  this, there are two fundamental issues that limit our ability to
  understand bright, rapidly evolving events on the Sun. These are 1)
  temporal cadence, and 2) image saturation. The combination of these
  two issues means that the fast dynamics on the Sun, particularly during
  eruptive events, are difficult to resolve in both time and space. This
  is problematic because models predict and observations show that
  during flares reconnection and particle acceleration processes can
  occur on < 1s timescales. These processes lead to rapidly varying
  thermal responses in chromospheric and coronal plasma. <P />We present
  the science case for the FISHA concept, a fast imager for the solar
  atmosphere. FISHA would image the Sun at high spatial resolution and
  sub-second temporal cadence, providing targeted observations of bright,
  transient features. This can be achieved while avoiding saturation
  effects using a combination of short exposure times and rapid readout
  detector capabilities. FISHA would also employ situational exposure
  and cadence control to allow observations of a wide range of solar
  phenomena. Here, we explore the potential science that FISHA could
  achieve and discuss methods of implementation.

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Title: LORRI observations of waves in Pluto's atmosphere
Authors: Jacobs, Adam D.; Summers, Michael E.; Cheng, Andrew F.;
   Gladstone, G. Randall; Lisse, Carey M.; Pesnell, W. Dean; Bertrand,
   Tanguy; Strobel, Darrell F.; Young, Leslie A.; Weaver, Harold A.;
   Kammer, Joshua; Gao, Peter
2021Icar..35613825J    Altcode:
  Observations during the New Horizons (NH) spacecraft flyby of Pluto
  in July 2015 revealed that Pluto's atmosphere supports an extensive
  circumplanetary haze with embedded layers, suggesting several possible
  microphysical and/or dynamical excitation processes. The purpose
  of this paper is to build upon existing observations and analyses of
  Pluto's atmosphere-specifically of the complex haze layer structures-to
  identify wave structure in Pluto's atmosphere. Here three NH/Long
  Range Reconnaissance Imager (LORRI) image sequences from the flyby
  at high phase angles (148°-169°) and three different resolutions
  (0.093 km/pix, 0.96 km/pix, and 3.86 km/pix) are analyzed. Several
  haze layer characteristics were extracted, namely-slope, amplitude,
  waveform, and the associated power spectral densities (PSDs); and
  their variations with local geography. These are then explored in the
  context of possible wave types in Pluto's atmosphere, such as tidal
  and orographically driven inertia-gravity (buoyancy) waves. PSD peaks
  at 8-10 km and 18-22 km vertical wavelength are found in NH images,
  which is consistent with the perturbations seen in Earth-based stellar
  occultations of Pluto's atmosphere. The 8-10 km signals are localized
  to low-latitudes and equatorial regions and the 18-22 km signals are
  more globally distributed. Haze layer background relative amplitudes
  were found to be around 0.01-0.04. Slopes of layers were found to
  be correlated with the emergence and disappearance of a 25 km layer
  around 30°N. An amplitude increase of oscillations below 30 km altitude
  exists in the high-resolution image sequence. These findings indicate
  the possibility of waves in Pluto's atmosphere and motivate further
  studies of wave dynamics combining NH data with state-of-the-art models
  of Pluto's atmosphere. These results are important because they can
  provide strong constraints to models and to the type of waves that
  can be present in Pluto's atmosphere.

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Title: A Study of Equatorial Coronal Holes and Active regions during
    the Maximum Phase of four Solar Cycles
Authors: Karna, Nishu; DeLuca, Edward; Pesnell, William; Saar, Steven;
   Karna, Mahendra
2021cosp...43E.920K    Altcode:
  The 11-year Solar Cycle (SC) is characterized by periodic changes
  in solar activity indicators such as number of sunspots, coronal
  holes, active regions (ARs), as well as the occurrence rate of solar
  energetic events such as filament eruptions, flares and coronal mass
  ejections (CMEs). In this work we performed a statistical study of the
  equatorial coronal holes (ECHs) and ARs during the maximum phase of the
  last four solar cycles: SC 21 (1979--1982), SC 22 (1989--1992), SC 23
  (1999--2002) and SC 24 (2012--2015). We compared the number of ECHs and
  ARs, separations between their centroids, solar wind speed, pressure
  and the number of intense geomagnetic storms (IGS) data over these four
  cycles. We note a strong anticorrelation between the number of ARs and
  ECHs. We found that the number of close ARs and ECHs, solar wind speed,
  and the number of IGS increases with average sunspot maximum number
  for even cycles and decreases with average sunspot maximum for odd
  cycles. These odd-even trends largely (though not entirely) disappear
  in the relation between the wind properties and the numbers of close
  AR and ECH. This suggests a possible link between ECH-AR interactions
  and the solar wind phenomena, though residual odd-even trends point to
  the importance of other effects (e.g., Sun-earth magnetic alignment)
  as well.

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Title: SunCET: The Sun Coronal Ejection Tracker Concept
Authors: Mason, James Paul; Chamberlin, Phillip C.; Seaton, Daniel;
   Burkepile, Joan; Colaninno, Robin; Dissauer, Karin; Eparvier, Francis
   G.; Fan, Yuhong; Gibson, Sarah; Jones, Andrew R.; Kay, Christina; Kirk,
   Michael; Kohnert, Richard; Pesnell, W. Dean; Thompson, Barbara J.;
   Veronig, Astrid M.; West, Matthew J.; Windt, David; Woods, Thomas N.
2021JSWSC..11...20M    Altcode: 2021arXiv210109215M
  The Sun Coronal Ejection Tracker (SunCET) is an extreme ultraviolet
  imager and spectrograph instrument concept for tracking coronal mass
  ejections through the region where they experience the majority
  of their acceleration: the difficult-to-observe middle corona. It
  contains a wide field of view (0-4 R<SUB>⊙</SUB>) imager and a 1 Å
  spectral-resolution-irradiance spectrograph spanning 170-340 Å. It
  leverages new detector technology to read out different areas of the
  detector with different integration times, resulting in what we call
  "simultaneous high dynamic range", as opposed to the traditional high
  dynamic range camera technique of subsequent full-frame images that
  are then combined in post-processing. This allows us to image the
  bright solar disk with short integration time, the middle corona
  with a long integration time, and the spectra with their own,
  independent integration time. Thus, SunCET does not require the use
  of an opaque or filtered occulter. SunCET is also compact - ~15 × 15
  × 10 cm in volume - making it an ideal instrument for a CubeSat or a
  small, complementary addition to a larger mission. Indeed, SunCET is
  presently in a NASA-funded, competitive Phase A as a CubeSat and has
  also been proposed to NASA as an instrument onboard a 184 kg Mission
  of Opportunity.

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Title: Predicting Solar Cycle 25 with an Ap/F10.7 Geomagnetic
    Precursor Pair
Authors: Pesnell, W. D.
2020AGUFMSH053..08P    Altcode:
  Long-term predictions of solar activity indices are used in orbital
  prediction and mission planning. We describe using an Ap/F10.7
  geomagnetic precursor pair to predict the amplitude of the just-started
  Solar Cycle 25. The method is an evolution of an earlier algorithm that
  now removes the baseline solar activity cycle-by-cycle. A recurrence
  index is used to determine the timing of the precursor peak used in
  the prediction. Unlike previous times, when the recurrence index showed
  well-defined peaks during the decline from solar maxima, the recurrence
  index in the decline of Solar Cycle 24 increases rapidly after solar
  maximum in 2014 and remains at a large value until 2020. The effect of
  this on the timing of the precursor value will be examined. We conclude
  that Solar Cycle 25 will be no stronger than average and could be much
  weaker than average.

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Title: Lessons learned from predictions of Solar Cycle 24
Authors: Pesnell, W. Dean
2020JSWSC..10...60P    Altcode:
  Solar Cycle 24 has almost faded and the activity of Solar Cycle 25 is
  appearing. We have learned much about predicting solar activity in Solar
  Cycle 24, especially with the data provided by SDO and STEREO. Many
  advances have come in the short-term predictions of solar flares and
  coronal mass ejections, which have benefited from applying machine
  learning techniques to the new data. The arrival times of coronal mass
  ejections is a mid-range prediction whose accuracy has been improving,
  mostly due to a steady flow of data from SoHO, STEREO, and SDO. Longer
  term (greater than a year) predictions of solar activity have benefited
  from helioseismic studies of the plasma flows in the Sun. While these
  studies have complicated the dynamo models by introducing more complex
  internal flow patterns, the models should become more robust with the
  added information. But predictions made long before a sunspot cycle
  begins still rely on precursors. The success of some categories of
  the predictions of Solar Cycle 24 will be examined. The predictions
  in successful categories should be emphasized in future work. The SODA
  polar field precursor method, which has accurately predicted the last
  three cycles, is shown for Solar Cycle 25. Shape functions for the
  sunspot number and F10.7 are presented. What type of data is needed
  to better understand the polar regions of the Sun, the source of the
  most accurate precursor of long-term solar activity, will be discussed.

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Title: A Study of Equatorial Coronal Holes during the Maximum Phase
    of Four Solar Cycles
Authors: Karna, Mahendra Lal; Karna, Nishu; Saar, Steven H.; Pesnell,
   W. Dean; DeLuca, Edward E.
2020ApJ...901..124K    Altcode:
  The 11 yr solar cycle (SC) is characterized by periodic changes in
  solar activity indicators such as the number of sunspots, coronal
  holes, and active regions (ARs), as well as the occurrence rate of
  solar energetic events such as filament eruptions, flares, and coronal
  mass ejections. In this work we performed a statistical study of the
  equatorial coronal holes (ECHs) and ARs during the maximum phase
  of the last four SCs: SC 21 (1979-1982), SC 22 (1989-1992), SC 23
  (1999-2002), and SC 24 (2012-2015). We compared the number of ECHs and
  ARs, separations between their centroids, solar wind speed, pressure,
  and the number of intense geomagnetic storm (IGS) data over these four
  cycles. We note a strong anticorrelation between the number of ARs and
  ECHs. We found that the number of close ARs and ECHs, solar wind speed,
  and the number of IGS increases with average sunspot maximum number
  for even cycles and decreases with average sunspot maximum for odd
  cycles. Also, we find strong odd-even trends in the relation between
  the wind properties and the numbers of close AR and ECH. These results
  obtained from the annual average data suggest a possible link between
  ECH and AR proximity and the solar wind phenomena, though odd-even
  trends point to the importance of other effects (e.g., Sun-Earth
  magnetic alignment) as well.

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Title: A Study of Equatorial Coronal Holes during the Maximum Phase
    of four Solar Cycles
Authors: Karna, N.; Karna, M.; Saar, S.; Pesnell, W.; DeLuca, E.
2020SPD....5120903K    Altcode:
  The 11-year Solar Cycle (SC) is characterized by periodic changes
  in solar activity indicators such as a number of sunspots, coronal
  holes, active regions (ARs), as well as the occurrence rate of solar
  energetic events such as filament eruptions, flares and coronal mass
  ejections (CMEs). In this work we performed a statistical study of
  the equatorial coronal holes (ECHs) and ARs during the maximum phase
  of the last four solar cycles: SC 21 (1979-1982), SC 22 (1989-1992),
  SC 23 (1999-2002) and SC 24 (2012-2015). We compared the number of
  ECHs and ARs, separations between their centroids, solar wind speed,
  pressure and the number of intense geomagnetic storms (IGS) data
  over these four cycles. We note a strong anticorrelation between the
  number of ARs and ECHs. We found that the number of close ARs and ECHs
  (which are potentially interacting), solar wind speed, and the number
  of IGS increases with average sunspot maximum number for even cycles
  and decreases with average sunspot maximum for odd cycles. Also,
  we find strong odd-even trends in the relation between the wind
  properties and the numbers of close AR and ECH. These results suggest a
  possible link between ECH-AR interactions and the solar wind phenomena,
  though odd-even trends point to the importance of other effects (e.g.,
  Sun-earth magnetic alignment) as well.

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Title: Using Ephemeral Coronal Holes to Validate the SPOCA Database
    of Coronal Holes
Authors: Pesnell, W. D.; Pant, N.; Kirk, M. S.; Inglis, A. R.
2019AGUFMSH11D3385P    Altcode:
  Given the relatively few examples of ephemeral coronal holes found
  by direct examination of data from the Solar Dynamics Observatory
  (SDO), we looked to the Spatial Possibilistic Clustering Algorithm
  (SPOCA) feature-finding algorithm to identify more examples. The
  SPOCA results are stored at the Heliophysics Event Knowledgebase
  (HEK), which was interrogated for this research. Unlike the direct
  examination, SPOCA identifies many small candidates for ephemeral
  coronal holes. We will report several causes for this difference,
  such as many candidates near the limb. Several filaments are also
  included as coronal holes. A dipole moment algorithm was developed
  to automatically eliminate these candidates from consideration. The
  magnetic configuration around a polarity inversion line underlying a
  filament has a more organized appearance than does the random field
  line placement within a coronal hole. The algorithm will be described,
  test cases presented, and solar examples will be presented.

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Title: Probing the solar corona with Sun-grazing comets: comparing
    MHDsimulations with EUV observations
Authors: Jia, Y. D.; Pesnell, W. D.; Liu, W.; Downs, C.; Bryans, P.
2019AGUFMSH13A..03J    Altcode:
  Sun -grazing comets can dive within one solar radii of the Sun
  's surface. The cometary materials expand along the comet's orbit,
  and undergo various stages of fierce thermal-chemical reactions on
  the scales of seconds to minutes. These reactions ionize cometary
  ions through successive charge states , which is revealed by certain
  emission lines in the AIA images. Such plasma reaction processes are
  significantly affected by the transient structures in the corona, and
  thus these structures are revealed by the structures and shapes of the
  comet tail. We combine three numerical models: a global corona model,
  particle transportation model, and cometary plasma interaction model
  into one framework to simulate the interaction of Sun -grazing comets
  in the low corona. In our framework, cometary ejecta are vaporized
  and then ionized via multiple channels, and then confined by the
  coronal magnetic field. Constrained by imaging observations of the
  and cometary interaction images, we apply our framework to trace back
  to the local condition of the ambient corona, and its spatiotemporal
  variation. Previously, our model confirmed the importance of the
  ambient magnetic field vector in shaping the tail. In this study,
  we use the C/2011 W3 (Lovejoy) perihelion to determine the local
  plasma and field conditions in the corona. Our framework is capable of
  resolving structures from thousands of meters to tens of million meters,
  so we can identify the fine spatial variations in plasma density and
  magnetic field intensity, which may be visible in future/on-going
  close-up coronal observations.

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Title: Tracking supergranulation near the poles with SDO/HMI
Authors: Attié, R.; Kirk, M. S.; Tremblay, B.; Muglach, K.; Hess
   Webber, S. A.; Pesnell, W. D.; Thompson, B. J.
2019AGUFMSH13B..01A    Altcode:
  Due to the spherical curvature of the Sun, solar observers suffer
  from an increasing loss of resolution as we move away from the solar
  equator. Thus knowledge of the photospheric flows near the poles
  has eluded the scope of traditional flow tracking algorithms that
  are using granules as tracers of the underlying flows. Using the new
  "Balltracking" framework which we adapted to the observations from
  SDO/HMI, we present an unprecedented analysis of the horizontal flow
  fields at latitudes beyond +/- 60 degrees. The flow fields are derived
  every 4 hours at a spatial resolution of 4 Mm. Using flow segmentation
  techniques, we extract geometric and spectral information on the
  supergranular cells and compare them with those of the supergranulation
  at lower latitude. The correlation with the dynamics of moving magnetic
  features is also investigated.

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Title: A Study of Equatorial Coronal Holes during the Maximum Phase
    of Four Solar Cycles
Authors: Karna, N.; Karna, M. L.; Saar, S. H.; Pesnell, W. D.;
   DeLuca, E.
2019AGUFMSH44A..03K    Altcode:
  The 11-year Solar Cycle (SC) is characterized by periodic changes
  in the solar activity such as sunspot numbers, coronal holes, active
  regions, eruptions such as prominence eruptions, flares and coronal
  mass ejections. In this work we performed a statistical study of the
  equatorial coronal holes and the active regions during the maximum
  phases of four solar cycles (SC 21 (1979, 1980, 1981 and 1982), SC 22
  (1989, 1990, 1991 and 1992), SC 23 (1999, 2000, 2001 and 2002) and SC 24
  (2012, 2013, 2014 and 2015)). We compared equatorial coronal hole and
  active region numbers, separations between equatorial coronal holes and
  active regions centroids, solar wind speed and the number of intense
  geomagnetic storms data over these four cycles. We found that the
  distance between equatorial coronal holes and active regions, the solar
  wind speed, and the the number of intense geomagnetic storms increases
  with average sunspot maximum number for even cycles and decreases
  with average sunspot maximum for odd cycles. We also noticed that the
  solar wind speeds, pressures, and the number of intense geomagnetic
  storms increase with the numbers of close equatorial coronal holes and
  active regions, suggesting a possible link between equatorial coronal
  holes--active regions interactions and the wind phenomena.

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Title: Comparing Polar Coronal Hole Size to Polar Magnetic Flux
Authors: Kirk, M. S.; Pesnell, W. D.; Arge, C. N.
2019AGUFMSH41B..02K    Altcode:
  Polar magnetic fields are a critical piece to understand the global
  state of the solar corona. However, measuring the solar polar magnetic
  fields are notoriously difficult because of the oblique viewing
  angle. Polar coronal holes are the longest-lived features on the
  sun and represent areas of open magnetic flux. We make comprehensive
  measurements of polar hole's perimeter and area in three EUV wavelengths
  between 1996 and 2018 using five different space-based imagers: SOHO
  EIT, STEREO A and B EUVI, PROBA2 SWAP, and SDO AIA. The generated
  time-series of coronal hole boundaries rarely agree with each other,
  which presents a difficult data problem: multi-band, multi-instrument,
  heteroscedastic measurements with periodic and systematic signals. We
  combine these measurements using a parametric bootstrap method to
  make an empirical estimation of the polar coronal hole's size and
  boundary. This technique allows us to accurately characterize the
  evolving area and boundary of the polar holes. From this timeseries
  of polar hole area, we infer the evolving polar field flux over the
  past 22 years.

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Title: A Time-Distance Helioseismology Method for Quasi-Linear
    Geometries
Authors: Hess Webber, Shea A.; Pesnell, W. Dean
2019SoPh..294..151H    Altcode:
  Helioseismology is the study of the solar interior, through which
  we extract flow and wave-speed information from Doppler velocity
  observations at the surface. Local helioseismology involves the study
  of small regions on the solar disk and is used to create a detailed
  picture of the interior in that particular region. Perturbations
  in the flow and wave-speed results indicate, e.g. magnetic-flux
  or temperature variations. There are multiple methods used in
  local-helioseismic research, but all current local-helioseismic
  techniques assume a point-source perturbation. For this study, we
  develop a new time-distance (TD) helioseismic methodology that can
  exploit the quasi-linear geometry of an elongated feature, allowing
  us to i) improve the signal-to-noise ratio of the TD results, and ii)
  greatly decrease the number of calculations required and therefore the
  computing time of the TD analysis. Ultimately, the new method will allow
  us to investigate solar features with magnetic-field configurations
  previously unexplored. We validate our new technique using a simple f
  -mode wave simulation, comparing results of point-source and linear
  perturbations. Results indicate that local-helioseismic analysis is
  dependent on the geometry of the system and can be improved by taking
  the magnetic-field configuration into account.

---------------------------------------------------------
Title: Characteristics of Ephemeral Coronal Holes
Authors: Inglis, A. R.; O'Connor, R. E.; Pesnell, W. D.; Kirk, M. S.;
   Karna, N.
2019ApJ...880...98I    Altcode: 2019arXiv190601757I
  Small-scale ephemeral coronal holes may be a recurring feature on the
  solar disk but have received comparatively little attention. These
  events are characterized by compact structures and short total
  lifetimes, which are substantially less than a solar disk crossing. We
  present a systematic search for these events, using Atmospheric Imaging
  Assembly extreme ultraviolet image data from the Solar Dynamics
  Observatory, covering the time period of 2010-2015. Following
  strict criteria, this search yielded four clear examples of the
  ephemeral coronal hole phenomenon. The properties of each event are
  characterized, including their total lifetime, growth and decay rates,
  and areas. The magnetic properties of these events are also determined
  using Helioseismic and Magnetic Imager data. Based on these four
  events, ephemeral coronal holes experience rapid initial growth of
  up to ∼3000 Mm<SUP>2</SUP> hr<SUP>-1</SUP>, while the decay phases
  are typically more gradual. Like conventional coronal holes, the mean
  magnetic field in each ephemeral coronal hole displays a consistent
  polarity, with mean magnetic flux densities generally &lt;10 G. No
  evidence of a corresponding signature is seen in solar wind data at
  1 au. Further study is needed to determine whether ephemeral coronal
  holes are underreported events or are truly rare phenomena.

---------------------------------------------------------
Title: Orbits through polytropes
Authors: Gjerløv, Amalia; Pesnell, W. Dean
2019AmJPh..87..452G    Altcode:
  We describe how orbital tunnels could be used to transport payloads
  through the Earth. If you use a brachistochrone for the tunnel, the
  body forces in the tunnel become overwhelmingly large for small angular
  distances traveled. Projectiles move along an orbital tunnel faster
  than they would along a brachistochrone connecting the same points but
  the body force components cancel. We describe how parabolic Keplerian
  orbits outside the object merge onto quasi-Keplerian orbits inside
  the object. We use models of the interior of the Earth with three
  values of the polytropic index (n) to calculate interior orbits that
  travel between surface points. The n = 3 results are also scaled to
  the Sun. Numerical integrations of the equations describing polytropes
  were used to generate the initial models. Numerical integration of the
  equations of motion are then used to calculate the angular distance you
  can travel along the surface and the traversal time as a function of
  the parabolic periapsis distance for each model. Trajectories through
  objects of low central condensation show a focussing effect that
  decreases as the central condensation increases. Analytic solutions
  for the trajectories in a homogeneous sphere are derived and compared
  to the numeric results. The results can be scaled to other planets,
  stars, or even globular clusters.

---------------------------------------------------------
Title: Characteristics of ephemeral coronal holes
Authors: Inglis, Andrew; O'Connor, Rachel; Pesnell, W. Dean; Kirk,
   Michael S.; Karna, Nishu
2019AAS...23410605I    Altcode:
  Small-scale ephemeral coronal holes may be a recurring feature on the
  solar disk, but have received comparatively little attention. These
  events are characterized by compact structure and short total lifetimes,
  substantially less than a solar disk crossing. Following a search of the
  time period 2010 - 2015 using Atmospheric Imaging Assembly EUV image
  data from the Solar Dynamics Observatory, we present analysis of four
  of the clearest examples of the ephemeral coronal hole phenomenon. The
  properties of each event are characterized, including their total
  lifetime, growth and decay rates, and areas. The magnetic properties
  of these events are also determined using Heliospheric Magnetic Imager
  data. These ephemeral coronal holes possess common characteristics,
  experiencing rapid initial growth of up to 3000 Mm<SUP>2</SUP> / hr,
  while the decay phases are typically more gradual. Like conventional
  coronal holes, the mean magnetic field in each ephemeral coronal
  hole displays a consistent polarity, with mean fields generally &lt;
  10 G. No evidence of a corresponding signature is seen in solar wind
  data at 1AU. Further study is needed to determine whether ephemeral
  coronal holes are under-reported events or a truly rare phenomenon.

---------------------------------------------------------
Title: A Comprehensive Assessment of EUV Polar Coronal Holes: 1996
    - 2018
Authors: Kirk, Michael S.; Pesnell, W. Dean; Arge, Charles
2019AAS...23412501K    Altcode:
  Polar Coronal Holes are the longest-lived features on the sun and
  are a critical piece to understand the global state of the solar
  corona. Because of the oblique viewing angle, obstruction due to
  the coronal plasma scale height, and lack of ground truth make
  segmentation of polar holes difficult. We make new measurements of
  polar hole's perimeter and area in three EUV wavelengths between 1996
  and 2018 using five different space-based imagers: SOHO EIT, STEREO
  A and B EUVI, PROBA2 SWAP, and SDO AIA. The generated time-series of
  coronal hole parameters rarely agree with each other, which presents a
  difficult data problem: multi-band, multi-instrument, heteroscedastic
  measurements with periodic and systematic signals. We combine these
  measurements using a parametric bootstrap method to make an empirical
  estimation of the polar coronal hole's size, boundary, and center of
  mass. This technique allows us to simultaneously analyze the physical
  properties of polar coronal holes and identify regular periodicities
  in our data from other origins. We present a comprehensive view of
  the EUV polar coronal hole over the past 22 years.

---------------------------------------------------------
Title: Listening to the Sun
Authors: Pesnell, W. Dean; Ingram-Johnson, Kyle
2019AAS...23410703P    Altcode:
  How many ways can we explore the Sun? We have images in many wavelengths
  and squiggly lines of many parameters that we can use to characterize
  the Sun. We learn that the Sun is bright with regions that are dark
  in some wavelengths and bright in others. But those classifications
  are both based on vision. Sound is another sense to use in exploring
  solar data. Some data, such as the sunspot number or the extreme
  ultraviolet spectral irradiance, can be easily sonified. Images are
  more difficult. A simple raster scan is dominated by moving on and off
  the limb of the Sun. Any sonification of the raster scan will contain
  discontinuities at the limbs that mask the information contained in the
  image. We propose to sample the curves with Hilbert curves to reduce
  those discontinuities. Hilbert curves are continuous space-filling
  curves that map the two-dimensional coordinates of an image onto a
  linear variable. We have investigated using Hilbert curves as ways to
  sample and analyze solar images. Reading the image along a Hilbert curve
  keeps neighborhoods close together as the resolution (i.e., the length
  of the Hilbert curve) increases. It also removes most of the detector
  size periodicities and actually shows the presence of longer-scale
  features. We shall provide several examples of sonified solar data,
  including the sunspot number, a selection of EUV spectral irradiances,
  an AIA 171 image, and a series of images during a solar flare.

---------------------------------------------------------
Title: Fractal Dimensions of Solar and Geomagnetic Indices
Authors: Pesnell, W. Dean
2019AAS...23411801P    Altcode:
  Correlations between solar and geomagnetic indices are often used
  in space weather research. How sensitive are these correlations
  to pre-whitening of the data and auto-correlation within the data
  sets? Statistical and timeseries analyses of the sunspot number are
  often used to predict solar activity. These methods have not been
  completely successful as the solar dynamo changes over time and one
  cycle's sunspots are not a faithful predictor of the next cycle's
  activity. Can more accurate predictions be produced by partitioning
  the data into periods when it obeys certain statistical properties? The
  Hurst exponent and the related fractal dimension are two such ways to
  partition the data. We can use these measures of complexity to compare
  the sunspot number with other solar and geomagnetic indices. We use
  five algorithms to calculate the Hurst exponent or fractal dimension
  and examine what happens when the mean and a linear trend trends
  are removed. We find that some algorithms are robust and return
  similar or identical values for the original, mean-removed, and
  linear-trend-subtracted data. The behavior of the Fourier transform
  at low frequencies is the most sensitive to the type of pre-whitening
  applied to the data. The rescaled-range algorithm is robust but needs
  to be corrected for autocorrelation in the data.

---------------------------------------------------------
Title: Characteristics of Ephemeral Coronal Holes
Authors: O'Connor, Rachel E.; Inglis, Andrew R.; Pesnell, W. Dean;
   Kirk, Michael S.; Karna, Nishu
2019shin.confE.202O    Altcode:
  Small-scale ephemeral coronal holes may be a recurring feature on the
  solar disk, but have received comparatively little attention. These
  events are characterized by compact structure and short total lifetimes,
  substantially less than a solar disk crossing. We present a systematic
  search for these events, using Atmospheric Imaging Assembly EUV
  image data from the Solar Dynamics Observatory, covering the time
  period 2010 - 2015. Following strict criteria, this search yielded
  four clear examples of the ephemeral coronal hole phenomenon. The
  properties of each event are characterized, including their total
  lifetime, growth and decay rates, and areas. The magnetic properties
  of these events are also determined using Helioseismic and Magnetic
  Imager data. Based on these four events, ephemeral coronal holes
  experience rapid initial growth of up to 3000 Mm2/hr, while the decay
  phases are typically more gradual. Like conventional coronal holes,
  the mean magnetic field in each ephemeral coronal hole displays a
  consistent polarity, with mean magnetic flux densities generally &lt;
  10 G. No evidence of a corresponding signature is seen in solar wind
  data at 1 AU. Further study is needed to determine whether ephemeral
  coronal holes are under-reported events or a truly rare phenomenon.

---------------------------------------------------------
Title: Quantifying the Variability of Coronal Hole Boundaries
Authors: Kirk, Michael S.; Pesnell, W. Dean; Arge, C. Nick
2019shin.confE..69K    Altcode:
  Polar Coronal Holes are the longest-lived features on the sun and
  are a critical piece to understand the global state of the solar
  corona. Because of the oblique viewing angle, obstruction due to the
  coronal plasma scale height, and lack of ground truth make segmentation
  of polar holes difficult. We make comprehensive measurements of polar
  hole’s perimeter and area in three EUV wavelengths between 1996
  and 2018 using five different space-based imagers: SOHO EIT, STEREO
  A and B EUVI, PROBA2 SWAP, and SDO AIA. The generated time-series of
  coronal hole boundaries rarely agree with each other, which presents a
  difficult data problem: multi-band, multi-instrument, heteroscedastic
  measurements with periodic and systematic signals. We combine these
  measurements using a parametric bootstrap method to make an empirical
  estimation of the polar coronal hole’s size, boundary, and center of
  mass. This technique allows us to accurately characterize the evolving
  boundary of the polar holes and identify the EUV band passes that best
  capture these structures.

---------------------------------------------------------
Title: Simulations of Observed Haze Layer Structure in Pluto's
    Atmosphere
Authors: Jacobs, A. D.; Summers, M. E.; Gladstone, R.; Cheng, A. F.;
   Strobel, D. F.; Lisse, C. M.; Gao, P.; Young, L. A.; Pesnell, W. D.;
   Kammer, J.; Weaver, H. A., Jr.
2018AGUFM.P51F2949J    Altcode:
  Observations during the New Horizons spacecraft flyby of Pluto in
  July 2015 revealed that Pluto's atmosphere has an extensive haze with
  embedded layers, suggesting several possible microphysical and/or
  dynamical processes operating in the atmosphere. Orographically driven
  gravity (buoyancy) waves are the main layering mechanism explored in
  this study. A single scattering model was implemented to simulate three
  LORRI image sequences at high phase angles (148˚-169<SUP>°</SUP>) and
  three different resolutions (0.093 km/pix: HIPHASE_HIRES, 0.96 km/pix:
  P_MULTI, and 3.5 km/pix: FULLFRAME). All scattering calculations were
  done for the LORRI pivot wavelength of 607.6 nm. A 2D gravity wave
  (GW) perturbation field created from an orographically-driven GW model
  was used to generate north/south and east/west oriented 3D layered
  structures. The two sets of GW perturbations were then applied to
  two types of background haze densities. Haze layer I/F simulations
  were further explored by applying LORRI's PSF to the simulated
  images. Some discrepancies between model results and observations
  still exist, including: (1) larger tilt/slope of modelled layers
  for both GW orientations than observed in the P_MULTI sequence, (2)
  smaller layer wavelength and larger layer distinctness/amplitude than
  observed at altitudes below 40 km in the HIPHASE_HIRES sequence,
  and (3) missing larger scale structure observed in the P_MULTI
  and FULLFRAME sequences where haze layering is geographically most
  distinct. These discrepancies may be accounted for by: (1) adjustments
  to the GW model wind speed over terrain and/or changing the assumed
  terrain/aspect ratio (i.e., by decreasing the assumed wind-aligned
  wavenumber), (2) the inclusion of mixing processes or consideration of
  faster layer dissipation processes for low altitude layers, and (3)
  the superposition of different wave types (i.e., Rossby waves) with
  orographically generated waves. Limitations on possible adjustments
  to the GW model perturbations intrinsic tilt/slope that still allow
  vertical propagation through Pluto's strong temperature inversion,
  as well as power spectra extracted from LORRI images, are evidence
  for the presence of other wave types that could cause haze layering
  through generation mechanisms not considered by the orographic gravity
  wave model.

---------------------------------------------------------
Title: Multi-wavelength Observations of Flare-Induced Acoustic Waves
    Around Active Regions with SDO AIA
Authors: Monsue, Teresa; Pesnell, W. Dean; Hill, Frank; Kirk, Michael
2018csc..confE.111M    Altcode:
  Active regions on the Sun are abundant with a variety of waves that are
  both acoustically helioseismic and magnetohydrodynamic in nature. The
  occurrence of a solar flare can disrupt these waves, through MHD
  mode-mixing or scattering by the excitation of these waves. We take
  a multi-wavelength observational approach to understand the source
  of these waves by studying active regions where flaring activity
  occurs. Utilizing a Fast Fourier Transform (FFT) algorithm, our approach
  is to search for signals within a time series of images by producing
  multi-frequency power map movies and spatially sampling the time
  series by radial sectors with constant area that minimizes the spatial
  variation of the acoustic power. With this application we are able to
  study the active region both spatially and temporally and correlate
  data over multiple wavelengths, allowing us to observe the behavior
  of the waves at different heights within the Solar atmosphere. We
  apply multi-wavelength measurements utilizing NASA's SDO AIA 1700
  (lower photosphere), 1600 (upper photosphere) and 304 (chromosphere)
  passbands. When we run power map movies of the chromosphere we are able
  to see a subtle propagating feature moving outward from the center of
  the flare; this could be an MHD-wave propagating outward by the flaring
  event. With our sector sampling method we observe power variation
  around the flaring active region. This power variation corresponds to
  the flare induced enhancement of the oscillations around the active
  region. Furthermore, there seems to be absorptive properties observed
  within the chromospheric line of the AIA 304 Å passband.

---------------------------------------------------------
Title: The Solar Dynamics Observatory, Eight Years of Science
Authors: Pesnell, W. Dean
2018csc..confE.110P    Altcode:
  The Solar Dynamics Observatory has been producing science and science
  data since May 2010. I will describe some highlights of SDO results,
  including filament eruptions, flares, and comets. The status of the
  observatory hardware will also be discussed. The future of SDO will be
  a series of extended missions, each lasting three years. Our second
  extended mission started October 1, 2017. That gives us another year
  to study the data before writing another proposal!

