Author name code: froehlich ADS astronomy entries on 2022-09-14 author:"Froehlich, Claus" -title:"nucleosynthesis" -title:"supernova" -title:"nuclei" -title:"isotope" -title:"element" ------------------------------------------------------------------------ Title: VizieR Online Data Catalog: PUSH CCSN to explosions in spherical symmetry. III. (Curtis+, 2019) Authors: Curtis, S.; Ebinger, K.; Frohlich, C.; Hempel, M.; Perego, A.; Liebendorfer, M.; Thielemann, F. -K. Bibcode: 2020yCat..18700002C Altcode: In a previously presented proof-of-principle study, we established a parameterized spherically symmetric explosion method (PUSH) that can reproduce many features of core-collapse supernovae (CCSNe) for a wide range of pre-explosion models. The method is based on the neutrino-driven mechanism and follows collapse, bounce, and explosion. There are two crucial aspects of our model for nucleosynthesis predictions. First, the mass cut and explosion energy emerge simultaneously from the simulation (determining, for each stellar model, the amount of Fe-group ejecta). Second, the interactions between neutrinos and matter are included consistently (setting the electron fraction of the innermost ejecta). In the present paper, we use the successful explosion models from Paper II (Ebinger+, 2019, J/ApJ/870/1) that include two sets of pre-explosion models at solar metallicity, with combined masses between 10.8 and 120Mȯ. We perform systematic nucleosynthesis studies and predict detailed isotopic yields. The resulting 56Ni ejecta are in overall agreement with observationally derived values from normal CCSNe. The Fe-group yields are also in agreement with derived abundances for metal-poor star HD84937. We also present a comparison of our results with observational trends in alpha element to iron ratios.

(4 data files). Title: VizieR Online Data Catalog: PUSH CCSN to explosions in spherical symmetry. II. (Ebinger+, 2019) Authors: Ebinger, K.; Curtis, S.; Frohlich, C.; Hempel, M.; Perego, A.; Liebendorfer, M.; Thielemann, F. -K. Bibcode: 2020yCat..18700001E Altcode: In a previously presented proof-of-principle study, we established a parameterized spherically symmetric explosion method (PUSH) that can reproduce many features of core-collapse supernovae (CCSN). The present paper goes beyond a specific application that is able to reproduce observational properties of SN1987A and performs a systematic study of an extensive set of nonrotating, solar metallicity stellar progenitor models in the mass range from 10.8 to 120Mȯ. This includes the transition from neutron stars to black holes as the final result of the collapse of massive stars, and the relation of the latter to supernovae, possibly faint supernovae, and failed supernovae. We discuss the explosion properties of all models and predict remnant mass distributions within this approach. The present paper provides the basis for extended nucleosynthesis predictions in a forthcoming paper to be employed in galactic evolution models.

(1 data file). Title: Methodology to create a new total solar irradiance record: Making a composite out of multiple data records Authors: Dudok de Wit, Thierry; Kopp, Greg; Fröhlich, Claus; Schöll, Micha Bibcode: 2017GeoRL..44.1196D Altcode: 2017arXiv170202341D Many observational records critically rely on our ability to merge different (and not necessarily overlapping) observations into a single composite. We provide a novel and fully traceable approach for doing so, which relies on a multiscale maximum likelihood estimator. This approach overcomes the problem of data gaps in a natural way and uses data-driven estimates of the uncertainties. We apply it to the total solar irradiance (TSI) composite, which is currently being revised and is critical to our understanding of solar radiative forcing. While the final composite is pending decisions on what corrections to apply to the original observations, we find that the new composite is in closest agreement with the PMOD composite and the NRLTSI2 model. In addition, we evaluate long-term uncertainties in the TSI, which reveal a 1/f scaling. Title: Were the May 2012 Emilia-Romagna earthquakes induced? A coupled flow-geomechanics modeling assessment Authors: Juanes, R.; Jha, B.; Hager, B. H.; Shaw, J. H.; Plesch, A.; Astiz, L.; Dieterich, J. H.; Frohlich, C. Bibcode: 2016GeoRL..43.6891J Altcode: Seismicity induced by fluid injection and withdrawal has emerged as a central element of the scientific discussion around subsurface technologies that tap into water and energy resources. Here we present the application of coupled flow-geomechanics simulation technology to the post mortem analysis of a sequence of damaging earthquakes (Mw = 6.0 and 5.8) in May 2012 near the Cavone oil field, in northern Italy. This sequence raised the question of whether these earthquakes might have been triggered by activities due to oil and gas production. Our analysis strongly suggests that the combined effects of fluid production and injection from the Cavone field were not a driver for the observed seismicity. More generally, our study illustrates that computational modeling of coupled flow and geomechanics permits the integration of geologic, seismotectonic, well log, fluid pressure and flow rate, and geodetic data and provides a promising approach for assessing and managing hazards associated with induced seismicity. Title: Determination of time-dependent uncertainty of the total solar irradiance records from 1978 to present Authors: Fröhlich, Claus Bibcode: 2016JSWSC...6A..18F Altcode:
Aims: The existing records of total solar irradiance (TSI) since 1978 differ not only in absolute values, but also show different trends. For the study of TSI variability these records need to be combined and three composites have been devised; however, the results depend on the choice of the records and the way they are combined. A new composite should be based on all existing records with an individual qualification. It is proposed to use a time-dependent uncertainty for weighting of the individual records.
Methods: The determination of the time-dependent deviation of the TSI records is performed by comparison with the square root of the sunspot number (SSN). However, this correlation is only valid for timescales of the order of a year or more because TSI and SSN react quite differently to solar activity changes on shorter timescales. Hence the results concern only periods longer than the one-year-low-pass filter used in the analysis.
Results: Besides the main objective to determine an investigator-independent uncertainty, the comparison of TSI with √SSN turns out to be a powerful tool for the study of the TSI long-term changes. The correlation of √SSN with TSI replicates very well the TSI minima, especially the very low value of the recent minimum. The results of the uncertainty determination confirm not only the need for adequate corrections for degradation, but also show that a rather detailed analysis is needed. The daily average of all TSI values available on that day, weighted with the correspondingly determined uncertainty, is used to construct a "new" composite, which, overall, compares well with the Physikalisch-Meteorologisches Observatorium Davos (PMOD) composite. Finally, the TSI - √SSN comparison proves to be an important diagnostic tool not only for estimating uncertainties of observations, but also for a better understanding of the long-term variability of TSI. Title: Total Solar Irradiance: What Have We Learned from the Last Three Cycles and the Recent Minimum? Authors: Fröhlich, Claus Bibcode: 2014crh..book..237F Altcode: No abstract at ADS Title: Total Solar Irradiance: What Have We Learned from the Last Three Cycles and the Recent Minimum? Authors: Fröhlich, Claus Bibcode: 2013SSRv..176..237F Altcode: 2011SSRv..tmp..209F; 2011SSRv..tmp..133F; 2011SSRv..tmp...66F; 2011SSRv..tmp..366F The record of total solar irradiance (TSI) during the past 35 years shows similarities of the three solar cycles, but also important differences. During the recent minimum with an unusually long periods with no sunspots, TSI was also extremely low, namely 25% of a typical cycle amplitude lower than in 1996. Together with the values during the previous minima this points to a long-term change related to the strength of solar activity. On the other hand, activity indices as the 10.7 cm radio flux (F10.7), the CaII and MgII indices and also the Ly- α irradiance, show a much smaller decrease. This means that proxy models for TSI based on the photometric sunspot index (PSI), and on e.g. MgII index to represent faculae and network have to be complemented by a further component for the long-term change. TSI values at minima are correlated with the simultaneous values of the open magnetic field of the Sun at 1 AU and thus, these values may be used as a surrogate for the long-term change component. Such a 4-component model explains almost 85% of the variance of TSI over the three solar cycles available. This result supports also the idea that the long-term change of TSI is not due to manifestations of surface magnetism as the solar cycle modulation, but due to a change of the global temperature of Sun modulated by the strength of activity—being lower during low activity. To explain the difference between the minima in 1996 and 2008 we need a change of only 0.25 K. Title: Reaction rate uncertainties and the ν p-process Authors: Fröhlich, C.; Rauscher, T. Bibcode: 2012AIPC.1484..232F Altcode: Current hydrodynamical simulations of core collapse supernovae find proton-rich early ejecta. At the same time, the models fail to eject neutron-rich matter, thus leaving the origin of the main r-process elements unsolved. However, the proton-rich neutrino-driven winds from supernovae have been identified as a possible production site for light n-capture elements beyond iron (such as Ge, Sr, Y, Zr) through the νp-process. The detailed nucleosynthesis patterns of the νp-process depend on the hydrodynamic conditions and the nuclear reaction rates of key reactions. We investigate the impact of reaction rate uncertainties on the νp-process nucleosynthesis. Title: Total Solar Irradiance Observations Authors: Fröhlich, Claus Bibcode: 2012SGeo...33..453F Altcode: 2011SGeo..tmp..123F The record of total solar irradiance (TSI) during the past 35 years has overlapping observations from space which can be merged to a composite, and three are available, namely the PMOD, the ACRIM and the IRMB composites. There are important differences between them, which are discussed in detail in order to find the best representation of solar variability during the last three cycles, for the following discussions of solar irradiance variability. Moreover, the absolute value of TSI from TIM on SORCE is 1,361 Wm-2, substantially lower than the value 1,365 Wm-2, which was observed by the classical radiometers. New results from specific experiments are now available, which are discussed in order to define the value to be used in, e.g., climate models. The most important issue regarding the recent TSI records is the low value observed during the minimum in 2009, which is 25% of a typical cycle amplitude lower than the value in 1996. The validity of this low value has been confirmed by comparing all existing TSI observations during cycle 23. On the other hand, activity indices, such as the sunspot number, the 10.7-cm radio flux (F10.7), the CaII and MgII indices and also the Ly-α irradiance or the frequency changes in low-order p modes, show a much smaller decreases relative to their respective typical cycle amplitude. It is most likely that an increasing contrast of the facular and network elements with decreasing magnetic field is responsible for this discrepancy. The value of TSI at minima is correlated with the open magnetic field of the Sun, B R, at minima. Using B R at minima, interpolated linearly in between as a fourth component of a proxy model based on the photometric sunspot index and on the MgII index improves