---------------------------------------------------------
Title: Roadmap for Reliable Ensemble Forecasting of the Sun-Earth
    System
Authors: Nita, Gelu; Angryk, Rafal; Aydin, Berkay; Banda, Juan;
   Bastian, Tim; Berger, Tom; Bindi, Veronica; Boucheron, Laura; Cao,
   Wenda; Christian, Eric; de Nolfo, Georgia; DeLuca, Edward; DeRosa,
   Marc; Downs, Cooper; Fleishman, Gregory; Fuentes, Olac; Gary, Dale;
   Hill, Frank; Hoeksema, Todd; Hu, Qiang; Ilie, Raluca; Ireland,
   Jack; Kamalabadi, Farzad; Korreck, Kelly; Kosovichev, Alexander;
   Lin, Jessica; Lugaz, Noe; Mannucci, Anthony; Mansour, Nagi; Martens,
   Petrus; Mays, Leila; McAteer, James; McIntosh, Scott W.; Oria, Vincent;
   Pan, David; Panesi, Marco; Pesnell, W. Dean; Pevtsov, Alexei; Pillet,
   Valentin; Rachmeler, Laurel; Ridley, Aaron; Scherliess, Ludger; Toth,
   Gabor; Velli, Marco; White, Stephen; Zhang, Jie; Zou, Shasha
2018arXiv181008728N    Altcode:
  The authors of this report met on 28-30 March 2018 at the New Jersey
  Institute of Technology, Newark, New Jersey, for a 3-day workshop
  that brought together a group of data providers, expert modelers, and
  computer and data scientists, in the solar discipline. Their objective
  was to identify challenges in the path towards building an effective
  framework to achieve transformative advances in the understanding
  and forecasting of the Sun-Earth system from the upper convection
  zone of the Sun to the Earth's magnetosphere. The workshop aimed to
  develop a research roadmap that targets the scientific challenge
  of coupling observations and modeling with emerging data-science
  research to extract knowledge from the large volumes of data (observed
  and simulated) while stimulating computer science with new research
  applications. The desire among the attendees was to promote future
  trans-disciplinary collaborations and identify areas of convergence
  across disciplines. The workshop combined a set of plenary sessions
  featuring invited introductory talks and workshop progress reports,
  interleaved with a set of breakout sessions focused on specific topics
  of interest. Each breakout group generated short documents, listing
  the challenges identified during their discussions in addition to
  possible ways of attacking them collectively. These documents were
  combined into this report-wherein a list of prioritized activities
  have been collated, shared and endorsed.

---------------------------------------------------------
Title: An Early Prediction of the Amplitude of Solar Cycle 25
Authors: Pesnell, W. Dean; Schatten, Kenneth H.
2018SoPh..293..112P    Altcode:
  A "Solar Dynamo" (SODA) Index prediction of the amplitude of Solar
  Cycle 25 is described. The SODA Index combines values of the solar
  polar magnetic field and the solar spectral irradiance at 10.7 cm
  to create a precursor of future solar activity. The result is an
  envelope of solar activity that minimizes the 11-year period of the
  sunspot cycle. We show that the variation in time of the SODA Index is
  similar to several wavelet transforms of the solar spectral irradiance
  at 10.7 cm. Polar field predictions for Solar Cycles 21 - 24 are used
  to show the success of the polar field precursor in previous sunspot
  cycles. Using the present value of the SODA index, we estimate that the
  next cycle's smoothed peak activity will be about 140 ±30 solar flux
  units for the 10.7 cm radio flux and a Version 2 sunspot number of 135
  ±25 . This suggests that Solar Cycle 25 will be comparable to Solar
  Cycle 24. The estimated peak is expected to occur near 2025.2 ±1.5
  year. Because the current approach uses data prior to solar minimum,
  these estimates may improve as the upcoming solar minimum draws closer.

---------------------------------------------------------
Title: Interaction between cool material from Sun-grazing comets
    and the low corona
Authors: Jia, Yingdong; Pesnell, William; Liu, Wei; Downs, Cooper;
   Bryans, Paul
2018cosp...42E1613J    Altcode:
  Sun-grazing comets dive into altitudes lower than 1 solar radius from
  the chromosphere. Cool materials of temperature lower than 10 ^{3}K
  explode from the comet into the 10 ^{6} K corona. These materials
  undergone various stages of rapid chemical reactions in scales of
  seconds to minutes. Such reactions Structures in such images of
  various wavelengths indicate strong variation in ambient conditions
  of the corona. We combine three numerical models: low corona model,
  particle transportation model, and cometary plasma interaction model
  into one framework to model the interaction of Sun-grazing comets in the
  low corona. In our framework, cometary vapor are ionized via multiple
  channels, and then detained by the coronal magnetic field. In seconds,
  these ions are further ionized into their highest charge state, which
  is revealed by certain emission lines. Constrained by coronal graphs
  and cometary interaction images, we apply our framework to trace back
  to the local condition of the ambient corona, and its spatial/time
  variation. Our frame work is able to resolve structures of sub-million
  meters to tens of million meters. Once trained by multiple stages of
  the comet's journey in the low corona, this framework can identify the
  fine spatial variations in plasma density and magnetic field intensity,
  which may be visible to future close-up observations.

---------------------------------------------------------
Title: Predicting the Sun: Black Swans or Dragon Kings?
Authors: Pesnell, William Dean
2018tess.conf22405P    Altcode:
  Our goal of predicting the Sun spans timescales from seconds to
  centuries and phenomena from flares to convective flows. We are
  faced with questions of what extremes to expect when predicting
  each phenomenon. Some extremes are obvious: What is the brightest
  flare, largest active region or fastest coronal mass ejection we
  can expect? Others are less so: What is the largest magnetic field
  strength? Or how often should we expect a Grand Minimum, an era of low
  to absent solar activity, and what happens to the irradiance of the
  Sun during that era? Most phenomena have a robust set of observations
  covering a wide range of possibilities that allows statistical methods
  to be used. Every so often, an exceptional event is seen, such as
  the X45 flare of November 2002 or the geomagnetic storm following
  the Carrington Event in September 1859, that sits outside of those
  statistics. Longer term examples include predicting sunspot cycles of
  unusually large or small amplitude. I will describe Black Swans and
  Dragon Kings and how they can be used to understand the predictions
  of extreme events in solar physics.

---------------------------------------------------------
Title: The Recalibrated Sunspot Number: What It Is and How Will It
    be Updated?
Authors: Clette, Frederic; Pesnell, William Dean; Lefevre, Laure
2018tess.conf30288C    Altcode:
  Recently, and for the first time since their creation, the definition
  of the sunspot number and group number series were revisited. A fully
  recalibrated version was officially released in July 2015 by the World
  Data Center SILSO (Brussels). Those long-term reference series are
  widely used as input data or as a calibration reference by many research
  projects in solar physics and space weather. To clarify the nature of
  the applied changes, we describe the different corrections applied to
  the sunspot and group number series, which affect extended time periods
  and can reach up to 40%. While some changes simply involve constant
  scale factors, other corrections vary with time or are modulated by
  the solar cycle. Depending on the research project and the selected
  time interval, this can lead to different responses and biases. For
  example, predictions of solar activity based on the sunspot number
  should be redone using the new sunspot series, and methods already
  used for predicting Solar Cycle 24 will require adaptations before
  attempting predictions of the next cycles. In addition, the revised
  sunspot series includes standard error estimates, which may help
  in deriving more accurate uncertainties for predicted activity
  indices. We conclude with the new round of recalibration that is
  now undertaken in the framework of a broad multi-team collaboration
  articulated around upcoming ISSI workshops. We outline the future
  corrections that can still be expected in the future, as part of a
  permanent upgrading process and quality control. From now on, future
  sunspot-based predictive models should thus be made more adaptable,
  and regular updates of such models should become common practice in
  order to track periodic upgrades of the sunspot number series, just
  like it is done when using other modern solar observational series.

---------------------------------------------------------
Title: Oscillations and Asymmetries in Polar Coronal Holes
Authors: Kirk, Michael S.; Pesnell, William Dean
2018tess.conf30921K    Altcode:
  Coronal holes are the origin of the fast solar wind and define the
  quiescent heliosphere. Polar coronal holes are prevalent during
  solar minimum, non-axisymmetric, and are stable. They also offer
  an indirect measurement of the polar magnetic flux. Polar holes are
  regularly observed capping the northern and southern solar poles in EUV
  images of the corona and are understood as the primary source of the
  fast solar wind. We make new measurements of polar hole's perimeter
  and area in three EUV wavelengths between 1996 and 2017 using five
  different space-based imagers: SOHO EIT, STEREO A and B EUVI, PROBA2
  SWAP, and SDO AIA. The generated time-series of coronal hole parameters
  have significant oscillatory power in them - however this produces a
  difficult data problem: multi-band, multi-instrument, heteroscedastic
  measurements with periodic signals. To separate the oscillations
  associated with physical phenomena from systematic measurement errors,
  we employ a generalized Lomb-Scargle periodic analysis. This technique
  allows us to simultaneously analyze the physical properties of polar
  coronal holes and identify regular periodicities in our data from
  other origins.

---------------------------------------------------------
Title: Using the Solar Polar Magnetic Field for Longterm Predictions
    of Solar Activity, Solar Cycles 21-25
Authors: Pesnell, W. D.; Schatten, K. H.
2017AGUFMSH13A2473P    Altcode:
  We briefly review the dynamo and geomagnetic precursor methods of
  long-term solar activity forecasting. These methods depend upon the
  most basic aspect of dynamo theory to predict future activity, future
  magnetic field arises directly from the amplification of pre-existing
  magnetic field. We then generalize the dynamo technique, allowing the
  method to be used at any phase of the solar cycle, to the Solar Dynamo
  Amplitude (SODA) index. This index is sensitive to the magnetic flux
  trapped within the Sun's convection zone but insensitive to the phase
  of the solar cycle. Since magnetic fields inside the Sun can become
  buoyant, one may think of the acronym SODA as describing the amount of
  buoyant flux. We will show how effective the SODA Index has been in
  predicting Solar Cycles 23 and 24, and present a unified picture of
  earlier estimates of the polar magnetic configuration in Solar Cycle
  21 and 22. Using the present value of the SODA index, we estimate
  that the next cycle's smoothed peak activity will be about 125 ± 30
  solar flux units for the 10.7 cm radio flux and a sunspot number of 70
  ± 25. This suggests that Solar Cycle 25 will be comparable to Solar
  Cycle 24. Since the current approach uses data prior to solar minimum,
  these estimates may improve when the upcoming solar minimum is reached.

---------------------------------------------------------
Title: Digging into the corona: A modeling framework trained with
    Sun-grazing comet observations
Authors: Jia, Y. D.; Pesnell, W. D.; Bryans, P.; Downs, C.; Liu, W.;
   Schwartz, S. J.
2017AGUFMSH11B2437J    Altcode:
  Images of comets diving into the low corona have been captured a few
  times in the past decade. Structures visible at various wavelengths
  during these encounters indicate a strong variation of the ambient
  conditions of the corona. We combine three numerical models: a global
  coronal model, a particle transportation model, and a cometary plasma
  interaction model into one framework to model the interaction of such
  Sun-grazing comets with plasma in the low corona. In our framework,
  cometary vapors are ionized via multiple channels and then captured
  by the coronal magnetic field. In seconds, these ions are further
  ionized into their highest charge state, which is revealed by certain
  coronal emission lines. Constrained by observations, we apply our
  framework to trace back to the local conditions of the ambient corona,
  and their spatial/time variation over a broad range of scales. Once
  trained by multiple stages of the comet's journey in the low corona,
  we illustrate how this framework can leverage these unique observations
  to probe the structure of the solar corona and solar wind.

---------------------------------------------------------
Title: Acoustic Oscillation Properties of Active Region 12193
Authors: Monsue, Teresa; Pesnell, William D.; Hill, Frank
2017SPD....4810904M    Altcode:
  Solar flares are dynamic objects occurring randomly and yet unannounced
  in nature. In order to find an efficient detection method, we require
  a greater breadth of knowledge of the system. One path to such a
  method is to observe the solar atmosphere in a region around a flare
  in different wavelengths of light and acoustic frequency bands. This
  provides information from different altitudes in the solar atmosphere
  and allows us to study the temporal evolution of each altitude through
  the flaring event. A more complete understanding of the time evolution
  may lead to yet undiscovered precursors of the flare. In this project,
  we study Active Region 12192 using acoustic observations near an
  X3 flare occurring on October 24, 2014 at 21:41UT. Our wavelet
  analysis utilizes time series data to create Fourier power spectra
  of individual pixels spatially resolved around the flare region, to
  study the frequency bands. In order to study the power distribution
  in regions around the flare and to search for any correlation we
  apply several methods. One method we partition sub-regions in our
  main flaring region and take a survey of the oscillations for each
  frequency band within power maps. Another method we average the FFT
  to take measurements within the p-modes (2-4 mHz) and chromospheric
  (4-6 mHz) frequencies. The application of these methods should be able
  to get us closer to tracking waveforms within power maps.

---------------------------------------------------------
Title: The Complexity of Solar and Geomagnetic Indices
Authors: Pesnell, W. Dean
2017SPD....48.0703P    Altcode:
  How far in advance can the sunspot number be predicted with any degree
  of confidence? Solar cycle predictions are needed to plan long-term
  space missions. Fleets of satellites circle the Earth collecting
  science data, protecting astronauts, and relaying information. All
  of these satellites are sensitive at some level to solar cycle
  effects. Statistical and timeseries analyses of the sunspot number
  are often used to predict solar activity. These methods have not
  been completely successful as the solar dynamo changes over time
  and one cycle's sunspots are not a faithful predictor of the next
  cycle's activity. In some ways, using these techniques is similar to
  asking whether the stock market can be predicted. It has been shown
  that the Dow Jones Industrial Average (DJIA) can be more accurately
  predicted during periods when it obeys certain statistical properties
  than at other times. The Hurst exponent is one such way to partition
  the data. Another measure of the complexity of a timeseries is the
  fractal dimension. We can use these measures of complexity to compare
  the sunspot number with other solar and geomagnetic indices. Our
  concentration is on how trends are removed by the various techniques,
  either internally or externally. Comparisons of the statistical
  properties of the various solar indices may guide us in understanding
  how the dynamo manifests in the various indices and the Sun.

---------------------------------------------------------
Title: The Formation and Maintenance of the Dominant Southern Polar
    Crown Cavity of Cycle 24
Authors: Karna, N.; Zhang, J.; Pesnell, W. D.
2017ApJ...835..135K    Altcode:
  In this article, we report a study of the longest-lived polar crown
  cavity of Solar Cycle 24, using an observation from 2013, and propose
  a physical mechanism to explain its sustained existence. We used high
  temporal and spatial resolution observations from the Atmospheric
  Imaging Assembly (AIA) and the Helioseismic Magnetic Imager (HMI)
  instruments on board the Solar Dynamics Observatory (SDO) to explore the
  structure and evolution of the cavity. Although it existed for more than
  a year, we examined the circumpolar cavity in great detail from 2013
  March 21 to 2013 October 31. Our study reinforces the existing theory
  of formation of polar crown filaments that involves two basic processes
  to form any polar crown cavity as well as the long-lived cavity that
  we studied here. First, the underlying polarity inversion line (PIL)
  of the circumpolar cavity is formed between (1) the trailing part of
  dozens of decayed active regions distributed in different longitudes and
  (2) the unipolar magnetic field in the polar coronal hole. Second, the
  long life of the cavity is sustained by the continuing flux cancellation
  along the PIL. The flux is persistently transported toward the polar
  region through surface meridional flow and diffusion. The continuing
  flux cancellation leads to the shrinking of the polar coronal hole.

---------------------------------------------------------
Title: Identifying Long-term Oscillations in Polar Coronal Holes
Authors: Kirk, M. S.; Pesnell, W. D.; Young, C. A.
2016AGUFMSH11A2223K    Altcode:
  Polar coronal holes offer an indirect measurement of the polar
  magnetic flux, which is a significant component to our understanding
  of the solar cycle. Polar holes are prevalent during solar minimum,
  non-axisymmetric, and are stable. They are regularly observed capping
  the northern and southern solar poles in EUV images of the corona and
  are understood as the primary source of the fast solar wind. We make
  measurements of polar hole area with three EUV wavelengths from 1996
  through 2016 using five different space-based imagers: SOHO EIT, STEREO
  A and B EUVI, PROBA2 SWAP, and SDO AIA. Each time series of coronal
  hole parameters have significant oscillatory power in them, however
  this produces a difficult data problem: multi-band, multi-instrument,
  heteroscedastic measurements with periodic signals. To separate the
  oscillations associated with systematic measurement errors from physical
  phenomena, we employ a Tikhonov regularization scheme to generalize the
  conventional Lomb-Scargle method to a multi-band periodic analysis. This
  technique allows us to simultaneously analyze the physical properties
  of polar coronal holes and identify regular periodicities in our data
  from other origins.

---------------------------------------------------------
Title: Comparing Time-Distance Results within a Coronal Hole to the
    Quiet Sun
Authors: Hess Webber, Shea A.; Pesnell, W. Dean; Duvall, Thomas, Jr.;
   Birch, Aaron; Cameron, Robert
2016usc..confE...1H    Altcode:
  Time-distance helioseismology studies perturbations in solar
  wave modes. We use these techniques with SDO/HMI time-distance
  velocity-tracked dopplergram data to investigate differences between f
  -mode wave propagation within a coronal hole feature and without. We
  use symmetry arguments to enhance the signal-to-noise ratio of the
  cross-correlation results. We then look for phase and amplitude
  discrepancies between the coronal hole and quiet sun by comparing
  statistically significant differences between the regions.

---------------------------------------------------------
Title: Space Oddities: The Search For Ephemeral Coronal Holes
Authors: O'Connor, Rachel E.; Pesnell, W. Dean; Kirk, Michael S.;
   Karna, Nishu
2016usc..confE...9O    Altcode:
  Ephemeral coronal holes are short-lived, volatile counterparts
  to equatorial coronal holes. Very little is known about their
  characteristics and behavior aside from their definition: open,
  unipolar magnetic field lines resulting in darkened regions of the
  corona. The first exemplar of this phenomenon was observed by NASA's
  Solar Dynamics Observatory (SDO) on October 26, 2010, which spurred
  our search for other occurrences in order to understand the frequency
  and evolution of these phenomena. To accomplish this, we visually
  evaluated SDO 211 Å images on a 12-hour cadence between June 2010
  and June 2016. Each compact and isolated dim region we encountered was
  flagged as a potential ephemeral coronal hole for further analysis. This
  preliminary effort resulted in 149 candidate holes. For further analysis
  of their characteristics, we applied a strict definition criterion of an
  ephemeral coronal hole. This criterion was a set of four factors that
  were created in order to ensure events being observed were isolated,
  individual events- the candidates had to be dark relative to the
  surrounding material, not influenced by a nearby eruption, not obviously
  connected to other coronal hole structures, and their lifetime had to
  occur completely within the disk crossing. This criterion was designed
  so that events could be completely analyzed, from beginning to end, to
  better understand the origins. Application of this criterion eliminated
  all candidates but 5 of the original 149. True ephemeral coronal holes
  are rare occurrences, appearing only five times in six years. Future
  research in this area is needed to both locate additional events and
  study the underlying driving forces behind these rare phenomena.

---------------------------------------------------------
Title: Estimating and Separating Noise from AIA Images
Authors: Kirk, Michael S.; Ireland, Jack; Young, C. Alex; Pesnell,
   W. Dean
2016usc..confE..26K    Altcode:
  All digital images are corrupted by noise and SDO AIA is no
  different. In most solar imaging, we have the luxury of high photon
  counts and low background contamination, which when combined with
  carful calibration, minimize much of the impact noise has on the
  measurement. Outside high-intensity regions, such as in coronal holes,
  the noise component can become significant and complicate feature
  recognition and segmentation. We create a practical estimate of noise
  in the high-resolution AIA images across the detector CCD in all seven
  EUV wavelengths. A mixture of Poisson and Gaussian noise is well suited
  in the digital imaging environment due to the statistical distributions
  of photons and the characteristics of the CCD. Using state-of-the-art
  noise estimation techniques, the publicly available solar images, and
  coronal loop simulations; we construct a maximum-a-posteriori assessment
  of the error in these images. The estimation and mitigation of noise
  not only provides a clearer view of large-scale solar structure in
  the solar corona, but also provides physical constraints on fleeting
  EUV features observed with AIA.

---------------------------------------------------------
Title: On the Formation Mechanism of A Long-lived Polar Crown Cavity
Authors: Karna, Nishu; Pesnell, William D.; Zhang, Jie
2016usc..confE..22K    Altcode:
  We report the study of the longest-lived polar crown cavity of Solar
  Cycle 24th observed in the year 2013 and propose a physical mechanism
  to explain the sustained existence. We used high temporal and spatial
  resolution observations from the Atmospheric Imaging Assembly (AIA)
  and the Helioseismic Magnetic Imager (HMI) instruments on board
  the Solar Dynamics Observatory (SDO) to explore the structure and
  evolution. We examined the circumpolar cavity in great detail from
  March 21, 2013, till October 31, 2013, while it existed for more
  than one year. Our study suggests two necessary conditions to form a
  long stable circumpolar cavity or any polar crown cavity. First, the
  underlying polarity inversion line (PIL) of the circumpolar cavity is
  formed between the trailing part of dozens of decayed active regions
  distributed in different longitudes and the unipolar magnetic field
  in the polar coronal hole. Second, the long life of the cavity is
  sustained by the continuing flux cancellation along the polarity
  inversion line. The flux is persistently transported toward the polar
  region through surface meridional flow and diffusion, which also leads
  to the shrinking of the polar coronal hole. Comparing with the existing
  theory of the formation of polarity inversion lines, we introduce a
  new category named as "Diffused trailing flux and polar coronal hole
  interaction region" to explain the polar crown cavity. The existence
  of such region also helps explain the process of polar reversal,
  which provides insight into the solar cycle.

---------------------------------------------------------
Title: The Solar Dynamics Observatory, Six Years of Science
Authors: Pesnell, W. Dean
2016usc..confE..57P    Altcode:
  The Solar Dynamics Observatory has been producing science and science
  data since May 2010. I will describe some highlights of SDO results,
  including filament eruptions, flares, and comets. The status of the
  observatory hardware will also be discussed. The future of SDO will
  be a series of extended missions, each lasting two years. Our next
  extended mission proposal will be due early next year and I will
  discuss part of that process.

---------------------------------------------------------
Title: SDO 2016: Unraveling the Suns Complexity
Authors: Pesnell, W. Dean; Thompson, Barbara
2016usc..conf.....P    Altcode:
  Living With a Star Solar Dynamics Observatory research connects to many
  areas of solar physics and many other solar missions. Tracing these
  connections allows us to build a more accurate understanding of the Sun
  and solar activity. The workshop will focus on our improved knowledge
  and understanding of the Suns magnetic field that have come from the
  SDO data, and what will come in the future. Scientific sessions will
  feature a broad spectrum of science topics fundamental to SDO science
  investigations: Atmospheric Imaging Assembly (AIA), EUV Variability
  Experiment (EVE), and Helioseismic and Magnetic Imager (HMI), as
  well as the overlap between SDO and other scientific missions and
  activities. We invite you to celebrate the breadth of research topics
  enabled by SDO during its Prime Mission and the First Extended Mission.

---------------------------------------------------------
Title: Solar Acoustic Oscillations Observations in SDO AIA and HMI
    around AR 12192
Authors: Monsue, Teresa; Pesnell, W. Dean; Hill, Frank
2016usc..confE..89M    Altcode:
  Solar flares are dynamic objects occurring randomly and yet unannounced
  in nature. In order to find an efficient detection method, we require a
  greater breadth of knowledge of the system. One such mode is to observe
  flares in different frequency bands at different depths and study
  their temporal evolution through the flaring event. In this project we
  obtain acoustic observations of an X3 flare occurring on October 24,
  2014 at 21:41UT. We employ the study of active regions, near sunspots,
  in which flaring activity is taking place. Our wavelet analysis utilizes
  time series data to create Fourier power spectra of individual pixels
  spatially resolved around the flare region, to study the frequency
  bands. In order to study the power distribution in regions around the
  flare and compare the measurements to magnetograms to search for any
  correlation, we combine observations of oscillations in three SDO AIA
  wavelengths: the 1600Å, 1700 Å and 304Å, and combine them with HMI
  data. We then study how the frequency distribution evolves temporally
  by constructing a Power Map Movie (PMM) of the regions. From these
  PMMs we can partition sub-regions in our main flaring region and take
  a survey of the oscillations for each frequency band.

---------------------------------------------------------
Title: Watching the Sun from space
Authors: Pesnell, W. Dean
2016AsJPh..25..233P    Altcode:
  Space-based solar observatories have made fundamental discoveries
  about the lifecycle of the solar magnetic field and how that field
  affects the solar system. Observing the Sun from space provides
  access to all wavelengths of light and eliminates the smearing
  of atmospheric seeing. Being in space means the emissions from
  the highly-ionized material that are the natural emissions of the
  corona can be measured. Continuous observations of the Sun can
  be made from a single satellite in certain orbits. This leads to
  unexpected discoveries, such as orbiting coronagraphs showing that
  sun grazing comets are the most common class of observed comets. Or
  when the coronal holes discovered with the solar X-ray telescopes on
  Skylab explained long-noticed correlations in particle fluxes from the
  Sun with solar longitudes. Space-based coronagraphs and heliospheric
  imagers are able to track coronal mass ejections from when they leave
  the Sun until they hit the Earth or another planet. In a more practical
  point, as humans have become more entwined in the use of technology,
  the magnetic field of the Sun has become more intrusive. Energetic
  particles and high-energy photons from solar fares can compromise humans
  and electronics in space. As a coronal mass ejection passes by and
  interacts with the Earth's magnetosphere, it generates large currents
  at the Earth's surface that can disrupt power distribution systems. The
  measurements of Sun made possible by being in space will be described,
  along with some highlights of the observatories that make them.

---------------------------------------------------------
Title: On the Formation Mechanism of A Long-lasting Polar Crown Cavity
Authors: Karna, Nishu; Pesnell, William Dean; Zhang, Jie
2016shin.confE.140K    Altcode:
  We report the observation of the longest-lived polar crown cavity
  of Solar Cycle 24th observed in the year 2013 and propose a physical
  mechanism to explain the sustained existence. We used high temporal and
  spatial resolution observations from the Atmospheric Imaging Assembly
  (AIA) and the Helioseismic Magnetic Imager (HMI) instruments on board
  the Solar Dynamics Observatory (SDO) to explore the structure and
  evolution. We examined the circumpolar cavity in great detail from
  March 21, 2013, till October 31, 2013., while it existed for more
  than one year. Our study suggests two necessary conditions to form a
  long stable circumpolar cavity or any polar crown cavity. First, the
  underlying polarity inversion line (PIL) of the circumpolar cavity is
  formed between the trailing part of dozens of decayed active regions
  distributed in different longitudes and the unipolar magnetic field
  in the polar coronal hole. Second, the long lasting of the cavity
  is sustained by the continuing flux cancellation along the polarity
  inversion line. The flux is persistently transported toward the polar
  region through surface meridional flow and diffusion, which also leads
  to the shrinking of the polar coronal hole. Comparing with the existing
  theory of the formation of polarity inversion lines, we introduce
  a new category named as "Diffused bipole and polar coronal hole
  interaction region" to explain the polar crown cavity. The existence
  of such region also helps explain the process of polar reversal,
  which provides insight into the solar cycle.

---------------------------------------------------------
Title: A Comprehensive study of Cavities on the Sun: Structure,
    Formation, and Evolution
Authors: Karna, Nishu; Zhang, Jie; Pesnell, William D.
2016SPD....4710302K    Altcode:
  Coronal cavities are large-scale structures in the Sun's corona that
  are closely related with the long-term evolution of the magnetic field
  in the photosphere as well as associated with the energetic solar
  activity such as prominence eruptions and coronal mass ejections. They
  are observed as circular or elliptical-shaped relatively low-density
  dark regions above the solar limb in EUV, X-ray, and white-light
  coronal images. We used SDO/AIA limb synoptic maps, constructed from
  annuli above the solar limb, to systematically identify cavities. We
  observed 429 coronal prominence cavities between May 20, 2010 and Feb
  1, 2015. We examined correlations between height, width, and length of
  the cavities. Based on the fitting of the shape of the cross section,
  we classified cavities in three types: prolate (38%), oblate (27%)
  and circular (35%). We found that the cavities of all shapes are
  common in shorter length while circular and oblate cavities are more
  common in the longer length. In general, we found that the overall 3-D
  topology of long stable cavities can be characterized as a long tube
  with an elliptical cross-section. Next, we investigated the pattern of
  cavity location and found that cavity systematically drifts towards
  the pole. We found that cavities form a belt by making a plot using
  SDO/HMI surface magnetogram similar to classical buttery diagram
  of sunspots, we call that the cavity belt. Our analysis showed that
  the cavity belts migrated towards higher latitude with time and the
  cavity belts disappeared after the polar magnetic field reversal. This
  result shows that cavity evolution provides new insight into the
  solar cycle. Moreover, we studied the underlying magnetic field of
  a circumpolar crown cavity (Mar 21, 2013- Oct 25, 2013) that was
  observed for several Carrington Rotations. Our results showed that
  the underlying polarity inversion line of cavities is formed between
  the trailing part of decayed active regions and the unipolar magnetic
  field in the pole. The long life of cavities was due to continuous
  and sustained adding of trailing flux from multiple active regions as
  their remnants diffused toward the pole.

---------------------------------------------------------
Title: Statistical Differences in Time-Distance Helioseismology
    Results
Authors: Hess Webber, Shea A.; Pesnell, William D.; Duvall, Thomas;
   Cameron, Robert; Birch, A. C.
2016SPD....4720301H    Altcode:
  Time-distance helioseismology studies phase correlations in solar wave
  modes. We use these techniques to investigate the phase differences in
  f-mode wave propagation within a coronal hole feature and without. We
  isolate the coronal hole boundary location using edge detection
  techniques on SDO AIA data. We then use this location information to
  inform the analysis of the corresponding HMI time-distance velocity
  tracked data product, provided by Stanford's JSOC archive. We look
  at time-distance results inside the coronal hole, outside the coronal
  hole, the coronal hole data as a whole, and an independent quiet sun
  region. We use Student's t-Test to evaluate the significance of the
  differences between the various regions.

---------------------------------------------------------
Title: On the Absence of EUV Emission from Comet C/2012 S1 (ISON)
Authors: Bryans, Paul; Pesnell, W. Dean
2016ApJ...822...77B    Altcode:
  When the sungrazing comet C/2012 S1 (ISON) made its perihelion passage
  within two solar radii of the Sun’s surface, it was expected to be
  a bright emitter at extreme ultraviolet (EUV) wavelengths. However,
  despite solar EUV telescopes repointing to track the orbit of the comet,
  no emission was detected. This “null result” is interesting in
  its own right, offering the possibility of placing limits on the size
  and composition of the nucleus. We explain the lack of detection by
  considering the properties of the comet and the solar atmosphere that
  determine the intensity of EUV emission from sungrazing comets. By
  comparing these properties with those of sungrazing comet C/2011 W3
  (Lovejoy), which did emit in the EUV, we conclude that the primary
  factor resulting in non-detectable EUV emission from C/2012 S1 (ISON)
  was an insufficiently large nucleus. We conclude that the radius
  of C/2012 S1 (ISON) was at least a factor of four less than that of
  C/2011 W3 (Lovejoy). This is consistent with white-light observations
  in the days before perihelion that suggested the comet was dramatically
  reducing in size on approach.

---------------------------------------------------------
Title: The Unusual Event of October 26, 2010: An "Almost" Coronal Hole
Authors: Pesnell, W. D.; O'Connor, R.
2015AGUFMSH52A..04P    Altcode:
  Coronal holes are dark regions in the solar corona that develop where
  open magnetic field lines are found. They come in many different shapes,
  sizes, and forms. Ephemeral coronal holes are a short-lived form of
  the phenomena, sometimes lasting only a few rotations. On October 26,
  2010, NASA's Solar Dynamics Observatory (SDO) observed what was first
  thought to be an unusual ephemeral coronal hole, appearing for less
  than 48 hours and surrounded by a filament. We present an analysis of
  the area and magnetic signatures of the filament and suspected hole,
  as well as solar wind data. Multiple EUV channels from SDO/AIA are
  combined with magnetograms from SDO/HMI and the GONG network to quantify
  the evolution of this event. Another ephemeral coronal hole from June
  2015 is used a comparison. Results from this analysis show that the 2010
  event was not an ephemeral coronal hole, but rather a solar 'hiccup' -
  the attempted, and failed, formation of a small coronal hole. While the
  reasons behind the failure remain speculative, these findings show that
  a lot of potential lies in future research of this event - in observing
  the interactions between the hole and the filament, and our continued
  understanding of the formation and characteristics of coronal holes.

---------------------------------------------------------
Title: The Solar Non-activity Cycle of Polar Coronal Holes
Authors: Kirk, M. S.; Pesnell, W. D.; Young, C. A.
2015AGUFMSH33D..07K    Altcode:
  After the unusually extended minimum in 2008 and 2009, solar cycle 24
  continues to be an exceptionally weak cycle both in sunspot number
  and number of large magnetic storms. Coronal holes offer a direct
  measurement of the non-activity solar cycle, a missing link in our
  understanding of solar cycle progression. They are prevalent during
  solar minimum, non-axisymmetric, and are stable. Polar coronal holes
  are regularly observed capping the northern and southern solar poles
  in EUV images of the corona and are understood as the primary source
  of the fast solar wind. We make measurements of these features from
  1996 through 2015 using four different NASA imagers: SOHO EIT, STEREO
  A and B EUVI, and SDO AIA. A measurement of the axial symmetry of
  the polar holes is seen to have clear solar cycle dependence. Polar
  coronal holes are aligned with the solar rotation axis during minimum
  and have a maximum asymmetry between holes of about 14 degrees in the
  declining phase of the current solar cycle.

---------------------------------------------------------
Title: A comprehensive study of cavities on the Sun: Structures
    and Evolution
Authors: Karna, N.; Pesnell, W. D.; Zhang, J.
2015AGUFMSH54B..03K    Altcode:
  Coronal cavities are often observed as circular or elliptical-shaped,
  darkned regions above the solar limb in EUV coronal images. They are
  believed to be regions of lower density relative to the surrounding
  corona. The cavity surrounds the prominence: prior to the eruption and
  as an aspect of CMEs. We used SDO/AIA limb synoptic maps, constructed
  from annuli above the solar limb; best show cavities in the 211Å,
  193Å and 171Å passbands. The prominence associated with each cavity
  is best seen in the 304Å synoptic maps. We observed 429 cavities
  between May 2010 - Feb 2015. We examined correlations between each
  cavity's height, width and length. Our findings showed that around 38%
  of cavities were prolate, 27% oblate and 35% circular in shape. The
  lengths of the cavities ranged from 0.06-2.9 R¤. When a cavity is
  longer than 1.5 R¤ it has a narrower height range (0.1-0.3 R¤),
  whereas when the cavity was shorter than 1.5 R¤, it had a wider height
  range (0.07-0.5 R¤). We find that the overall 3-D topology of the long
  stable cavities can be characterized as a long tube with an elliptical
  cross section. We also noticed that the circular and oblate cavities are
  longer in length than prolate cavities. We also studied the physical
  mechanisms behind the cavity drift towards the pole and found it to
  be tied to the meridional flow. Finally, by observing the evolution
  cavity regions using SDO/HMI surface magnetic field observations, we
  found cavity belt formed near the polar coronal hole boundary. Results
  showed that the cavity belt migrated towards higher latitude with
  time and the cavity belt disappeared after the polar magnetic field
  reversal. This result shows that cavity evolution provides new insight
  into the solar cycle. Moreover, we selected 30 random cavities from
  our catalog and studied their morphology, thermal properties, linear
  polarization signatures, precursors of eruption, and underlying magnetic
  field and tried to interpret the shapes and stability of the cavities.

---------------------------------------------------------
Title: Study of the 3D Geometric Structure and Temperature of a
    Coronal Cavity Using the Limb Synoptic Map Method
Authors: Karna, N.; Zhang, J.; Pesnell, W. Dean; Hess Webber, S. A.
2015ApJ...810..124K    Altcode:
  We present the three-dimensional geometric structure and thermal
  properties of a coronal cavity deduced from limb synoptic maps. The
  observations are extreme ultraviolet images from the Atmospheric Imager
  Assembly (AIA) and magnetic images from the Helioseismic Magnetic
  Imager instruments on board the Solar Dynamics Observatory. We describe
  a limb synoptic-map method used to effectively identify and measure
  cavities from annuli of radiance above the solar limb. We find that
  cavities are best seen in the 211, 193, and 171 Å passbands. The
  prominence associated with each cavity is best seen in the 304 Å
  synoptic maps. We also estimate the thermal properties of the cavity and
  surrounding plasma by combining the AIA radiances with a differential
  emission measure analysis. This paper focuses on one long cavity
  from a catalog of coronal cavities that we are developing. Cavities
  in this catalog are designated by a coded name using the Carrington
  Rotation number and position. Cavity C211347177N was observed during
  Carrington Rotation 2113 at the northwestern limb of the solar disk
  with an average latitude of 47° N and a central longitude of 177°. We
  showed the following. (1) The cavity is a long tube with an elliptical
  cross-section with ratios of the length to width and the length to
  height of 11:1 and 7:1, respectively. (2) The cavity is about 1360
  Mm long, or 170° in longitude. (3) It is tilted in latitude. (4)
  And it is slightly hotter than its surroundings.

---------------------------------------------------------
Title: Appearances and Statistics of Coronal Cavities During the
    Ascending Phase of Solar Cycle 24
Authors: Karna, N.; Pesnell, W. D.; Zhang, J.
2015ApJ...810..123K    Altcode:
  We present a survey of 429 coronal prominence cavities found between
  2010 May and 2015 February using the Solar Dynamics Observatory
  (SDO)/Atmospheric Imaging Assembly limb synoptic maps. We examined
  correlations between each cavity’s height, width, and length. Our
  findings showed that around 38% of the cavities were prolate, 27%
  oblate, and 35% circular in shape. The lengths of the cavities ranged
  from 0.06 to 2.9 {R}<SUB>⊙ </SUB>. When a cavity is longer than
  1.5 {R}<SUB>⊙ </SUB>, it has a narrower height range (0.1-0.3
  {R}<SUB>⊙ </SUB>), whereas when the cavity was shorter than 1.5
  {R}<SUB>⊙ </SUB>, it had a wider height range (0.07-0.5 {R}<SUB>⊙
  </SUB>). We find that the overall three-dimensional topology of the
  long, stable cavities can be characterized as a long tube with an
  elliptical cross section. We also noted that the circular and oblate
  cavities are longer in length than the prolate cavities. We also studied
  the physical mechanisms behind the cavity drift toward the pole and
  found it to be tied to the meridional flow. Finally, by observing the
  evolution of the cavity regions using SDO/Helioseismic Magnetic Imager
  (HMI) surface magnetic field observations, we found that the cavities
  formed a belt near the polar coronal hole boundary; we call this the
  cavity belt. Our results showed that the cavity belt migrated toward
  higher latitude over time and the cavity belt disappeared after the
  polar magnetic field reversal. This result shows that cavity evolution
  provides new insight into the solar cycle.

---------------------------------------------------------
Title: Appearances and Statistics of Coronal Cavities During the
    Ascending Phase of Solar Cycle 24
Authors: Karna, Nishu; Pesnell, William Dean; Zhang, Jie
2015shin.confE..72K    Altcode:
  We present a survey of 429 coronal prominence cavities found between May
  2010-Feb 2015 using SDO/AIA limb synoptic maps. We examined correlations
  between each cavity's height, width and length. Our findings showed
  that around 38% of cavities were prolate, 27% oblate and 35% circular
  in shape. The lengths of the cavities ranged from 0.06 - 2.9 R⊙
  When a cavity is longer than 1.5 R⊙, it has a narrower height range
  (0.1 - 0.3 R⊙), whereas when the cavity was shorter than 1.5 R⊙,
  it had a wider height range (0.07 - 0.5 R). We find that the overall 3-D
  topology of the long stable cavities can be characterized as a long tube
  with an elliptical cross section. We also noticed that the circular
  and oblate cavities are longer in length than prolate cavities. We
  also studied the physical mechanisms behind the cavity drift towards
  the pole and found it to be tied to the meridional flow. Finally, by
  observing the evolution cavity regions using SDO/HMI surface magnetic
  field observations, we found that cavities formed a belt near the
  polar coronal hole boundary; we call this the cavity belt. Results
  showed that the cavity belt migrated towards higher latitude with
  time and the cavity belt disappeared after the polar magnetic field
  reversal. This result shows that cavity evolution provides new insight
  into the solar cycle.

---------------------------------------------------------
Title: Connecting the Evolution of Polar Coronal Holes to the
    Heliosphere
Authors: Kirk, Michael S.; Pesnell, W. Dean; Hess-Webber, Shea
2015shin.confE.123K    Altcode:
  Polar coronal holes are regularly observed capping the northern and
  southern solar poles in EUV images of the corona and are understood
  as the primary source of the fast solar wind. Polar holes are also
  the longest-lived solar magnetic features and observed to have strong
  solar cycle dependence - becoming more stable and prominent in solar
  minimum and disappearing at solar maximum. We make measurements of these
  features from 1996 through 2015 using four different NASA imagers: SOHO
  EIT, STEREO A and B EUVI, and SDO AIA. This dataset reveals several
  long-term trends in the corona. A measurement of the axial symmetry
  of the polar holes is seen to have clear solar cycle dependence. Polar
  coronal holes are aligned with the solar rotation axis during minimum
  and have a maximum off-axial perturbation of about 8 degrees in the
  declining phase of the solar cycle. With nearly 20 years of coronal
  hole measurements, we are able correlate the evolution of the polar
  holes to complementary measurements of the solar wind.

---------------------------------------------------------
Title: Solar Cycle 24 up to Now: Flying Over Peaks and Through Streams
Authors: Pesnell, W. Dean
2015TESS....130804P    Altcode:
  Solar Cycle 24 has been a below-average sunspot cycle. There were
  peaks in the daily and monthly-averaged sunspot number in the Northern
  hemisphere in 2011 and in the Southern hemisphere in 2014. Now that
  sunspot activity appears to be on the decline, another part of the
  solar cycle becomes important. Energetic events from high-speed streams
  flowing from the Sun can produce crippling radiation storms in the
  magnetosphere. Predicting those events that will affect our assets in
  space requires a different kind of solar prediction and some idea of how
  the radiation will propagate through the solar system. With the rapid
  increase in solar data and capability of numerical models of the solar
  convection zone we are developing the ability to forecast the level of
  the next solar cycle. But no prediction based only on sunspot number
  will be usable for predicting the variation of the decline of a sunspot
  cycle. I will describe the status of Solar Cycle 24, our need for solar
  activity predictions at all phases of the solar cycle, and anticipate
  how those predictions could be made more accurate in the future.

---------------------------------------------------------
Title: Trends Of The Void: Solar Cycles Observed Through Polar
    Coronal Holes
Authors: Kirk, Michael S.; Hess Webber, Shea; Pesnell, W. Dean
2015TESS....130802K    Altcode:
  Coronal holes are defined by their open magnetic field configuration
  and lack of emitting plasma. Holes that cap the northern and southern
  solar poles are the longest-lived features observed on the Sun -
  persisting for nearly an entire solar cycle. Polar holes disappear
  briefly at solar maximum for about a year before returning. The size
  and evolution of the polar holes are also strongly anti-correlated
  with the solar activity cycle. Their longevity combined with this
  solar activity relationship makes polar coronal holes an ideal proxy
  for measuring the long-term evolution of the solar magnetic field. We
  use a perimeter tracking technique to measure the size and location of
  the polar coronal holes for 19 years starting in 1996. Utilizing the
  SOHO EIT archive and current SDO AIA images, we present a comprehensive
  look at how polar coronal holes evolve and what they can tell us about
  our current and unusual solar cycle.

---------------------------------------------------------
Title: Statistical Studies of Coronal Cavities Since the Launch of SDO
Authors: Karna, Nishu; Zhang, Jie; Pesnell, W. Dean
2015TESS....140905K    Altcode:
  We present a survey of 409 coronal prominence cavities found between
  May 2010- Sep 2014 using SDO/AIA limb synoptic maps. We examined
  correlations between cavity’s height, width and length. Our finding
  showed that around 50% of cavities were taller than wider, 40% wider and
  10% circular in shape. The length of the cavity ranged from 0.09-2.9
  R⊙. When the cavity length is greater than 1.5 R⊙, cavity had a
  narrow height range (0.1-0.3 R⊙), whereas when the cavity length was
  smaller than 1.5 R⊙, cavity had wider height range (0.07-0.5 R⊙). We
  find that the overall 3-D topology of the long stable cavities can
  be characterized as a long tube with an elliptical cross section. We
  also studied the physical mechanisms behind the cavity drift towards
  the pole and found it to be tied to the polar reversal. Finally, by
  observing the evolution of the cavity region using SDO/HMI surface
  magnetic field observations, we found that cavities formed a belt
  between the polar coronal hole boundary and the active region belt; we
  call this new belt the cavity belt. Results showed that the cavity belt
  migrated towards higher and higher latitude with time and the cavity
  belt disappeared after the polar magnetic field reversal. This result
  shows that cavity evolution provides another dimension of knowledge
  of studying the solar cycle.

---------------------------------------------------------
Title: Solar Dynamics Observatory (SDO)
Authors: Pesnell, W. Dean
2015hchp.book..179P    Altcode:
  No abstract at ADS

---------------------------------------------------------
Title: Pushing the Envelope of Extreme Space Weather
Authors: Pesnell, W. D.
2014AGUFMSH21C4129P    Altcode:
  Extreme Space Weather events are large solar flares or geomagnetic
  storms, which can cost billions of dollars to recover from. We have few
  examples of such events; the Carrington Event (the solar superstorm) is
  one of the few that had superlatives in three categories: size of solar
  flare, drop in Dst, and amplitude of aa. Kepler observations show that
  stars similar to the Sun can have flares releasing millions of times
  more energy than an X-class flare. These flares and the accompanying
  coronal mass ejections could strongly affect the atmosphere surrounding
  a planet. What level of solar activity would be necessary to strongly
  affect the atmosphere of the Earth? Can we map out the envelope
  of space weather along the evolution of the Sun? What would space
  weather look like if the Sun stopped producing a magnetic field? To
  what extreme should Space Weather go? These are the extremes of Space
  Weather explored in this talk.

---------------------------------------------------------
Title: Areas of Polar Coronal Holes from 1996 Through 2010
Authors: Hess Webber, S. A.; Karna, N.; Pesnell, W. D.; Kirk, M. S.
2014SoPh..289.4047H    Altcode: 2014SoPh..tmp..103H
  Polar coronal holes (PCHs) trace the magnetic variability of the
  Sun throughout the solar cycle. Their size and evolution have
  been studied as proxies for the global magnetic field. We present
  measurements of the PCH areas from 1996 through 2010, derived from an
  updated perimeter-tracing method and two synoptic-map methods. The
  perimeter-tracing method detects PCH boundaries along the solar
  limb, using full-disk images from the SOlar and Heliospheric
  Observatory/Extreme ultraviolet Imaging Telescope (SOHO/EIT). One
  synoptic-map method uses the line-of-sight magnetic field from the
  SOHO/Michelson Doppler Imager (MDI) to determine the unipolarity
  boundaries near the poles. The other method applies thresholding
  techniques to synoptic maps created from EUV image data from EIT. The
  results from all three methods suggest that the solar maxima and
  minima of the two hemispheres are out of phase. The maximum PCH area,
  averaged over the methods in each hemisphere, is approximately 6 %
  during both solar minima spanned by the data (between Solar Cycles
  22/23 and 23/24). The northern PCH area began a declining trend in
  2010, suggesting a downturn toward the maximum of Solar Cycle 24 in
  that hemisphere, while the southern hole remained large throughout 2010.

---------------------------------------------------------
Title: Evolving Solar Activity and Its Influence on Space and Earth
Authors: Pesnell, W. Dean; Thompson, Barbara
2014esai.conf.....P    Altcode:
  The 2014 Living with a Star (LWS) Science Meeting will focus on
  advancing the understanding of the integral system coupling the Sun
  to the Earth. An important part of this meeting is the inclusion of
  the Hinode-8 and IRIS-2 meetings with complementary objectives towards
  improved understanding of the evolving solar activity.

---------------------------------------------------------
Title: Deciphering Solar Magnetic Activity. I. On the Relationship
    between the Sunspot Cycle and the Evolution of Small Magnetic Features
Authors: McIntosh, Scott W.; Wang, Xin; Leamon, Robert J.; Davey,
   Alisdair R.; Howe, Rachel; Krista, Larisza D.; Malanushenko, Anna V.;
   Markel, Robert S.; Cirtain, Jonathan W.; Gurman, Joseph B.; Pesnell,
   William D.; Thompson, Michael J.
2014ApJ...792...12M    Altcode: 2014arXiv1403.3071M
  Sunspots are a canonical marker of the Sun's internal magnetic
  field which flips polarity every ~22 yr. The principal variation of
  sunspots, an ~11 yr variation, modulates the amount of the magnetic
  field that pierces the solar surface and drives significant variations
  in our star's radiative, particulate, and eruptive output over that
  period. This paper presents observations from the Solar and Heliospheric
  Observatory and Solar Dynamics Observatory indicating that the 11
  yr sunspot variation is intrinsically tied to the spatio-temporal
  overlap of the activity bands belonging to the 22 yr magnetic activity
  cycle. Using a systematic analysis of ubiquitous coronal brightpoints
  and the magnetic scale on which they appear to form, we show that the
  landmarks of sunspot cycle 23 can be explained by considering the
  evolution and interaction of the overlapping activity bands of the
  longer-scale variability.

---------------------------------------------------------
Title: Using Polar Coronal Hole Area Measurements to Determine the
    Solar Polar Magnetic Field Reversal in Solar Cycle 24
Authors: Karna, N.; Hess Webber, S. A.; Pesnell, W. D.
2014SoPh..289.3381K    Altcode: 2014SoPh..tmp...80K
  An analysis of solar polar coronal hole (PCH) areas since the launch
  of the Solar Dynamics Observatory (SDO) shows how the polar regions
  have evolved during Solar Cycle 24. We present PCH areas from mid-2010
  through 2013 using data from the Atmospheric Imager Assembly (AIA) and
  Helioseismic and Magnetic Imager (HMI) instruments onboard SDO. Our
  analysis shows that both the northern and southern PCH areas have
  decreased significantly in size since 2010. Linear fits to the areas
  derived from the magnetic-field properties indicate that, although
  the northern hemisphere went through polar-field reversal and reached
  solar-maximum conditions in mid-2012, the southern hemisphere had not
  reached solar-maximum conditions in the polar regions by the end of
  2013. Our results show that solar-maximum conditions in each hemisphere,
  as measured by the area of the polar coronal holes and polar magnetic
  field, will be offset in time.

---------------------------------------------------------
Title: Predicting Solar Cycle 24 Using a Geomagnetic Precursor Pair
Authors: Pesnell, W. Dean
2014SoPh..289.2317P    Altcode: 2014SoPh..tmp...18P
  We describe using Ap and F<SUB>10.7</SUB> as a geomagnetic-precursor
  pair to predict the amplitude of Solar Cycle 24. The precursor is
  created by using F<SUB>10.7</SUB> to remove the direct solar-activity
  component of Ap. Four peaks are seen in the precursor function during
  the decline of Solar Cycle 23. A recurrence index that is generated by
  a local correlation of Ap is then used to determine which peak is the
  correct precursor. The earliest peak is the most prominent but coincides
  with high levels of non-recurrent solar activity associated with the
  intense solar activity of October and November 2003. The second and
  third peaks coincide with some recurrent activity on the Sun and show
  that a weak cycle precursor closely following a period of strong solar
  activity may be difficult to resolve. A fourth peak, which appears in
  early 2008 and has recurrent activity similar to precursors of earlier
  solar cycles, appears to be the "true" precursor peak for Solar Cycle
  24 and predicts the smallest amplitude for Solar Cycle 24. To determine
  the timing of peak activity it is noted that the average time between
  the precursor peak and the following maximum is ≈ 6.4 years. Hence,
  Solar Cycle 24 would peak during 2014. Several effects contribute to
  the smaller prediction when compared with other geomagnetic-precursor
  predictions. During Solar Cycle 23 the correlation between sunspot
  number and F<SUB>10.7</SUB> shows that F<SUB>10.7</SUB> is higher than
  the equivalent sunspot number over most of the cycle, implying that the
  sunspot number underestimates the solar-activity component described by
  F<SUB>10.7</SUB>. During 2003 the correlation between aa and Ap shows
  that aa is 10 % higher than the value predicted from Ap, leading to
  an overestimate of the aa precursor for that year. However, the most
  important difference is the lack of recurrent activity in the first
  three peaks and the presence of significant recurrent activity in the
  fourth. While the prediction is for an amplitude of Solar Cycle 24 of
  65±20 in smoothed sunspot number, a below-average amplitude for Solar
  Cycle 24, with maximum at 2014.5±0.5, we conclude that Solar Cycle 24
  will be no stronger than average and could be much weaker than average.

---------------------------------------------------------
Title: Coronal Cavity Catalog from SDO Observations
Authors: Karna, Nishu; Zhang, Jie; Pesnell, William D; Hess Webber,
   Shea A.
2014AAS...22432355K    Altcode:
  We present a catalog of coronal cavities and prominences associated with
  cavities since the launch of Solar Dynamics Observatory (SDO). Coronal
  cavities are dark, circular regions observed above the solar limb in
  white light and EUV coronal images. They are believed to be regions
  of lower density relative to the surrounding corona. We use synoptic
  maps made from EUV images from the Atmospheric Imager Assembly (AIA)
  instrument on board SDO to study coronal cavities. The synoptic maps,
  constructed from annuli above the solar limb, best show cavities in 211
  A (Fe XIV, 2.0 MK) and 193 A (Fe XII, 1.6 MK) and 171 A (Fe IX, 0.6 MK)
  passbands. Moreover, 304 A (He II, 0.05 MK) synoptic maps best show the
  evolution of any prominences associated with a cavity. The catalog lists
  the number of cavities seen in each Carrington rotation starting from
  CR 2097, the cavity’s size, shape, and the heliographic longitudes
  and latitudes of the appearance and disappearance of the cavity. Our
  goal is to provide a consistent set of the cavity structures for broad
  scientific use.

---------------------------------------------------------
Title: Coronal Diagnostics from Cometary Emission
Authors: Bryans, Paul; Pesnell, William D; Seaton, Daniel B; West,
   Matthew J
2014AAS...22442203B    Altcode:
  The extreme ultraviolet (EUV) emission observed from sungrazing comets
  as they pass through the solar atmosphere can be used to infer the
  properties of the corona. In this paper we will discuss several of these
  properties that can be estimated from the EUV observations of Comet
  Lovejoy from AIA/SDO and SWAP/PROBA2. The longevity of the emission
  allows us to constrain the coronal electron density through which
  the comet passes. We will also discuss how dispersion of the emitting
  cometary material we can be used to estimate the local Alfven speed in
  the corona. Finally, measuring the deformation of the magnetic field
  as it is impacted by the comet can be used to estimate the magnetic
  field strength in this location. In the absence of the comet, none
  of these parameters are directly measurable in the corona. Sungrazing
  comets are thus unique probes of the solar atmosphere.

---------------------------------------------------------
Title: Asymmetries and the Off-Axial Wandering of Polar Coronal Holes
Authors: Kirk, Michael S.; Hess-Webber, Shea; Pesnell, W. Dean;
   Karna, Nishu
2014shin.confE..23K    Altcode:
  Polar coronal holes are regularly observed capping the northern and
  southern solar poles in EUV images of the corona and are understood
  as the primary source of the fast solar wind. Polar holes are also
  observed to have strong solar cycle dependence: becoming more stable and
  prominent in solar minimum and disappearing at solar maximum. We extend
  the perimeter tracking methods of Kirk et al. (2009) and Hess-Webber
  et al. (2014, submitted) to examine the centroid of identified polar
  coronal holes during solar cycle 24 by utilizing the entirety of the
  EIT image archive on SOHO. We demonstrate that the centroids of the
  polar holes have clear solar cycle dependence. Polar coronal holes are
  symmetrically aligned during minimum and have a maximum asymmetry at
  solar maximum of about 17 degrees.

---------------------------------------------------------
Title: Taking Extreme Space Weather to the Milky Way
Authors: Pesnell, W. Dean
2014AAS...22432359P    Altcode:
  Extreme Space Weather events are large solar flares or geomagnetic
  storms, which can cause economic damage that cost billions of dollars to
  recover from. We have few examples of such events; only the Carrington
  Event (the solar superstorm) has superlatives in three categories: size
  of solar flare, drop in Dst, and amplitude of aa. Kepler observations
  show that stars similar to the Sun can have flares releasing thousands
  of times more energy than an X-class flare. These flares would
  strongly affect the atmosphere surrounding a planet orbiting such a
  star. Particle and magnetic field outflows from these stars could
  also be present. We are investigating the level of solar activity
  that is necessary to strongly affect the atmosphere of terrestrial
  planets. We assume that a habitable planet requires an atmosphere
  with a temperature and composition that is stable in time. Can we
  then extrapolate results from our solar system to determine a space
  of stellar parameters in which habitable planets can exist?

---------------------------------------------------------
Title: Time-Series Analysis of Supergranule Characteristics at
    Solar Minimum
Authors: Williams, Peter E.; Pesnell, W. Dean
2014SoPh..289.1101W    Altcode:
  Sixty days of Doppler images from the Solar and Heliospheric
  Observatory (SOHO) / Michelson Doppler Imager (MDI) investigation
  during the 1996 and 2008 solar minima have been analyzed to show
  that certain supergranule characteristics (size, size range,
  and horizontal velocity) exhibit fluctuations of three to five
  days. Cross-correlating parameters showed a good, positive correlation
  between supergranulation size and size range, and a moderate, negative
  correlation between size range and velocity. The size and velocity
  do exhibit a moderate, negative correlation, but with a small time
  lag (less than 12 hours). Supergranule sizes during five days of
  co-temporal data from MDI and the Solar Dynamics Observatory (SDO) /
  Helioseismic Magnetic Imager (HMI) exhibit similar fluctuations with
  a high level of correlation between them. This verifies the solar
  origin of the fluctuations, which cannot be caused by instrumental
  artifacts according to these observations. Similar fluctuations are
  also observed in data simulations that model the evolution of the
  MDI Doppler pattern over a 60-day period. Correlations between the
  supergranule size and size range time-series derived from the simulated
  data are similar to those seen in MDI data. A simple toy-model using
  cumulative, uncorrelated exponential growth and decay patterns at
  random emergence times produces a time-series similar to the data
  simulations. The qualitative similarities between the simulated and
  the observed time-series suggest that the fluctuations arise from
  stochastic processes occurring within the solar convection zone. This
  behavior, propagating to surface manifestations of supergranulation, may
  assist our understanding of magnetic-field-line advection, evolution,
  and interaction.

---------------------------------------------------------
Title: The Time-dependent Chemistry of Cometary Debris in the
    Solar Corona
Authors: Pesnell, W. D.; Bryans, P.
2014ApJ...785...50P    Altcode:
  Recent improvements in solar observations have greatly progressed the
  study of sungrazing comets. They can now be imaged along the entirety
  of their perihelion passage through the solar atmosphere, revealing
  details of their composition and structure not measurable through
  previous observations in the less volatile region of the orbit further
  from the solar surface. Such comets are also unique probes of the solar
  atmosphere. The debris deposited by sungrazers is rapidly ionized and
  subsequently influenced by the ambient magnetic field. Measuring the
  spectral signature of the deposited material highlights the topology
  of the magnetic field and can reveal plasma parameters such as the
  electron temperature and density. Recovering these variables from the
  observable data requires a model of the interaction of the cometary
  species with the atmosphere through which they pass. The present paper
  offers such a model by considering the time-dependent chemistry of
  sublimated cometary species as they interact with the solar radiation
  field and coronal plasma. We expand on a previous simplified model by
  considering the fully time-dependent solutions of the emitting species'
  densities. To compare with observations, we consider a spherically
  symmetric expansion of the sublimated material into the corona and
  convert the time-dependent ion densities to radial profiles. Using
  emissivities from the CHIANTI database and plasma parameters derived
  from a magnetohydrodynamic simulation leads to a spatially dependent
  emission spectrum that can be directly compared with observations. We
  find our simulated spectra to be consistent with observation.

---------------------------------------------------------
Title: Analysis of Supergranule Sizes and Velocities Using Solar
    Dynamics Observatory (SDO)/ Helioseismic Magnetic Imager (HMI) and
    Solar and Heliospheric Observatory (SOHO)/ Michelson Doppler Imager
    (MDI) Dopplergrams
Authors: Williams, Peter E.; Pesnell, W. Dean; Beck, John G.; Lee,
   Shannon
2014SoPh..289...11W    Altcode:
  Co-temporal Doppler images from Solar and Heliospheric Observatory
  (SOHO)/Michelson Doppler Imager (MDI) and Solar Dynamics Observatory
  (SDO)/Helioseismic Magnetic Imager (HMI) have been analyzed to extract
  quantitative information about global properties of the spatial
  and temporal characteristics of solar supergranulation. Preliminary
  comparisons show that supergranules appear to be smaller and have
  stronger horizontal velocity flows within HMI data than was measured
  with MDI. There appears to be no difference in their evolutionary
  timescales. Supergranule sizes and velocities were analyzed over a
  ten-day time period at a 15-minute cadence. While the averages of
  the time-series retain the aforementioned differences, fluctuations
  of these parameters first observed in MDI data were seen in both
  MDI and HMI time-series, exhibiting a strong cross-correlation. This
  verifies that these fluctuations are not instrumental, but are solar
  in origin. The observed discrepancies between the averaged values from
  the two sets of data are a consequence of instrument resolution. The
  lower spatial resolution of MDI results in larger observed structures
  with lower velocities than is seen in HMI. While these results offer a
  further constraint on the physical nature of supergranules, they also
  provide a level of calibration between the two instruments.

---------------------------------------------------------
Title: The Perihelion Passage of Comet ISON as seen by SDO
Authors: Pesnell, W. D.; Schrijver, C. J.; Boerner, P.; DeRosa, M. L.;
   Liu, W.; Thompson, B. J.
2013AGUFM.P24A..10P    Altcode:
  Comet ISON will fly through perihelion on November 28, 2013. It is one
  of the largest sungrazing comets to be seen in the Space Age. The Solar
  Dynamics Observatory (SDO) has seen two previous sungrazing comets in
  the extreme ultraviolet channels of the Atmospheric Imaging Assembly
  (AIA). Comet ISON will fly farther from the Sun (perihelion distance
  of 2.7 Rsun compared to 1.15 for Comet Lovejoy), meaning it probes
  a different part of the solar corona, but its larger size should
  provide enough mass to illuminate the path of the nucleus. Based on
  the latest ephemeris, SDO will be able to track Comet ISON through
  the entire perihelion passage by a series of off-point maneuvers. We
  will present the AIA data obtained from the Comet ISON perihelion,
  discussing the differences between Comets ISON and Lovejoy. We will
  then summarize what we have learned from the observations and offer
  some thoughts on what sungrazing comets may reveal about comets,
  the Sun, and their interaction.

---------------------------------------------------------
Title: What EUV Observations of Comet ISON Reveal About the Solar
    Corona
Authors: Bryans, P.; Pesnell, W. D.
2013AGUFM.P31A1787B    Altcode:
  Recent advances in space-based solar observations have greatly
  progressed the study of sungrazing comets. They can now be imaged along
  the entirety of their perihelion passage, revealing details of their
  composition, structure, and size. Such comets are also unique probes
  of the solar corona. The debris deposited by sungrazers is rapidly
  ionized and subsequently forced to follow the ambient magnetic field. In
  this paper we present preliminary results from EUV observations of
  Comet ISON. We estimate the size of the comet nucleus based on the
  EUV radiance and compare with independent estimates. The variation
  of the EUV emission with wavelength provides limits on the density of
  the ambient corona, and the motion of ionized debris will be used to
  infer the coronal magnetic field structure.

---------------------------------------------------------
Title: Inter-hemispheric coupling during northern polar summer
    periods of 2002-2010 using TIMED/SABER measurements
Authors: Goldberg, R. A.; Feofilov, A. G.; Pesnell, W. D.; Kutepov,
   A. A.
2013JASTP.104..277G    Altcode:
  It has been found that for more than one polar summer season between
  2002 and 2010, the northern polar mesospheric region near and above
  about 80 km was warmer than normal. The strongest warming effect of this
  type was observed to occur during northern summer 2002. Observational
  and theoretical studies imply that these “anomalies” were preceded
  by unusual dynamical processes in the southern hemisphere. We have
  analyzed temperature distributions measured by the SABER limb scanning
  infrared radiometer aboard the NASA TIMED satellite between 2002 and
  2010 at altitudes from 15 to 110 km and for latitudes between 83°S
  and 83°N. We describe the approach to trace the spatial extent
  of inter-hemispheric temperature correlations demonstrating the
  global features that were unique for the “anomalous” northern
  polar summers. From our analysis of SABER data from 2002 to 2010,
  the anomalous heating for the northern mesopause region during
  northern summer was accompanied by stratospheric heating in the
  equatorial region. In the winter hemisphere it is accompanied by
  heating in the lower stratosphere and mesopause region, and cooling
  in the stratopause region. Also, all the elements of the temperature
  anomaly structure appear to develop and fade away nearly simultaneously,
  thereby suggesting either a global influence or a short lagging period
  (less than 7 days).

---------------------------------------------------------
Title: Time-dependent chemisty of outgassed cometary detritus in
    the solar corona
Authors: Bryans, Paul; Pesnell, W. D.
2013SPD....44...32B    Altcode:
  Recent observations of sungrazing comets have opened an exciting novel
  methof of probing the solar atmosphere. As well as providing valuable
  insight on the magnetic field of the lower corona, sungrazing comets
  also promise the potential of measuring the solar wind as their detritus
  follows the open field lines of the corona. In this work, we model the
  chemisty of the material sublimated from comets as they skim across
  the Sun. This material, largely water ice, is rapidly dissociated and
  ionized by the solar radiation field and coronal electrons. We track
  the evolution of the ionizing material as it expands into the corona
  using a generalized Haser-like model. Based on these results, we have
  predicted the emission resulting from these ions in different regions
  of the corona and compared the results with SDO/AIA observations.

---------------------------------------------------------
Title: What Will Comet ISON Debris Teach Us About the Sun?
Authors: Pesnell, W. D.; Bryans, P.
2013SPD....44...34P    Altcode:
  Comet ISON is a large sun-grazing comet due to pass perihelion on
  November 28, 2013. It will go through the corona 2.7 Rsun above
  the surface, much higher than earlier EUV comets. We will use our
  time-dependent models of cometary debris to discuss how the trail of
  Comet ISON can be used to probe the solar corona. The debris trail left
  behind as a sun-grazing comet passes by the Sun undergoes different
  chemical processes at different distances from the Sun. Near the Sun
  the material is rapidly converted to atomic ions and becomes part of
  the solar corona. Far from the Sun the evaporated material can remain in
  molecular form for a long time, while the grains of asteroidal material
  can exist long enough to become meteors in planetary atmospheres. The
  larger fragments may survive as independent comets, until the next
  perihelion passage. In between those limits the material moves in the
  solar wind acceleration region. The debris could become entrained in
  the solar wind and be measured by satellites far from the Sun. This
  material would be observed as abundance anomalies in the solar wind. We
  will describe the fate of the cometary debris trail left by Comet ISON
  and what the trail can tell us about the solar corona and solar wind.

---------------------------------------------------------
Title: The study of the cavity’s morphology, density, thermal and
    magnetic properties from the SDO observations
Authors: Karna, Nishu; Zhang, J.; Pesnell, W. D.; Hess Webber, S. A.
2013SPD....44...47K    Altcode:
  Coronal cavities are circular darkened regions observed above the
  solar limb in white light and EUV coronal images. It is a region
  of low density relative to the surrounding corona. In this study,
  we are using synoptic maps made from EUV images from the Atmospheric
  Imager Assembly (AIA) instrument and vector magnetogram images from
  Helioseismic and Magnetic Imager (HMI) on the SDO to determine the
  structure and evolution of cavities. The EUV synoptic maps, constructed
  from circular rings above the limb, are found to best show cavities in
  211Å (Fe XIV, ~2.0 MK) and 193 Å (Fe XII, ~1.6 MK) and171 Å (Fe IX,
  ~0.6 MK) pass bands. Moreover, 304Å (He II, ~0.05 MK) synoptic map best
  shows the evolution of prominence associated with cavity. Magnetogram
  synoptic map constructed from the central meridian, shows the underlying
  magnetic structure of the cavity and prominence. We have also used EUV
  synoptic map to construct the polar view of the cavities. DEM analysis
  was used to calculate the temperature and density of the cavities. The
  high spatial and time resolution combined with the broad temperature
  coverage provides a consistent picture of the cavity material and
  the dynamics of the structure.Abstract (2,250 Maximum Characters):
  Coronal cavities are circular darkened regions observed above the
  solar limb in white light and EUV coronal images. It is a region
  of low density relative to the surrounding corona. In this study,
  we are using synoptic maps made from EUV images from the Atmospheric
  Imager Assembly (AIA) instrument and vector magnetogram images from
  Helioseismic and Magnetic Imager (HMI) on the SDO to determine the
  structure and evolution of cavities. The EUV synoptic maps, constructed
  from circular rings above the limb, are found to best show cavities in
  211Å (Fe XIV, ~2.0 MK) and 193 Å (Fe XII, ~1.6 MK) and171 Å (Fe IX,
  ~0.6 MK) pass bands. Moreover, 304Å (He II, ~0.05 MK) synoptic map best
  shows the evolution of prominence associated with cavity. Magnetogram
  synoptic map constructed from the central meridian, shows the underlying
  magnetic structure of the cavity and prominence. We have also used EUV
  synoptic map to construct the polar view of the cavities. DEM analysis
  was used to calculate the temperature and density of the cavities. The
  high spatial and time resolution combined with the broad temperature
  coverage provides a consistent picture of the cavity material and the
  dynamics of the structure.

---------------------------------------------------------
Title: Coronal Cavities from SDO Observations
Authors: Karna, Nishu; Zhang, J.; Pesnell, W. D.; Hess Webber, S. A.
2013shin.confE.101K    Altcode:
  Coronal cavities are circular darkened regions observed above the
  solar limb in white light and EUV coronal images. It is a region
  of low density relative to the surrounding corona. In this study,
  we are using synoptic maps made from EUV images from the Atmospheric
  Imager Assembly (AIA) instrument and vector magnetogram images from
  Helioseismic and Magnetic Imager (HMI) on the SDO to determine
  the structure and evolution of cavities. The EUV synoptic maps,
  constructed from circular rings above the limb, are found to best
  show cavities in 211Å (Fe XIV, 2.0 MK) and 193Å (Fe XII, 1.6 MK)
  and171Å (Fe IX, 0.6 MK) pass bands. Moreover, 304Å (He II, 0.05
  MK) synoptic map best shows the evolution of prominence associated
  with cavity. Magnetogram synoptic map constructed from the central
  meridian, shows the underlying magnetic structure of the cavity and
  prominence. We have also used EUV synoptic map to construct the polar
  view of the cavities. The high spatial and time resolution combined
  with the broad temperature coverage provides a consistent picture of
  the cavity material and the dynamics of the structure.