the explanation of the variance of TSI over the full period of the last three solar cycles to 84.7%. Results from other models are also discussed. Title: Astrophysical analysis of the measurement of (α,γ) and (α,n) cross sections of 169Tm Authors: Rauscher, T.; Kiss, G. G.; Szücs, T.; Fülöp, Zs.; Fröhlich, C.; Gyürky, Gy.; Halász, Z.; Kertész, Zs.; Somorjai, E. Bibcode: 2012PhRvC..86a5804R Altcode: 2012arXiv1206.6113R Reaction cross sections of 169Tm(α,γ)173Lu and 169Tm(α,n)172Lu have been measured in the energy range 12.6≤Eα≤17.5 MeV and 11.5≤Eα≤17.5 MeV, respectively, using the recently introduced method of combining activation with x-ray counting. Improved shielding made it possible to measure the (α,γ) to lower energy than previously possible. The combination of (α,γ) and (α,n) data made it possible to study the energy dependence of the α width. While absolute value and energy dependence are perfectly reproduced by theory at the energies above 14 MeV, the observed change in energy dependence at energies below 14 MeV requires a modification of the predicted α width. Using an effective, energy-dependent, local optical α+nucleus potential it is possible to reproduce the data but the astrophysical rate is still not well constrained at γ-process temperatures. The additional uncertainty stemming from a possible modification of the compound formation cross section is discussed. Including the remaining uncertainties, the recommended range of astrophysical reaction rate values at 2 GK is higher than the previously used values by factors of 2-37. Title: Observing and Modelling Earth's Energy Flows Authors: Bengtsson, Lennart; Koumoutsaris, Symeon; Bonnet, Roger; Allan, Richard P.; Fröhlich, Claus; Heintzenberg, Jost; Ingmann, Paul; Kandel, Robert; Loeb, Norman G.; Soden, Brian; Trenberth, Kevin Bibcode: 2012omee.book.....B Altcode: No abstract at ADS Title: Total Solar Irradiance Observations Authors: Fröhlich, Claus Bibcode: 2012omee.book..121F Altcode: No abstract at ADS Title: A four-component proxy model for total solar irradiance calibrated during solar cycles 21-23 Authors: Fröhlich, C. Bibcode: 2011CoSka..41..113F Altcode: The last solar activity minimum during 2008/09 was unusually long and with extended periods without sunspots. During this period the total solar irradiance (TSI) was much lower than during the previous minima and no solar activity proxies show similarly low values. Proxy models for TSI use a measure for the darkening of sunspots, the so-called photometric sunspot index (PSI) and for the brightening of faculae and network a chromospheric index. Because none of these can explain the low TSI, a further component is needed, which describes the trend between minima due to a still controversially discussed mechanism. A new algorithm for the calculation of PSI is described which uses individual factors for the different observing stations and a better representation of the size-dependent contrast of spots. The proxy model based on the new PSI, the long- and short-term Mg II index and a trend based on the minima values of the open field explains almost 85 % of the variance of TSI over the last three solar cycles. Moreover, it confirms the factor of ≈ 4 between the observed trend of TSI and those of the chromospheric and other solar activity indices. Title: Determining reaction cross sections via characteristic X-ray detection: α-induced reactions on 169Tm for the astrophysical γ-process Authors: Kiss, G. G.; Rauscher, T.; Szücs, T.; Kertész, Zs.; Fülöp, Zs.; Gyürky, Gy.; Fröhlich, C.; Farkas, J.; Elekes, Z.; Somorjai, E. Bibcode: 2011PhLB..695..419K Altcode: 2010arXiv1012.0660K The cross sections of the Tm169(α,γ)Lu173 and Tm169(α,n)Lu172 reactions have been measured first time using a new method, by detecting the characteristic X-ray radiation following the electron capture-decay of 172,173Lu. Despite the relatively long half-life of the reaction products (T=500 and 6.7 days, respectively) it was possible to measure the cross section of the Tm169(α,γ)Lu173 reaction close to the Gamow window (T=3.5 GK), between E=13.16 and 17.08 MeV. The Tm169(α,n)Lu172 reaction cross section was measured from E=11.21 MeV up to E=17.08 MeV. The experimental results have been compared to theoretical predictions. Title: Spectral Solar Irradiance over Solar Cycle 23 from Sunphotometers of VIRGO on SOHO (Invited) Authors: Frohlich, C. Bibcode: 2010AGUFMGC33C..08F Altcode: Within the VIRGO experiment on SOHO two 3-channel sunphotometers (SPM) measure solar spectral irradiance at 402, 500 and 862 nm with a bandwidth (FWHM) of 5 nm. The time series cover the period from April 1996 until present, more than 14 years and a full solar cycle from the minimum in 1996 to the one in late 2008. SPMA measures the irradiance continuously with a 1-minute sampling and after being exposed to the sun during more than 14 years the sensitivities of the red, green and blue channels are at 74.1, 24.3 and 7.1 percent of their first light values, respectively. SPMB, is exposed rarely and is used to monitor degradation; the result of a detailed analysis of these data can then be used to correct SPMA for long-term changes and degradation effects. These are determined by a degradation model and the result shows that the changes due to exposure to the sun depend not only on the exposure time and the cumulated dose of radiation received, but also on the temperature of the instrument (Boltzmann factor). This indicates that simple degradation corrections by e.g. fitting multi-degree polynomials may not be adequate. The result of this detailed analysis are reliable time series of solar spectral irradiance at the three wavelengths. The results confirm the positive correlation of all three channels with solar activity and TSI, which is in contrast to the results from SIM on SORCE - at least for the green channel. A possible long-term trend of the spectral irradiance is also discussed in comparison with the behaviour of total solar irradiance (TSI). Title: Total Solar Irradiance during the Holocene using cosmogenic 10Be measured in polar ice cores Authors: Steinhilber, F.; Beer, J.; Fröhlich, C. Bibcode: 2010ems..confE.791S Altcode: The Sun is the main source of energy for the Earth, and its activity has changed between states of high and low activity during the Holocene. From paleo records it is known that climate changes coincide with these changes in solar activity, raising the question about the solar radiative forcing in past, present, and future climate. To answer this question, one has to quantify how much the solar forcing has changed. One important measure of the solar radiative forcing is total solar irradiance (TSI). It has been measured with instruments onboard spacecrafts since 1978. Besides the distinct 11-year solar cycle variation, these measurements show also a decreasing trend in the 11-year cycle minima. This indicates that like other solar activity records TSI also varies on time scales longer than 11 years. Prior to 1978 TSI has to be reconstructed. Of special interest is thereby to know TSI not only for periods of high solar activity as we had in the past 50 years, but also for periods when the Sun was very quiet, such as during the Maunder Minimum (1645-1715). Here we present the first record of TSI covering almost the entire Holocene. Our record is based on a relationship between TSI and the open solar magnetic field both observed with spacebased instruments. The open solar magnetic field is obtained for the past from cosmogenic radionuclides, such as e.g. 10Be, which is measured in polar ice cores. Using 10Be enabled us to reconstruct TSI much further back than the existing record of sunspots, which is widely used as a proxy for TSI. The resulting increase in the 11-year cycle averaged TSI from the Maunder Minimum to the present is (0.9±0.4) Wm^-2, corresponding to a global average radiative forcing of about (0.16±0.07) Wm^-2. This change compares well with very recent sunspot-based reconstructions of TSI, but is smaller by a factor of three than those TSI reconstructions commonly used in climate studies. Our reconstruction together with climate models allows for exploring the role of solar forcing in climate change. Title: The Signature of Flares in VIRGO Total Solar Irradiance Measurements Authors: Quesnel, A.; Dennis, B. R.; Fleck, B.; Fröhlich, C.; Hudson, H. S.; Tolbert, A. K. Bibcode: 2010ASPC..428..133Q Altcode: 2010arXiv1003.4194Q We use Total Solar Irradiance (TSI) measurements from the VIRGO (Variability of solar Irradiance and Gravity Oscillations) instrument on board SOHO to obtain preliminary estimates of the mean total radiative energy emitted by X-class solar flares. The basic tool is that of summed-epoch analysis, which has also enabled us to detect and partially characterize systematic errors present in the basic data. We describe these errors, which significantly degrade the photometry at high frequencies. We find the ratio of GOES 1-8 Å luminosity to total bolometric luminosity to be of order 0.01. Title: The quest for the solar g modes Authors: Appourchaux, T.; Belkacem, K.; Broomhall, A. -M.; Chaplin, W. J.; Gough, D. O.; Houdek, G.; Provost, J.; Baudin, F.; Boumier, P.; Elsworth, Y.; García, R. A.; Andersen, B. N.; Finsterle, W.; Fröhlich, C.; Gabriel, A.; Grec, G.; Jiménez, A.; Kosovichev, A.; Sekii, T.; Toutain, T.; Turck-Chièze, S. Bibcode: 2010A&ARv..18..197A Altcode: 2010A&ARv.tmp....1A; 2009arXiv0910.0848A Solar gravity modes (or g modes)—oscillations of the solar interior on which buoyancy acts as the restoring force—have the potential to provide unprecedented inference on the structure and dynamics of the solar core, inference that is not possible with the well-observed acoustic modes (or p modes). The relative high amplitude of the g-mode eigenfunctions in the core and the evanesence of the modes in the convection zone make the modes particularly sensitive to the physical and dynamical conditions in the core. Owing to the existence of the convection zone, the g modes have very low amplitudes at photospheric levels, which makes the modes extremely hard to detect. In this article, we review the current state of play regarding attempts to detect g modes. We review the theory of g modes, including theoretical estimation of the g-mode frequencies, amplitudes and damping rates. Then we go on to discuss the techniques that have been used to try to detect g modes. We review results in the literature, and finish by looking to the future, and the potential advances that can be made—from both data and data-analysis perspectives—to give unambiguous detections of individual g modes. The review ends by concluding that, at the time of writing, there is indeed a consensus amongst the authors that there is currently no undisputed detection of solar g modes. Title: An Investigation Of The Metallicity Dependence Of The Sn Type Ii Mn Production Authors: Kim, Yeunjin; Sobeck, J.; Frohlich, C.; Truran, J. Bibcode: 2010AAS...21542509K Altcode: 2010BAAS...42..337K Element abundance trends over the history of our Galaxy serve as important guides in establishing relative contributions from supernovae of Types Ia and II. In particular, spectroscopic studies have revealed a deficiency of manganese (Mn) relative to the abundances of neighboring iron-peak nuclei in metal-poor stars. However, more recent analyses of the observational data have found a constant Mn/Fe abundance ratio over a wide range of metallicity and hence, contradict these previous findings. In this project, we will study the nucleosynthetic yields of Type II supernovae as a function of metallicity by parameterizing the initial properties of the shock. We will compare our results with the two distinct manganese abundance trends identified above. Once we study the metallicity dependency of Type II yields as reflected in observations at lower metallicities, we will explore the constraints this imposes on Type Ia supernova contributions to Mn in different stellar and galactic populations.