---------------------------------------------------------
Title: Exploring the Network of SDO Science
Authors: Pesnell, W. Dean; Thompson, Barbara
2013enss.conf.....P    Altcode:
  Living With a Star's Solar Dynamics Observatory invites you to its
  2013 Science Workshop to be held March 3-8, 2013 at the Hyatt Regency
  Chesapeake Bay in Cambridge, MD (http://chesapeakebay.hyatt.com/). The
  workshop is a follow-on to the "Many Spectra of Solar Activity" workshop
  held May 1-5, 2011 in Squaw Valley, CA. <P />Scientific sessions will
  feature a broad spectrum of science topics fundamental to SDO's science
  investigations: Atmospheric Imaging Assembly (AIA), EUV Variability
  Experiment (EVE), and Helioseismic and Magnetic Imager (HMI), as well
  as the overlap between SDO and other scientific missions and activities.

---------------------------------------------------------
Title: Polar Coronal Hole Areas from 1996 through Present
Authors: Hess Webber, S. A.; Karna, N.; Pesnell, W. D.
2013enss.confE..20H    Altcode:
  The evolutionary analysis of the polar coronal hole (PCH) areas from
  the beginning of solar cycle 23 through the cycle 24 minimum has
  introduced several new scientific results regarding changes in the
  magnetic field configuration during the past solar cycle. Observations
  show that the PCH sizes peak at discrete times in the two hemispheres,
  suggesting that the two poles reach solar minimum (magnetic maximum)
  up to three years apart. The northern polar hole has also decreased
  significantly in size since 2010, while the southern hole has remained
  stable. This indicates that the northern hemisphere has already reached
  solar maximum even though the southern hemisphere has yet to peak.

---------------------------------------------------------
Title: EUV Emission from Sungrazing Comets
Authors: Bryans, Paul; Pesnell, W. Dean
2013enss.confE..33B    Altcode:
  The EUV emission resulting from comets' passage through the solar
  atmosphere has opened many exciting avenues of study. The observations
  show the sublimated cometary material to interact with ambient magnetic
  field and highlight magnetic features that are not normally visible with
  EUV telescopes. The first step, however, is to explain why the comet
  produces the EUV emission. In this talk, I will outline a model that
  describes the interaction of the cometary atmosphere with the quiescent
  solar background and results in such emission. In particular, the model
  accurately predicts the temporal and wavelength response of the emission
  detected by SDO/AIA. After describing the emission process, I will go on
  to discuss what we can learn about the corona from these observations.

---------------------------------------------------------
Title: Coronal Cavities from SDO Observations
Authors: Karna, N.; Zhang, J.; Pesnell, W. D.; Hess Webber, S. A.
2013enss.confE.134K    Altcode:
  Coronal cavities are circular darkened regions observed above the solar
  limb in white light and EUV coronal images. It is believed a region of
  low density relative to the surrounding corona. In this study, we are
  using synoptic maps made from EUV images from the Atmospheric Imager
  Assembly (AIA) instrument on the SDO to determine the structure and
  evolution of cavities. The synoptic maps, constructed from circular
  rings above the limb, are found to best show cavities in 211Å (Fe
  XIV, 2.0 MK) and 193 Å (Fe XII, 1.6 MK) and171 Å (Fe IX, 0.6 MK)
  pass bands. Moreover, 304Å (He II, 0.05 MK) synoptic map best shows
  the evolution of prominence associated with cavity. The high spatial
  and time resolution combined with the broad temperature coverage
  provides a consistent picture of the cavity material and the dynamics
  of the structure. Our goal in this work is to study the cavity's sizes
  (height, diameter and length), density and temperature properties.

---------------------------------------------------------
Title: The Solar Dynamics Observatory after three years in orbit
Authors: Poland, D.; Ekinci, F. M.; Fink, D.; Pesnell, W. D.
2013aero.confE.183P    Altcode:
  There are three instruments aboard the Solar Dynamics Observatory
  (SDO): EVE, which measures the extreme ultraviolet irradiance of the
  Sun; AIA, which images the Sun at high cadence in ten wavelengths; and
  HMI, which measures the solar magnetic field and velocity of the solar
  surface. These instruments have returned roughly 1.5 Tbytes of solar
  data per day nearly continuously since the beginning of SDO's science
  operations in May 2010, which has been facilitated by a continuous
  downlink from geosynchronous orbit to SDO's dedicated pair of 18-m
  antennas in White Sands, New Mexico. Science data returned from SDO
  is continually advancing knowledge of and research in prominence and
  filament eruptions, late phase flares, and the solar vector magnetic
  field, amongst other areas. Additionally, observations made during orbit
  maintenance, collision avoidance, and ground system operations have
  yielded lessons learned about the need to account for extreme weather
  in antenna design and the importance of clear, direct communication
  channels with other satellite operators. These observations and lessons
  are being used to improve the SDO ground system and operations approach
  and may prove useful for future mission design.

---------------------------------------------------------
Title: Investigating Coronal Activity by Release Using Sublimation
Authors: Moore, T. E.; Bryans, P.; Pesnell, W. D.; Thompson, B. J.
2012AGUFMSH21D..05M    Altcode:
  Plasma tails left by sun-grazing comets are visible in EUV, expanding
  their traditional role as "windsocks" into the low corona and serving
  as natural "chemical release" experiments. SDO obtained spectrally
  resolved video imagery of passages as close as 0.15 Rs to the solar
  photosphere at 12 sec frame cadence. Vaporized cometary materials
  form sublimation trails or "subtrails" that persist as long as 20
  min. in 13.1 and 17.1 nm channels. Striation along local magnetic flux
  tubes implies filamentation of the visible plasma, and the subtrails
  exhibit substantial deviations from the comet orbital track. These
  reveal coronal winds and shears with velocities that are comparable to
  the comet velocity of up to 600 km/s. We analyze the likely origins
  and directionality of these winds and their implications for coronal
  heating in the altitude range where ion-neutral collision mean free
  paths are longer than the gyro radius but shorter than the atmospheric
  scale height, that is, the solar transition region. With active impact
  or photo-ionization, and charge exchange, the inferred super-thermal,
  sub-Alfvenic ion-neutral relative velocities will lead to ion pick-up
  distributions that decay or relax into "kappa" distributions with
  super-thermal power law tails that are relevant to the formation of
  the corona.

---------------------------------------------------------
Title: Time-dependent Chemistry of Detritus from Sun-grazing Comets
Authors: Pesnell, W. D.; Bryans, P.
2012AGUFMSH13B2253P    Altcode:
  As a sun-grazing comet passes the Sun at perihelion it leaves behind
  a trail of water vapor and detritus. The latter are grains of stony
  material that rapidly heat and vaporize in the intense radiation field
  of the solar photosphere. A large amount of O is produced from both the
  water and the stony material. The atomic material does not continue
  along the comet's orbital path but appears to move along the ambient
  magnetic field. This requires an ionization mechanism that rapidly
  converts the neutral atoms into ions. We propose two models of the
  time-dependent chemistry that can be used to calculate the ionization
  balance of O and Fe. One is an extension of the Haser model to include
  many stages of ionization but without recombination. The advantage
  is that an analytic solution can be derived for an arbitrary numbers
  of ionization stages. Once the time dependence is known it can be
  converted to the radial profile in either spherical or cylindrical
  symmetry. The other model integrates in time the equations describing
  ionization/recombination balance. Both types of solutions can be
  numerically inverted to estimate the radiance profiles. The models give
  the same sequence to the ionization stages, but the time dependence
  and radial profiles are shown to differ. Although we concentrate on
  the O and Fe chemistry because it is observed from SDO/AIA, any atom
  can be considered.

---------------------------------------------------------
Title: Solar Cycle Predictions (Invited Review)
Authors: Pesnell, W. Dean
2012SoPh..281..507P    Altcode: 2012SoPh..tmp..135P; 2012SoPh..tmp..105P
  Solar cycle predictions are needed to plan long-term space missions,
  just as weather predictions are needed to plan the launch. Fleets
  of satellites circle the Earth collecting many types of science data,
  protecting astronauts, and relaying information. All of these satellites
  are sensitive at some level to solar cycle effects. Predictions of drag
  on low-Earth orbit spacecraft are one of the most important. Launching
  a satellite with less propellant can mean a higher orbit, but
  unanticipated solar activity and increased drag can make that a
  Pyrrhic victory as the reduced propellant load is consumed more
  rapidly. Energetic events at the Sun can produce crippling radiation
  storms that endanger all assets in space. Solar cycle predictions also
  anticipate the shortwave emissions that cause degradation of solar
  panels. Testing solar dynamo theories by quantitative predictions
  of what will happen in 5 - 20 years is the next arena for solar
  cycle predictions. A summary and analysis of 75 predictions of the
  amplitude of the upcoming Solar Cycle 24 is presented. The current
  state of solar cycle predictions and some anticipations of how those
  predictions could be made more accurate in the future are discussed.

---------------------------------------------------------
Title: The Extreme-ultraviolet Emission from Sun-grazing Comets
Authors: Bryans, P.; Pesnell, W. D.
2012ApJ...760...18B    Altcode: 2012arXiv1209.5708B
  The Atmospheric Imaging Assembly (AIA) on the Solar Dynamics Observatory
  has observed two Sun-grazing comets as they passed through the solar
  atmosphere. Both passages resulted in a measurable enhancement of
  extreme-ultraviolet (EUV) radiance in several of the AIA bandpasses. We
  explain this EUV emission by considering the evolution of the cometary
  atmosphere as it interacts with the ambient solar atmosphere. Molecules
  in the comet rapidly sublimate as it approaches the Sun. They are
  then photodissociated by the solar radiation field to create atomic
  species. Subsequent ionization of these atoms produces a higher
  abundance of ions than normally present in the corona and results in
  EUV emission in the wavelength ranges of the AIA telescope passbands.

---------------------------------------------------------
Title: Coronal Cavities from SDO Observations
Authors: Karna, Nishu; Hess Webber, Shea A.; Pesnell, W. Dean; Zhang,
   Jie; Kirk, M. S.
2012shin.confE.207K    Altcode:
  Coronal cavities are circular darkened regions observed above the
  solar limb in white light and EUV coronal images. It is a region of
  low density relative to the surrounding corona. In this study, we are
  using synoptic maps made from EUV images from the Atmospheric Imager
  Assembly (AIA) instrument on the SDO to determine the structure and
  evolution of cavities. The synoptic maps, constructed from circular
  rings above the limb, are found to best show cavities in 211Å (Fe XIV,
  2.0 MK) and 193 Å (Fe XII, 1.6 MK) pass bands. The high spatial and
  time resolution combined with the broad temperature coverage provides
  a consistent picture of the cavity material and the dynamics of the
  structure. Our goal is to study the cavity"s sizes (height, diameter
  and length), density and temperature properties. Moreover, we will
  examine the correlation between cavity morphology and underlying
  magnetic field distribution using Heliosesmic and Magnetic imager
  (HMI) instrument on SDO. This study will shed light on the origin,
  evolution and dynamics of coronal cavities.

---------------------------------------------------------
Title: Solar Cycle 23/24 Polar Coronal Hole Areas: Scientific Results
Authors: Hess Webber, Shea A.; Karna, Nishu; Pesnell, W. Dean
2012shin.confE.118H    Altcode:
  The evolutionary analysis of the polar coronal hole (PCH) areas from
  the beginning of solar cycle 23 through the cycle 24 minimum has
  introduced several new scientific results regarding changes in the
  magnetic field configuration during the past solar cycle. Observations
  show that the PCH sizes peak at discrete times in the two hemispheres,
  suggesting that the two poles reach solar minimum (magnetic maximum)
  up to three years apart. The northern polar hole has also decreased
  significantly in size since 2010, while the southern hole has remained
  stable. This indicates that the northern hemisphere has already reached
  solar maximum even though the southern hemisphere has yet to peak. The
  relationship between the temporal difference of the PCH area peaks at
  solar minimum and that of the area drop-offs during solar maximum are
  under investigation.

---------------------------------------------------------
Title: The Journey of Sungrazing Comet Lovejoy
Authors: Bryans, Paul; A'Hearn, M.; Battams, K.; Biesecker, D.;
   Bodewits, D.; Boice, D.; Brown, J.; Caspi, A.; Chodas, P.; Hudson,
   H.; Jia, Y.; Jones, G.; Keller, H. U.; Knight, M.; Linker, J.; Lisse,
   C.; Liu, W.; McIntosh, S.; Pesnell, W. D.; Raymond, J.; Saar, S.;
   Saint-Hilaire, P.; Schrijver, C.; Snow, M.; Tarbell, T.; Thompson,
   W.; Weissman, P.; Comet Lovejoy Collaboration Team
2012AAS...22052507B    Altcode:
  Comet Lovejoy (C/2011 W3) was the first sungrazing comet, observed
  by space-based instruments, to survive perihelion passage. First
  observed by ground-based telescopes several weeks prior to perihelion,
  its journey towards the Sun was subsequently recorded by several solar
  observatories, before being observed in the weeks after perihelion by
  a further array of space- and ground-based instruments. Such a surfeit
  of wide-ranging observations provides an unprecedented insight into
  both sungrazing comets themselves, and the solar atmosphere through
  which they pass. This paper will summarize what we have learnt from the
  observations thus far and offer some thoughts on what future sungrazing
  comets may reveal about comets, the Sun, and their interaction.

---------------------------------------------------------
Title: The Solar Polar Coronal Holes in Solar Cycle 24
Authors: Hess Webber, Shea; Karna, N.; Pesnell, W. D.; Kirk, M. S.
2012AAS...22020201H    Altcode:
  We have measured the area of the solar polar coronal holes in both
  hemispheres. One data series uses synoptic maps from two instruments
  on SOHO and the AIA instrument on SDO. The other used the perimeter
  tracking method on data from SoHO EIT. This allows us to calculate the
  areas of the solar polar coronal holes from the beginning of Solar Cycle
  23 up to late 2010. This method used synoptic maps constructed from
  170 Carrington Rotations of the 171, 195, and 304 Å channels of the
  Extreme-ultraviolet Imaging Telescope (EIT) on SoHO. Our second method
  used synoptic maps constructed from the Michelson Doppler Imager (MDI)
  for 187 Carrington Rotations from mid 1996 through 2010. In this method,
  polar coronal holes are easily distinguished from the equatorial coronal
  hole regions. The north and south polar hole areas were noticeably
  smaller in the recent minimum than they were at the beginning of Solar
  Cycle 23. We compared these polar hole areas with the polar coronal
  hole area found using a perimeter tracking to analyze a series of 171,
  195, and 304 Å full disk images from EIT to measure the perimeter of
  polar coronal holes as they appear on the limbs. It is found that both
  the Northern and Southern polar coronal hole areas obtained from the
  perimeter tracking method similar to those from the synoptic maps. The
  coronal hole areas will be compared with the polar magnetic fields to
  estimate what phase of the solar cycle the hemispheres have reached.

---------------------------------------------------------
Title: The EUV Emission from Sun-Grazing Comets
Authors: Bryans, Paul; Pesnell, W. D.
2012AAS...22042305B    Altcode:
  The Atmospheric Imaging Assembly (AIA) on the Solar Dynamics Observatory
  (SDO) has, to date, viewed two Sun-grazing comets as they passed
  through the solar corona. Both passages resulted in the significant
  enhancement of Extreme Ultraviolet (EUV) emission in several of
  the AIA bandpasses. We explain this EUV emission by considering the
  evolution of the cometary atmosphere as it interacts with the ambient
  solar atmosphere. Water ice in the comet rapidly sublimates as it
  approaches the Sun. This water vapor is then photodissociated by
  the solar radiation field to create atomic H and O. Other molecules
  present in the comet also evaporate and dissociate to give atomic
  Fe and other metals. Subsequent ionization of these atoms produces a
  high abundance of ions not normally present at the temperature of the
  corona and results in EUV emission in the wavelength ranges of the
  AIA telescopes. Understanding the EUV emission places constraints on
  the cometary composition and provides valuable insight to the nature
  of the upper solar atmosphere.

---------------------------------------------------------
Title: Coronal Cavities from SDO Observations
Authors: Karna, Nishu; Hess Webber, S. A.; Pesnell, W. D.; Zhang,
   J.; Kirk, M. S.
2012AAS...22020204K    Altcode:
  Coronal cavities are circular darkened regions observed above the
  solar limb in white light and EUV coronal images. It is a region of
  low density relative to the surrounding corona. In this study, we are
  using synoptic maps made from EUV images from the Atmospheric Imager
  Assembly (AIA) instrument on the SDO to determine the structure and
  evolution of cavities. The synoptic maps, constructed from circular
  rings above the limb, are found to best show cavities in 211Å (Fe XIV,
  2.0 MK) and 193 Å (Fe XII, 1.6 MK) pass bands. The high spatial and
  time resolution combined with the broad temperature coverage provides
  a consistent picture of the cavity material and the dynamics of the
  structure. Our goal is to study the cavity’s sizes (height, diameter
  and length), density and temperature properties. Moreover, we will
  examine the correlation between cavity morphology and underlying
  magnetic field distribution using Heliosesmic and Magnetic imager
  (HMI) instrument on SDO. This study will shed light on the origin,
  evolution and dynamics of coronal cavities.

---------------------------------------------------------
Title: The Solar Dynamics Observatory (SDO) Education and Outreach
(E/PO) Program: Changing Perceptions One Program at a Time
Authors: Drobnes, E.; Littleton, A.; Pesnell, W. D.; Beck, K.; Buhr,
   S.; Durscher, R.; Hill, S.; McCaffrey, M.; McKenzie, D. E.; Myers,
   D.; Scherrer, D.; Wawro, M.; Wolt, A.
2012SoPh..275..391D    Altcode: 2011SoPh..tmp..420D; 2011SoPh..tmp..424D; 2011SoPh..tmp..367P
  We outline the context and overall philosophy for the combined Solar
  Dynamics Observatory (SDO) Education and Public Outreach (E/PO)
  program, present a brief overview of all SDO E/PO programs along with
  more detailed highlights of a few key programs, followed by a review
  of our results to date, conclude a summary of the successes, failures,
  and lessons learned, which future missions can use as a guide, while
  incorporating their own content to enhance the public's knowledge
  and appreciation of science and technology as well as its benefit
  to society.

---------------------------------------------------------
Title: Destruction of Sun-Grazing Comet C/2011 N3 (SOHO) Within the
    Low Solar Corona
Authors: Schrijver, C. J.; Brown, J. C.; Battams, K.; Saint-Hilaire,
   P.; Liu, W.; Hudson, H.; Pesnell, W. D.
2012Sci...335..324S    Altcode:
  Observations of comets in Sun-grazing orbits that survive solar
  insolation long enough to penetrate into the Sun's inner corona provide
  information on the solar atmosphere and magnetic field as well as on
  the makeup of the comet. On 6 July 2011, the Solar Dynamics Observatory
  (SDO) observed the demise of comet C/2011 N3 (SOHO) within the low solar
  corona in five wavelength bands in the extreme ultraviolet (EUV). The
  comet penetrated to within 0.146 solar radius (~100,000 kilometers)
  of the solar surface before its EUV signal disappeared. Before that,
  material released into the coma - at first seen in absorption - formed
  a variable EUV-bright tail. During the final 10 minutes of observation
  by SDO's Atmospheric Imaging Assembly, ~6 × 10^8 to 6 × 10^10 grams
  of total mass was lost (corresponding to an effective nucleus diameter
  of ~10 to 50 meters), as estimated from the tail's deceleration due to
  interaction with the surrounding coronal material; the EUV absorption
  by the comet and the brightness of the tail suggest that the mass was
  at the high end of this range. These observations provide evidence
  that the nucleus had broken up into a family of fragments, resulting
  in accelerated sublimation in the Sun's intense radiation field.

---------------------------------------------------------
Title: The Solar Dynamics Observatory (SDO)
Authors: Pesnell, W. Dean; Thompson, B. J.; Chamberlin, P. C.
2012SoPh..275....3P    Altcode:
  The Solar Dynamics Observatory (SDO) was launched on 11 February 2010 at
  15:23 UT from Kennedy Space Center aboard an Atlas V 401 (AV-021) launch
  vehicle. A series of apogee-motor firings lifted SDO from an initial
  geosynchronous transfer orbit into a circular geosynchronous orbit
  inclined by 28° about the longitude of the SDO-dedicated ground station
  in New Mexico. SDO began returning science data on 1 May 2010. SDO
  is the first space-weather mission in NASA's Living With a Star (LWS)
  Program. SDO's main goal is to understand, driving toward a predictive
  capability, those solar variations that influence life on Earth and
  humanity's technological systems. The SDO science investigations will
  determine how the Sun's magnetic field is generated and structured,
  how this stored magnetic energy is released into the heliosphere and
  geospace as the solar wind, energetic particles, and variations in the
  solar irradiance. Insights gained from SDO investigations will also
  lead to an increased understanding of the role that solar variability
  plays in changes in Earth's atmospheric chemistry and climate. The
  SDO mission includes three scientific investigations (the Atmospheric
  Imaging Assembly (AIA), Extreme Ultraviolet Variability Experiment
  (EVE), and Helioseismic and Magnetic Imager (HMI)), a spacecraft bus,
  and a dedicated ground station to handle the telemetry. The Goddard
  Space Flight Center built and will operate the spacecraft during
  its planned five-year mission life; this includes: commanding the
  spacecraft, receiving the science data, and forwarding that data to the
  science teams. The science investigations teams at Stanford University,
  Lockheed Martin Solar Astrophysics Laboratory (LMSAL), and University
  of Colorado Laboratory for Atmospheric and Space Physics (LASP) will
  process, analyze, distribute, and archive the science data. We will
  describe the building of SDO and the science that it will provide
  to NASA.

---------------------------------------------------------
Title: The EUV Emission in Comet-Solar Corona Interactions
Authors: Bryans, P.; Pesnell, W. D.; Schrijver, C. J.; Brown, J. C.;
   Battams, K.; Saint-Hilaire, P.; Liu, W.; Hudson, H. S.
2011AGUFMSH34B..05B    Altcode:
  The Atmospheric Imaging Assembly (AIA) on the Solar Dynamics Observatory
  (SDO) viewed a comet as it passed through the solar corona on 2011 July
  5. This was the first sighting of a comet by a EUV telescope. For 20
  minutes, enhanced emission in several of the AIA wavelength bands marked
  the path of the comet. We explain this EUV emission by considering
  the evolution of the cometary atmosphere as it interacts with the
  ambient solar atmosphere. Water ice in the comet rapidly sublimates
  as it approaches the Sun. This water vapor is then photodissociated,
  primarily by Ly-α, by the solar radiation field to create atomic H and
  O. Other molecules present in the comet also evaporate and dissociate
  to give atomic Fe and other metals. Subsequent ionization of these
  atoms can be achieved by a number of means, including photoionization,
  electron impact, and charge exchange with coronal protons and other
  highly-charged species. Finally, particles from the cometary atmosphere
  are thermalized to the background temperature of the corona. Each step
  could cause emission in the AIA bandpasses. We will report here on
  their relative contribution to the emission seen in the AIA telescopes.

---------------------------------------------------------
Title: Time-Series Analyses of Supergranule Characteristics Compared
    Between SDO/HMI, SOHO/MDI and Simulated Datasets
Authors: Williams, P. E.; Pesnell, W. D.
2011AGUFMSH23D..03W    Altcode:
  Supergranulation is a well-observed solar phenomenon despite its
  underlying mechanisms remaining a mystery. Originally considered to
  arise due to convective motions, alternative mechanisms have been
  suggested such as the cumulative downdrafts of granules as well as
  displaying wave-like properties. Supergranule characteristics are well
  documented, however. Supergranule cells are approximately 35 Mm across,
  have lifetimes on the order of a day and have divergent horizontal
  velocities of around 300 m/s, a factor of 10 higher than their central
  radial components. While they have been observed using Doppler methods
  for more than half a century, their existence is also observed in
  other datasets such as magnetograms and Ca II K images. These datasets
  clearly show the influence of supergranulation on solar magnetism
  and how the local field is organized by the flows of supergranule
  cells. The Heliospheric and Magnetic Imager (HMI) aboard the Solar
  Dynamics Observatory (SDO) continues to produce Doppler images enabling
  the continuation of supergranulation studies made with SOHO/MDI, but
  with superior temporal and spatial resolution. The size-distribution
  of divergent cellular flows observed on the photosphere now reaches
  down to granular scales, allowing contemporaneous comparisons between
  the two flow components. SOHO/MDI Doppler observations made during the
  minima of cycles 22/23 and 23/24 exhibit fluctuations of supergranule
  characteristics (global averages of the supergranule size, size-range
  and horizontal velocity) with periods of 3-5 days. Similar fluctuations
  have been observed in SDO/HMI Dopplergrams and the high correlation
  between co-temporal HMI &amp; MDI suggest a solar origin. Their nature
  has been probed by invoking data simulations that produce realistic
  Dopplergrams based on MDI data.

---------------------------------------------------------
Title: Using the EUV to Weigh a Sun-grazing Comet as it Disappears
    in the Solar Corona
Authors: Pesnell, W. D.; Schrijver, C. J.; Brown, J. C.; Battams,
   K.; Saint-Hilaire, P.; Hudson, H. S.; Lui, W.
2011AGUFMSH33A2040P    Altcode:
  On July 6, 2011, the Atmospheric Imaging Assembly (AIA) on the
  Solar Dynamics Observatory (SDO) observed a comet in most of its
  EUV passbands. The comet disappeared while moving through the solar
  corona. The comet penetrated to 0.146 solar radii ( ∼~100,000
  km) above the photosphere before its EUV faded. Before then, the
  comet's coma and a tail were observed in absorption and emission,
  respectively. The material in the variable tail quickly fell behind
  the nucleus. An estimate of the comet's mass based on this effect,
  one derived from insolation, and one using the tail's EUV brightness,
  all yield ∼ 50 giga-grams some 10 minutes prior to the end of
  its visibility. These unique first observations herald a new era in
  the study of Sun-grazing comets close to their perihelia and of the
  conditions in the solar corona and solar wind. We will discuss the
  observations and interpretation of the comet by SDO as well as the
  coronagraph observations from SOHO and STEREO. A search of the SOHO
  comet archive for other comets that could be observed in the SDO/AIA
  EUV channels will be described.

---------------------------------------------------------
Title: A Comparison of Solar Polar Coronal Hole Areas Between Solar
    Cycles 23 and 24
Authors: Hess Webber, Shea A.; Karna, Nishu; Pesnell, W. Dean; Kirk,
   Michael S.
2011mfpc.confE...1H    Altcode:
  We have used the perimeter tracing algorithm and analysis of EUV
  and magnetic field synoptic maps to extend our time series of polar
  coronal hole areas through solar minimum between cycles 23 and 24
  (through 2010). Both EUV algorithms use 171, 195, and 304 Å images
  from the Extreme ultraviolet Imaging Telescope (EIT) on SOHO. The
  perimeter tracing algorithm measures the polar coronal hole boundaries
  as they appear on the limbs over each polar rotation and calculates
  the enclosed area, while the synoptic method calculates the area of
  the polar coronal holes from the meridional boundary through each
  Carrington rotation. Line-of-sight magnetic field synoptic maps from
  SOHO's Michelson Doppler Imager (MDI) instrument are used to estimate
  the polar coronal hole areas via polarity signatures. We remain
  convinced that the northern polar hole area is measurably smaller in
  the recent minimum than it was at the beginning of cycle 23, while
  the southern polar hole area is roughly the same.

---------------------------------------------------------
Title: Solar Dynamics and Magnetism from the Interior to the
    Atmosphere
Authors: Pesnell, W. Dean; Thompson, Barbara
2011sdmi.conf.....P    Altcode:
  The goal of the workshop is to discuss recent advances and new problems
  in the exploration of the Sun's interior structure, solar dynamics and
  dynamo, mechanisms of sunspot and active regions formation, sources of
  solar irradiance variations, and links between the subsurface dynamics,
  flaring and CME activity. <P />NASA's Solar Dynamics Observatory (SDO)
  mission is providing a large amount of new data on solar dynamics and
  magnetic activities during the rising phase of the current and highly
  unusual solar cycle. These data are complemented by the continuing
  SOHO mission, and by ground-based observatories that include the GONG
  helioseismology network and the New Solar Telescope. This unprecedented
  amount of data provides a unique opportunity for multi-instrument
  investigations that address fundamental problems of the origin of
  solar magnetic activity at various spatial and temporal scales. <P
  />The data is being used to develop new methods for forecasting
  solar cycles, emergence and evolution of active regions and their
  flaring and CME activity. <P />The scientific program will begin
  on Monday, October 31 at 9 AM, and conclude on Friday, November
  4 at 1PM. Abstracts are solicited on the following topics: <P />-
  "Local and Global Helioseismology" - "Large-Scale Dynamics, Magnetism
  and Dynamo" - "Emerging Magnetic Flux and Subsurface Dynamics" -
  "Formation, Structure and Evolution of Sunspots and Active Regions" -
  "Numerical Simulations and Laboratory Experiments" - "Observations of
  the Solar Dynamics and Magnetism" - "Links between the Solar Interior
  and Atmosphere" - "Sources of Spectral and Total Irradiance Variations"
  - "Dynamics and Magnetic Topology of Flares and CMEs" <P />The workshop
  program will include invited and contributed talks, as well as poster
  sessions. On the last day, 4 splinter working group meetings will be
  organized: <P />1. Helioseismology (organizers R. Bogart, R. Komm,
  A. Kosovichev) 2. Vector Magnetometry (organizer T. Hoeksema and
  A. Pevtsov) 3. Feature Recognition, and Data Distribution and Access
  (organizers P. Martens and N. Hurlburt) 4. Numerical Simulations and
  Modeling (organizers N. Mansour and I. Kitiashvili)

---------------------------------------------------------
Title: An Error Analysis of Oscillations in Solar Polar Coronal
    Hole Areas
Authors: Hess Webber, Shea A.; Pesnell, W. Dean; Karna, Nishu
2011shin.confE.169H    Altcode:
  The results obtained from our polar coronal hole (PCH) area analysis
  of EUV images from the Extreme ultraviolet Imaging Telescope (EIT)
  on SOHO show an annual periodicity propagating through the data
  set. Investigations into the cause of this variability have been
  inconclusive. However, the frequency of the oscillation suggests that
  the uncertainty comes from orbital effects. We discuss the relevant
  orbital variations of the SOHO spacecraft and analytically determine
  the potential error due to those variations. These effects include the
  variations in solar B0 and L0 angles within the working coordinate
  system, and B0 projection effects of coronal material. Our goal in
  conducting this error analysis is to gain a better understanding of how
  SOHO's orbital variations affect the determination of solar coordinates,
  particularly at the limb and poles. This work is supported by the
  Solar Dynamics Observatory.

---------------------------------------------------------
Title: An Error Analysis of Oscillations in Solar Polar Coronal
    Hole Areas
Authors: Hess Webber, Shea A.; Karna, Nishu; Pesnell, W. Dean
2011shin.confE...1H    Altcode:
  The results obtained from our polar coronal hole (PCH) area analysis
  of EUV images from the Extreme ultraviolet Imaging Telescope (EIT)
  on SOHO show an annual periodicity propagating through the data
  set. Investigations into the cause of this variability have been
  inconclusive. However, the frequency of the oscillation suggests that
  the uncertainty comes from orbital effects. We discuss the relevant
  orbital variations of the SOHO spacecraft and analytically determine
  the potential error due to those variations. These effects include the
  variations in solar B0 and L0 angles within the working coordinate
  system, and B0 projection effects of coronal material. Our goal in
  conducting this error analysis is to gain a better understanding of how
  SOHO's orbital variations affect the determination of solar coordinates,
  particularly at the limb and poles. This work is supported by the
  Solar Dynamics Observatory.

---------------------------------------------------------
Title: The evolution of the Polar Coronal Hole During Solar Cycles
    23 and 24
Authors: Karna, Nishu; Hess Webber, Shea A.; Pesnell, W. Dean; Kirk,
   M. S.
2011shin.confE.168K    Altcode:
  Synoptic maps made from two instruments on SOHO are analyzed to track
  the size of the solar polar coronal holes (PCH) over Solar Cycles
  23 and 24. The first method uses 171 Å, 195 Å, and 304 Å synoptic
  maps constructed from the Extreme-ultraviolet Imaging Telescope (EIT)
  on SOHO for 145 Carrington Rotations from mid 1996 through mid 2007
  from archive. After this time, we have created the synoptic maps for
  42 Carrington Rotation to compare the fractional PCH area between two
  solar minima and extending our time series up to 2010. Our second method
  used line-of-sight magnetic field synoptic maps from SOHO's Michelson
  Doppler Imager (MDI) instrument to estimate the polar coronal hole
  area via polarity signatures for 187 Carrington Rotations from mid
  1996 through 2010. There is a good correlation between the estimated
  PCH extracted form EIT and MDI. This work was supported by the Solar
  Dynamics Observatory.

---------------------------------------------------------
Title: Solar Polar Coronal Hole Areas Through the Past Solar Minimum
Authors: Hess Webber, Shea A.; Karna, Nishu; Pesnell, W. Dean; Kirk,
   Michael S.
2011lws..workE...1H    Altcode:
  We have used the perimeter tracking algorithm and analysis of EIT
  synoptic maps to extend our time series of polar coronal hole areas
  through solar minimum (through 2010). Both algorithms use 171, 195,
  and 304 Å images from the Extreme ultraviolet Imaging Telescope (EIT)
  on SOHO, the first to measure the perimeter of polar coronal holes as
  they appear on the limbs and the second the area of the polar coronal
  hole during each Carrington rotation. Line-of-sight magnetic field
  synoptic maps are also used to estimate the polar coronal hole area. We
  have updated the time series and we are analyzing uncertainties in
  EIT ephemeris data. We remain convinced that the northern polar hole
  area is measurably smaller in the recent minimum than it was at the
  beginning of cycle 23, while the southern polar hole area is roughly
  the same. Polar hole areas found via perimeter tracking agree within
  uncertainty with those determined using EIT synoptic map analysis.

---------------------------------------------------------
Title: Solar Polar Coronal Hole Areas Through the Past Solar Minimum
Authors: Hess Webber, Shea; Karna, N.; Pesnell, W. D.; Kirk, M.
2011SPD....42.1825H    Altcode: 2011BAAS..43S.1825H
  We have used the perimeter tracking algorithm and analysis of EIT
  synoptic maps to extend our timeseries of polar coronal hole areas
  through solar minimum (through 2010). Both algorithms use 171, 195,
  and 304 Å images from the Extreme ultraviolet Imaging Telescope (EIT)
  on SOHO, the first to measure the perimeter of polar coronal holes as
  they appear on the limbs and the second the area of the polar coronal
  hole during each Carrington rotation. Line-of-sight magnetic field
  synoptic maps are also used to estimate the polar coronal hole area. We
  have updated the time series and we are analyzing uncertainties in
  EIT ephemeris data. We remain convinced that the northern polar hole
  area is measurably smaller in the recent minimum than it was at the
  beginning of cycle 23, while the southern polar hole area is roughly
  the same. Polar hole areas found via perimeter tracking agree within
  uncertainty with those determined using EIT synoptic map analysis. This
  work was supported by the Solar Dynamics Observatory.