We acknowledge the financial support by the National Science Foundation for the Frontier Center Joint Institute for Nuclear Astrophysics (JINA). C.F. acknowledges an Enrico Fermi Fellowship. Title: Photons - from source to detector Authors: Wilhelm, Klaus; Frohlich, Claus Bibcode: 2010ISSIR...9...23W Altcode: The central theme of the book "Observing Photons in Space" is the detection and characterization of photons with instruments aboard spacecraft. This chapter presents a global overview of the fundamental processes that accompany photons all the way from their origin in the source region to their detection in our instruments. The radiation of the Sun is taken as example in some cases and is treated in more detail. Title: The r-, p-, and νp-Process Authors: Thielemann, F. -K.; Dillmann, I.; Farouqi, K.; Fischer, T.; Fröhlich, C.; Kelic-Heil, A.; Korneev, I.; Kratz, K. -L.; Langanke, K.; Liebendörfer, M.; Panov, I. V.; Martinez-Pinedo, G.; Rauscher, T. Bibcode: 2010JPhCS.202a2006T Altcode: The processes discussed in this review are three of the four nucleosynthesis processes involved in producing heavy nuclei beyond Fe (not counting the rp-process in X-ray bursts). Opposite to the fourth process (the s-process), which operates in stellar evolution during He- and C-burning, they are all related to explosive burning phases, (presumably) linked to core collapse supernova events of massive stars. The (classical) p-process is identified with explosive Ne/O-burning in outer zones of the progenitor star. It is intitiated by the passage of the supernova shock wave and acts via photodisintegration reactions like a spallation process which produces neighboring (proton-rich) isotopes from pre-existing heavy nuclei. The reproduction of some of the so-called lighter p-isotopes with A < 100 faces problems in this environment. The only recently discovered νp-process is related to the innermost ejecta, the neutrino wind expelled from the hot proto-neutron star after core collapse in the supernova explosion. This neutrino wind is proton-rich in its early phase and reactions with neutrinos permit to overcome decay/reaction bottlenecks for the flow beyond the Fe-group, thus permitting the production of those p-isotopes, which face problems in the classical p-process scenario. The understanding of the r-process, being identified for a long time with rapid neutron captures - and passing through nuclei far from stability - is still experiencing major problems. These are on the one hand related to nuclear uncertainties far from stability (masses and half-lives), affecting the process speed and abundance peaks, on the other hand the site is still not definitely located, yet. Later neutron-rich, high entropy phases of the neutrino wind could permit its operation, other options include the ejection of very neutron-rich neutron star matter. Two different environments are required for a weak and a main/strong r-process, witnessed by observations of low metallicity stars. Title: Solar radiometry Authors: Frohlich, Claus Bibcode: 2010ISSIR...9..525F Altcode: The classical radiometry for total solar irradiance (TSI) measurements is described using examples of the four types of radiometers currently used in space. The design, characterization and operation of these radiometers are described. Besides the instrumental characteristics determining the measurement uncertainties, an important issue is possible long-term changes of the radiometers exposed to solar irradiance -- especially in the EUV -- and the space environment. A model for the degradation has been developed which can explain the behaviour of most radiometers in space. The TSI record since 1978 from different platforms and radiometers can be combined in a composite time series which demonstrates that although the assumed uncertainty of the present state-of-the-art radiometers is insufficient, their short- and long-term precision is good enough to produce a reliable time series of TSI over almost 30 years. Title: Total Solar Irradiance during the past 9300 Years inferred from the Cosmogenic Radionuclide Beryllium-10 Authors: Steinhilber, F.; Beer, J.; Frohlich, C. Bibcode: 2009AGUFMGC24A..03S Altcode: The Sun is the main source of energy for the Earth. There is growing evidence that climate changes in the past coincide with changes in solar activity. This raises the question about the Sun’s role in past, present, and future global change. To answer this question, the total solar irradiance (TSI) has to be known not only for the present period of high solar activity, but also for periods when the Sun was very quiet, such as the Maunder Minimum (1645-1715). Direct instrumental data of TSI goes only back to 1978. We present the first reconstruction of TSI covering the past 9300 years. It is based on a recently derived relationship between observed TSI and the open solar magnetic field. The open solar magnetic field can be obtained from the cosmogenic radionuclide Beryllium-10 measured in ice cores. Thus, Beryllium-10 allows reconstructing TSI much further back than the existing record of sunspots, which is often used as a proxy. The resulting increase in the average TSI from the Maunder Minimum to the present amounts to (0.9±0.4)Wm-2 corresponding to a global radiative forcing of (0.16±0.07)Wm-2. This change is smaller than previous TSI reconstructions commonly used in climate studies. In combination with climate models, our reconstruction offers the possibility to quantitatively test the claimed links between solar forcing and climate change. Title: Total solar irradiance during the Holocene Authors: Steinhilber, F.; Beer, J.; Fröhlich, C. Bibcode: 2009GeoRL..3619704S Altcode: For the first time a record of total solar irradiance covering 9300 years is presented, which covers almost the entire Holocene. This reconstruction is based on a recently observationally derived relationship between total solar irradiance and the open solar magnetic field. Here we show that the open solar magnetic field can be obtained from the cosmogenic radionuclide 10Be measured in ice cores. Thus, 10Be allows to reconstruct total solar irradiance much further back than the existing record of the sunspot number which is usually used to reconstruct total solar irradiance. The resulting increase in solar-cycle averaged TSI from the Maunder Minimum to the present amounts to (0.9 ± 0.4) Wm-2. In combination with climate models, our reconstruction offers the possibility to test the claimed links between climate and TSI forcing. Title: Solar Surface Magnetism and Irradiance on Time Scales from Days to the 11-Year Cycle Authors: Domingo, V.; Ermolli, I.; Fox, P.; Fröhlich, C.; Haberreiter, M.; Krivova, N.; Kopp, G.; Schmutz, W.; Solanki, S. K.; Spruit, H. C.; Unruh, Y.; Vögler, A. Bibcode: 2009SSRv..145..337D Altcode: The uninterrupted measurement of the total solar irradiance during the last three solar cycles and an increasing amount of solar spectral irradiance measurements as well as solar imaging observations (magnetograms and photometric data) have stimulated the development of models attributing irradiance variations to solar surface magnetism. Here we review the current status of solar irradiance measurements and modelling efforts based on solar photospheric magnetic fields. Thereby we restrict ourselves to the study of solar variations from days to the solar cycle. Phenomenological models of the solar atmosphere in combination with imaging observations of solar electromagnetic radiation and measurements of the photospheric magnetic field have reached high enough quality to show that a large fraction (at least, about 80%) of the solar irradiance variability can be explained by the radiative effects of the magnetic activity present in the photosphere. Also, significant progress has been made with magnetohydrodynamic simulations of convection that allow us to relate the radiance of the photospheric magnetic structures to the observations. Title: Evidence of a long-term trend in total solar irradiance Authors: Fröhlich, C. Bibcode: 2009A&A...501L..27F Altcode: Aims: During the solar minimum of 2008, the value of total solar irradiance at 1 AU (TSI) was more than 0.2 Wm-2 lower than during the last minimum in 1996, indicating for the first time a directly observed long-term change. On the other hand, chromospheric indices and hence solar UV irradiance do not exhibit a similar change.