---------------------------------------------------------
Title: Time-Series Analysis of Supergranule Characteristics Derived
    from SOHO/MDI Dopplergrams.
Authors: Williams, Peter E.; Pesnell, W. D.
2011SPD....42.1725W    Altcode: 2011BAAS..43S.1725W
  Supergranulation exhibits both radial and horizontal velocity
  components within Doppler data. The weak, radial flows drag magnetic
  field lines to the surface while their strong, divergent, horizontal
  counterparts advect the field to the edges of the supergranulation
  cells. Field congregation at supergranule boundaries is observed in
  magnetic filed images and via Ca II K observations of the chromospheric
  network. <P />Supergranulation characteristics, such as typical sizes
  and velocities, have been studied using MDI Doppler data and tracked
  over 60-days of observations made in 1996 and 2008, relating to periods
  of solar minimum. Time-series of these characteristics exhibit regular
  fluctuations on the order of 3-5 days. These time-series are analyzed
  to extract frequency information and cross-correlated to investigate any
  temporal link between the characteristics. <P />Whether the fluctuations
  are an instrumental artifact is studied by comparing contemporaneous
  time series produced from SOHO/MDI and SDO/HMI Dopplergrams. There
  exists a high correlation between the two time-series showing that
  the fluctuations are solar in origin.

---------------------------------------------------------
Title: Comparisons of Supergranule Characteristics During the Solar
    Minima of Cycles 22/23 and 23/24
Authors: Williams, Peter E.; Pesnell, W. Dean
2011SoPh..270..125W    Altcode: 2011SoPh..tmp...28W; 2011arXiv1103.1696W
  Supergranulation is a component of solar convection that manifests
  itself on the photosphere as a cellular network of around 35 Mm across,
  with a turnover lifetime of 1 - 2 days. It is strongly linked to the
  structure of the magnetic field. The horizontal, divergent flows within
  supergranule cells carry local field lines to the cell boundaries, while
  the rotational properties of supergranule upflows may contribute to the
  restoration of the poloidal field as part of the dynamo mechanism, which
  controls the solar cycle. The solar minimum at the transition from cycle
  23 to 24 was notable for its low level of activity and its extended
  length. It is of interest to study whether the convective phenomena
  that influence the solar magnetic field during this time differed in
  character from periods of previous minima. This study investigates
  three characteristics (velocity components, sizes and lifetimes) of
  solar supergranulation. Comparisons of these characteristics are made
  between the minima of cycles 22/23 and 23/24 using MDI Doppler data from
  1996 and 2008, respectively. It is found that whereas the lifetimes are
  equal during both epochs (around 18 h), the sizes are larger in 1996
  (35.9 ± 0.3 Mm) than in 2008 (35.0 ± 0.3 Mm), while the dominant
  horizontal velocity flows are weaker (139 ± 1 m s<SUP>−1</SUP>
  in 1996; 141 ± 1 m s<SUP>−1</SUP> in 2008). Although numerical
  differences are seen, they are not conclusive proof of the most recent
  minimum being inherently unusual.

---------------------------------------------------------
Title: Comparison of Vector Magnetograms from the Solenoidal and
    Irrotational Components of the Magnetic Field
Authors: Bryans, Paul; Pesnell, W. D.
2011SPD....42.2108B    Altcode: 2011BAAS..43S.2108B
  According to the Helmholtz Theorem, the solar magnetic field can be
  defined in terms of an irrotational and a solenoidal component. We will
  discuss the partitioning of the field into these components as a means
  of attributing elements of the magnetic field to its vorticity and
  divergence. We will then discuss the advantages of this decomposition
  as a metric for comparing vector magnetograms of varying spatial and
  temporal resolution.

---------------------------------------------------------
Title: Properties of Supergranulation During the Solar Minima of
    Cycles 22/23 and 23/24
Authors: Williams, Peter E.; Pesnell, W. Dean
2011JPhCS.271a2082W    Altcode:
  The solar minimum at the transition from cycle 23 to 24 was notable for
  its low level of activity and its extended duration. Among the various
  fields of study, the evolution of the solar convection zone may provide
  insight into the causes and consequences of this recent minimum. This
  study continues previous investigations of the characteristics of
  solar supergranulation, a convection component strongly linked to the
  structure of the magnetic field, namely the time-evolution of the global
  mean of supergranule cell size, determined from spectral analysis of
  MDI Dopplergrams from the two previous solar minima. Analyses of the
  global mean of supergranule sizes show a quasi-oscillatory nature to the
  evolution of this particular supergranule characteristic. Performing
  similar analyses on realistic, synthetic Doppler images show similar
  time-dependent characteristics. We conclude that the observed
  fluctuations are not observational artifacts, and that an underlying
  trend exists within the evolution of the supergranulation network.

---------------------------------------------------------
Title: Analysis of Photospheric Convection Cells with SDO/HMI
Authors: Williams, P. E.; Pesnell, W. D.
2010AGUFMSH14A..06W    Altcode:
  Supergranulation is a component of solar convection that assists in
  the outward transportation of internal energy. Supergranule cells
  are approximately 35 Mm across, have lifetimes on the order of a day
  and have divergent horizontal velocities of around 300 m/s, a factor
  of 10 higher than their central radial components. While they have
  been observed using Doppler methods for around half a century, their
  existence is also observed in other datasets such as magnetograms
  and Ca II K images. These datasets clearly show the influence of
  supergranulation on solar magnetism and how the local field is organized
  by the flows of supergranule cells. The Heliospheric and Magnetic Imager
  (HMI) aboard SDO is making fresh observations of convection phenomena
  at a higher cadence and a higher resolution that should make granular
  features visible. Granulation and supergranulation characteristics can
  now be compared within the same datasets, which may lead to further
  understanding of any mutual influences. The temporal and spatial
  enhancements of HMI will also reduce the noise level within studies
  of convection so that more detailed studies of their characteristics
  may be made. We present analyses of SDO/HMI Dopplergrams that provide
  new estimates of convection cell sizes, lifetimes, and velocity flows,
  as well as the rotation rates of the convection patterns across the
  solar disk. We make comparisons with previous data produced by MDI,
  as well as from data simulations.

---------------------------------------------------------
Title: Comparisons of Supergranule Properties from SDO/HMI with
    Other Datasets
Authors: Pesnell, W. D.; Williams, P. E.
2010AGUFMSH21C..02P    Altcode:
  While supergranules, a component of solar convection, have been well
  studied through the use of Dopplergrams, other datasets also exhibit
  these features. Quiet Sun magnetograms show local magnetic field
  elements distributed around the boundaries of supergranule cells,
  notably clustering at the common apex points of adjacent cells, while
  more solid cellular features are seen near active regions. Ca II K
  images are notable for exhibiting the chromospheric network representing
  a cellular distribution of local magnetic field lines across the solar
  disk that coincides with supergranulation boundaries. Measurements
  at 304 Å further above the solar surface also show a similar pattern
  to the chromospheric network, but the boundaries are more nebulous in
  nature. While previous observations of these different solar features
  were obtained with a variety of instruments, SDO provides a single
  platform, from which the relevant data products at a high cadence and
  high-definition image quality are delivered. The images may also be
  cross-referenced due to their coincidental time of observation. We
  present images of these different solar features from HMI &amp; AIA
  and use them to make composite images of supergranules at different
  atmospheric layers in which they manifest. We also compare each data
  product to equivalent data from previous observations, for example
  HMI magnetograms with those from MDI.

---------------------------------------------------------
Title: “ALTITUDE Variation” of the CO2(V2)-O Quenching Rate
    Coefficient in Mesosphere and Lower Thermosphere
Authors: Feofilov, A.; Kutepov, A.; She, C.; Smith, A. K.; Pesnell,
   W. D.; Goldberg, R. A.
2010AGUFMSA52A..07F    Altcode:
  Among the processes governing the energy balance in the mesosphere and
  lower thermosphere (MLT), the quenching of CO2(ν2) vibrational levels
  by collisions with oxygen atoms plays an important role. However, the
  k(CO2-O) values measured in the lab and retrieved from atmospheric
  measurements vary from 1.5 x 10-12 cm3 s-1 through 9.0 x 10-12 cm3
  s-1 that requires further studying. In this work we used synergistic
  data from a ground based lidar and a satellite infrared radiometer
  to estimate k(CO2-O). We used the night- and daytime temperatures
  between 80 and 110 km measured by the Colorado State University
  narrow-band sodium (Na) lidar located at Fort Collins, Colorado
  (41N, 255E) as ground truth of the SABER/TIMED nearly simultaneous
  (±10 minutes ) and common volume (within ±1 degree in latitude,
  ±2 degrees in longitude) observations. For each altitude in 80-110
  km interval we estimate an “optimal” value of k(CO2-O) needed to
  minimize the discrepancy between the simulated 15 μm CO2 radiance and
  that measured by the SABER/TIMED instrument. The k(CO2-O) obtained in
  this way varies in altitude from 3.5 x 10-12 cm3 s-1 at 80 km to 5.2
  x 10-12 cm3 s-1 for altitudes above 95 km. We discuss this variation
  of the rate constant and its impact on temperature retrievals from 15
  μm radiance measurements and on the energy budget of MLT.

---------------------------------------------------------
Title: An Update of the Automatic Detection of Polar Coronal Holes
    in the EUV
Authors: Hess Webber, Shea A.; Karna, Nishu; Pesnell, W. Dean; Kirk,
   Michael S.
2010eddy.confE...1H    Altcode:
  An automated detection method of polar coronal holes was presented
  by Kirk et al. in 2009. This method, called perimeter tracking, uses
  a series of 171, 195, and 304 Å full disk images from the Extreme
  ultraviolet Imaging Telescope (EIT) on SOHO to measure the perimeter
  of polar coronal holes as they appear on the limbs. We have updated
  the previous time series, which ranged from mid 1996 through 2007,
  up to the most recently available EIT data in 2010, and refined the
  detection parameters, adjusting them to fit the data more precisely
  and accurately. Additionally, we increased our analysis to utilize
  all available EIT images rather than one image per day in the previous
  work. We find the wavelength average of the northern hole is about 5.5%
  of the solar surface area while the southern hole average measures
  about 4.5% during 1996 in the revised data set. These values are
  somewhat larger then we previously reported due to the improvements in
  the algorithm. We also find that in 2010, the northern and southern
  hole areas are about 3.0% and 3.5% of the total solar surface,
  respectively. The north and south polar hole areas are now noticeably
  smaller in the recent minimum than they were at the beginning of cycle
  23. This is especially true in the northern hemisphere. We will compare
  these polar hole areas with the total coronal hole area found using
  EIT synoptic maps over the same time series and wavelengths.

---------------------------------------------------------
Title: An Update of the Automatic Detection of Polar Coronal Holes
    in the EUV
Authors: Hess Webber, Shea A.; Karna, Nishu; Pesnell, W. Dean; Kirk,
   Michael S.
2010shin.confE...1H    Altcode:
  An automated detection method of polar coronal holes was presented
  by Kirk et al. in 2009. This method, called perimeter tracking, uses
  a series of 171, 195, and 304 Å full disk images from the Extreme
  ultraviolet Imaging Telescope (EIT) on SOHO to measure the perimeter
  of polar coronal holes as they appear on the limbs. We have updated
  the previous time series, which ranged from mid 1996 through 2007,
  up to the most recently available EIT data in 2010, and refined the
  detection parameters, adjusting them to fit the data more precisely
  and accurately. Additionally, we increased our analysis to utilize
  all available EIT images rather than one image per day in the previous
  work. We had observed the area of the northern polar hole in 1996, at
  the beginning of solar cycle 23, to be about 4.2% of the total solar
  surface area. The area of the southern polar hole was observed to be
  about 4.0% in 1996. These numbers are slightly larger in the revised
  data set, the northern hole at about 5.5% of the solar surface area in
  1996 and the southern hole measuring about 4.5%. We further find that
  in 2010, the northern and southern hole areas are about 2.8% and 3.0%
  of the total solar surface, respectively. The north and south polar
  hole areas are no more than 1/3 smaller now than they were at the
  beginning of cycle 23. We will compare these polar hole areas with
  the total coronal hole area found using EIT synoptic maps over the
  same time series and wavelengths

---------------------------------------------------------
Title: Automated Detection of Polar Coronal Holes in EUV
Authors: Pesnell, W. Dean; Hess Webber, Shea A.; Karna, Nishu; Kirk,
   Michael S.
2010shin.confE.158P    Altcode:
  Perimeter tracking is an automated detection method of polar coronal
  holes that uses full-disk images to measure the perimeter of polar
  coronal holes as they appear on the limbs. We applied this technique
  to images at three wavelengths (171, 195, and 304 Å) from the
  Extreme ultraviolet Imaging Telescope (EIT) on SOHO. We have updated
  the previous time series to the most recently available EIT data in
  2010, and refined the detection parameters, adjusting them to more
  accurately fit the data. We also modified the analysis to use all
  available EIT images rather than the one image per day used in the
  previous work. With these changes, the northern polar hole area in the
  304 channel is observed to be about 4.4% of the solar surface area in
  the previous solar minimum (1996/1997) while the southern hole measures
  about 4%. We also find that the northern polar hole reached a maximum
  area of about 3.7% in 2007/2008 while the southern hole area reached
  a maximum of about 4% in mid-2009. We will compare these polar hole
  areas with the areas found using EIT synoptic maps over the same time
  period and wavelengths.

---------------------------------------------------------
Title: Photospheric Manifestations of Supergranules during the Last
    Two Solar Minima
Authors: Williams, P. E.; Pesnell, W. D.
2010ASPC..428..127W    Altcode: 2010arXiv1004.0936W
  Solar supergranulation plays an important role in generating
  and structuring the solar magnetic field and as a mechanism
  responsible for the 11-year solar cycle. It is clearly detected
  within SOHO/MDI Dopplergrams, from which a variety of properties may
  be derived. Techniques that extract spatial, temporal, and kinematic
  characteristics and provide comparisons for the two most recent solar
  minima are described. Although supergranule lifetimes are comparable
  between these minima, their sizes may be slightly smaller during the
  recent minimum.

---------------------------------------------------------
Title: Comparisons of Photospheric Convection Cell Characteristics
    During the Solar Minima of Cycles 22-23 and 23-24
Authors: Williams, Peter E.; Pesnell, W. D.
2010AAS...21631702W    Altcode: 2010BAAS...41..898W
  With its elongated tail and extended periods of zero activity, the
  period marking the transition from solar cycle 23 to 24 has seemed
  peculiar when compared to other minima. Among the various phenomena
  studied, the evolution of the solar convection zone may provide
  insight into the causes and consequences of this recent minimum. <P
  />Convection in the Sun plays an important role in generating and
  structuring the solar magnetic field and as a mechanism responsible
  for the 11-year solar cycle. The observed phenomena are strongly
  linked within both observational and physical regimes. <P />This study
  uses SOHO/MDI Dopplergrams to highlight supergranulation within the
  line-of-sight velocity data. Suites of analysis methods are applied to
  time-series of Doppler images to quantitatively describe supergranule
  flow velocities, spatial scales and temporal lifetimes. <P />The
  results show similarities in supergranule evolution (1/e lifetimes
  of 18 hours), while their sizes are smaller and their flows stronger
  during the 23-24 minimum compared to 22-23. We also present provisional
  results of statistical analyses performed both within and between
  the various data sets, some of which tend to show a quasi-oscillatory
  nature. <P />Future studies to place this work in the wider context of
  the solar cycle are discussed, as a whole as well as investigations
  of supergranule characteristics found in various other data such as
  magnetograms and CaIIK images. Observed hemispheric asymmetries will be
  presented and how our methods may be applied to further these enquiries.

---------------------------------------------------------
Title: The Solar Dynamics Observatory: Your eye on the Sun
Authors: Pesnell, William
2010cosp...38.4183P    Altcode: 2010cosp.meet.4183P
  The Solar Dynamics Observatory (SDO) was launched on February 11,
  2010 into partly cloudy skies over Cape Canaveral, Florida. SDO has
  since moved into a 28 degree inclined geosyn-chronous orbit over the
  longitude of the ground station in New Mexico. SDO is the first Space
  Weather Mission in NASA's Living With a Star Program. SDO's main goal
  is to understand and predict those solar variations that influence life
  on Earth and our technological systems. The SDO science investigations
  will determine how the Sun's magnetic field is generated and structured,
  how this stored magnetic energy is released into the heliosphere and
  geospace as the solar wind, energetic particles, and variations in
  the solar irradiance. The SDO mission consists of three scientific
  investigations (AIA, EVE, and HMI), a spacecraft bus, and a ded-icated
  Ka-band ground station to handle the 150 Mbps data flow. Science teams
  at LMSAL, LASP, and Stanford are responsible for processing, analyzing,
  distributing, and archiving the science data. We will talk about the
  building of SDO, its launch, and the data and science it will provide
  to NASA.

---------------------------------------------------------
Title: Conditions for PMC formation in 2002-2008 estimated from
    TIMED/SABER measurements
Authors: Feofilov, Artem; Goldberg, Richard A.; Kutepov, Alexander;
   Pesnell, William
2010cosp...38.1232F    Altcode: 2010cosp.meet.1232F
  In this work, mesospheric temperature, pressure, and water vapor
  concentration measured by the Sounding of the Atmosphere using Broadband
  Emission Radiometry (SABER) instrument on board the Thermosphere
  Ionosphere Mesosphere Energetics and Dynamics (TIMED) satel-lite are
  used to estimate the probability of the polar mesospheric ice clouds
  (PMC) formation for the summer periods of 2002-2008. We show the
  zonal averages of the PMC probability distri-butions and estimated
  PMC heights for both hemispheres and compare them to ground-based and
  satellite observations.

---------------------------------------------------------
Title: Recent STEREO Observations of Coronal Mass Ejections
Authors: St Cyr, O. C.; Xie, H.; Mays, M. L.; Davila, J. M.; Gilbert,
   H. R.; Jones, S. I.; Pesnell, W. D.; Gopalswamy, N.; Gurman, J. B.;
   Yashiro, S.; Wuelser, J.; Howard, R. A.; Thompson, B. J.; Thompson,
   W. T.
2009AGUFMSH11A1491S    Altcode:
  Over 400 CMEs have been observed by STEREO SECCHI COR1 during
  the mission's three year duration (2006-2009). Many of the solar
  activity indicators have been at minimal values over this period,
  and the Carrington rotation-averaged CME rate has been comparable to
  that measured during the minima between Cycle 21-22 (SMM C/P) and
  Cycle 22-23 (SOHO LASCO). That rate is about 0.5 CMEs/day. During
  the current solar minimum (leading to Cycle 24), there have been
  entire Carrington rotations where no sunspots were detected and the
  daily values of the 2800 MHz solar flux remained below 70 sfu. CMEs
  continued to be detected during these exceptionally quiet periods,
  indicating that active regions are not necessary to the generation of
  at least a portion of the CME population. In the past, researchers were
  limited to a single view of the Sun and could conclude that activity
  on the unseen portion of the disk might be associated with CMEs. But
  as the STEREO mission has progressed we have been able to observe an
  increasing fraction of the Sun's corona with STEREO SECCHI EUVI and
  were able to eliminate this possibility. Here we report on the nature
  of CMEs detected during these exceptionally-quiet periods, and we
  speculate on how the corona remains dynamic during such conditions.

---------------------------------------------------------
Title: Comparisons of Photospheric Convection Cell Characteristics
Authors: Pesnell, W. D.; Wiliams, P. E.
2009AGUFMSH11A1500P    Altcode:
  Solar convection plays an important role in generating and structuring
  the solar magnetic field as well as a mechanism responsible for
  the 11-year solar cycle. The observed phenomena are strongly linked
  within both observational and physical regimes. Our main focus is
  the study of supergranulation from SOHO/MDI Dopplergrams. Suites
  of analysis methods are applied to time-series of Doppler images to
  quantitatively describe supergranule flow velocities, spatial scales
  and temporal lifetimes. SOHO/MDI magnetograms also show cellular
  structures, which trace the clustering of magnetic field lines around
  supergranule boundaries. These boundaries are extrapolated into the
  chromosphere where they are observed as a cellular network. We present
  preliminary results of applying methods similar to those applied to the
  Dopplergrams for estimating the spatial and temporal characteristics
  of this network. We extend our study to above the photosphere to the
  chromosphere where another cellular network is seen. Once again the
  responsibility lies with supergranulation. Spatial analysis on CaIIK
  data from the Precision Solar Photometric Telescope (PSPT) provides
  typical size scales for the network that can be compared to both the
  magnetogram network and supergranulation itself. Data comparisons
  over time can be made, notably between Doppler data received
  during the current (2008) and previous (1996) solar minima. Our
  provisional findings show that horizontal and radial velocity
  flows within supergranules are stronger during the current minimum,
  while the supergranules themselves appear larger during the previous
  minimum. However, comparable results are found for the 1/e lifetimes
  derived from each data set. We extend these provisional results by
  performing statistical analyses both within and between the various
  data sets.

---------------------------------------------------------
Title: CO2(ν2)-O Quenching Rate Coefficient Derived From Coincidental
    Fort Collins Lidar and SABER Measurements
Authors: Feofilov, A.; Kutepov, A.; She, C.; Smith, A. K.; Pesnell,
   W. D.; Goldberg, R. A.
2009AGUFMSA53A1238F    Altcode:
  Among the processes governing the energy balance in the mesosphere and
  lower thermosphere (MLT), the quenching of CO2(ν2) vibrational levels
  in collisions with oxygen atoms plays an important role. However,
  neither the rate coefficient of this process (k(CO2-O)) nor the
  atomic oxygen concentrations ([O]) in the MLT are well known. The
  discrepancy between k(CO2-O) measured in the lab and retrieved from
  atmospheric measurements is of about factor of 2.5. At the same
  time, the discrepancy between [O] in the MLT measured by different
  instruments is of the same order of magnitude. In this work we combine
  temperature data from a ground based lidar with limb radiances from
  a satellite infrared radiometer to estimate k(CO2-O). We used the
  night- and daytime temperatures between 80 and 110 km measured by the
  Colorado State University narrow-band sodium (Na) lidar located at
  Fort Collins, Colorado (41N, 255E) as ground truth of the SABER/TIMED
  nearly simultaneous (±10 minutes ) and common volume (within ±1 degree
  in latitude, ±2 degrees in longitude) observations. We used ALI-ARMS
  non-LTE research code designed to calculate the non-equilibrium radiance
  in planetary atmospheres to retrieve the product of k(CO2-O) x [O] from
  15 μm CO2 limb radiance measured by SABER. The values retrieved for
  all overlapping measurements were then used to estimate the k(CO2-O)
  rate coefficient and its possible variation range by utilizing the
  [O] values measured by the SABER and other instruments.

---------------------------------------------------------
Title: What is an Extreme Solar Minimum?
Authors: Pesnell, William Dean
2009shin.confE.143P    Altcode:
  The study of solar minimum has been a poor cousin to solar maximum
  due to the large variations seen in the Sun during maximum. Solar
  activity is low or absent during solar minimum and all of the phenomena
  that follow the sunspot number are also smaller in frequency and
  strength. Even the definition of solar minimum is difficult because
  the main indicator of solar activity is zero for an extended period of
  time. But the Sun presents a different face at minimum. The magnetic
  field is weaker but far more symmetric, almost a dipole for the few
  minimum that have been measured. A similar behavior is seen in the
  corona measured by coronagraphs and magnetic fields measured in the
  heliosphere. Particle fluxes in the solar wind are smaller. As a result
  the scattering of galactic cosmic rays is reduced and a larger flux of
  GCRs is be seen at Earth. The current solar minimum has been extreme in
  having weaker surface fields than previous measurements, few spots for
  longer than average, and an interesting signature in Earth's magnetic
  field. We shall discuss these magnetic signatures and the implications
  for Space Weather and climate of a time with weak solar activity.

---------------------------------------------------------
Title: Automated detection of EUV Polar Coronal Holes during Solar
    Cycle 23
Authors: Kirk, M. S.; Pesnell, W. D.; Young, C. A.; Hess Webber, S. A.
2009SoPh..257...99K    Altcode: 2009arXiv0901.1158K
  A new method for automated detection of polar coronal holes is
  presented. This method, called perimeter tracing, uses a series of
  171, 195, and 304 Å full disk images from the Extreme ultraviolet
  Imaging Telescope (EIT) on SOHO over solar cycle 23 to measure the
  perimeter of polar coronal holes as they appear on the limbs. Perimeter
  tracing minimizes line-of-sight obscurations caused by the emitting
  plasma of the various wavelengths by taking measurements at the solar
  limb. Perimeter tracing also allows for the polar rotation period to
  emerge organically from the data as 33 days. We have called this the
  Harvey rotation rate and count Harvey rotations starting 4 January
  1900. From the measured perimeter, we are then able to fit a curve to
  the data and derive an area within the line of best fit. We observe
  the area of the northern polar hole area in 1996, at the beginning of
  solar cycle 23, to be about 4.2% of the total solar surface area and
  about 3.6% in 2007. The area of the southern polar hole is observed
  to be about 4.0% in 1996 and about 3.4% in 2007. Thus, both the north
  and south polar hole areas are no more than 15% smaller now than they
  were at the beginning of cycle 23. This compares to the polar magnetic
  field measured to be about 40% less now than it was a cycle ago.

---------------------------------------------------------
Title: Automated Detection of Polar Coronal Holes in the EUV
Authors: Kirk, Michael S.; Pesnell, W. D.
2009SPD....40.1407K    Altcode:
  A new method for automatically detecting and measuring Polar Coronal
  Holes in the EUV is presented. We use a series of full solar disk
  images over solar cycle 23 to measure the perimeter of polar coronal
  holes as they appear on the limbs. This method utilizes 171, 195,
  and 304 Å solar images from the Extreme ultraviolet Imaging Telescope
  (EIT) on SOHO. We are able to more accurately define the size and shape
  of the polar hole by taking measurements on the limb and making two
  measurements per image rather than the one used to construct synoptic
  maps. This method also minimizes line-of-sight obscurations caused
  by the emitting plasma of the various wavelengths. Perimeter tracking
  allows for the polar coronal rotation period to emerge organically from
  the data as 33 days. We have called this the Harvey Rotation rate and
  count Harvey Rotations starting January 4, 1900. From the measured
  perimeter we are then able to fit a curve to the data and derive an
  area within the line of best fit. This method can be adapted to work
  with any extended data set of full disk solar images. Extending our
  data set to past NSO full disk spectroheliograms creates a base line
  of more than three solar cycles. In the future, SDO images will be
  added to further expand polar hole measurements.

---------------------------------------------------------
Title: Predicting Solar Cycle 24 With Geomagnetic Precursors
Authors: Pesnell, W. Dean
2009SPD....40.1105P    Altcode:
  We describe using a geomagnetic precursor to predict the amplitude of
  the upcoming solar cycle. The amplitude prediction for Solar Cycle 24
  is 65 +/- 20 in smoothed sunspot number, indicating a below-average
  amplitude for Solar Cycle 24. Four precursor peaks are seen in the
  decline of Solar Cycle 23. The earliest is the most prominent but
  coincides with large levels of non-recurrent geomagnetic activity
  associated with the Halloween storms. The second and third peaks are
  for smaller amplitudes and show that a weak cycle precursor closely
  following a period of strong solar activity may be difficult to
  resolve. A fourth peak, in early 2008, which has recurrent activity
  similar to precursors of earlier solar cycles and appears to be the
  “true" precursor peak for Solar Cycle 24, predicts the smallest
  amplitude for Solar Cycle 24. Several effects contribute to the
  smaller prediction when compared to other geomagnetic precursor
  predictions. During Solar Cycle 23 the correlation between sunspot
  number and F10.7 shows that F10.7 is greater than the equivalent
  sunspot number over most of the cycle, implying the sunspot
  number underestimates the solar activity component. During 2003 the
  correlation between aa and Ap shows that aa is much greater than the
  value predicted from Ap, leading to an overestimate of the aa precursor
  for that year. But the most important effect is the lack of recurrent
  geomagnetic activity until 2008. We conclude that Solar Cycle 24 will
  be no stronger than average and could be much weaker than average.

---------------------------------------------------------
Title: Analysis of Photospheric Convection Flows Over a Solar Cycle
Authors: Williams, Peter E.; Pesnell, W. D.
2009SPD....40.0919W    Altcode:
  Convection in the Sun plays an important role as a mechanism
  responsible for the 11-year solar cycle. Magnetic field phenomena
  are thus inextricably linked to the convective process, an example
  being the gathering of magnetic field lines around supergranule
  boundaries observed as the chromospheric network. <P />Our research
  asks to what extent variations in the global magnetic field affect
  particular characteristics of photospheric convection features,
  using Dopplergrams derived from SOHO/MDI data during the course of
  Solar Cycle 23. <P />We look ahead to the higher resolution data that
  SDO/HMI will provide and any further insight such data may provide.

---------------------------------------------------------
Title: Temperature Trends in the Polar Mesosphere between 2002--2007
    using TIMED/SABER Data
Authors: Goldberg, R. A.; Feofilov, A. G.; Kutepov, A. A.; Pesnell,
   W. D.; Latteck, R.; Russell, J. M.
2008AGUFMSA43A1574G    Altcode:
  The TIMED Satellite was launched on December 7, 2001 to study the
  dynamics and energy of the mesosphere and lower thermosphere. The
  TIMED/SABER instrument is a limb scanning infrared radiometer designed
  to measure a large number of minor constituents as well as the
  temperature of the region. In this study, we have concentrated on the
  polar mesosphere, to investigate the temperature characteristics as a
  function of spatial and temporal considerations. We used the recently
  revised SABER dataset (1.07) that contains improved temperature
  retrievals in the Earth polar summer regions. Weekly averages are
  used to make comparisons between the winter and summer, as well as to
  study the variability in different quadrants of each hemisphere. For
  each year studied, the duration of polar summer based on temperature
  measurements compares favorably with the PMSE (Polar Mesospheric Summer
  Echoes) season measured by radar at the ALOMAR Observatory in Norway
  (69°N). The PMSE period should also define the summer period suitable
  for the occurrence of polar mesospheric clouds. The unusual short and
  relatively warm polar summer in the northern hemisphere during 2002
  is also clearly defined in this analysis and shown to be unique for
  the period analyzed.

---------------------------------------------------------
Title: Temperature and water vapor measured by SABER/TIMED and
    implications for mesospheric ice clouds
Authors: Feofilov, A. G.; Kutepov, A. A.; Marshall, B. T.; Pesnell,
   W. D.; Goldberg, R. A.; Gordley, L. L.; Russell, J. M.
2008AGUFMSA43A1575F    Altcode:
  The SABER instrument on board the TIMED Satellite is a limb
  scanning infrared radiometer designed to measure temperature and
  minor constituent vertical profiles and energetics parameters in
  the mesosphere and lower thermosphere. We applied an updated non-LTE
  model for the interpretation of the 6.3 micron H2O radiance measured
  by SABER. The obtained meridional and seasonal distributions of the
  H2O density in the mesosphere are discussed. The conditions for the
  mesospheric ice particle formation are estimated using the combination
  of SABER H2O and temperature (V1.07) profiles.

---------------------------------------------------------
Title: Recent studies of the behavior of the Sun's white-light corona
    over time
Authors: St. Cyr, O. C.; Young, D.; Pesnell, W. D.; Lecinski, A.;
   Eddy, J.
2008AGUFMSH44A..06S    Altcode:
  Predictions of upcoming solar cycles are often related to the nature
  and dynamics of the Sun's polar magnetic field and its influence on
  the corona. For the past 30 years we have a more-or-less continuous
  record of the Sun's white-light corona from groundbased and spacebased
  coronagraphs. Over that interval, the large scale features of the corona
  have varied in what we now consider a "predictable" fashion--complex,
  showing multiple streamers at all latitudes during solar activity
  maximum; and a simple dipolar shape aligned with the rotational pole
  during solar minimum. Over the past three decades the white-light
  corona appears to be a better indicator of "true" solar minimum than
  sunspot number since sunspots disappear for months (even years) at
  solar minimum. Since almost all predictions of the timing of the next
  solar maximum depend on the timing of solar minimum, the white-light
  corona is a potentially important observational discriminator for future
  predictors. In this contribution we describe recent work quantifying
  the large-scale appearance of the Sun's corona to correlate it with
  the sunspot record, especially around solar minimum. These three
  decades can be expanded with the HAO archive of eclipse photographs
  which, although sparse compared to the coronagraphic coverage, extends
  back to 1869. A more extensive understanding of this proxy would give
  researchers confidence in using the white-light corona as an indicator
  of solar minimum conditions.

---------------------------------------------------------
Title: Predictions of Solar Cycle 24
Authors: Pesnell, William Dean
2008SoPh..252..209P    Altcode: 2008SoPh..tmp..152P
  A summary and analysis of more than 50 predictions of the amplitude
  of the upcoming Solar Cycle 24 is presented. All of the predictions
  were published before solar minimum and represent our efforts to
  anticipate solar maximum at ever-earlier epochs. The consistency of the
  predictions within their assigned categories is discussed. Estimates
  of the significance of the predictions, compared to the climatological
  average, are presented.

---------------------------------------------------------
Title: SABER/TIMED Mesospheric Water Vapor and Temperature
Authors: Feofilov, A. G.; Kutepov, A. A.; Garci­A-Comas, M.;
   Lopez-Puertas, M.; Marshall, B. T.; Gordley, L. L.; Manuilova, R. O.;
   Yankovsky, V. A.; Pesnell, W. D.; Goldberg, R. A.; Petelina, S.;
   Russell, J. M.
2008AGUSMSA41D..09F    Altcode:
  Low temperatures and abundant water vapor are the necessary components
  for the mesospheric water ice forming. The SABER instrument on board
  the TIMED Satellite is a limb scanning infrared radiometer designed
  to measure temperature and minor constituent vertical profiles and
  energetics parameters in the mesosphere and lower thermosphere. This
  paper describes the methodology of the water vapor retrieval from the
  broadband 6.3μm non-LTE emissions and discusses some aspects of the
  temperature retrieval from the 15μm non-LTE CO2 emissions measured
  by SABER. The non-LTE models of H2O and CO2 are validated using
  the comparisons with the ACE-FTS occultation measurement and lidar
  temperature measurements, respectively. The seasonal and latitudinal
  distributions of water vapor and temperatures retrieved from the
  SABER measurements are shown and the conditions for ice clouds forming
  are discussed.

---------------------------------------------------------
Title: Seasonal variations of magnesium atoms in the
    mesosphere-thermosphere
Authors: Correira, J.; Aikin, A. C.; Grebowsky, J. M.; Pesnell, W. D.;
   Burrows, J. P.
2008GeoRL..35.6103C    Altcode:
  UV radiances from the Global Ozone Monitoring Experiment (GOME)
  spectrometer on the ERS-2 satellite are used to determine long-term
  dayside temporal variations of the total vertical column density below
  795 km of the meteoric metal species Mg and Mg<SUP>+</SUP> in the upper
  atmosphere. The GOME instrument has the ability to observe the ground
  state transition lines of Mg I at 285.2 nm and resolve the Mg II at
  280 nm. A retrieval algorithm has been developed to determine column
  densities and applied to the years 1996-1997. Results show the middle
  latitude dayside Mg<SUP>+</SUP> peaks in total vertical content during
  the summer, while neutral Mg demonstrates a much more subtle maximum
  in summer. Dayside trends are opposite previous midlatitude nighttime
  lidar observations, with the exception of calcium. The Mg<SUP>+</SUP>/Mg
  ratio has a seasonal variation, reaching a maximum in the summer. The
  total content of Mg<SUP>+</SUP> is twice that of neutral Mg.