Methods: Comparison of TSI with other activity parameters indicates that only the open solar magnetic field, BR, observed from satellites at 1 AU show a similar long-term behaviour. The values at the minima correlate well and the linear fit provides a direct physical relationship between TSI and BR during the minimum times.
Results: This correlation allows an unambiguous reconstruction of TSI back in time, provided the open solar magnetic field can be determined from e.g. geomagnetic indices or cosmogenic radionucleides. Since the solar UV irradiance has no long-term trend, the mechanism for the secular change of TSI must differ from the effect of surface magnetism, as manifested by sunspots, faculae, and network which indeed explain well the intra-cycle variability of both total and spectral irradiance.
Conclusions: The long-term trend of TSI is most probably caused by a global temperature change of the Sun that does not influence the UV irradiance in the same way as the surface magnetic fields.

Appendix is only available in electronic form at http://www.aanda.org Title: Recent Anomalous TSI Decrease Not Due To Low Polar Facula and Network Areas: Time to Broaden Our View of Solar Luminosity Variation? Authors: Foukal, Peter V.; Bernasconi, P.; Frohlich, C. Bibcode: 2009SPD....40.1113F Altcode: Total solar irradiance (TSI) values measured during the present activity minimum by the VIRGO, ACRIM, and TIM radiometers are significantly ( 0.018% +/- 0.006 % rms) lower than reported during the last minimum in 1996 (1). This decrease represents 1/4 the amplitude of 11 - yr TSI variation. Differences in spots, faculae and active network cannot account for this anomalous decrease. A sufficient difference in the TSI contribution from quiet network also seems unlikely, since the solar microwave flux index, F10.7, has dipped only 4 % below its 1996 minimum. This is an order of magnitude less than required to explain the TSI decrease by a decline in network area.

The remaining explanation in terms of photospheric magnetic structures, might lie in a decrease in the area of polar faculae, whose cycle amplitude is presently at a minimum for this century. We evaluate their TSI contribution using area and contrast measurements with the Solar Bolometric Imager (SBI), together with polar facula counts (2). We find that their TSI contribution between the present and 1996 activity minima, is below 0.002%. This is again, an order of magnitude below the observed TSI decrease.

We conclude that the anomalous TSI decrease is unlikely to be caused by photospheric magnetic changes. This suggests that solar luminosity may be able to change significantly over decadal time scales through an as- yet- unidentified, relatively shallow mechanism that avoids the 10*5 year thermal relaxation time of the solar convection zone.

This work was supported at Heliophysics, Inc by NSF grant ATM 0718305, and at APL by NASA grant NNG 05WC07G

References:

1. Frohlich, C. 2008, AGU Fall Meeting, Abstract # SH21C-05.

2. Sheeley, N. 2008, Ap.J. , 680, 1553. Title: Total solar irradiance variability: What have we learned about its variability from the record of the last three solar cycles? Authors: Fröhlich, C. Bibcode: 2009cwse.conf..217F Altcode: Since November 1978 a set of total solar irradiance (TSI) measurements from space is available, yielding a time series of almost 30~years. Presently, there are three TSI composites available, called PMOD, ACRIM and IRMB, which are all constructed from the same original data, but use different procedures to correct for sensitivity changes. The PMOD composite is the only one which also corrects the early HF data for degradation. The origin of the differences between the three composite are discussed by comparison with the record of ERBE. For the discussion of the similarities and differences of the three cycles the PMOD composite is used. The most interesting feature is the low value of TSI at the present minimum which cannot be seen in proxies such as F10.7, CaK and MgII indices. Thus, we see for the first time an effect on TSI which is not due to the direct effect of the superficial magnetic structures of solar activity Title: Erratum: "Iron-60 Evidence for Early Injection and Efficient Mixing of Stellar Debris in the Protosolar Nebula" (2008, APJ, 686, 560) Authors: Dauphas, N.; Cook, D. L.; Sacarabany, A.; Fröhlich, C.; Davis, A. M.; Wadhwa, M.; Pourmand, A.; Rauscher, T.; Gallino, R. Bibcode: 2009ApJ...691.1943D Altcode: Due to an error in processing the data, some values of epsilon60 Ni corrected for instrumental mass fractionation using 61Ni/58Ni ratios are incorrect. The corrected Table 2 is appended below. Nevertheless, the shifts that result from this correction are all within error bars and do not affect the conclusions of the paper. The figures are also unaffected. Title: Cause of Deep Moonquakes Authors: Nakamura, Y.; Frohlich, C. Bibcode: 2008AGUFM.P31B1407N Altcode: It is well known that the occurrence of deep moonquakes is highly correlated with the solid tides raised by Earth and the Sun. However, it has long been debated whether the tides are simply acting as a triggering mechanism for a release of accumulated tectonic stresses in the Moon's interior or the tides themselves are responsible for their generation, releasing tidally dissipated energy in the form of moonquakes. One way to test which of these two hypotheses is correct is to see when deep moonquakes occur relative to the long- term tidal amplitude variations caused by the changing position of the Sun relative to the eccentric orbit of the Moon around Earth. If the tides are simply acting as a trigger mechanism, deep moonquakes are more likely to occur when the tidal stress amplitudes are increasing, while if the tides are the main cause of deep moonquakes, they are more likely to occur shortly after the peaks in tidal stress amplitudes. We thus examined the frequency of deep moonquake occurrence as reported in the recently updated lunar event catalog relative to the difference between the anomalistic and synodic phases. Tidal stress amplitude reaches maxima when this phase difference is 0°, i.e., a new moon coincides with a perigee crossing, and when it is 180°, i.e., a full moon coincides with a perigee crossing. The result shows a general trend of maximum activity shortly following each of the tidal amplitude maxima, supporting the tidal generation hypothesis. However, an additional peak activity is found shortly before the tidal amplitude maximum at phase difference of 180°, also supporting the tidal triggering hypothesis in certain restricted cases. This secondary peak is limited only to some, but not all, deep moonquake nests. These trends are independent of whether the deep moonquake epicenters are located in either of the E-W hemispheres and in which of the tidal stress regimes as determined by the distance to the sub-earth point. Thus it appears that deep moonquakes generally represent release of tidally dissipated energy with additional triggered release of accumulated tectonic stress at a limited number of specific locations. However, this conclusion is provisional because the Apollo data did not cover the entire 18-year tidal cycle of the Moon. Title: Total solar irradiance during the last three cycles: Uncertainities of the long-term behaviour Authors: Frohlich, C. Bibcode: 2008AGUFMGC32A..06F Altcode: Since November 1978 a set of total solar irradiance (TSI) measurements from space is available, yielding a time series of 30 years. Presently, there are three TSI composites available, called PMOD, ACRIM and IRMB, which are all constructed from the same original data, but use different procedures to correct for long-term sensitivity changes. The PMOD composite is the only one which also corrects the early HF data for degradation and thus allows to compare all three cycles. This composite can now be used to assess the uncertainty of the long-term behaviour of TSI by comparison with independent measurements from ERBE and for the cycle 23 which is based on VIRGO data also with ACRIM-II on UARS, ACRIM-III on ACRIM-Sat and TIM on SORCE. Also different reconstructions from magnetograms and proxy data can be used, although the long-term behaviour of the reconstructions may not be comparable to the one of TSI. The result of this assessment is important not only for climate studies, but also for reconstructions of TSI back to e.g. the Maunder Minimum time. Title: Total solar irradiance during the last three cycles: What does the low present solar minimum tell us about long-term trends? Authors: Frohlich, C. Bibcode: 2008AGUFMSH21C..05F Altcode: Since November 1978 a set of total solar irradiance (TSI) measurements from space is available, yielding a time series of 30 years. Presently, there are three TSI composites available, called PMOD, ACRIM and IRMB, which are all constructed from the same original data, but use different procedures to correct for long-term sensitivity changes. The PMOD composite is the only one which also corrects the early HF data for degradation. The results are not only important for solar radiometry from space, but they also provide a more reliable TSI during cycle 21. The comparison with a 3-component proxy model during this cycle allows also to expand it back to the minimum around 1975. Moreover, the PMOD composite uses VIRGO TSI data which cover the full cycle 23 with the same radiometers. This allows a direct comparison of the present minimum with the one in 1996 which can then be used to determine trends over a solar cycle. Comparison with the minima of the other two cycles allows some conclusions about the origin of long-term trends in TSI. The long- term variation of TSI must be due to another mechanism than the well established cycle variation, which is very similar to the variation of the spectral irradiance. This mechanism is most probably a global temperature change which is somewhat related to the amplitude of the cycle, that is to the total magnetic field. Title: Mass measurements in the vicinity of the rp-process and the νp-process paths with the Penning trap facilities JYFLTRAP and SHIPTRAP Authors: Weber, C.; Elomaa, V. -V.; Ferrer, R.; Fröhlich, C.; Ackermann, D.; Äystö, J.; Audi, G.; Batist, L.; Blaum, K.; Block, M.; Chaudhuri, A.; Dworschak, M.; Eliseev, S.; Eronen, T.; Hager, U.; Hakala, J.; Herfurth, F.; Heßberger, F. P.; Hofmann, S.; Jokinen, A.; Kankainen, A.; Kluge, H. -J.; Langanke, K.; Martín, A.; Martínez-Pinedo, G.; Mazzocco, M.; Moore, I. D.; Neumayr, J. B.; Novikov, Yu. N.; Penttilä, H.; Plaß, W. R.; Popov, A. V.; Rahaman, S.; Rauscher, T.; Rauth, C.; Rissanen, J.; Rodríguez, D.; Saastamoinen, A.; Scheidenberger, C.; Schweikhard, L.; Seliverstov, D. M.; Sonoda, T.; Thielemann, F. -K.; Thirolf, P. G.; Vorobjev, G. K. Bibcode: 2008PhRvC..78e4310W Altcode: 2008arXiv0808.4065W The masses of very neutron-deficient nuclides close to the astrophysical rp- and νp-process paths have been determined with the Penning trap facilities JYFLTRAP at JYFL/Jyväskylä and SHIPTRAP at GSI/Darmstadt. Isotopes from yttrium (Z=39) to palladium (Z=46) have been produced in heavy-ion fusion-evaporation reactions. In total, 21 nuclides were studied, and almost half of the mass values were experimentally determined for the first time: Tc88, Ru90-92, Rh92-94, and Pd94,95. For the Pd95m, (21/2+) high-spin state, a first direct mass determination was performed. Relative mass uncertainties of typically δm/m=5×10-8 were obtained. The impact of the new mass values has been studied in νp-process nucleosynthesis calculations. The resulting reaction flow and the final abundances are compared with those obtained with the data of the Atomic Mass Evaluation 2003. Title: Iron 60 Evidence for Early Injection and Efficient Mixing of Stellar Debris in the Protosolar Nebula Authors: Dauphas, N.; Cook, D. L.; Sacarabany, A.; Fröhlich, C.; Davis, A. M.; Wadhwa, M.; Pourmand, A.; Rauscher, T.; Gallino, R. Bibcode: 2008ApJ...686..560D Altcode: 2008arXiv0805.2607D Among extinct radioactivities present in meteorites,60Fe (t1/2 = 1.49 Myr) plays a key role as a high-resolution chronometer, a heat source in planetesimals, and a fingerprint of the astrophysical setting of solar system formation. A critical issue with 60Fe is that it could have been heterogeneously distributed in the protoplanetary disk, calling into question the efficiency of mixing in the solar nebula or the timing of 60Fe injection relative to planetesimal formation. If this were the case, one would expect meteorites that did not incorporate 60Fe (either because of late injection or incomplete mixing) to show 60Ni deficits (from lack of 60Fe decay) and collateral effects on other neutron-rich isotopes of Fe and Ni (coproduced with 60Fe in core-collapse supernovae and AGB stars). Here, we show that measured iron meteorites and chondrites have Fe and Ni isotopic compositions identical to Earth. This demonstrates that 60Fe must have been injected into the protosolar nebula and mixed to less than 10% heterogeneity before formation of planetary bodies. Title: 60Fe in the cosmic blender Authors: Dauphas, N.; Cook, D. L.; Sacarabany, A.; Fröhlich, C.; Davis, A. M.; Wadhwa, M.; Pourmand, A.; Rauscher, T.; Gallino, R. Bibcode: 2008GeCAS..72Q.200D Altcode: No abstract at ADS Title: What can observed solar irradiance variability tell us about possible long-term changes of the Sun? Authors: Frohlich, C.; Beer, J.; Steinhilber, F. Bibcode: 2008AGUSMSP23A..05F Altcode: Total solar irradiance (TSI) measurements from different satellites are available since late 1978 and may be extended by reliable models back to the minimum between cycles 19 and 20 around 1976. This time series shows a downward trend of the cycle averaged data since the eighties. Although this trend is also present in other solar activity related parameters, such as the sunspot numbers, the 10.7cm radio flux, or the MgII index, only the open magnetic flux from the sun (from OMNI2 IMF-B data set) shows besides the same trend values during the minima which are comparable to the ones observed in TSI. Thus, a sensitivity of TSI during the minima relative to the ones of the open magnetic field can be determined. This sensitivity allows to determine TSI during past minima back to the 1880ties when the measurements started on which the reconstruction of the open field can be based. This allows also to compare TSI with the 10Be data and possibly 'calibrate' them back in time. Title: Iron-60 Injection in the Protosolar Nebula: How Early and How Well Mixed? Authors: Dauphas, N.; Cook, D. L.; Sacarabany, A.; Frohlich, C.; Davis, A. M.; Wadhwa, M.; Pourmand, A.; Rauscher, T.; Gallino, R. Bibcode: 2008LPI....39.1170D Altcode: Iron and nickel isotopic analyses of meteorites indicate that 60Fe must have been injected into the protosolar nebula and mixed at the 10% level before formation of planetary bodies. Title: How Tides Control Some Individual Deep Moonquake Nests Authors: Frohlich, C.; Nakamura, Y. Bibcode: 2007AGUFM.P43C..06F Altcode: Seismic stations emplaced during the Apollo missions operated from 1969 to 1977, and the most numerous signals identified in these data were deep moonquakes (DMQ). These occurred mostly at depths of 700-1200 km within a few hundred discrete clusters or nests, and within individual nests DMQ occurrence times correlated strongly with the gravitational tide generated by the Earth. However, the relationship with tides differs markedly at different nests, and we still don't understand either the mechanical origin of DMQ or why the tides exercise such strong control on their occurrence. We here investigate what controls episodes of DMQ occurrence in about a dozen DMQ nests where the temporal pattern is distinct and highly repeatable. In these nests, plots of occurrence times vs anomalistic phase exhibit a very regular drift pattern influenced by both the anomalistic and draconic periods, and often modulated by a roughly sinusoidal component having a period of about seven months. We show that extrema of the normal component of the tidal stress often exhibit a nearly identical pattern. In several of these nests there is a linear relationship between the normal and shear components of the tidal stress when DMQ occur. If we use a Mohr circle analysis to interpret these observations they suggest the static friction coefficient is extraordinarily low, about 0.1 or less. This is lower than ordinary geological materials, and may indicate that trapped fluids or other exotic phases play a role in the faulting process. Title: Geographic Variations in the Tidal Control of Deep Moonquake Nests and Speculation About Their Mechanical Origin Authors: Frohlich, C.; Nakamura, Y. Bibcode: 2007LPI....38.1749F Altcode: We group nests of deep moonquakes into categories depending on how their occurrence depends on the anomalistic or draconic month. For well-located nests having 20 or more individual events, we show that epicenters of some categories are geographically sep Title: Reconstruction of solar irradiance variations in cycles 21-23 based on surface magnetic fields Authors: Wenzler, T.; Solanki, S. K.; Krivova, N. A.; Fröhlich, C. Bibcode: 2006A&A...460..583W Altcode: Aims.We present a reconstruction of total solar irradiance (TSI) back to 1974, i.e. from the minimum of cycle 21 to the declining phase of cycle 23. We also present a cross-calibration between the magnetograms obtained by the 512 channel magnetograph and the spectromagnetograph at Kitt Peak.
Methods: .The TSI reconstruction is carried out using data from the 512-channel Diode Array Magnetograph and the newer spectromagnetograph on Kitt Peak. The model is based on the assumption that all irradiance changes on time-scales of a day and longer are entirely due to the variations of the surface distribution of the solar magnetic field. The reconstructed irradiance is compared with the composite of total solar irradiance measurements from PMOD/WRC (version 41).
Results: .A good correspondence is found with the PMOD TSI composite, with no bias between the three cycles on time-scales longer than the solar rotation period, although the accuracy of the TSI reconstruction is somewhat lower when 512 channel magnetograph data are used. This suggests that the same driver of the irradiance variations, namely the evolution of the magnetic flux at the solar surface, is acting in cycles 21-23. Different methods of comparing the magnetograms obtained by the two Kitt Peak magnetographs give somewhat different results, with factors by which 512 channel data must be divided in the range 1.38-1.63 being found. This is due to the non-linearity of the relationship between the magnetic field measured by the two instruments.