---------------------------------------------------------
Title: The Solar Dynamics Observatory: Your eye on the Sun
Authors: Pesnell, William
2008cosp...37.2412P    Altcode: 2008cosp.meet.2412P
  The Sun hiccups and satellites die. That is what NASA's Living With a
  Star Program is all about. The Solar Dynamics Observatory (SDO) is the
  first Space Weather Mission in LWS. SDO's main goal is to understand,
  driving towards a predictive capability, those solar variations that
  influence life on Earth and humanity's technological systems. The past
  decade has seen an increasing emphasis on understanding the entire Sun,
  from the nuclear reactions at the core to the development and loss of
  magnetic loops in the corona. SDO's three science investigations (HMI,
  AIA, and EVE) will determine how the Sun's magnetic field is generated
  and structured, how this stored magnetic energy is released into the
  heliosphere and geospace as the solar wind, energetic particles,
  and variations in the solar irradiance. SDO will return fulldisk
  Dopplergrams, full-disk vector magnetograms, full-disk images at seven
  EUV wavelengths, and EUV spectral irradiances, all taken at a rapid
  cadence. This means you can "observe the database" to study events,
  but we can also move forward in producing quantitative models of what
  the Sun is doing today. SDO is scheduled to launch in 2008 on an Atlas
  V rocket from the Kennedy Space Center, Cape Canaveral, Florida. The
  satellite will fly in a 28 degree inclined geosynchronous orbit about
  the longitude of New Mexico, where a dedicated Ka-band ground station
  will receive the 150 Mbps data flow. How SDO data will transform
  the study of the Sun and its affect on Space Weather studies will
  be discussed.

---------------------------------------------------------
Title: Chromospheric Lines as Diagnostics of Stellar Oscillations
Authors: Paulson, Diane B.; Pesnell, W. Dean; Deming, L. Drake; Snow,
   Martin; Metcalfe, Travis S.; Woods, Tom; Hesman, Brigette
2008psa..conf..311P    Altcode:
  Gravitational waves in the chromosphere, theorized as early as
  1963 [10], are thoroughly explored in the more recent papers by
  [7, 8]. Theory predicts that the convective overshoot in the upper
  photosphere and low chromosphere will readily excite gravity waves. [9]
  note that these waves are not easily detected because of the long
  periods, short wavelengths required and slanted propagation angles of
  the waves themselves (causing small velocity shifts and short duration
  on individual detector pixels). Recently, [9] find evidence for gravity
  waves manifested in the f 700Å chromospheric line with frequencies
  &lt;1 mHz.

---------------------------------------------------------
Title: SDO in Virtual Reality: A New Spacecraft Interactive
Authors: Drobnes, Emilie; Pesnell, W. D.
2007AAS...211.9408D    Altcode: 2007BAAS...39..893D
  Have you ever dreamed of rocketing into space as an astronaut? Or
  wished you could just float out among the stars and satellites? Well,
  now you can! With the new Solar Dynamics Observatory (SDO) Spacecraft
  Interactive you can spin, rotate, and explore the various parts of a
  spacecraft as if you were in space, without leaving the comforts and
  gravity of our home planet. This new and innovative interactive is a
  great cross-cutting tool with applications from project management to
  Education and Public Outreach (EPO). The current model allows users
  to explore the spacecraft and all of its various components creating
  a user-unique experience. When adapted to an immersive technology
  environment, users will be able to experience this exploration as if
  actually floating in space with the star field projected all around
  you. In either form, this interactive could also be used by program
  managers to navigate a photograph and video archive.

---------------------------------------------------------
Title: Variability of Solar Irradiances Using Wavelet Analysis
Authors: Pesnell, W. D.
2007AGUFMSH13A1100P    Altcode:
  We have used wavelets to analyze the sunspot number, F10.7 (the solar
  irradiance at a wavelength of 10.7~cm), and Ap (a geomagnetic activity
  index). Three different wavelets are compared, showing how each selects
  either temporal or scale resolution. Our goal is an envelope of solar
  activity that better bounds the large amplitude fluctuations form solar
  minimum to maximum. We show how the 11-year cycle does not disappear
  at solar minimum, that minimum is only the other part of the solar
  cycle. Power in the fluctuations of solar-activity-related indices
  may peak during solar maximum but the solar cycle itself is always
  present. The Ap index has a peak after solar maximum that appears
  to be better correlated with the current solar cycle than with the
  following cycle.

---------------------------------------------------------
Title: Self-consistent Non-LTE Model of Infrared Molecular Emissions
    and Oxygen Dayglows in the Mesosphere and Lower Thermosphere
Authors: Kutepov, A. A.; Feofilov, A. G.; Yankovsky, V. A.; Manuilova,
   R. O.; Pesnell, W. D.; Goldberg, R. A.
2007AGUFMSA41A0293K    Altcode:
  We describe the new version of the ALI-ARMS (for Accelerated
  Lambda Iterations for Atmospheric Radiation and Molecular Spectra)
  model. The model allows simultaneous, self-consistent calculations
  of the non-LTE populations of the electronic- vibrational levels of
  ozone and O2 photolysis products and the vibrational level populations
  of CO2, N2, O2, O3, H2O, CO, and other molecules with a detailed
  accounting of electronic-vibrational, vibrational-vibrational and
  vibrational-translational energy exchange processes. The model
  is used as the reference for modeling O2 dayglow experiments and
  for the infrared molecular emissions measured by the multi-channel
  observations of MLT in the SABER experiment on TIMED. It also permits
  the re-evaluation of the thermalization efficiency of absorbed solar
  ultraviolet energy and infrared radiative cooling/heating of MLT
  through a detailed accounting of the electronic-vibrational relaxation
  of excited photolysis products via a complex chain of collisional energy
  conversion processes down to the vibrational energy of optically active
  trace gas molecules.

---------------------------------------------------------
Title: Mesospheric Water Vapor Retrieved From SABER/TIMED Measurements
Authors: Feofilov, A. G.; Marshall, B. T.; Garci-A-Comas, M.; Kutepov,
   A. A.; Lopez-Puertas, M.; Manuilova, R. O.; Yankovsky, V. A.; Pesnell,
   W. D.; Goldberg, R. A.; Gordley, L. L.; Petelina, S.; Russell, J. M.
2007AGUFMSA41A0291F    Altcode:
  The SABER instrument on board the TIMED Satellite is a limb
  scanning infrared radiometer designed to measure temperature and
  minor constituent vertical profiles and energetics parameters in
  the mesosphere and lower thermosphere (MLT). The H2O concentrations
  are retrieved from 6.3 micron band radiances. The interpretation of
  this radiance requires developing a non-LTE H2O model that includes
  energy exchange processes with the system of O3 and O2 vibrational
  levels populated at the daytime through a number of photoabsorption
  and photodissociation processes. We developed a research model based
  on an extended H2O non-LTE model of Manuilova et al, 2001 coupled
  with the novel model of the electronic-vibrational kinetics of the
  O2 and O3 photolysis products suggested by Yankovsky and Manuilova,
  2006. The performed study of this model helped us to develop and test
  an optimized operational model for interpretation of SABER 6.3 micron
  band radiances. The sensitivity of retrievals to the parameters of
  the model is discussed. The H2O retrievals are compared to other
  measurements for different seasons and locations.

---------------------------------------------------------
Title: Methods of Detecting Polar Coronal Holes in the EUV
Authors: Kirk, M. S.; Pesnell, W. D.
2007AGUFMSH13A1099K    Altcode:
  One method of forecasting the peak amplitude of future solar cycles uses
  the polar magnetic field strength at solar minimum to predict the value
  of the upcoming maximum. Because the polar field is closely related to
  the polar coronal hole, we would like to consider the size and shape
  of the polar hole on the prediction. We measure the perimeter of polar
  coronal holes over solar cycle 23 as they appear on the limb of the
  sun in 171, 195, and 304 Å\ solar images from the Extreme ultraviolet
  Imaging Telescope (EIT) on SOHO. The area within the perimeter can
  easily be determined. Taking measurements on the limb minimizes the
  effects of differences in scale height between the material emitting
  the various wavelengths. Perimeter tracking also allows for the coronal
  rotation rate to emerge organically from the data rather than forcing
  a period on the data. This method should help to improve our estimates
  of the size and shape of the polar coronal holes.

---------------------------------------------------------
Title: Getting Something from Nothing: Polar Coronal Holes in Cycles
    22 and 23
Authors: Hess Webber, Shea A.; Kirk, Michael S.; Pesnell, W. Dean
2007fste.conf...38H    Altcode:
  Methods of predicting the peak amplitude of solar cycles currently
  disagree as to whether Solar Cycle 24 will have a high or low level
  activity. One method uses the polar magnetic field lines at minimum
  to predict the value of the upcoming maximum. Because it uses the
  polar field, we would like to assess the impact of the size and
  shape of the polar coronal hole on the prediction. We will measure
  the area of the polar coronal holes during solar cycles 22 and 23
  by measuring the opening angle of the hole as it appears on the limb
  of the sun. A correlation of coronal hole parameters from Kitt Peak
  10,830Å solar images with 171, 195, and 304Å solar images from the
  Extreme ultraviolet Imaging Telescope (EIT) on the SoHO satellite taken
  during the ascending phase of Solar Cycle 23 will be used to produce
  a continuous set of coronal holes during Cycles 22 and 23. This will
  also provide a smooth transition between the current EIT images and the
  Kitt Peak data. Using multiple wavelengths will allow a more consistent
  definition of the boundaries of the polar coronal holes. To accomplish
  these tasks, an automatic detection method is employed. This method
  should help to refine our understanding of the polar field precursor
  of solar activity.

---------------------------------------------------------
Title: SDO Asks: What's The Sun Doing Now?
Authors: Pesnell, W. D.
2007AAS...21010101P    Altcode: 2007BAAS...39..228P
  Solar observations have tended to emphasize events like flares and
  CMEs, and what leads to these events. The past decade has seen an
  increasing emphasis on understanding the entire Sun, from the nuclear
  reactions at the core to the development and loss of magnetic loops
  in the corona. The Solar Dynamics Observatory (SDO) will return
  synoptic data, taken at a regular cadence and covering the entire
  Sun. This means you can still study events, but can also move forward
  to producing a quantitative model of what the Sun is doing today. The
  science investigations of SDO will determine how the Sun's magnetic
  field is generated and structured, how this stored magnetic energy is
  released into the heliosphere and geospace as the solar wind, energetic
  particles, and variations in the solar irradiance. How SDO data will
  transform the study of the Sun and the affect on stellar astrophysics
  will be discussed.

---------------------------------------------------------
Title: Solar Cycle 24 and the Solar Dynamo
Authors: Pesnell, W. D.; Schatten, K.
2007AAS...210.9204P    Altcode: 2007BAAS...39..209P
  We will discuss the polar field precursor method for solar activity
  prediction, which predicts cycle 24 will be significantly lower than
  recent activity cycles, and some new ideas rejuvenating Babcock's
  shallow surface dynamo. The polar field precursor method is based on
  Babcock and Leighton's dynamo models wherein the polar field at solar
  minimum plays a major role in generating the next cycle's toroidal field
  and sunspots. Thus, by examining the polar fields of the Sun near solar
  minimum, a forecast for the next cycle's activity is obtained. With
  the current low value for the Sun's polar fields, this method predicts
  solar cycle 24 will be one of the lowest in recent times, with smoothed
  F10.7 radio flux values peaking near 135 ± 35 (2 σ), in the 2012-2013
  timeframe (equivalent to smoothed Rz near 80 ± 35 [2 σ]). One may
  have to consider solar activity as far back as the early 20th century
  to find a cycle of comparable magnitude. We discuss unusual behavior
  in the Sun's polar fields that support this prediction. Normally, the
  solar precursor method is consistent with the geomagnetic precursor
  method, wherein geomagnetic variations are thought to be a good measure
  of the Sun's polar field strength. Because of the unusual polar field,
  the Earth does not appear to be currently bathed in the Sun's extended
  polar field (the interplanetary field), hence negating the primal
  cause behind the geomagnetic precursor technique. We also discuss how
  percolation may support Babcock's original shallow solar dynamo. In
  this process ephemeral regions from the solar magnetic carpet, guided
  by shallow surface fields, may collect to form pores and sunspots.

---------------------------------------------------------
Title: Family Science Night: Changing Perceptions One Family at a Time
Authors: Pesnell, W. D.; Drobnes, E.; Mitchell, S.; Colina-Trujillo, M.
2007AAS...210.0503P    Altcode: 2007BAAS...39Q.100P
  If students are not encouraged to succeed in science, mathematics,
  and technology classes at school, efforts to improve the quality of
  content and teaching in these subjects may be futile. Parents and
  families are in a unique position to encourage children to enroll and
  achieve in these classes. The NASA Goddard Space Flight Center Family
  Science Night program invites middle school students and their families
  to explore the importance of science and technology in our daily lives
  by providing a venue for families to comfortably engage in learning
  activities that change their perception and understanding of science
  - making it more practical and approachable for participants of all
  ages. Family Science Night strives to change the way that students and
  their families participate in science, within the program and beyond.

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Title: The Polar Summer MLT Plasma Environment as Seen by the DROPPS
    Sounding Rockets
Authors: Assis, M. P.; Goldberg, R. A.; Webb, P. A.; Pesnell, W. D.;
   Voss, H. D.
2006AGUFMSA21A0240A    Altcode:
  During early July, 1999, the DROPPS (Distribution and Role of Particles
  in the Polar Summer Mesosphere) campaign launched two rocket payloads
  whose purpose was to study the polar summer MLT (mesosphere and lower
  thermosphere), particularly PMSEs (polar mesospheric summer echoes)
  and PMCs (polar mesospheric clouds). The rockets were launched from
  the Andøya Rocket Range in Norway the nights of the 5th and 14th
  of July. Both payloads included a front-mounted PID (Particle Impact
  Detector) consisting of charge and mass telescopes to measure aerosol
  and dust mass distributions. Ice particles of nanometer size are
  believed to be responsible for PMSEs through the process of electron
  scavenging. Evidence for this process is suggested, for example,
  by the presence of an electron "biteout" simultaneously measured by
  several instruments at an altitude of ~82-87 km during the first
  DROPPS launch. This presentation will characterize similarities
  and differences between both flights as seen by the charge and mass
  telescopes, starting at launch until the loss of data on the downleg
  of each flight. Various stages of the flights will be considered in
  detail, such as the PMSE layer and the apogee at 117 km, as well as
  the calibration of the data before launch.

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Title: Revised correlation between Odin/OSIRIS PMC properties and
    coincident TIMED/SABER mesospheric temperatures
Authors: Feofilov, A.; Petelina, S. V.; Kutepov, A. A.; Pesnell,
   W. D.; Goldberg, R. A.; Llewellyn, E. J.; Russell, J. M.
2006AGUFMSA21A0243F    Altcode:
  The Optical Spectrograph and Infrared Imaging System (OSIRIS) instrument
  on board the Odin satellite detects Polar Mesospheric Clouds (PMCs)
  through the enhancement in the limb-scattered solar radiance. The
  Sounding of the Atmosphere using the Broadband Emission Radiometry
  (SABER) instrument on board the TIMED satellite is a limb scanning
  infrared radiometer that measures temperature and vertical profiles
  and energetic parameters for minor constituents in the mesosphere
  and lower thermosphere. The combination of OSIRIS and SABER data
  has been previously used to statistically derive thermal conditions
  for PMC existence [Petelina et al., 2005]. In this work, we employ
  the simultaneous common volume measurements of PMCs by OSIRIS and
  temperature profiles measured by SABER for the Northern Hemisphere
  summers of 2002--2005 and corrected in the polar region by accounting
  for the vibrational-vibrational energy exchange among the CO2 isotopes
  [Kutepov et al., 2006]. For each coincidence identified within ±1
  degree latitude, ±2 degrees longitude and ≤1 hour time the frost
  point temperatures were calculated using the corresponding SABER
  temperature profile and water vapor densities of 1, 3, and 10 ppmv. We
  found that the PMC presence and brightness correlated only with
  the temperature threshold that corresponds to the frost point. The
  absolute value of the temperature below the frost point, however,
  didn't play a significant role in the intensity of PMC signal for the
  majority of selected coincidences. The presence of several bright
  clouds at temperatures above the frost point is obviously related
  to the limitation of the limb geometry when some near- or far-field
  PMCs, actually located at higher (and colder) altitudes are detected
  at lower altitudes. S.V. Petelina, D.A. Degenstein, E.J. Llewellyn,
  N.D. Lloyd, C.J. Mertens, M.G. Mlynczak, and J.M. Russell III, "Thermal
  conditions for PMC existence derived from Odin/OSIRIS and TIMED/SABER
  data", Geophys. Res. Lett., 32, L17813, doi: 10.1029/2005GL023099,
  (2005) A.A. Kutepov, A.G. Feofilov, B.T. Marshall, L.L. Gordley,
  W. D. Pesnell, R.A. Goldberg, and J.M. Russell III, "SABER temperature
  observations in the summer polar mesosphere and lower thermosphere:
  importance of accounting for the CO2 ν_2 quanta V -V exchange",
  accepted for publication in Geophys. Res. Lett., (2006)

---------------------------------------------------------
Title: Sources, Propagators, and Sinks of Space Weather
Authors: Pesnell, W. D.
2006AGUFMSA53A1371P    Altcode:
  Space Weather is a complex web of sources, propagators, and sinks of
  energy, mass, and momentum. A complete understanding of Space Weather
  requires specifying, and an ability to predict, each link in this
  web. One important problem in Space Weather is ranking the importance of
  a particular measurement or model in a research program. One way to do
  this ranking is to examine the simplest linked diagram of the sources,
  propagators, and sinks and produce. By analyzing only those components
  that contribute to a particular area the individual contributions can
  be better appreciated. Several such diagrams will be shown and used
  to discuss how long-term effects of Space Weather can be separated
  from the impulsive effects.

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Title: SABER temperature observations in the summer polar
mesosphere and lower thermosphere: Importance of accounting for the
    CO<SUB>2</SUB> ν<SUB>2</SUB> quanta V-V exchange
Authors: Kutepov, Alexander A.; Feofilov, Artem G.; Marshall, Benjamin
   T.; Gordley, Larry L.; Pesnell, W. Dean; Goldberg, Richard A.; Russell,
   James M.
2006GeoRL..3321809K    Altcode:
  The polar summer thermal structure, with its cold mesopause and steep
  temperature gradients, both below and above the mesopause, produces
  the largest non-LTE effects in the CO<SUB>2</SUB> ν<SUB>2</SUB> mode
  manifold states. In this paper we focus on validating the non-LTE
  model applied for operational temperature retrievals from the SABER
  15 μm limb radiance observations for these extreme conditions. We
  demonstrate that accounting for the redistribution of ν<SUB>2</SUB>
  quanta among various CO<SUB>2</SUB> isotopes shifts the retrieved
  summer 2002 polar mesopause altitude upwards by 2 to 4 km. It brings
  the SABER temperature measurements into a better agreement with those
  of falling sphere experiments, lidar observations, as well as with
  climatological data.

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Title: Sensitivity of IR Temperature Retrievals in the Polar Summer
    MLT to NLTE considerations
Authors: Kutepov, A.; Feofilov, A.; Marshall, B. T.; Gordley, L. L.;
   Pesnell, W. D.; Goldberg, R. A.; Russell, J. M.
2006AGUSMSA53A..07K    Altcode:
  Adequate retrieval of kinetic temperature and other parameters in the
  summer polar mesosphere and lower thermosphere (MLT) from limb infrared
  radiances requires detailed accounting for the breakdown of local
  thermodynamic equilibrium (NLTE). A large fraction of the limb radiance
  is formed by resonant scattering of the upwelling radiation from the
  stratosphere and therefore, does not have links to the local thermal
  radiation sources. Moreover, in case of CO2, this scattering depends
  strongly on the V-V rate of the ν2 quanta exchange between isotopes. As
  a result, both the temperature values and the position of the retrieved
  mesopause depend on the rate coefficient of this process. On the other
  hand, the lower boundary of a noctilucent cloud (NLC) lies near the
  lower crossing point of the temperature profile and the frost point
  curve. This suggests that NLC observations may provide an important
  tool for validating temperature and water vapor density retrievals as
  well as the NLTE model describing the formation of infrared radiance
  in the MLT. This paper will describe these considerations including
  examples using the TIMED-SABER data for the polar summer mesosphere.

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Title: Particulate and plasma variations in NLC and PMSE during
    DROPPS 1 and 2 flights
Authors: Voss, H. D.; Webb, P. A.; Pesnell, W. D.; Gumbel, J.; Assiss,
   M. P.; Goldberg, R. A.
2006cosp...36.3336V    Altcode: 2006cosp.meet.3336V
  High-time resolution rocket measurements have been made of charged
  particulates under polar summer mesospheric conditions on 5 and 14 July
  1999 during the DROPPS campaign at And o ya Rocket Range Norway Each
  rocket carried a Particle Impact Detector PID composed of two telescopes
  with three biased grids and which were pointed into the rocket ram
  during both up- and downleg On the first night the rocket DROPPS 1 was
  flown into a strong PMSE polar mesospheric summer echo condition with a
  weak NLC noctilucent cloud located at the base of the PMSE The second
  flight DROPPS 2 was launched into a bright NLC with no PMSE present
  For DROPPS 1 large amounts of negatively charged particulates were
  observed in the PMSE region with relatively small size distributions
  1 nm radius Net positive charge particulates were measured in the
  NLC regions for both flights Ions and charged particulates have been
  simulated using a finite difference code SIMION 3D to trace particle
  paths and resulting grid currents For the simulations the thermal
  effects through the shock and within the sensor cause the ice rocky
  particulates to sublimate and lose mass In addition the particulates
  are observed to decelerate due to the ram pressure and electric fields
  for subsequent charge collection on the grids The background current
  on grid 2 -4 volt is consistent with the altitude variation and flux
  expected for UV photoionization Consistent effects were observed on
  another instrument PAT particle trap during the same flights

---------------------------------------------------------
Title: Non-LTE effects in the polar summer mesosphere and lower
    thermosphere and TIMED SABER temperature retrievals
Authors: Feofilov, A. G.; Kutepov, A. A.; Marshall, B. T.; Gordley,
   L. L.; Pesnell, W. D.; Goldberg, R. A.; Russell, J. M., III
2006cosp...36.2516F    Altcode: 2006cosp.meet.2516F
  The mesosphere lower thermosphere MLT is one of the most intriguing
  regions of Earth s atmosphere In past decades a large number of rocket
  and lidar experiments have been performed to explore catalogue and
  explain the thermal structure of MLT However the description of this
  region is sophisticated due to the large number of processes which
  govern the vibrational molecular levels populations The frequency of
  inelastic molecular collisions in MLT becomes low and one has to take
  into account various other processes which populate and de-populate
  the levels absorption and emission of radiation in molecular bands
  redistribution of excitation between colliding molecules chemical
  excitation The populations must be found by solving the system
  of rate equations expressing the balance of all these processes
  non-LTE Therefore the interpretation of radiance measurements in MLT
  depends on accuracy of non-LTE model Non-LTE effects for the CO 2 nu
  2 manifold levels responsible for the 15 mu m CO 2 emission are more
  pronounced in the polar summer MLT than in other regions due to the
  cold mesopause and high vertical temperature gradients both below and
  above the mesopause region This case provides an example of a very
  strong infrared radiative coupling between warm stratosphere and cold
  mesosphere The SABER a instrument on board the TIMED b satellite is
  a limb scanning infrared radiometer designed to measure temperature
  and minor constituent vertical profiles and energetics parameters in
  the MLT Temperatures in the MLT are retrieved from the

---------------------------------------------------------
Title: Refinement of the DROPPS Polar Summer Mesosphere Particle Data
Authors: Webb, P.; Goldberg, R.; Pesnell, W.; Voss, H.; Assis, M.
2006cosp...36.3413W    Altcode: 2006cosp.meet.3413W
  The two Black Brant payloads flown during the DROPPS Distribution and
  Role of Particles in the Polar Summer Mesosphere rocket program were
  launched during early July 1999 from And o ya Rocket Range ARR Norway
  The purpose was to investigate the polar summer mesosphere particularly
  polar mesospheric summer echoes PMSE Both DROPPS payloads included
  front mounted side by side Particle Impact Detector PID charge and mass
  telescopes Computer simulations have shown that the PID telescopes
  have the potential to detect atmospheric ice particles within the
  mesosphere having dimensions of a few nanometers Ice particles of
  nanometer size are believed to be responsible for PMSEs through the
  process of scavenging Evidence for this process is suggested by the
  presence of an electron biteout observed in the same region as the
  observation of nanometer size particles at an altitude of sim 82-87 km
  over And o ya during the first DROPPS launch sequence Evidence for this
  dusty plasma was observed independently by several instruments aboard
  the DROPPS payload By comparing PID observations with the computer
  simulations we can obtain information concerning the properties of the
  PMSE particles including their rocky core size ice mantle thickness and
  distribution We have previously presented results from an analysis of
  the two detectors that suggested on the first flight particles with
  radius of approximately 2 nm were present in the PMSE layer We have
  recently realised that our interpretation of the PID data required
  further refinement For example we have now

---------------------------------------------------------
Title: Sources, Propagators, and Sinks of Space Weather
Authors: Pesnell, W. D.
2006cosp...36.2994P    Altcode: 2006cosp.meet.2994P
  Space Weather is a complex web of sources propagators and sinks of
  energy mass and momentum A complete understanding of Space Weather
  would require specifying and an ability to predict each link in this
  web One important problem in Space Weather is ranking the importance
  of a particular measurement or model in a research program One way to
  do this ranking is to identify the sources propagators and sinks and
  produce the simplest linked diagram of the components Such a diagram
  will be shown and used to discuss how longterm effects of Space Weather
  can be separated from the impulsive effects

---------------------------------------------------------
Title: Using the Far-Infrared to Understand the Thermosphere
Authors: Pesnell, W. D.; Arnett, K.
2005AGUFMSA51B1140P    Altcode:
  Atomic oxygen is the dominant constituent of the thermospheres of the
  Earth, Venus, and Mars. It is formed by photodissociation of a major
  molecular species from the lower atmosphere of each planet. Remote
  sensing of O greatly increases the amount of data available from each
  atmosphere. Several parts of the electromagnetic spectrum can be used
  to sense O, but the far-infrared line at 63~μm has several advantages,
  which we will discuss. The greatest advantage to using this line is
  the ability to resolve the tidal structure of the thermosphere. Using
  broadband radiometry to measure the limb radiance of this spectral
  feature will be discussed in the context of the OPIE (Oxygen Profiling
  Infrared Experiment) instrument. Some thoughts on the optimal orbit
  for these instruments with be presented.

---------------------------------------------------------
Title: The Temperature Climatology of the Polar Mesosphere in
    2002-2004 Using SABER/TIMED Data
Authors: Feofilov, A.; Kutepov, A.; Goldberg, R. A.; Pesnell, W. D.;
   Russell, J. M.; Mlynczak, M. G.
2005AGUFMSA43A1086F    Altcode:
  The TIMED Satellite was launched on December 7, 2001 to study the
  dynamics and energy of the mesosphere and lower thermosphere. The
  SABER instrument is a limb scanning infrared telescope designed
  to measure minor atmospheric constituents as well as temperature
  and pressure of the region. In this study we have concentrated on
  data retrieved for the polar mesosphere, to investigate spatial
  and temporal temperature characteristics of this region. We made the
  comparisons between the winter and summer, and studied both short- and
  long-term variability in different quadrants of each hemisphere. The
  sharp transition between summer and winter, first demonstrated using
  falling-sphere meteorological rocket data, will be described for each
  hemisphere with a data base including variations in many geophysical
  parameters. Differences in this climatological base between 2002-2004
  will also be discussed.

---------------------------------------------------------
Title: The Nature of Icy Dust Particles in the Polar Summer Mesosphere
    From Rocket Measurements During DROPPS
Authors: Goldberg, R. A.; Webb, P. A.; Pesnell, W. D.; Voss, H. D.
2005AGUFMSA22A..08G    Altcode:
  The two Black Brant payloads flown during the DROPPS (Distribution
  and Role of Particles in the Polar Summer Mesosphere) rocket program
  were launched during early July, 1999 from Andoya Rocket Range (ARR),
  Norway. Both payloads included front mounted side by side Particle
  Impact Detector (PID) charge and mass telescopes. Computer simulations
  have shown that the PID telescopes have the potential to detect
  atmospheric ice particles within the mesosphere, having dimensions of
  a few nanometers. Ice particles of nanometer size are believed to be
  responsible for polar mesospheric summer echoes (PMSEs), such as those
  observed at an altitude of ~82-87 km over Andoya during the first DROPPS
  launch sequence. We have previously presented results from the longer
  PID charge telescope that indicated two possible particle distributions
  differing by mean particle size. Due to the different geometries of
  the PID telescopes (primarily, that the charge telescope is longer than
  the mass telescope) each PID telescope collects a different portion of
  the nanometer sized PMSE particles distribution. When compared to the
  previous PID charge telescope results, the PID mass telescope results
  allow the true PMSE particle size distribution to be estimated. This
  talk will introduce the new observations from the shorter PID mass
  telescope and the comparison to the previous PID charge telescope. By
  then comparing PID observations with the computer simulations provides
  information concerning the properties of the PMSE particles, including
  their "rocky" core size, ice mantle thickness and distribution.

---------------------------------------------------------
Title: Venus Metal ion and Metal Neutral Species Distributions and
    Meteor Magnitudes
Authors: Webb, P. A.; Grebowsky, J. M.; Pesnell, W. D.
2005AGUFM.P33A0237W    Altcode:
  The lower ionospheres of all planetary atmospheres and any of those
  satellites that hold substantial atmospheres have a high likelihood
  of containing complex layers of metallic ions and their neutral
  species. These metal species arise from the ablation and subsequent
  ionization of small particles from the solar system cloud of meteoroids
  impacting their atmospheres. Venus is no exception and is unique in that
  it has the highest upper limit for incoming meteoroid velocities in
  the solar system and its extremely slow atmosphere revolution makes a
  one-dimensional modeling a better approximation than for other faster
  rotating bodies in the solar system. Previous modeling of one of the
  major meteoroid species, Mg, showed that indeed a prominent metallic
  layer expected with ion concentrations comparable to those seen
  at Earth. However the modeled Mg+ peak altitude was lower than any
  total electron density peak observed by spacecraft radio occultation
  measurements at Venus. A further analysis adding the contributions of
  other metal species and their chemistry has now shown that each metal
  ion species layers at a different altitude. Indeed the metal species
  Fe has its counterpart ion layer above 120 km in a region where there
  are sometimes traces of occultation electron density structures. Also,
  the new analysis includes estimates of the visual magnitudes of typical
  meteors as they would be observed from a satellite above the atmosphere.

---------------------------------------------------------
Title: Temporal evolution of the vertical content of metallic ion
    and neutral species
Authors: Aikin, A. C.; Grebowsky, J. M.; Burrows, J. P.; Correira,
   J.; Pesnell, W. D.
2005JASTP..67.1238A    Altcode: 2005JATP...67.1238A
  Temporal changes in the vertical column contents of the meteoric
  metals Mg<SUP>+</SUP>, Mg, Fe<SUP>+</SUP>, and Fe have been measured
  at ∼1030 LT for all longitudes in the latitude zone of 10°N 30°N
  during November 1996, encompassing the period of the Leonid meteor
  shower. The column contents were obtained using UV radiances measured
  by the GOME instrument on the ERS-2 satellite. Throughout the month
  there are several interesting prominent content enhancements of all
  species. After the Leonid shower peak on 17 November the ion species
  contents increase before the contents of the neutrals. However, it
  is difficult to confirm that this is a shower effect given the other
  similar variations seen earlier in the contents and in the sporadic
  meteor flux enhancements. The peaks in visual meteors on 17 November
  are not observed in the total metal column amounts. The GOME instrument
  has been in continuous operation since April 1995 and is an excellent
  resource for studying the temporal behavior of meteoric metals on a
  global scale.

---------------------------------------------------------
Title: The Physical Properties of PMSE Ice Particles as Determined
    During DROPPS by Measurements With the Particle Impact Detector
Authors: Webb, P. A.; Goldberg, R. A.; Pesnell, W. D.; Voss, H. D.
2005AGUSMSA43A..07W    Altcode:
  The two Black Brant payloads flown during the DROPPS (Distribution
  and Role of Particles in the Polar Summer Mesosphere) rocket program
  were launched during early July, 1999 from Andoya Rocket Range (ARR),
  Norway. Both payloads included a Particle Impact Detector (PID)
  charge telescope onboard. Computer simulations have shown that the PID
  instrument had the potential to detect atmospheric ice particles within
  the mesosphere, having dimensions of a few nanometers. Ice particles
  of nanometer size are believed to be responsible for polar mesospheric
  summer echoes (PMSEs), such as those observed at an altitude of ~82-87
  km over Andoya during the first DROPPS launch sequence. This talk will
  discuss the analysis of the PID data obtained from the DROPPS campaign
  and comparison of these data to the results obtained from the nanometer
  scale ice particle computer simulations. Intercomparison of the PID
  observations with the computer simulations provides information
  concerning the properties of the PMSE particles, including their
  "rocky" core size, ice mantle thickness and distribution.

---------------------------------------------------------
Title: Non-LTE Analysis of SABER 15 μm Limb Observations of the
    Summer 2002 Polar Mesopause Region
Authors: Kutepov, A. A.; Feofilov, A. G.; Pesnell, W. D.; Goldberg,
   R. A.; Gusev, O. A.; Marshall, T.
2005AGUSMSA43A..13K    Altcode:
  The SABER instrument on TIMED measures the limb radiance in ten
  broadband infrared channels for an altitude range that includes the
  mesosphere and lower thermosphere. In this altitude range the effects of
  non-local thermal equilibrium (non-LTE) must be included to understand
  the measurements. The non-LTE algorithms and computer code package
  developed to analyze CRISTA infrared spectral limb radiances were
  adapted for this purpose. We retrieved temperature profiles from the
  15 μm limb radiances measured in the summer 2002 polar mesopause. The
  retrieved temperature profiles will be compared with other retrievals,
  the coincident falling sphere experiments of the MaCWAVE campaign,
  and climatological data. Sources of the discrepancies between the
  various results are discussed.

---------------------------------------------------------
Title: From the Sun to You at the Speed of Light: The SDO Data System
Authors: Pesnell, W. D.
2005AGUSMSH42A..06P    Altcode:
  The Solar Dynamics Observatory (SDO) is on track to launch in April
  2008. Solar images in the extreme ultraviolet, the EUV spectral
  irradiance, magnetic field maps, and Dopplergrams are the primary data
  products of this mission. Each primary data product is produced on a
  rapid cadence. For example, some space weather products, suitable for
  use in ionosphere-thermosphere models, should be produced every 10--20
  seconds with a 5--10 minute delay between observation and appearance
  in the data system. Derived data products, including helioseismic
  properties and active region tracked in various wavelengths, will also
  be available from the data system. As part of NASA's Living With a
  Star Program, SDO will release data to the public as soon as possible
  after receipt from the satellite. The science teams will make the data
  available through Web-oriented interfaces, such as the Virtual Solar
  Observatory, allowing external people to make inquiries and have data
  delivered to their site. We will present an overview of the SDO data
  system and philosophy.