Title: Geographic Variations in Tidal Control of Deep Moonquake Nests Authors: Frohlich, C.; Nakamura, Y. Bibcode: 2006AGUFM.U41C0831F Altcode: Understanding variations in the tidal response of deep moonquake (DMQ) nests may help us understand the origin of deep moonquakes. We have grouped nests of deep moonquakes into categories depending on how strongly their occurrence is influenced by the anomalistic or draconic month and the phase of this dependence. For well-located nests having 20 or more individual events, epicenters of some categories are geographically separated from one another on the Moon. The tidal potential caused by the Earth with mass M at distance R varies over the Moon's surface and is proportional to (3cos2θ - 1)M/R3, where θ is the angle between the point of interest and an axis E-M joining the line of centers. The solid tidal deformation causes the Moon's shape to be ellipsoidal with the long axis directed along E-M. The potential is zero when θ is 24° and thus along a small circle of this radius the tangential strain is zero. When θ is 55° the surface curvature of the tidal ellipsoid is unchanged and thus the radial strain is zero. For any fixed location on the Moon the tidal deformation changes because the E-M axis moves ±8° EW over the Moon's surface during the anomalistic month as the Earth-Moon distance changes and affects the angular rate at which the Moon orbits Earth. The E-M axis moves ±7° NS during the draconic month because the orbital plane doesn't coincide with the Moon's equator. The Sun affects the orientation of the long axis of the tidal deformation ellipsoid by less than 0.3°. We thus determine the angular distance θ between individual DMQ and the E-M axis, and search for features in the distribution of hypocenters near the nodes at 24° and 55°. We separate DMQ into three categories: wA - occurrence weakly correlated with anomalistic phase; sAp - occurrence strongly correlated with anomalistic phase; DMQ occur mostly as Moon approaches perigee; sAa - occurrence strongly correlated with anomalistic phase; DMQ occur mostly as Moon approaches apogee. DMQ in the sAp group are rare or absent at θ<~20°; DMQ in the sAa group are common at θ<~20°; the wA group doesn't appear to correlate with distance. Similarly, if we use draconic phase behavior as a classifier we find that DMQ strongly correlated with draconic phase are rare or absent at θ<~20° whereas DMQ weakly correlated with draconic phase do not appear to correlate with distance. We speculate that the different categories of DMQ may represent distinct mechanical phenomena. For example, the sAa group may represent the growth of faults as the shape of the Moon changes in response to its slow retreat from the Earth. The sAp group may come about because tidal shear stresses drive fluids that repeatedly shift blocks within the lunar mantle. Title: The internal structure of the Sun inferred from g modes and low-frequency p modes Authors: Elsworth, Y. P.; Baudin, F.; Chaplin, W; Andersen, B; Appourchaux, T.; Boumier, P.; Broomhall, A. -M.; Corbard, T.; Finsterle, W.; Fröhlich, C.; Gabriel, A.; García, R. A.; Gough, D. O.; Grec, G.; Jiménez, A.; Kosovichev, A.; Provost, J.; Sekii, T.; Toutain, T.; Turck-Chièze, S. Bibcode: 2006ESASP.624E..22E Altcode: 2006soho...18E..22E The Phoebus group is an international collaboration of helioseismologists, its aim being to detect low-frequency solar g modes. Here, we report on recent work, including the development and application of new techniques based on the detection of coincidences in contemporaneous datasets and the asymptotic properties of the g-mode frequencies. The length of the time series available to the community is now more than ten years, and this has reduced significantly the upper detection limits on the g-mode amplitudes. Furthermore, low-degree p modes can now be detected clearly at frequencies below 1000 μHz. Title: Variations in solar luminosity and their effect on the Earth's climate Authors: Foukal, P.; Fröhlich, C.; Spruit, H.; Wigley, T. M. L. Bibcode: 2006Natur.443..161F Altcode: Variations in the Sun's total energy output (luminosity) are caused by changing dark (sunspot) and bright structures on the solar disk during the 11-year sunspot cycle. The variations measured from spacecraft since 1978 are too small to have contributed appreciably to accelerated global warming over the past 30 years. In this Review, we show that detailed analysis of these small output variations has greatly advanced our understanding of solar luminosity change, and this new understanding indicates that brightening of the Sun is unlikely to have had a significant influence on global warming since the seventeenth century. Additional climate forcing by changes in the Sun's output of ultraviolet light, and of magnetized plasmas, cannot be ruled out. The suggested mechanisms are, however, too complex to evaluate meaningfully at present. Title: Solar Irradiance Variability Since 1978. Revision of the PMOD Composite during Solar Cycle 21 Authors: Fröhlich, C. Bibcode: 2006SSRv..125...53F Altcode: 2006SSRv..tmp...90F Since November 1978 a set of total solar irradiance (TSI) measurements from space is available, yielding a time series of more than 25 years. Presently, there are three TSI composites available, called PMOD, ACRIM and IRMB, which are all constructed from the same original data, but use different procedures to correct for sensitivity changes. The PMOD composite is the only one which also corrects the early HF data for degradation. The results from the detailed analysis of the VIRGO radiometry allow a good understanding of the effects influencing the long-term behaviour of classical radiometers in space. Thus, a re-analysis of the behaviour of HF/NIMBUS-7 and ACRIM-I/SMM was indicated. For the former the situation is complicated by the fact that there are no in-flight means to determine changes due to exposure to solar radiation by comparison with a less exposed radiometer on the same spacecraft. The geometry and optical property of the cavity of HF is, however, very similar to the PMO6-type radiometers, so the behaviour of the PMO6V radiometers on VIRGO can be used as a model. ACRIM-I had to be revised mainly due to a henceforth undetected early increase and a more detailed analysis of its degradation. The results are not only important for solar radiometry from space, but they also provide a more reliable TSI during cycle 21. The differences between the revised PMOD composite and the ACRIM and IRMB are discussed by comparison with a TSI reconstruction from Kitt-Peak magnetograms. As the PMOD composite is the only one which has reliable data for cycle 21, the behaviour of the three solar cycles can now be compared and the similarities and differences discussed. Title: Review of the Long-Term Performance of the PMO6 Radiometers on VIRGO/SOHO Authors: Finsterle, W.; Fröhlich, C.; Schlifkowitz, U. Bibcode: 2006ESASP.617E..58F Altcode: 2006soho...17E..58F No abstract at ADS Title: Recent Progresses on g-Mode Search Authors: Appourchaux, T.; Andersen, B.; Baudin, F.; Boumier, P.; Broomhall, A. -M.; Chaplin, W.; Corbard, T.; Elsworth, Y.; Finsterle, W.; Fröhlich, C.; Gabriel, A.; Garcia, R.; Gough, D. O.; Grec, G.; Jiménez, A.; Kosovichev, A.; Provost, J.; Sekii, T.; Toutain, T.; Turck-Chièze, S. Bibcode: 2006ESASP.617E...2A Altcode: 2006soho...17E...2A No abstract at ADS Title: Total Solar Irradiance Variability: What Have We Learned from SOHO/VIRGO about Solar Cycle 23? Authors: Fröhlich, C. Bibcode: 2006ESASP.617E..60F Altcode: 2006soho...17E..60F No abstract at ADS Title: Possible Extra-Solar-System Cause for Certain Lunar Seismic Events Authors: Nakamura, Y.; Frohlich, C. Bibcode: 2006LPI....37.1048N Altcode: All but a few of a rare class of events detected by the Apollo lunar seismic network occurred when the Moon faced a fixed direction on the celestial sphere. This suggests that a source outside the solar system may be responsible for causing them. Title: ISS-SOLAR: Total (TSI) and spectral (SSI) irradiance measurements Authors: Schmidtke, G.; Fröhlich, C.; Thuillier, G. Bibcode: 2006AdSpR..37..255S Altcode: The primary objective of the ISS-SOLAR mission on Columbus (to be launched in 2006) is the quasi-continuous measurement of the solar irradiance variability with highest possible accuracy. For this reason the total spectral range will be recorded simultaneously from 3000 to 17 nm by three sets of instruments: SOVIM is combining two types of absolute radiometers and three-channel filter radiometers. SOLSPEC is composed of three double monochromators using concave gratings, covering the wavelength range from 3000 to 180 nm. SOL-ACES has four grazing incidence planar grating spectrometers plus two three-signal ionization chambers (two signals from a two stage chamber plus a third signal from a silicon diode at the end of the chamber) with exchangeable band pass filters to determine the absolute fluxes from 220 to 17 nm repeatedly during the mission. For the TSI the relative standard uncertainty (RSU) to be achieved is of the order of 0.15% and for the SSI from 1% in the IR/Vis, 2% in the UV, 5% in the FUV up to 10% in the XUV spectral regions. The general requirements for the TSI and SSI measurements and their conceptual realization within this payload will be discussed with emphasis on instrumental realization and calibration aspects. Title: Possible extra-solar-system cause for shallow moonquakes Authors: Frohlich, C.; Nakamura, Y. Bibcode: 2006epsc.conf..301F Altcode: Reanalysis of lunar seismic data collected during the Apollo program indicates that 23 of the 28 rare events known as high-frequency teleseismic (HFT) events or shallow moonquakes occurred during one-half of the sidereal month when the seismic network on the Moon's near side faced approximately towards right ascension of 12 hours on the celestial sphere. Statistical analysis demonstrates that there is about a 1 per cent probability that this pattern would occur by chance. In a coordinate system fixed to the celestial sphere, the 26 located HFT events tend to cluster around a direction approximately between the constellations Leo and Cancer (L-C); in this coordinate system the clustering is significant at about the 97% level. With respect to this celestial coordinate system and direction L-C, 13 of 26 events are situated near the Moon's limb (between 70° and 110° from the point on the lunar surface closest to L-C). Although there is a possibility that the observed clustering of HFT events is purely a statistical coincidence, if it isn't a random phenomenon it has great scientific importance and thus we here seriously consider other possibilities. HFT events are clearly a seismic phenomenon and not an artifact of the data collection process. Most are observed on all four stations of the Apollo lunar network, exhibiting onset times of P and S that are separated by intervals appropriate for seismic wave transmission through the Moon. These observations cannot be explained by, for example, a shower of cosmic rays that interferes with seismograph electronics or data transmission. We also show that HFT events are not caused by ordinary meteoroid impacts or by tidal stresses. One possibility is that high-energy objects from a fixed source outside the solar system trigger or even cause the HFT events. High-energy astrophysicists have proposed that exotic particles such as nuggets of strange quark matter (SQM) might cause or trigger HFT events and this has motivated so-far-unsuccessful searches for terrestrial seismic signals produced by SQM passage. Recent estimates show that the seismically quiet lunar surface provides a better environment than Earth to observe the signals produced by SQM nuggets. The observations of HFT events occurring preferentially near the Moon's limb as observed from direction L-C might indicate that these exotic particles release residual seismic stresses as they pass horizontally through the Moon's lithosphere. Title: A renewed look at deep moonquakes in the Apollo seismic data Authors: Nakamura, Y.; Frohlich, C. Bibcode: 2006epsc.conf..281N Altcode: We have recently been reanalyzing the deep moonquake data from the US Apollo project because recent advancement of computer capability now allows us to perform much more sophisticated analyses to extract further information from this 30-year old data set. In this presentation, we will review our new findings to date and discuss future directions. We started with identifying the more than 9000 catalogued but unidentified events with waveform cross-correlation and single-link analysis, which resulted in more than fivefold increase in positively identified deep moonquakes to over 7000 and a discovery of nearly 250 new deep moonquake nests. We then examined the newly discovered deep moonquake nests to see if any of them were located on the far side, considering that seismic sources located on the opposite side from seismic stations would provide information on very deep interior of the Moon, including a possible lunar core. About 30 nests were identified as likely candidates, but none of them were within 40 degrees from the antipode of the Moon, suggesting that either that the antipodal region of the Moon is aseismic, or the very deep interior of the Moon severely attenuates or deflects seismic waves. With the newly expanded list of deep moonquakes, we reexamined the distribution of hypocenters in the A1 deep moonquake nest using relative hypocenter locations with cross-spectral analysis. Contrary to our expectations with greatly increased number of events belonging to this nest, the extent of the A1 source region remained the same as in our earlier analysis, i.e., within about 1-km radius. This strengthens our earlier conclusion that time-varying slip direction at the source is necessary to explain the variation in waveforms of events belonging to the nest. Similar analyses for several other nests appear to show similar results. Although the data clearly indicate that tidal stress influences many nests, the physical mechanism responsible is not apparent. Our new analysis correlating the tidal deformation of the Moon with temporal distribution of events at different nests appears to suggest some systematic trends, but it is too early to draw any conclusions. A good understanding of this relationship will be a great help in understanding of earthquake occurrence here on Earth, where tidal triggering of earthquakes has been an elusive subject for a long time. Title: Weak interaction rates Authors: Martinez-Pinedo, Gabriel; Kelic, A.; Langanke, K.; Schmidt, K. -H.; Mocelj, D.; Fröhlich, C.; Thielemann, F. -K.; Panov, I.; Rauscher, T.; Liebendörfer, M.; Zinner, N. T.; Pfeiffer, B.; Buras, R.; Janka, H. -Th. Bibcode: 2006isna.confE..64M Altcode: 2006PoS....28E..64M This manuscript reviews recent progress in our understanding of the nucleosynthesis of medium and heavy elements in supernovae. Recent hydrodynamical models of core-collapse supernovae show that a large amount of proton rich matter is ejected under strong neutrino fluxes. This matter constitutes the site of the ν p-process where antineutrino absorption reactions catalyze the nucleosynthesis of nuclei with A > 64. Supernovae are also associated with the r-process responsible for the synthesis of the heaviest elements in nature. Fission during the r-process can play a major role in determining the final abundance patter and in explaining the almost universal features seen in metal-poor r-process-rich stars. Title: Correlation Between Cosmic-Ray Intensity and Total Solar Irradiance during the last three Solar Cycles Authors: Frohlich, C.; Beer, J.; Muscheler, R. Bibcode: 2005AGUFMSH41A1110F Altcode: For reconstructions of the total solar irradiance (TSI) into the past it is important to understand the relation between the production of cosmogenic isotopes and TSI. The production rate is a function of the cosmic-ray intensity reaching the Earth, which is well represented by the neutron monitors. As theses data are available since well before the start of cycle 21 a direct comparison with the PMOD composite of TSI can be performed. For the correlation different lags of the cosmic-ray intensity for the odd and even cycles have to be taken into account, as well as different amplitudes. Both the cosmic-ray intensity and TSI are modulated by the solar activity related magnetic fields. While the cosmic ray intensity depends only on the open fields a major question is still how the open fields are related to the weak fields in the network on the Sun which seem to be responsible for the solar-cycle modulation of TSI. The much stronger fields on the solar surface on the other hand are responsible for the short-term variation related to sunspots and faculae. The implications of this comparison for the understanding of the relation between the production of cosmogenic isotopes and TSI will be discussed. Title: Comparison of the PMOD, ACRIM and IRMB Composite Total Solar irradiance time series Authors: Frohlich, C. Bibcode: 2005AGUFMSH33C..02F Altcode: Since November 1978 a set of total solar irradiance (TSI) measurements from space is available, yielding a time series of more than 25 years. From measurements made by different space radiometers (HF on NIMBUS~7, ACRIM I on SMM, ACRIM II on UARS, VIRGO on SOHO, ACRIM III on ACRIMSat and TIM on SORCE) a composite record of TSI can be constructed. Presently, there are three composites available, called PMOD, ACRIM and IRMB, which all are based on the same original data before the advent of VIRGO on SOHO. Afterwards, the ACRIM composite is using ACRIM-II and III and the PMOD and IRMB VIRGO data. The differences arise from the different ways to correct for sensitivity changes. A further difference is that the PMOD composite also corrects the early HF data for degradation and thus can provide reliable data for TSI around the maximum of solar cycle 21 before the advent of ACRIM-I. The origin of the differences will be discussed in detail and illustrated by comparison with ERBE data and a independent TSI reconstruction from Kitt-Peak magnetograms. Title: Solar Irradiance Variability since 1978 Authors: Fröhlich, C. Bibcode: 2005MmSAI..76..731F Altcode: Since November 1978 a set of total solar irradiance (TSI) measurements from space is available, yielding a time series of more than 25 years. From measurements made by different space radiometers (HF on NIMBUS 7, ACRIM I on SMM, ACRIM II on UARS, VIRGO on SOHO, ACRIM III on ACRIMSat and TIM on SORCE) a composite record of TSI can be constructed. Presently, there are three such composites available, called PMOD, ACRIM and IRMB, which all are based on the same original data, but use different ways to correct for sensitivity changes. The PMOD composite is the only one which also corrects the early HF data for degradation and can provide reliable data for TSI around the maximum of solar cycle 21. The results from the detailed analysis of the VIRGO radiometry allow a good understanding of the effects influencing the long-term behaviour of classical radiometers in space. Thus, a re-analysis of the long-term behaviour of HF and ACRIM-I was performed. The results are not only important for solar radiometry from space, but they also provide a more credible TSI during cycle 21. Thus the revised PMOD composite allows to better quantify the behaviour of solar cycle 21 relative to the two recent ones which differ in several aspects. Title: The Sun, from Core to Corona and Solar Wind Authors: von Steiger, R.; Fröhlich, C. Bibcode: 2005ISSIR...3...99V Altcode: 2005ssb..book...99V; 2005ESASR...3...99V No abstract at ADS Title: Solar radiative output and its variability: evidence and mechanisms Authors: Fröhlich, Claus; Lean, Judith Bibcode: 2004A&ARv..12..273F Altcode: 2004A+ARv..12..273F Electromagnetic radiation from the Sun is Earth’s primary energy source. Space-based radiometric measurements in the past two decades have begun to establish the nature, magnitude and origins of its variability. An 11-year cycle with peak-to-peak amplitude of order 0.1 % is now well established in recent total solar irradiance observations, as are larger variations of order 0.2 % associated with the Sun’s 27-day rotation period. The ultraviolet, visible and infrared spectral regions all participate in these variations, with larger changes at shorter wavelengths. Linkages of solar radiative output variations with solar magnetism are clearly identified. Active regions alter the local radiance, and their wavelength-dependent contrasts relative to the quiet Sun control the relative spectrum of irradiance variability. Solar radiative output also responds to sub-surface convection and to eruptive events on the Sun. On the shortest time scales, total irradiance exhibits five minute fluctuations of amplitude ≈ 0.003 %, and can increase to as much as 0.015 % during the very largest solar flares. Unknown is whether multi-decadal changes in solar activity produce longer-term irradiance variations larger than observed thus far in the contemporary epoch. Empirical associations with solar activity proxies suggest reduced total solar irradiance during the anomalously low activity in the seventeenth century Maunder Minimum relative to the present. Uncertainties in understanding the physical relationships between direct magnetic modulation of solar radiative output and heliospheric modulation of cosmogenic proxies preclude definitive historical irradiance estimates, as yet. Title: Re-analysis of the long-term changes of the NIMBUS-7 radiometer and behaviour of total solar irradiance during solar cycle 21 Authors: Frohlich, C. Bibcode: 2004AGUFMSH53A0301F Altcode: Only one radiometer - called Hickey-Frieden (HF) - is within the ERB package on NIMBUS-7 for the measurement of total solar irradiance (TSI) and thus changes due to exposure to solar radiation cannot be directly determined by comparison with a less exposed radiometer on the same spacecraft. The geometry and optical property of the cavity of HF is, however, very similar to the PMO6-type radiometers, it is essentially a copy of it with increased size. For the PMO6V on VIRGO/SOHO two main effects have been identified, a rapid early increase and a slow decrease, normally termed degradation, which can be modelled with a hyperbolic function taking the actual dose into account (Fröhlich, 2003). The corrections used by Fröhlich and Lean (1998) for the composite were based on early results from VIRGO and used simple exponential functions. With the recent results from VIRGO a re-analysis of the long-term behaviour of HF is necessary. The results are not only important for solar radiometry from space, but also to improve the reliability of TSI before the start of ACRIM-I in early 1980. The latter will allow to better quantify the behaviour of solar cycle 21 and to compare it with the two recent ones which differ in several aspects. C. Fröhlich. Long-term