---------------------------------------------------------
Title: Meteoric Ions in Venus' Atmosphere
Authors: Pesnell, W. D.; Grebowsky, J.; Webb, P. A.
2004AGUFM.P23A0238P    Altcode:
  From a thorough modeling of the altitude profile of meteoric ionization
  in the cytherean atmosphere we have deduced that layers of magnesium,
  iron, and sodium ions should exist between altitudes between 115
  and 120~km. Based on the estimated meteoroid mass flux density, a
  peak ion density of several 10<SUP>3</SUP> ions cm{}<SUP>-3</SUP>
  is predicted. Allowing for the uncertainties in all of the model
  parameters, this value is probably within an order of magnitude
  of the correct density. The peak density is most sensitive to the
  meteoroid mass flux density, which determines the source function for
  Mg from the ablating meteoroids, the eddy viscosity coefficient, which
  determines the effectiveness of mixing the meteoric input downwards,
  and the presence of sulfuric acid droplets, which is an efficient sink
  of metallic compunds. We examine the effect of the aerosol layers in
  the upper mesosphere of Venus' atmosphere on the metallic layers.

---------------------------------------------------------
Title: Comparisons of PMSE Ice Particle Simulations With Observations
    From the DROPPS Rocket Campaign
Authors: Goldberg, R. A.; Webb, P. A.; Pesnell, W. D.
2004AGUFMSA24A..01G    Altcode:
  The origin of polar mesospheric summer echoes (PMSEs) and their proposed
  relationship to dust and aerosol particles and to noctilucent clouds
  (NLCs) are among the most pressing questions governing the physics of
  the polar summer mesosphere. Recent studies show increasing evidence
  for the presence of these particles, and their importance particularly
  in a charged state. One theory for the formation of the PMSE particles
  is that they are composed of a rocky core of meteoritic origin, which
  acts as a seed about which an ice mantle forms. Computer simulations
  have been conducted to model the flight trajectory and sublimation of
  spherical ice/rock particles with radius of 0.5 - 6.0 nm through the
  Particle Impact Detector (PID) charge telescope onboard two rockets
  that were part of the DROPPS (Distribution and Role of Particles in the
  Polar Summer Mesosphere) campaign. DROPPS involved two rocket sequences
  in July, 1999 launched from Andoya, Norway. The first launch sequence
  was nighttime (July 5-6) during the presence of a strong PMSE and a
  weak NLC. The second sequence (July 13-14) occurred during a bright
  NLC, but with no PMSE present. By comparing the PID observations from
  these two flights with the computer simulations, information about
  the properties of the PMSE particles, including their core size,
  ice mantle thickness and distribution, can be deduced.

---------------------------------------------------------
Title: Watching meteors on Triton
Authors: Pesnell, W. Dean; Grebowsky, J. M.; Weisman, Andrew L.
2004Icar..169..482P    Altcode: 2004Icar..169..482D
  The thin atmosphere of Neptune's moon Triton is dense enough to
  ablate micrometeoroids as they pass through. A combination of Triton's
  orbital velocity around Neptune and its orbital velocity around the
  Sun gives a maximum meteoroid impact velocity of approximately 19 km
  s <SUP>-1</SUP>, sufficient to heat the micrometeoroids to visibility
  as they enter. The ablation profiles of icy and stony micrometeoroids
  were calculated, along with the estimated brightness of the meteors. In
  contrast to the terrestrial case, visible meteors would extend very
  close to the surface of Triton. In addition, the variation in the
  meteoroid impact velocity as Triton orbits Neptune produces a large
  variation in the brightness of meteors with orbital phase, a unique
  Solar System phenomenon.

---------------------------------------------------------
Title: SABER observations of mesospheric temperatures and comparisons
    with falling sphere measurements taken during the 2002 summer
    MaCWAVE campaign
Authors: Mertens, Christopher J.; Schmidlin, Francis J.; Goldberg,
   Richard A.; Remsberg, Ellis E.; Pesnell, W. Dean; Russell, James M.;
   Mlynczak, Martin G.; López-Puertas, Manuel; Wintersteiner, Peter P.;
   Picard, Richard H.; Winick, Jeremy R.; Gordley, Larry L.
2004GeoRL..31.3105M    Altcode: 2004GeoRL..3103105M
  The SABER instrument was launched onboard the TIMED satellite in
  December 2001. Vertical profiles of kinetic temperature (Tk) are
  derived from broadband measurements of CO<SUB>2</SUB> 15 μm limb
  emission, in combination with measurements of CO<SUB>2</SUB> 4.3
  μm limb emission used to derive CO<SUB>2</SUB> volume mixing ratio
  (vmr). Infrared emission from the CO<SUB>2</SUB> ro-vibrational bands
  are in non-local thermodynamic equilibrium (non-LTE) in the mesosphere
  and lower thermosphere (MLT), requiring new radiation transfer and
  retrieval methods. In this paper we focus on Tk and show some of the
  first SABER observations of MLT Tk and compare SABER Tk profiles with
  rocket falling sphere (FS) measurements taken during the 2002 summer
  MaCWAVE campaign at Andøya, Norway (69°N, 16°E). The comparisons are
  very encouraging and demonstrate a significant advance in satellite
  remote sensing of MLT limb emission and the ability to retrieve Tk
  under extreme non-LTE conditions.

---------------------------------------------------------
Title: Global measurements of atmospheric content of metallic ion
    and neutral species
Authors: Aikin, A. C.; Grebowsky, J. M.; Pesnell, W. D.; Burrows, J. P.
2004cosp...35..371A    Altcode: 2004cosp.meet..371A
  Changes in the ion and neutral composition of the persistent atmospheric
  metal layers associated with the Leonid showers are determined using
  solar-induced resonant radiation measurements from the European Remote
  Sensing Satellite (ERS-2) platform. The nadir-viewing Global Ozone
  Measuring Experiment (GOME) UV/VIS spectrometer on ERS-2 is utilized
  to measure vertical column densities of meteoric metals including,
  Mg, Mg^+, Fe, Fe^+, and Si. The satellite orbits the Earth 14 times
  per day at 795 km with an equatorial crossing time of 10:30 AM. The
  spectral range of GOME is 237 to 793 nm with a wavelength resolution
  of 0.2 nm between 237 to 316 nm - the region in which the metal species
  lines we analyze are observed. The instrument measures all wavelengths
  simultaneously during a scan through the satellite nadir every 1.5
  seconds. The spectral range is divided into 5 channels. The 2 channels
  comprising the 237 to 316 nm range are integrated for 12 seconds giving
  a spatial resolution of 100 by 960 km. Metal data are examined for
  periods bracketing several Leonid meteor showers to isolate changes
  in the mesospheric and thermospheric abundances of meteoric material
  due to the showers. Since the Leonids occur annually in mid-November,
  global data from the entire month of November are analyzed for the
  years 1996 through 2002.

---------------------------------------------------------
Title: Experimental evidence for dusty plasmas in the polar summer
    mesosphere using rocket, lidar, and radar measurements
Authors: Goldberg, R. A.; Pesnell, W. D.
2004cosp...35..321G    Altcode: 2004cosp.meet..321G
  The origin of PMSEs (polar mesospheric summer echoes)and their proposed
  relationship to dust and aerosol particles and to NLCs (noctilucent
  clouds) are among the most important questions governing the physics
  of the polar summer mesosphere. Recent studies show increasing
  evidence for the presence of these particles, and their importance
  particularly in a charged state. Several recent experimental programs
  have concentrated on detection of these particles in the MLT (mesosphere
  and lower thermosphere) region, with an attempt to determine their
  role in the structure, dynamics and chemistry of the MLT. Here, we
  concentrate on results of the DROPPS program (Andøya, Norway,1999)
  and the MaCWAVE program (Andoya, 2002), both of which were designed
  to study problems relating to this issue. DROPPS involved two rocket
  sequences in July, 1999. The first launch sequence was nighttime (July
  5-6) during the presence of a strong PMSE and a weak NLC. The second
  sequence (July 13-14) occurred during a bright NLC, but with no PMSE
  present. MaCWAVE also involved two summertime launch sequences, with
  emphasis on the influence of gravity waves on the MLT region, but with
  adequate instrumentation to search for charged dust or aerosols. In
  this case, launch sequences occurred on the nights of July 1-2, and
  4-5, each during the presence of PMSE events. By combining results
  from the rocket instruments with radar and lidar soundings from ALOMAR
  Observatory (also at Andøya), it has been possible to analyze each
  event in sufficient detail to gain an improved understanding of the
  polar summer MLT and it's response to a dusty plasma environment.

---------------------------------------------------------
Title: SABER Observations of Polar Summer/Winter Mesospheric and
    Lower Thermospheric Temperatures and Comparisons With Correlative
    Measurements Taken During the MaCWAVE Campaign
Authors: Remsberg, E. E.; Mertens, C. J.; Schmidlin, F. J.; Goldberg,
   R. A.; She, C.; Williams, B. P.; Pesnell, W. D.; Russell, J. M.;
   Mlynczak, M. G.; Gordley, L. L.; Lopez-Puertas, M.; Picard, R. H.;
   Winick, J. R.; Wintersteiner, P. P.
2003AGUFMSA41B0439R    Altcode:
  The Sounding of the Atmosphere using Broadband Emission Radiometry
  (SABER) experiment was launched onboard the TIMED satellite in December
  2001. SABER derives kinetic temperature (Tk) in the mesosphere and
  lower thermosphere (MLT) from broadband measurements of CO<SUB>2</SUB>
  15 um limb emission, in combination with measurements of CO<SUB>2</SUB>
  4.3 um limb emission used to derive CO<SUB>2</SUB> volume mixing
  ratio. Infrared emissions from the CO<SUB>2</SUB> ro-vibrational
  bands are in non-local thermodynamic equilibrium (non-LTE) in the MLT,
  requiring non-LTE processes to be accurately modeled in the retrieval
  algorithm. In this paper we focus on Tk and show results derived
  from the non-LTE retrieval algorithm. We demonstrate the ability
  to retrieve Tk in an extreme non-LTE environment by comparing SABER
  MLT Tk with rocket falling sphere (FS) and sodium lidar measurements
  taken during the 2002 summer MaCWAVE campaign. The summer Tk profiles
  show that the SABER non-LTE retrieval algorithm improves upper
  mesospheric Tk retrievals by 35 K to 45 K, as compared to SABER LTE
  Tk retrievals. Combined measurements from SABER and MaCWAVE show a
  mesopause region that is highly variable in space and time. SABER data
  also show a mesopause altitude that changes with latitude and season,
  consistent with the bimodal character of the mesopause height. We also
  show preliminary comparisons with the recently available FS and sodium
  lidar measurements taken during the 2003 winter MaCWAVE campaign.

---------------------------------------------------------
Title: Occultation of π Arietis by asteroid (828) Lindemannia on
    November 10 2002
Authors: Sada, Pedro V.; Nugent, Richard; Maley, Paul; Frankenberger,
   Rick; Preston, Steve; Dunham, David; Pesnell, W. Dean
2003OccN....9d...9S    Altcode:
  The occultation of the bright star π Arietis (HIP 13165) by the
  asteroid (828) Lindemannia was recorded by 10 observers in Texas on
  November 10, 2002. Clouds hampered many more potential observers. Nine
  disappearances, ten reappearances, and 2 near misses are reported. A
  least-squares fit to the data results in a 52.6 km × 50.8 km ellipse
  with the major axis oriented at a PA of 90.0o. However, deviations
  from a perfect ellipse were observed.

---------------------------------------------------------
Title: Evolution of relativistic electrons during a magnetic storm
    as seen in low-earth orbit
Authors: Pesnell, W. Dean; Goldberg, Richard A.; Chenette, D. L.;
   Schulz, M.; Gaines, E. E.
2003AdSpR..31.1059P    Altcode:
  Highly relativistic electron events (HREs) are periods of intense,
  long-lived, energetic electron fluxes in the outer radiation zone. We
  are using measurements from the High Energy Particle Spectrometer (HEPS)
  on the Upper Atmosphere Research Satellite (UARS) to develop a database
  of the pitch-angle and energy-resolved electron fluxes with energies
  between 30 keV and 5 MeV. The data acquired by HEPS have overlapped
  with the declining phase of solar cycle 22 making these data very
  important, since HREs are thought to peak in frequency and intensity
  during this phase of the solar cycle. We find a consistent scenario
  of electrons being injected into the radiation belts by a magnetic
  storm (deduced from Dst) and being slowly accelerated to ever higher
  energies over days to weeks. The energy dependence of the flux is an
  essential part of the analysis. Electrons with energies greater than
  300 keV are the last to appear following an injection and also linger
  longer than electrons with lower energies.

---------------------------------------------------------
Title: Meteoric Material-An Important Component of Planetary
    Atmospheres
Authors: Grebowsky, Joseph M.; Moses, Julianne I.; Pesnell, W. Dean
2002GMS...130..235G    Altcode: 2002assc.book..235G
  Interplanetary dust particles (IDPs) interact with all planetary
  atmospheres and leave their imprint as perturbations of the background
  atmospheric chemistry and structure. They lead to layers of metal
  ions that can become the dominant positively charged species in
  lower ionospheric regions. Theoretical models and radio occultation
  measurements provide compelling evidence that such layers exist in all
  planetary atmospheres. In addition IDP ablation products can affect
  neutral atmospheric chemistry, particularly at the outer planets where
  the IDPs supply oxygen compounds like water and carbon dioxide to the
  upper atmospheres. Aerosol or smoke particles from incomplete ablation
  or recondensation of ablated IDP vapors may also have a significant
  impact on atmospheric properties.

---------------------------------------------------------
Title: Growth and decay of relativistic electrons during a magnetic
    storm as seen in low-Earth orbit
Authors: Pesnell, W. Dean; Goldberg, Richard A.; Chenette, D. L.;
   Gaines, E. E.; Schulz, M.
2001JGR...10630039P    Altcode:
  Highly relativistic electron events (HREs) are periods of intense,
  long-lived, energetic electron fluxes in the outer radiation zone. We
  are using measurements from the High Energy Particle Spectrometer (HEPS)
  on the Upper Atmosphere Research Satellite (UARS) to develop a database
  of the pitch-angle-resolved and energy-resolved electron fluxes with
  energies between 30 keV and 5 MeV. The data acquired by HEPS have
  overlapped with the declining phase of solar cycle 22, making these
  data very important, since HREs are thought to peak in frequency and
  intensity during this phase of the solar cycle. We find a consistent
  scenario of electrons being injected into the radiation belts by a
  magnetic storm (deduced from Dst) and being slowly accelerated to ever
  higher energies over days to weeks. The energy dependence of the flux
  is an essential part of the analysis. Above 700 keV the most energetic
  electrons are the last to appear and the slowest to fade following an
  injection event.

---------------------------------------------------------
Title: Meteoric Material - One of the Least Explored Components of
    Planetary Atmospheres
Authors: Moses, J. I.; Grebowsky, J. M.; Pesnell, W. D.; Weisman, A. L.
2001AGUFMSA42A..09M    Altcode:
  Interplanetary dust particles (IDPs) continuously impact all the planets
  and their satellites in the solar system. In all planetary atmospheres
  IDPs leave their imprint as aerosols or smoke particles that are left
  behind when the IDPs do not ablate completely or when the ablated vapors
  recondense. In addition, in all atmospheres they produce ionization
  layers comprised of metallic ions, predominantly Mg<SUP>+</SUP> and
  Fe<SUP>+</SUP>. On Earth the metal ions are frequently measured to be
  the dominant positively charged species in low-latitude ionospheric
  layers. Theoretical models provide evidence that such layers exist at
  Venus, Mars, Jupiter, Saturn, Neptune and Saturn's moon Titan. Even
  the sparse atmosphere of Triton may be lit up by meteors. Spacecraft
  radio occultation measurements reveal low altitude, narrow ionosphere
  layers at each of the giant planets. These narrow features appear
  to be consistent with the presence of metallic ions that have been
  compressed by electrodynamic processes as on Earth. Observations at
  Mars and Venus do not show clear evidence of such layers. The IDPs
  also deposit nonmetal neutral species in the ablation process. For
  the inner planets these species blend unnoticed into the atmosphere,
  but for the outer planets they can lead to persistent amounts of water
  vapor and carbon dioxide. Although many measurements are available for
  the Earth, measurements of the IDP distributions and their atmospheric
  signatures at other planets are in their initial stages at the present
  time. Modeling efforts are still qualitative as the chemical reaction
  rates for many of the ablated gases are not established. Most of our
  knowledge of long lasting IDP atmospheric effects is derived from
  what we know about Earth, for which our understanding is still far
  from complete. This component of all atmospheres must be treated as
  a key factor in all planetary atmospheric aeronomy systems.

---------------------------------------------------------
Title: Ionospheric Dynamics Effects on the Ionospheric Magnesium-Iron
    Ion Concentration Ratios
Authors: Grebowsky, J. M.; Pesnell, W. D.; Aikin, A. C.
2001AGUSM..SA31A04G    Altcode:
  Sounding rocket and satellite ion composition measurements show that
  the meteoric Fe<SUP>+</SUP> concentration typically exceeds that of
  Mg <SUP>+</SUP> in the main meteor ionization layer and above. This
  is a puzzle because the assumed source of the metal ions is the
  sporadic background of infalling meteoroids, which are on average
  chondritic in nature and hence should deposit a higher portion
  of Mg in the atmosphere than Fe. A more detailed investigation
  the ionosphere measurements revealed that the ratio varies from
  measurement to measurement with Mg <SUP>+</SUP> and Fe <SUP>+</SUP>
  often switching dominance roles, although on average Fe <SUP>+</SUP>
  dominates. Possible sources for the relative variations between the two
  species include differential ablation, species-dependent ion-neutral
  chemical processes, non-isotropic interplanetary particle populations
  and neutral wind and electrodynamic influences. We will discuss the
  observations and show that ionospheric dynamics and electrodynamic
  processes can play an important role.

---------------------------------------------------------
Title: Meteoric Ions in the Ionosphere of Jupiter
Authors: Kim, Y. H.; Pesnell, W. Dean; Grebowsky, J. M.; Fox, J. L.
2001Icar..150..261K    Altcode:
  A reanalysis of the Voyager 2 radio occultation data has recently
  revealed a low-altitude layer in the jovian ionosphere (Hinson et
  al. 1998, J. Geophys. Res. 103, 9505-9520). The peak electron density
  of the layer measured on egress, which was at 93° solar zenith angle
  near the morning terminator, was inferred to be of the order of 10
  <SUP>4</SUP> cm <SUP>-3</SUP>. A substantial low-altitude layer of
  hydrocarbon ions in the jovian ionosphere was predicted by Kim and
  Fox (1994), but the peak total ion density at predawn was about 10
  <SUP>2</SUP> cm <SUP>-3</SUP>, two orders of magnitude smaller than
  the noon values, due to the efficient recombination of molecular ions
  during the night. The existence of large electron densities in the
  jovian ionospheric E region at predawn suggests the presence of ions
  with long lifetimes and/or those produced by a source that exhibits
  little local time dependence, such as ions originating from meteoroid
  ablation in Jupiter's atmosphere. We have modeled the production
  rates and subsequent chemistry of seven meteoric ions, including O
  <SUP>+</SUP>, C <SUP>+</SUP>, Si <SUP>+</SUP>, Fe <SUP>+</SUP>, Mg
  <SUP>+</SUP>, Na <SUP>+</SUP>, and S <SUP>+</SUP>, their compounds
  with H, H <SUP>2</SUP>, and hydrocarbons, and the corresponding
  neutral species. The models predict a layer of meteoric ions in the
  altitude region of 350-450 km above the 1-bar level, with peak total ion
  densities of several times 10 <SUP>4</SUP> cm <SUP>-3</SUP>, which are
  comparable to the observed values. The peak of the meteoric atomic ion
  layer is most apparent at predawn and is located higher than that of the
  hydrocarbon ion layer during the daytime and higher than the altitude
  of peak production of ions by meteor ablation. At the altitude of peak
  ablation, about 350 km, meteoric ions are mainly removed by reactions
  with hydrocarbons in either two-body or three-body reactions, and the
  molecular ions produced are neutralized efficiently by dissociative
  recombination. Meteoric ions may also form adduct ions by termolecular
  reactions with hydrogen molecules, but metallic ions, such as Na
  <SUP>+</SUP>, Mg <SUP>+</SUP>, and Fe <SUP>+</SUP>, may be reformed
  from the adduct ions by a series of reactions with H atoms. Thus the
  net ion loss process at the metal ion peak may be dominated by rediative
  recombination, and the meteoric ion density profiles show little diurnal
  variation. The predicted peak electron density and altitude and the
  relative densities of the ions are dependent on the rate coefficients
  assumed for many of the reactions involved, and measurements of key
  rate coefficients are needed to further constrain the models.

---------------------------------------------------------
Title: Meteoric ions in planetary ionospheres
Authors: Pesnell, W. Dean; Grebowsky, J. M.
2001AdSpR..27.1807P    Altcode: 2001AdSpR..27.1807D
  Solar system debris, in the form of meteoroids, impacts every
  planet. The flux, relative composition and speed of the debris at
  each planet depends on the planet's size and location in the solar
  system. Ablation of this debris by the atmosphere leaves behind metal
  atoms. During the ablation process metallic ions are formed by impact
  ionization. For small inner solar system planets, including Earth,
  this source of ionization is typically small compared to either
  photoionization or charge exchange with ambient molecular ions. For
  Earth, the atmosphere above the main deposition region absorbs the
  spectral lines capable of ionizing the major metallic atoms (Fe
  and Mg) so that charge exchange with ambient ions is the dominant
  cause of ionization. Within the carbon dioxide atmosphere of Mars
  (and possibly Venus), photoionization is important in determining the
  ion density. For a heavy planet like Jupiter, far from the sun, impact
  ionization of ablated neutral atoms by impacts with molecules becomes a
  prominent source of ionization due to the gravitational acceleration to
  high incident speeds. We will describe the processes and location and
  extent of metal ion layers for Mars, Earth and Jupiter, concentrating
  on flagging the uncertainties in the models at the present time. This
  is an important problem, because low altitude ionosphere layers for
  the planets, particularly at night, probably consist predominantly of
  metallic ions. Comparisons with Earth will be used to illustrate the
  differing processes in the three planetary atmospheres.

---------------------------------------------------------
Title: Variation of mesospheric ozone during the highly relativistic
    electron event in May 1992 as measured by the High Resolution Doppler
    Imager instrument on UARS
Authors: Pesnell, W. Dean; Goldberg, Richard A.; Jackman, Charles H.;
   Chenette, D. L.; Gaines, E. E.
2000JGR...10522943P    Altcode:
  Highly relativistic electron precipitation events (HREs) include
  long-lived enhancements of the flux of electrons with E&gt;1MeV
  into the Earth's atmosphere. HREs also contain increased fluxes of
  electrons with energies above 100 keV that have been predicted to
  cause large depletions of mesospheric ozone. For some of the measured
  instantaneous values of the electron fluxes during the HRE of May
  1992, relative depletions greater than 22% were predicted to occur
  between altitudes of 55 and 80 km, where HO<SUB>x</SUB> reactions
  cause local minima in both the ozone number density and mixing ratio
  altitude profiles. These ozone depletions should follow the horizontal
  distribution of the electron precipitation, having a distinct boundary
  equatorward of the L=3 magnetic shell. To search for these effects,
  we have analyzed ozone data from the High Resolution Doppler Imager
  (HRDI) instrument on UARS. Owing to the multiple, off-track viewing
  angles of HRDI, observations in the region affected by the electrons
  are taken at similar local solar times before, during, and after the
  electron flux increase. Our analysis limits the relative ozone depletion
  to values &lt;10% during the very intense May 1992 HRE. We do observe
  decreases in the ozone mixing ratio at several points in the diurnal
  cycle that may be associated with the transport of water vapor into the
  mesosphere during May 1992. This masking of the precipitating electron
  effects by the seasonal variations in water vapor can complicate the
  detection of those effects.

---------------------------------------------------------
Title: Meteoric magnesium ions in the Martian atmosphere
Authors: Pesnell, William Dean; Grebowsky, Joseph
2000JGR...105.1695P    Altcode:
  From a thorough modeling of the altitude profile of meteoric
  ionization in the Martian atmosphere we deduce that a persistent
  layer of magnesium ions should exist around an altitude of 70 km. On
  the basis of the estimated meteoroid mass flux density, a peak ion
  density of ~10<SUP>4</SUP>ionscm<SUP>-3</SUP> is predicted. Allowing
  for the uncertainties in all of the model parameters, this value is
  probably within an order of magnitude of the correct density. Of these
  parameters, the peak density is most sensitive to the meteoroid mass
  flux density which determines the source function for Mg from the
  ablating meteoroids. Unlike the terrestrial case, where the metallic
  ion production is dominated by charge-exchange of the deposited neutral
  Mg with the ambient ions, Mg<SUP>+</SUP> in the Martian atmosphere
  is produced predominantly by photoionization. The low ultraviolet
  absorption of the Martian atmosphere makes Mars an excellent laboratory
  in which to study meteoric ablation. Resonance lines in the ultraviolet
  that cannot be seen in the spectra of terrestrial meteors may be
  visible to a surface observatory in the Martian highlands.

---------------------------------------------------------
Title: Theoretical Stellar Evolution
Authors: Cox, Arthur N.; Becker, Stephen A.; Pesnell, W. Dean
2000asqu.book..499C    Altcode:
  No abstract at ADS

---------------------------------------------------------
Title: A search of UARS data for ozone depletions caused by the
    highly relativistic electron precipitation events of May 1992
Authors: Pesnell, W. Dean; Goldberg, Richard A.; Jackman, Charles H.;
   Chenette, D. L.; Gaines, E. E.
1999JGR...104..165P    Altcode:
  Highly relativistic electron precipitation (HRE) events containing
  significant fluxes of electrons with E&gt;1MeV have been predicted
  by models to deplete mesospheric ozone. For the electron fluxes
  measured during the great HRE of May 1992, depletions were predicted
  to occur between altitudes of 55 and 80 km, where HO<SUB>x</SUB>
  reactions cause a local minimum in the ozone number density and mixing
  ratio. Measurements of the precipitating electron fluxes by the particle
  environment monitor (PEM) tend to underestimate their intensity; thus
  the predictions of ozone depletion should be considered an estimate
  of a lower limit. Since the horizontal distribution of the electron
  precipitation follows the terrestrial magnetic field, it would show
  a distinct boundary equatorward of the L=3 magnetic shell and be
  readily distinguished from material that was not affected by the HRE
  precipitation. To search for possible ozone depletion effects, we
  have analyzed data from the cryogenic limb array etalon spectrometer
  and microwave limb sounder instruments on UARS for the above HRE. A
  simplified diurnal model is proposed to understand the ozone data from
  UARS, also illustrating the limitations of the UARS instruments for
  seeing the ozone depletions caused by the HRE events. This diurnal
  analysis limits the relative ozone depletion at around 60 km altitude to
  values of &lt;10% during the very intense May 1992 event, consistent
  with our prediction using an improved Goddard Space Flight Center
  two-dimensional model.

---------------------------------------------------------
Title: Uptake coefficient of charged aerosols—implications for
    atmospheric chemistry
Authors: Aikin, Arthur C.; Pesnell, W. Dean
1998GeoRL..25.1309A    Altcode:
  Gas uptake onto liquid particles is influenced by the electrical charge
  on the particle. This charge rearranges the spatial distribution of
  the dissolved reactant ions, modifying the solute-solvent reaction
  at the surface and for some distance into the liquid. This results
  in a modification of the uptake coefficient. A general expression,
  applicable to laboratory and atmospheric conditions, is presented. The
  change in the uptake coefficient is proportional to particle charge
  and the square of the Debye length within the liquid. It is inversely
  proportional to the square of the particle radius.

---------------------------------------------------------
Title: Do meteor showers significantly perturb the ionosphere?
Authors: Grebowsky, J. M.; Goldberg, R. A.; Pesnell, W. D.
1998JASTP..60..607G    Altcode: 1998JATP...60..607G
  More than 40 rocket flights through the main meteoric ionization
  layer, which peaks near 95 km, have sampled the meteoric metallic ion
  concentrations. Five of these flights were conducted during or near
  the peak times of a meteor shower. In each of the latter studies the
  observed meteoric ion concentrations were assumed to be a consequence
  of the shower. These measurements were not complemented by baseline
  observations made for similar ionospheric conditions immediately before
  the shower and no rigorous quantitative comparisons were made using
  average non-shower distributions. In order to further investigate the
  impact of the shower on the ionosphere, all published ion concentration
  altitude profiles obtained from sounding rockets in the meteoric
  ionization regime have been scanned to develop a digital data base
  of meteoric ion concentrations. These data are used to provide the
  first empirical altitude profile of the metallic ions. The average
  observed Mg<SUP>+</SUP> concentrations are lower than those yielded by
  the most comprehensive model to date. This compiled ensemble of data
  provides supporting evidence that meteor showers do have a significant
  impact on the average ionosphere composition. Although there is much
  variability in the observed meteoric layers, the peaks in the total
  metallic ion concentrations at mid-latitudes, on the dayside, observed
  during meteor showers had concentrations comparable to, or exceeding,
  the highest concentrations measured in the same altitude regions during
  non-shower periods.

---------------------------------------------------------
Title: Pioneer Venus Orbiter Measurements of Solar EUV Flux During
    Solar Cycles 21 and 22
Authors: Mahajan, K. K.; Upadhyay, Hari Om; Sethi, N. K.; Hoegy,
   W. R.; Pesnell, W. D.; Brace, L. H.
1998SoPh..177..203M    Altcode:
  The Pioneer Venus Orbiter (PVO) had on board the electron temperature
  probe experiment which measured temperature and concentration of
  electrons in the ionosphere of Venus. When the probe was outside the
  Venus ionosphere and was in the solar wind, the probe current was
  entirely due to solar photons striking the probe surface. This probe
  thus measured integrated solar EUV flux (Ipe) over a 13-year period from
  January 1979 to December 1991, thereby covering the declining phase of
  solar cycle 21 and the rising phase of solar cycle 22. In this paper, we
  examine the behavior of Ipe translated to the solar longitude of Earth
  (to be called EIpe) during the two solar cycles. We find that total
  EUV flux changed by about 60% during solar cycle 21 and by about 100%
  in solar cycle 22. We also compare this flux with other solar activity
  indicators such as F_10.7 , Lα, and the solar magnetic field. We find
  that while the daily values of EIpe are highly correlated with F_10.7
  (correlation coefficient 0.87), there is a large scatter in EIpe for
  any value of this Earth-based index. A comparison of EIpe with SME
  and UARS SOLSTICE Lα measurements taken during the same period shows
  that EIpe tracks Lα quite faithfully with a correlation coefficient
  of 0.94. Similar comparison with the solar magnetic field (Bs) shows
  that EIpe correlates better with Bs than with F_10.7 . We also compare
  EIpe with total solar irradiance measured during the same period.

---------------------------------------------------------
Title: A New Graphical Interface for the Paczynski Stellar Evolution
    Code
Authors: Odell, A. P.; Pesnell, W. D.
1998ASPC..135...69O    Altcode: 1998hcsp.conf...69O
  The output of stellar structure and evolution codes has traditionally
  been in enormous tabular form. We have extensively modified the
  public-domain Paczynski Code to provide real-time screen-graphical
  output for use in undergraduate and graduate courses at the college
  level. Thus anyone studying the structure and evolution of stars
  can compute such models of varying mass and composition, and see the
  results (run of composition, energy generation, and gas properties
  with mass) presented visually as the evolution through core carbon
  burning proceeds.It is possible to determine the structure of the gray
  atmosphere of a star assuming the mixing length theory of convection,
  including the effects of different mixing length. One can watch as
  the main- sequence homogeneous model converges. A summary program is
  included which, at the end of an evolution sequence, will show the
  various model characteristics as a function of time, and also an H-
  R Diagram for comparison to real stars. We are currently working on
  a pulsation code which will allow the user to generate and display
  eigenfunctions for various modes.

---------------------------------------------------------
Title: Pioneer Venus Orbiter Measurements of Solar EUV Flux during
    Solar Cycles 21 and 22
Authors: Mahajan, K. K.; Upadhyay, Hari Om; Sethi, N. K.; Hoegy,
   W. R.; Pesnell, W. D.; Brace, L. H.
1998sers.conf..203M    Altcode:
  No abstract at ADS

---------------------------------------------------------
Title: The Evolutionary and Pulsational Characteristics of Alpha
    Virginis Including Turbulent Diffusive Mixing
Authors: Pesnell, W. D.; Odell, A. P.
1998ASPC..135...22P    Altcode: 1998hcsp.conf...22P
  The best-observed star (besides the sun) for comparison to stellar
  evolution and pulsation theory is Alpha Virginis, a double-line
  spectroscopic and "visual" binary which shows apsidal motion and
  Beta Cephei-type pulsation. Unfortunately, it is impossible to fit
  simultaneously all of the observed properties of this star with
  one model that also exhibits an unstable pulsation mode of the
  correct period (see Odell and Pesnell, 32nd Liege Colloquium 1995
  procedings), even with new opacities computed by the OPAL group
  of Rogers and Iglesias (Ap. J. Suppl. 79, 507, 1992).Lyubimkov et
  al. (Astronomicheskii Zhurnal 72, 212, 1995) have observed that the
  composition of Alpha Vir A differs from Alpha Vir B in that the helium
  abundance in the atmosphere of the primary star is significantly higher
  than the secondary, by approximately a factor of two. Denissenkov
  (A&amp;A 287, 113, 1994) has suggested that this and other abundance
  anomolies (CN-cycle processed material) can be explained by Turbulent
  Diffusive Mixing in early B-stars near the main sequence. Thus it is
  of interest to determine the effects of this helium abundance change
  on the properties and stability of models of Alpha Virginis.

---------------------------------------------------------
Title: Meteoric Ionization Layers in the Martian Atmosphere
Authors: Pesnell, W. D.; Grebowsky, J. M.
1997AAS...191.2703P    Altcode: 1997BAAS...29.1254P
  Mars, like the other planets, is bombarded by meteorites. At least two
  families of particles impact the planets: sporadic and shower. In the
  terrestrial atmosphere both families cause sporadic-E layers when the
  introduced material is ionized by charge-exchange, photoionization, or
  impact ionization. Narrow layers of ionized material are produced when
  the long-lived metallic ions are compressed by tidal or gravity wave
  motions in the atmosphere. We will examine how the ion-neutral chemistry
  and dynamics of the Martian atmosphere affect the deposited meteoric
  material. Our emphasis is on magnesium, an easily ionized species that
  is a major component of the meteoric debris. The parameters that affect
  the meteoric ionization differ between Earth and Mars. In particular,
  the atmospheric compositions and ionospheric densities differ. Further,
  the lower atmospheric pressure on Mars means lower altitudes for the
  bulk of the atmospheric ablation of the meteorites. However, the range
  of atmospheric density variation at high altitudes is greater at Mars
  than at Earth, so that sputtering of high speed shower streams which
  occurs at high altitudes may be relatively more important at Mars
  than Earth.

---------------------------------------------------------
Title: A Student-Oriented Graphical Interface for the Paczynski
    Stellar Evolution Code
Authors: Odell, A. P.; Pesnell, W. D.
1997AAS...191.1202O    Altcode: 1997BAAS...29.1227O
  The output of stellar structure and evolution codes has traditionally
  been in enormous tabular form. We have extensively modified the
  public-domain Paczynski Code to provide real-time screen-graphical
  output for use in undergraduate and graduate college courses. Thus
  anyone studying the structure and evolution of stars can compute models
  of chosen mass and composition, and see the results (run of composition,
  energy generation, and gas properties with mass) presented visually
  as the evolution through core carbon burning proceeds. Programs
  are included to generate gray stellar envelopes with mixing-length
  convection, converge homogeneous main-sequence models, integrate
  evolution sequences, and create summaries of model characteristics as
  a function of time, such as a theoretical H-R diagram.

---------------------------------------------------------
Title: A comparison of solar EUV flux from langmuir probe
    photoelectron measurements on the pioneer venus orbiter with other
    solar activity indicators
Authors: Mahajan, K. K.; Hoegy, W. R.; Pesnell, W. D.; Brace, L. H.;
   Sethi, N. K.
1997AdSpR..20..187M    Altcode:
  The electron temperature probe acted as a photo-diode on the Pioneer
  Venus Orbiter (PVO) and measured the integrated solar EUV flux
  (I_pe) over a 13 year period from January 1979 to December 1991, thus
  covering the declining phase of solar cycle 21 and the rising phase
  of solar cycle 22. Gross features in the solar activity variations
  of this flux during the 13 year period have earlier been studied
  by Brace et al. (1988) and Hoegy et al. (1993). In this paper,
  we study the fine features by translating the observed I_pe to the
  solar longitude of Earth (to be called as EI_pe) and comparing it with
  other solar activity indicators like F_10.7, Lyman alpha and the solar
  magnetic field. We find that while the daily values of EI_pe are highly
  correlated with F10.7 (correlation coefficient 0.87), there is a large
  scatter in EI_pe for any value of this earth based index. Comparison
  of EI_pe with SME and UARS-SOLSTICE Lyman-alpha measurements taken
  during the same period indicates that EI_pe tracks Lyman-alpha quite
  faithfully. Similar comparison with the solar magnetic field (B_s)
  shows that EI_pe correlates better with B_s than with F10.7.

---------------------------------------------------------
Title: High-speed correction factor to the O(+)-O resonance charge
    exchange collision frequency
Authors: Omidvar, K.; Pesnell, W. D.
1995AnGeo..13..253O    Altcode:
  The high-speed correction factor to the O+-O collision frequency,
  resulting from drift velocities between ions and neutrals, is calculated
  by solving the integral expression in this factor both numerically and
  analytically. Although the analytic solution is valid for either small
  or large drift velocities between ions and neutrals, for temperatures of
  interest and all drift velocities considered, agreement is found between
  analytic and detailed numerical integration results within less than 1%
  error. Let Tr designate the average of the ion and neutral temperatures
  in K, and u=vd/&lt;alpha&gt;, where vd is the relative drift velocity
  in cm s-1, and &lt;alpha&gt;=4.56×10<SUP>3</SUP>sqrtT<SUB>r</SUB>
  cm s<SUP>-1</SUP> is the thermal velocity of the O<SUP>+</SUP>-O
  system. Then, as u ranges from 0 to 2, the correction factor multiplying
  the collision frequency increases monotonically from 1 to about
  1.5. An interesting result emerging from this calculation is that the
  correction factor for temperatures of aeronomical interest is to a
  good approximation independent of the temperature, depending only on
  the scaled velocity u.

---------------------------------------------------------
Title: Alpha Virginis : A Test of Upper Main Sequence Stellar
    Structure and Evolution
Authors: Odell, A. P.; Pesnell, W. D.
1995LIACo..32..417O    Altcode: 1995sews.book..417O
  No abstract at ADS

---------------------------------------------------------
Title: O<SUP>+</SUP>-O collision frequency in high-speed flows
Authors: Pesnell, William Dean; Omidvar, Kazem; Hoegy, Walter R.;
   Wharton, Larry E.
1994JGR....9921375P    Altcode:
  Throughout much of the terrestrial thermosphere and ionosphere,
  the motions of the neutral and ionized constituents are
  closely coupled and relative velocities are small, of the
  order of 100 ms<SUP>-</SUP><SUP>1</SUP> or less. This is
  particularly true at midlatitudes to low latitudes where typical
  velocities in the neutral gas due to tidal forcing are only 20-50
  ms<SUP>-</SUP><SUP>1</SUP>. However, the solar wind-magnetosphere
  interaction drives a large-scale convection pattern in the polar
  ionosphere. When the rapid adjustment of the plasma to changes in
  the solar wind is combined with the slower response of the more
  massive neutral gas, large relative velocities on the order of 1
  kms<SUP>-</SUP><SUP>1</SUP> can exist for substantial lengths of
  time. This will be more common during periods of high geomagnetic
  activity, as a result of the greater number of magnetic substorms
  and other particle precipitation events. When a significant relative
  velociy is present, the calculation of interaction parameters of the
  two gases passing through each other, such as collision frequency,
  must include that velocity. These effects are usually neglected when
  interpreting wind and ion drift observations. We show how the collision
  frequency is affected by a directed relative velocity between any two
  gases interacting with a power law or exponential potential energy
  curves. The directed velocity increases the collision frequency at all
  temperatures for most ion-neutral interactions. For certain power law
  potentials, such as the charge quadrupole, the collision frequency is
  decreased. We present an analytic solution for the high-speed collision
  integral using the resonance charge exchange cross section.

---------------------------------------------------------
Title: Accuracy of O<SUP>+</SUP>-O collision cross-section deduced
    from ionosphere-thermosphere observations
Authors: Reddy, C. A.; Hoegy, W. R.; Pesnell, W. D.; Mayr, H. G.;
   Hines, C. O.
1994GeoRL..21.2429R    Altcode:
  Aeronomic observations applied to the empirical derivation of the
  ion-neutral collision cross-section—a basic parameter governing
  the mutual interactions between the neutral and plasma components in
  the Earth's upper atmosphere—have given values considerably larger
  than those derived from theory. The empirical scheme uses the plasma
  velocities obtained with the Incoherent Scatter Radar and the neutral
  winds obtained with the Fabry-Perot Interferometer. It is shown here
  that such an analysis overestimates the collision cross-section due to
  the effects of errors in the observables. The effect may be sufficiently
  large to bring about agreement with theory, and calls for a re-analysis
  of the aeronomic data using methods which minimize the bias caused by
  measurement errors.

---------------------------------------------------------
Title: A Solar Dynamo Pediction: Cycle 23-Cycle 22
Authors: Schatten, K. H.; Pesnell, W. D.
1993AAS...183.2507S    Altcode: 1993BAAS...25.1332S
  No abstract at ADS

---------------------------------------------------------
Title: The Solar Cycle in the Extreme Ultraviolet
Authors: Pesnell, W. D.; Hoegy, W. R.
1993AAS...183.2506P    Altcode: 1993BAAS...25.1331P
  We present Pioneer Venus Orbiter observations of the solar EUV flux. The
  13 years of measurements cover the last part of Solar Cycle 21 and
  the majority of Solar Cycle 22. The Ipe flux is a direct measure of
  the solar EUV flux that correlated extremely well with earth based
  measurements until the onset of Solar Cycle 22. We demonstrate this
  correlation with the 10.7 cm. radio flux and ionospheric conditions. Our
  measurements show that Solar Cycle 22 was one of the most active ever
  recorded. The Ipe flux is a yield-weighted integration over wavelengths
  from 100 Angstroms to 1300 Angstroms. It is dominated by emission
  in L_alpha lambda 1216, with roughly 50% of the flux coming from the
  remaining wavelengths. Other EUV proxy measurements are compared to
  the Ipe flux.

---------------------------------------------------------
Title: An Early Solar Dynamo Prediction: Cycle 23 ∼ Cycle 22
Authors: Schatten, Kenneth H.; Pesnell, W. Dean
1993GeoRL..20.2275S    Altcode:
  In this paper, we briefly review the “dynamo” and “geomagnetic
  precursor” methods of long-term solar activity forecasting. These
  methods depend upon the most basic aspect of dynamo theory to predict
  future activity, future magnetic field arises directly from the
  magnification of pre-existing magnetic field. We then generalize the
  dynamo technique, allowing the method to be used at any phase of the
  solar cycle, through the development of the “Solar Dynamo Amplitude”
  (SODA) index. This index is sensitive to the magnetic flux trapped
  within the Sun's convection zone but insensitive to the phase of the
  solar cycle. Since magnetic fields inside the Sun can become buoyant,
  one may think of the acronym SODA as describing the amount of buoyant
  flux. Using the present value of the SODA index, we estimate that
  the next cycle's smoothed peak activity will be about 210 ± 30 solar
  flux units for the 10.7 cm radio flux and a sunspot number of 170 ±
  25. This suggests that solar cycle #23 will be large, comparable to
  cycle #22. The estimated peak is expected to occur near 1999.7 ± 1
  year. Since the current approach is novel (using data prior to solar
  minimum), these estimates may improve when the upcoming solar minimum
  is reached.

---------------------------------------------------------
Title: Momentum transfer collision frequency of O<SUP>+</SUP>-O
Authors: Pesnell, W. D.; Omidvar, Kazem; Hoegy, Walter R.
1993GeoRL..20.1343P    Altcode:
  The interaction of the thermosphere and ionosphere is largely
  governed by collisions between ions and neutral particles. On
  Venus and the Earth, O<SUP>+</SUP> is a dominant ion, and atomic O
  dominates throughout much of the thermosphere; therefore an accurate
  O<SUP>+</SUP>-O cross section is an important prerequisite for
  understanding the dynamics of planetary upper atmospheres. The cross
  section and momentum, transfer collision frequency are calculated with
  a quantum mechanical code which includes resonance charge exchange,
  polarization, and charge-quadrupole effects. Our results agree well
  with earlier calculations of Stubbe [1968] and Stallcop et al [1991].

---------------------------------------------------------
Title: How active was solar cycle 22?
Authors: Hoegy, W. R.; Pesnell, W. D.; Woods, T. N.; Rottman, G. J.
1993GeoRL..20.1335H    Altcode:
  Solar EUV observations from the Langmuir probe on Pioneer Venus Orbiter
  suggest that at EUV wavelengths solar cycle 22 was more active than
  solar cycle 21. The Langmuir probe, acting as a photodiode, measured the
  integrated solar EUV flux over a 13 1/2 year period from January 1979
  to June 1992, the longest continuous solar EUV measurement. The Ipe EUV
  flux correlated very well with the SME measurement of L<SUB>α</SUB>
  during the lifetime of SME and with the UARS SOLSTICE L<SUB>α</SUB>
  from October 1991 to June 1992 when the Ipe measurement ceased. Starting
  with the peak of solar cycle 21, there was good general agreement
  of Ipe EUV with the 10.7 cm, Ca K, and He 10830 solar indices, until
  the onset of solar cycle 22. From 1989 to the start of 1992, the 10.7
  cm flux exhibited a broad maximum consisting of two peaks of nearly
  equal magnitude, whereas Ipe EUV exhibited a strong increase during
  this time period making the second peak significantly higher than the
  first. The only solar index that exhibits the same increase in solar
  activity as Ipe EUV and L<SUB>α</SUB> during the cycle 22 peak is
  the total magnetic flux. The case for high activity during this peak
  is also supported by the presence of very high solar flare intensity.

---------------------------------------------------------
Title: Dynamical interactions between the middle atmosphere and
    thermosphere
Authors: Mayr, H. G.; Harris, I.; Pesnell, W. D.
1992AdSpR..12j.335M    Altcode: 1992AdSpR..12..335M
  Based on modeling, we discuss some interactions between the middle
  atmosphere and thermosphere: (1) Upward propagating tides affect
  the wind field and the temperature (and density) variations of the
  thermosphere at higher altitudes. (2) The thermospheric circulations
  driven by radiative and auroral heating affect the O concentration and
  temperature of the upper mesosphere through the exchange of chemical
  energy. (3) Gravity waves excited by auroral processes are ducted
  through the lower atmosphere and leak back into the thermosphere,
  permitting them to propagate large distances away from the source.

---------------------------------------------------------
Title: Properties of thermospheric gravity waves on Earth, Venus
    and Mars.
Authors: Mayr, H. G.; Harris, I.; Pesnell, W. D.
1992GMS....66...91M    Altcode:
  The authors review a spectral model with sherical harmonics and
  Fourier components that can simulate atmospheric perturbations in the
  global geometry of a multiconstituent atmosphere. The boundaries are
  the planetary surface where the transport velocities vanish and the
  exobase where molecular heat conduction and viscosity dominate. The
  time consuming integration of the conservation equations is reduced
  to computing the transfer function (TF) which describes the dynamic
  properties of the medium divorced from the complexities in the temporal
  and horizontal variations of the excitation source. Given the TF, the
  atmospheric response to a chosen source distribution is then obtained
  in short order. Theoretical studies are presented to illuminate some
  properties of gravity waves on Earth, Venus and Mars.

---------------------------------------------------------
Title: Thermospheric Gravity Waves - Observations and Interpretation
    Using the Transfer Function Model / Ftm
Authors: Mayr, H. G.; Harris, I.; Herrero, F. A.; Spencer, N. W.;
   Varosi, F.; Pesnell, W. D.
1990SSRv...54..297M    Altcode:
  Gravity waves are prominent in the polar region of the terrestiral
  thermosphere, and can be excited by perturbations in Joule heating and
  Lorents force due to magnetospheric processes. We show observations
  from the Dynamics Explorer-2 satellite to illustrate the complexity
  of the phenomenon and review the transfer function model (TFM) which
  has guided our interpretation. On a statistical basis, the observed
  atmospheric perturbations decrease from the poles toward the equator
  and tend to correlate with the magnetic activity index, Ap, although
  individual measurements indicate that the magnetic index is often a poor
  measure of gravity wave excitation. The theoretical models devised
  to describe gravity waves are multifaceted. On one end are fully
  analytical, linear models which are based on the work of Hines. On
  the other end are fully numerical, thermospheric general circulation
  models (TGCMs) which incorporate non-linear processes and wave mean
  flow interactions. The transfer function model (TFM) discussed in this
  paper is between these two approaches. It is less restrictive than the
  analytical approach and relates the global propagation of gravity waves
  to their excitation. Compared with TGCMs, the TFM is simplified by its
  linear approximation; but it is not limited in spatial and temporal
  resolution, and the TFM describes the wave propagation through the
  lower atmosphere. Moreover, the TFM is semianalytical which helps in
  delineating the wave components. Using expansions in terms of spherical
  harmonics and Fourier components, the transfer function is obtained from
  numerical height integration. This is time consuming computationally but
  needs to be done only once. Once such a transfer function is computed,
  the wave response to arbitrary source distributions on the globe can
  then be constructed in very short order. In this review, we discuss some
  numerical experiments performed with the TFM, to study the various wave
  components excited in the auroral regions which propagate through the
  thermosphere and lower atmosphere, and to elucidate the properties of
  realistic source geometries. The model is applied to the interpretation
  of satellite measurements. Gravity waves observed in the thermosphere
  of Venus are also discussed.

---------------------------------------------------------
Title: Nonradial, Nonadiabatic Stellar Pulsations
Authors: Pesnell, W. Dean
1990ApJ...363..227P    Altcode:
  This paper describes how nonradial stellar pulsations can be modeled
  using a Lagrangian formulation. The adiabatic eigenvalues of this
  operator are compared to previously published results, using simple
  stellar models to show the equivalence of this method and other
  techniques. Nonadiabatic effects are included by appending the thermal
  equation to the adiabatic operator. At this point, it becomes necessary
  to include variations in the convective energy transport. Several ways
  of doing this by 'freezing' the convection are examined.

---------------------------------------------------------
Title: Line Profile Variations in BW Vulpeculae
Authors: Pesnell, W. D.; Odell, A. P.
1990BAAS...22.1209P    Altcode:
  No abstract at ADS

---------------------------------------------------------
Title: Transfer Function Model for Thermospheric Gravity Waves
Authors: Mayr, Hans G.; Harris, Isadore; Pesnell, W. Dean
1990rete.conf...49M    Altcode:
  No abstract at ADS

---------------------------------------------------------
Title: Properties of Eoetvoes Spheres
Authors: Pesnell, W. Dean
1989ApJ...344..851P    Altcode:
  Derivations of the equations governing Eotvos spheres and degenerate
  Eotvos objects are presented. These simplified stellar models
  incorporate a short-range component in their gravitational potential. A
  Yukawa formulation to agree with other workers in this field is used,
  although any form that multiplies the normal inverse square law would
  be acceptable. Both polytropic and completely degenerate equations of
  state are used and separate equations governing the density distribution
  derived. Various global relationships are obeyed by these objects,
  much like the polytropes to which they are similar. A discussion of
  whether the simplified potential is accurate enough for astrophysics
  is included, along with a more accurate integral equation for the
  potential.

---------------------------------------------------------
Title: Some Thoughts on the Rapidly Oscillating AP Stars
Authors: Pesnell, W. Dean
1989ApJ...339.1038P    Altcode:
  The effects of combining a weak, axisymmetric magnetic field and
  slow rotation on the adiabatic pulsation frequencies of Ap stars are
  discussed. It is shown that standing wave patterns on the surface of the
  star are produced when the magnetic field dominates the rotation. When
  rotation is more important than the magnetic field, the standing
  waves are split into the usual running waves. It is shown how the
  standing waves affect the line profiles of the star during a pulsation
  cycle. When compared to the line profile variations of a running wave,
  distinct differences are seen. The standing waves resemble a radial
  pulsation at some rotation phases and almost disappear one-quarter of
  a rotation cycle later.

---------------------------------------------------------
Title: On the Possibility of Detecting Weak Magnetic Fields in
    Variable White Dwarfs
Authors: Jones, Philip W.; Pesnell, W. Dean; Hansen, Carl J.; Kawaler,
   Steven D.
1989ApJ...336..403J    Altcode:
  It is suggested that 'weak' magnetic fields of strengths less than
  10 to the 6th G may be detectable in some variable white dwarfs. Weak
  fields can cause subtle changes in the Fourier power spectra of these
  stars in the form of 'splitting' in frequency of otherwise degenerate
  signals. Present-day observational and analysis techniques are capable
  of detecting these changes. It is suggested suggested, by listing some
  well-studied candidate stars, that perhaps the magnetic signature of
  splitting has already been observed in at least one object and that
  the difficult task of intensive measurements of weak fields should
  now be undertaken of those candidates.

---------------------------------------------------------
Title: Pulsation Induced HeI Line Profile Variations
Authors: Pesnell, W. Dean
1989BAAS...21..714P    Altcode:
  No abstract at ADS

---------------------------------------------------------
Title: Pulsations of EÖTVÖS Spheres
Authors: Pesnell, W. Dean
1989upsf.conf..282P    Altcode: 1989IAUCo.111..282P
  No abstract at ADS

---------------------------------------------------------
Title: A Catalogue of Line Profile Variations Due to Nonradial
    Pulsations
Authors: Jones, P. W.; Pesnell, W. D.; Hansen, C. J.; Smith, M. A.
1988BAAS...20..673J    Altcode:
  No abstract at ADS

---------------------------------------------------------
Title: Pulsations of White Dwarf Stars with Thick Hydrogen or Helium
    Surface Layers
Authors: Cox, A. N.; Starrfield, S. G.; Kidman, R. B.; Pesnell, W. D.
1988IAUS..123..333C    Altcode:
  In order to see if there could be agreement between results of stellar
  evolution theory and those of nonradial pulsation theory, calculations
  of white dwarf models have been made for hydrogen surface masses of
  10<SUP>-4</SUP>M_sun;. Earlier results by Winget et al. (1982) indicated
  that surface masses greater than 10<SUP>-8</SUP>M_sun; would not allow
  nonradial pulsations, even though all the driving and damping is in
  surface layers only 10<SUP>-12</SUP> of the mass thick. The authors
  show that the surface mass of hydrogen in the pulsating white dwarfs
  (ZZ Ceti variables) can be any value as long as it is thick enough to
  contain the surface convection zone.

---------------------------------------------------------
Title: Weight functions in adiabatic stellar pulsations. I - Radially
    symmetric motion
Authors: Pesnell, W. Dean
1987PASP...99..975P    Altcode:
  Through the use of two classes of simple stellar models, the author
  illustrates a weight function for radial pulsations that can be
  interpreted in terms of two types of potential energy. The traditional
  weight function is related to the present one via an integration by
  parts, and it is argued that both formulations should be examined to
  minimize possible errors that can arise from neglecting several surface
  terms. The present form provides a different interpretation of radial
  oscillations of stars with small central condensations. The author
  also follows the radial fundamental of a highly centrally condensed
  polytrope through the dynamic instability at γ = 4/3 and demonstrates
  that the envelope is not involved in the instability.

---------------------------------------------------------
Title: Angular Standing Waves in Stellar Pulsations
Authors: Pesnell, W. D.
1987BAAS...19.1052P    Altcode:
  No abstract at ADS

---------------------------------------------------------
Title: Pulsations of White Dwarf Stars with Thick Hydrogen or Helium
    Surface Layers
Authors: Cox, Arthur N.; Starrfield, Sumner G.; Kidman, Russell B.;
   Pesnell, W. Dean
1987ApJ...317..303C    Altcode:
  Models for DA white dwarf stars with effective temperatures between 9000
  and 12,000 K and models for DB white dwarfs with effective temperatures
  of 25,000 K and 27,000 K have been tested for stability against both
  radial and nonradial pulsations. The construction of the models
  is discussed, and linear nonadiabatic nonradial pulsation results
  for these models are given assuming frozen-in convection. The time
  variation of convection is simulated in a crude way, and it is shown
  that many unstable modes can be completely stabilized. The results
  show that thick hydrogen shells can produce nonradial pulsations
  and that the existence of convection blocking exists for both radial
  and nonradial modes in DA and DB white dwarf stars. It is found that
  convection at the surface of white dwarfs must be very efficient in
  order for the theoretical nonradial instability strip to have a blue
  edge hot enough to agree with observations.

---------------------------------------------------------
Title: A New Driving Mechanism for Stellar Pulsations
Authors: Pesnell, W. Dean
1987ApJ...314..598P    Altcode:
  A new driving mechanism termed "convective blocking", a variation
  of the normal κ- and γ-mechanisms in Cepheids, is demonstrated
  using two models of hydrogen white dwarf stars. This mechanism is
  shown to be physically reasonable in the limit of frozen convection
  (implying the time scale for convective readjustment is long compared
  to a pulsation period). Some qualitative effects are given for when
  the two time scales are not as disparate.

---------------------------------------------------------
Title: Ensampling White Dwarf g-Modes
Authors: Pesnell, W. Dean
1987LNP...274..363P    Altcode: 1987stpu.conf..363P
  We examine the pulsation spectrum of zero temperature models as a
  first approximation to white dwarf stars. The g-mode spectrum of such
  objects is found by using a constant adiabatic exponent and we have
  found that the core is an important region for the determination of
  the eigenvalue. A comparison to an evolutionary model is given.

---------------------------------------------------------
Title: Pulsations in Completely Degenerate Objects
Authors: Pesnell, W. D.
1986BAAS...18..951P    Altcode:
  No abstract at ADS

---------------------------------------------------------
Title: Pulsations of white dwarf stars with thick hydrogen or helium
    surface layers
Authors: Cox, A. N.; Starrfield, S. G.; Kidman, R. B.; Pesnell, W. D.
1986STIN...8721774C    Altcode:
  In order to see if there could be agreement between results of
  stellar evolution theory and those of nonradial pulsation theory,
  calculations of white dwarf models have been made for hydrogen surface
  masses of 10 to the -4 solar masses. Earlier results indicated that
  surface masses greater than 10 to the -8 solar masses would not allow
  nonradial pulsations, even though all the driving and damping is in
  surface layers only 10 to the -12 of the mass thick. It is shown that
  the surface mass of hydrogen in the pulsating white dwarfs (ZZ Ceti
  variables) can be any value as long as it is thick enough to contain
  the surface convection zone.

---------------------------------------------------------
Title: The Structure of the Thermal Modes in Pulsating Stars
Authors: Pesnell, W. D.; Buchler, J. R.
1986ApJ...303..740P    Altcode:
  The eigenvectors and eigenvalues of the linearized thermal diffusion
  operator are studied and their effect on the thermal structure of
  radial stellar pulsations is examined. It is shown on the basis of
  two specific cases that the difference between these eigenvectors
  may explain the lack of pulsational instability of radial modes in
  the Beta Cephei stars. A rigorous definition of the thermal response
  time of a model is attempted and the location of the transition from
  adiabatic to highly nonadiabatic motion is discussed.

---------------------------------------------------------
Title: Brunt-Vaeisaelae Frequency and Semiconvection
Authors: Pesnell, W. D.
1986ApJ...301..204P    Altcode:
  A derivation of the Brunt-Väisälä frequency, valid in regions of a
  star where both partial ionization and a varying nuclear composition
  are present, is given. The final result shows that even in regions
  where the total ionization approximation is valid, a reduction
  of the Brunt-Väisälä when compared to the Ledoux criterion is
  necessary. Areas where this function is important are discussed,
  and examples are presented using different forms of equations of state.

---------------------------------------------------------
Title: The Connection Between Nonradial Pulsations and Stellar Winds
    in Massive Stars
Authors: Abbott, D. C.; Garmany, C. D.; Hansen, C. J.; Henrichs,
   H. F.; Pesnell, W. D.
1986PASP...98...29A    Altcode:
  No abstract at ADS

---------------------------------------------------------
Title: On one-zone models of stellar pulsation
Authors: Pesnell, W. D.
1985ApJ...299..161P    Altcode:
  A version of the one-zone model, the weakly coupled monomode model,
  is derived, showing that the small parameter in stellar pulsation is
  the coupling term in the momentum equation. A crude model of similar
  derivation is found that describes a portion of the convection-pulsation
  interaction. The latter model shows that the time dependence of the
  perturbation in the convection variables can be an important part
  of the convection-pulsation interaction. With the assumptions made,
  the pulsation is stabilized when the convection field is unstable and
  vice versa.

---------------------------------------------------------
Title: Ionization Driving Mechanisms in Pulsating Stars
Authors: Pesnell, W. D.
1985BAAS...17..894P    Altcode:
  No abstract at ADS

---------------------------------------------------------
Title: Observable quantities of nonradial pulsations in the presence
    of slowrotation.
Authors: Pesnell, W. D.
1985ApJ...292..238P    Altcode:
  Theoretical power spectra of both light and radial velocity variations
  of a nonradially pulsating star that include the effects of rotation
  are presented. Three classes of motion are defined, depending on the
  symmetry of the mode of interest and its orientation with respect to
  the rotating axis. The use of tabulated model atmospheres to predict
  color variations is compared to the blackbody approximation for two
  cases, a hydrogen white dwarf (DA) and a main-sequence B Star.

---------------------------------------------------------
Title: Rotational mode splitting about an inclined axis
Authors: Aizenman, M. L.; Hansen, C. J.; Pesnell, W. D.; Cox, J. P.
1984ApJ...286L..43A    Altcode:
  The authors have derived the "m-splitting" formula for the frequencies
  of nonradial oscillations of stars due to slow rotation about an axis
  which is inclined with respect to the pulsation axis. They obtain
  the simple result that the usual formula applies, except that only
  the component of the angular rotation velocity along the pulsation
  axis, rather than the full angular rotation velocity, is to be used
  in this formula.

---------------------------------------------------------
Title: Thermal response of stellar envelopes during nonradial
    pulsations
Authors: Pesnell, W. D.
1984ApJ...285..778P    Altcode:
  The response of spherical stellar envelopes in hydrostatic and thermal
  balance to nonradial thermal distributions is outlined. Because of the
  nature of the initial model, the governing equations yield an operator
  that is almost identical to the radial case. The use of propagation
  velocities to estimate the nonadiabatic effects in a pulsation is
  demonstrated.

---------------------------------------------------------
Title: An Analysis of the Nonradial Oscillations of the Central Star
    of the Planetary Nebula K1-16
Authors: Starrfield, S.; Cox, A. N.; Kidman, R. B.; Pesnell, W. D.
1984BAAS...16R.975S    Altcode:
  No abstract at ADS

---------------------------------------------------------
Title: A Simple Model of the Convection-Pulsation Interaction
Authors: Pesnell, W. D.
1984BAAS...16.1012P    Altcode:
  No abstract at ADS

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Title: Critique of the iterative theory of stellar pulsations
Authors: Buchler, J. R.; Pesnell, W. D.
1984ApJ...283..316B    Altcode:
  An attempt to define a mathematical formalism for computing the periodic
  or multiperiodic oscillations of a weakly nonlinear oscillator is
  presented. Attention is focused on iterative theory (IT), i.e., the
  method of harmonic balances, applied to radial pulsators. The IT is
  shown capable of predicting adiabatic oscillations correctly, provided
  modifications are introduced to avoid divergences due to internal
  resonance. Chaotic solutions are, however, not amenable to IT asymptotic
  perturbation models. The IT is also extended to the nonadiabatic case
  through the addition of a work integral. The technique is demonstrated
  to be effective in the case of two incommensurate resonance modes in
  a stellar evolutionary scenario.

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Title: Nonradial instability strips based on carbon and oxygen
    partial ionization in hot, evolved stars.
Authors: Starrfield, S.; Cox, A. N.; Kidman, R. B.; Pesnell, W. D.
1984ApJ...281..800S    Altcode:
  The authors have calculated periods and growth rates for a new class
  of nonradially pulsating variable stars in the linear, nonradial,
  nonadiabatic theory. The best observed member of this class is PG
  1159-035 which is observed to be pulsating in a number of periods
  around 500 s and may well have an effective temperature exceeding
  10<SUP>5</SUP>K. Stellar envelopes constructed for a 0.6 M_sun; star are
  in the effective temperature range 7×10<SUP>4</SUP>K ≤ T<SUB>e</SUB>
  ≤ 1.5×10<SUP>5</SUP>K following the white dwarf cooling track at
  radii 0.016 - 0.030 R_sun;. These envelopes have compositions of half
  carbon and half oxygen by mass. The authors present their nonradial
  results and discuss the newly discovered instability strip in some
  detail. All unstable nonradial modes in the period range from ≡25
  s to ≡1200 s and their growth rates are described. The implications
  of these results for stellar evolution studies are examined.

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Title: Qualitative Aspects of the Convection-Pulsation Interaction
Authors: Pesnell, W. D.
1984LIACo..25..294P    Altcode: 1984tpss.conf..294P; 1984trss.conf..294P
  No abstract at ADS

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Title: Lagrangian, Non-Radial Stellar Pulsations
Authors: Pesnell, W. Dean
1984BAAS...16..409P    Altcode:
  No abstract at ADS

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Title: The discovery of nonradial instability strips for hot,evolved
    stars.
Authors: Starrfield, S. G.; Cox, A. N.; Hodson, S. W.; Pesnell, W. D.
1983ApJ...268L..27S    Altcode:
  Three different interior compositions are used in the present radial
  and nonradial, linear, nonadiabatic pulsation analyses of model stellar
  envelopes in the effective temperature range of 80,000-150,000 K,
  with total masses of 0.6 solar masses and radii chosen so that they
  line up along a prewhite dwarf cooling curve: (1) 100 percent C; (2)
  50 percent C-12 and 50 percent O-16 by mass; and (3) 10 percent C-12
  and 90 percent O-16 by mass. Radial and nonradial instability strips
  are found for each composition, caused the partial ionization of C,
  or O, or both. Attention is given to the cause of the pulsations of
  the hot, evolved star PG 1159-035, which, although perhaps too hot
  to lie within the proposed instability strips, is in some measure
  of agreement with models having significant amounts of O-16 near the
  stellar surface. This implies a greater production of O-16 through He
  burning than previously supposed.

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Title: Thermal Effects in Stellar Pulsations.
Authors: Pesnell, W. D.
1983PhDT........14P    Altcode: 1984DiAbI..45.1218P
  A Sturm-Liouville operator, embedded in the linearized radial
  pulsation equations, is used to analyze the thermal effects of stellar
  pulsations. Asymptotic expansions are utilized to demonstrate the
  nature of these eigenfunctions and to define the thermal response time
  of a stellar model. The eigenvalues and eigenvectors for models of a
  Cepheid and Beta Cephei variable are given showing the differences
  in the two classes of variables. The time scales introduced agree
  with earlier ones in their common use of predicting the location of
  possible driving zones. In addition, a way of displaying the temperature
  variations in the hydrogen ionization zone without the customary "spike"
  is demonstrated, and a new class of pulsations, called "sudden" modes,
  is introduced.

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Title: Thermal effects in stellar pulsations
Authors: Pesnell, William Dean
1983PhDT.......114P    Altcode:
  No abstract at ADS

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Title: The Non-Radial Pulsation Properties of Hot Hydrogen-Poor,
    Evolved Stars
Authors: Starrfield, S.; Cox, A. N.; Hodson, S. N.; Pesnell, W. D.
1982BAAS...14..901S    Altcode:
  No abstract at ADS

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Title: Linear theory radial and nonradial pulsations of DA dwarf stars
Authors: Starrfield, S.; Cox, A. N.; Hodson, S.; Pesnell, W. D.
1982pccv.conf...78S    Altcode:
  The stellar envelope and radial linear nonadiabatic computer code, along
  with a nonradial code are used to investigate the total hydrogen mass
  necessary to produce the nonradial instability of DA dwarfs. Opacities
  and equations of state are obtained for pure mixtures of hydrogen,
  helium, and carbon. In some cases, a small amount of metals are included
  in the composition in order to have a variety of mixtures available
  to make gradual changes in composition from hydrogen to helium. The
  presence of metals in these mixtures has no effect on the results.

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Title: Application of Two-Time Methods in Stellar Pulsations
Authors: Pesnell, W. D.; Regev, O.; Buchler, J. R.
1982pccv.conf..216P    Altcode:
  No abstract at ADS

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Title: Stability analysis of slow spherical motion for a gravitating
    fluid
Authors: Livio, M.; Buchler, J. R.; Pesnell, W. D.
1981ApJ...243..617L    Altcode:
  The stability of equations governing the spherical motion of a
  gravitating compressible fluid against adiabatic perturbations
  is analyzed. Assuming that the perturbation of the gravitational
  potential can be neglected and that motion is slow, a perturbative
  approach is used to obtain first-order corrections to the hydrostatic
  eigenvalues. The expression for this correction may be used to study the
  effect of velocity and acceleration fields on both stable and unstable
  hydrostatic modes. When applied to the homogeneous compressible case
  the correction gives the expected results, and stability criteria can
  be obtained for specific modes. Possible implications for the study
  of stellar collapse are noted.

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Title: The Light and Velocity Curve Bumps for Bw-Vulpeculae
Authors: Pesnell, W. D.; Cox, A. N.
1980SSRv...27..337P    Altcode: 1980IAUCo..58..337P
  BW Vulpeculae (HD 199140) is a well known Beta Cephei star, with
  several unusual characteristics. It possesses the largest amplitude
  in both light and radial velocity variations of any star in this
  classification. The most outstanding feature of the observations is a
  standstill, or bump, on the light curve, accompanied by doubled lines
  in the radial velocity observations. In this paper, an attempt has been
  made to explain these phenomena with two different models: firstly,
  the resonance mechanism, from Simon and Schmidt (1976), and secondly,
  a nonlinear calculation.

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Title: Spherical oscillation patterns
Authors: Pesnell, W. Dean; Coggins, James M.
1980SSRv...27..473P    Altcode: 1980IAUCo..58..473P
  Spherical harmonics are an integral part of the study of stellar
  pulsations. To gain an understanding of how the star is affected by
  non-radial pulsations, the radial part of the oscillation is plotted,
  with an assumed sinusoidal time variation. The amplitude of the motion
  is arbitrarily set at 20% of the radius.