behaviour of space radiometers. Metrologia, 40:60--65, 2003. C. Fröhlich and J. Lean. The sun's total irradiance: Cycles and trends in the past two decades and associated climate change uncertainties. Geophys. Res. Lett., 25:4377--4380, 1998. Title: Total Solar Irradiance Variation During Rapid Sunspot Growth Authors: Zahid, H. Jabran; Hudson, Hugh S.; Fröhlich, Claus Bibcode: 2004SoPh..222....1Z Altcode: Large sunspot areas correspond to dips in the total solar irradiance (TSI), a phenomenon associated with the local suppression of convective energy transport in the spot region. This results in a strong correlation between sunspot area and TSI. During the growth phase of a sunspot other physics may affect this correlation; if the physical growth of the sunspot resulted in surface flows affecting the temperature, for example, we might expect to see an anomalous variation in TSI. In this paper we study NOAA active region 8179, in which large sunspots suddenly appeared near disk center, at a time (March 1998) when few competing sunspots or plage regions were present on the visible hemisphere. We find that the area/TSI correlation does not significantly differ from the expected pattern of correlation, a result consistent with a large thermal conductivity in solar convection zone. In addition we have searched for a smaller-scale effect by analyzing white-light images from MDI (the Michelson Doppler Imager) on SOHO. A representative upper-limit energy consistent with the images is on the order of 3×1031 ergs, assuming the time scale of the actual spot area growth. This is of the same order of magnitude as the buoyant energy of the spot emergence even if it is shallow. We suggest that detailed image analyses of sunspot growth may therefore show `transient bright rings' at a detectable level. Title: Excess facular emission from an isolated active region during solar minimum: the example of NOAA AR 7978 Authors: Ortiz, A.; Domingo, V.; Sanahuja, B.; Fröhlich, C. Bibcode: 2004JASTP..66...67O Altcode: 2004JATP...66...67O The facular contribution to solar irradiance variations on the short time scale is studied by analyzing a simple case of an isolated active region that crossed the solar disk during the 1996 minimum of activity, NOAA AR 7978. Its passage during several Carrington rotations, specifically from rotation 1911 to 1916, allows us to analyze the evolution of the angular distribution of the excess radiance of the facular region using SOHO/VIRGO and MDI data. We associate this evolution with the evolution of the extent corresponding to the isolated active region as well as with the aging of the region itself. Finally, we evaluate the total (i.e. in all directions) emission of this facular region and its spectral and temporal evolution. Title: Resonance analysis of 147 Sm ( n,α ) cross sections: Comparison to optical model calculations and indications of nonstatistical effects Authors: Koehler, P. E.; Gledenov, Yu. M.; Rauscher, T.; Fröhlich, C. Bibcode: 2004PhRvC..69a5803K Altcode: 2003astro.ph.12088K We have measured the 147 Sm ( n,α ) cross section from 3 eV to 500 keV and performed an R -matrix analysis in the resolved region ( En <700 eV ) to extract α widths for 104 resonances. We computed strength functions from these resonance parameters and compared them to transmission coefficients calculated using optical model potentials similar to those employed as inputs to statistical model calculations. The statistical model often is used to predict cross sections and astrophysical reaction rates. Comparing resonance parameters rather than cross sections allows more direct tests of potentials used in the model and hence should offer greater insight into possible improvements. In particular, an improved α+nucleus potential is needed for applications in nuclear astrophysics. In addition to providing a more direct test of the α+nucleus potential, the α -width distributions show indications of nonstatistical effects. Title: Total solar irradiance variation during rapid sunspot growth Authors: Zahid, H. J.; Hudson, H. S.; Frohlich, C. Bibcode: 2004cosp...35.2769Z Altcode: 2004cosp.meet.2769Z Large sunspot areas correspond to dips in the total solar irradiance (TSI), a phenomenon associated with the local suppression of convective energy transport in the spot region. During the growth of a sunspot other physics might conceivably affect the resulting correlation between sunspot area and TSI. We study NOAA active region 8179, in which large sunspots suddenly appeared near disk center, at a time (March 1998) when few competing sunspots or plage regions were present on the visible hemisphere. We find that the area/TSI correlation does not significantly differ from the expected pattern of correlation, a result consistent with the expected thermal conductivity of the solar convection zone. In addition we have searched for a smaller-scale effect by analyzing white-light images from MDI (the Michelson Doppler Imager) on SOHO. A representative upper-limit energy consistent with the images is on the order of 3 X 1031 ergs, assuming the time scale of the actual spot area growth. This is the same order of magnitude as the buoyant energy of the spot emergence even if it is shallow. We suggest that detailed image analyses of sunspot growth may therefore show "transient bright rings" at a detectable level. Title: Solar Variability and its Effects on Climate. Geophysical Monograph 141 Authors: Pap, Judit M.; Fox, Peter; Frohlich, Claus; Hudson, Hugh S.; Kuhn, Jeffrey; McCormack, John; North, Gerald; Sprigg, William; Wu, S. T. Bibcode: 2004GMS...141.....P Altcode: This monograph presents a state-of-the-art description of the most recent results on solar variability and its possible influence on the Earth's climate and atmosphere. Our primary goal in doing so is to review solar energy flux variations (both electromagnetic and particle) and understand their relations to solar magnetic field changes and global effects, their impact on different atmospheric layers, and—as a collaboration of scientists working on solar-terrestrial physics—to note unresolved questions on an important interdisciplinary area.

One of the highest-level questions facing science today is whether the Earth's atmosphere and climate system changes in a way that we can understand and predict. The Earth's climate is the result of a complex and incompletely understood system of external inputs and interacting parts. Climate change can occur on various time scales as a consequence of natural variability—including solar variability—or anthropogenic causes, or both. The Sun's variability in the form of sunspots and related magnetic activity has been the subject of careful study ever since the earliest telescopic observations. High precision photometric observations of solar-type stars clearly show that year-to-year brightness variations connected with magnetic activity are a widespread phenomenon among such stars. As our nearest star, the Sun is the only star where we can observe and identify a variety of structures and processes which lead to variations in the solar energy output, in both radiative and particle fluxes. Studying event tiny changes in solar energy flux variations may teach us about internal processes taking place in the Sun's convective zone and below. Title: Solar Irradiance Variability Authors: Fröhlich, Claus Bibcode: 2004GMS...141...97F Altcode: Since November 1978 a set of total solar irradiance (TSI) measurements from space is available, yielding a time series of more than 23 years. From measurements made by different space radiometers (HF on NIMBUS 7, ACRIM I on SMM, ACRIM II on UARS and VIRGO on SOHO) a composite record of TSI can be compiled. This leads to a reliable record of TSI with an overall precision of the order of 0.05 Wm-2. This time series is compared to an empirical model based on sunspot darkening and brightening due to faculae and network. Since early 1996 spectral measurements by filter-radiometers of VIRGO provide continuous time series of spectral solar irradiance (SSI) at 402, 500 and 862 nm. These time series are analyzed and compared to TSI yielding information about the redistribution of energy within the spectrum during changes of TSI. Title: ISS-SOLAR: Total (TSI) and Spectral (SSI) Irradiance Measurements Authors: Schmidtke, G.; Thuillier, G.; Fröhlich, C. Bibcode: 2004cosp...35.2503S Altcode: 2004cosp.meet.2503S Related to the climatic aspects in atmospheric science the primary objective of the ISS-SOLAR Mission on Columbus (to be launched in 2006) is the quasi-continuous measurement of the solar irradiance variation with highest possible accuracy. For this reason the total spectral range will be recorded simultaneously for the first time from 3000-16 nm by three sets of instruments: SOVIM(3) is combining two types of absolute radiometers and three-channel filterradiometers. SOLSPEC(2) is composed of three concave grating spectrometers with two monochromators, each, covering the wavelength range from 3000-180 nm. SOL-ACES(1) has four grazing incidence planar grating spectrometers plus two three-signal ionization chambers with exchangeable band pass filters to determine the absolute fluxes from 220-16 nm repeatedly during the mission. For the TSI the absolute accuracy to be achieved is of the order of 0.1 % and for the SSI from 1 % in the VIS, 2 % in the UV, 5 % in the FUV to 10 % in the XUV spectral regions. The general requirements for the TSI and SSI measurements and their conceptual realization within the payload will be discussed with emphasis on instrumental realization and calibration aspects. Title: Preface Authors: Pap, Judit M.; Fox, Peter; Fröhlich, Claus; Hudson, Hugh S.; Kuhn, Jeffrey; McCormack, John; North, Gerald; Sprigg, William; Wu, S. T. Bibcode: 2004GMS...141D...7P Altcode: This monograph presents a state-of-the-art description of the most recent results on solar variability and its possible influence on the Earth's climate and atmosphere. Our primary goal in doing so is to review solar energy flux variations (both electromagnetic and particle) and understand their relations to solar magnetic field changes and global effects, their impact on different atmospheric layers, and—as a collaboration of scientists working on solar-terrestrial physics—to note unresolved questions on an important interdisciplinary area.

One of the highest-level questions facing science today is whether the Earth's atmosphere and climate system changes in a way that we can understand and predict. The Earth's climate is the result of a complex and incompletely understood system of external inputs and interacting parts. Climate change can occur on various time scales as a consequence of natural variability—including solar variability—or anthropogenic causes, or both. The Sun's variability in the form of sunspots and related magnetic activity has been the subject of careful study ever since the earliest telescopic observations. High precision photometric observations of solar-type stars clearly show that year-to-year brightness variations connected with magnetic activity are a widespread phenomenon among such stars. As our nearest star, the Sun is the only star where we can observe and identify a variety of structures and processes which lead to variations in the solar energy output, in both radiative and particle fluxes. Studying even tiny changes in solar energy flux variations may teach us about internal processes taking place in the Sun's convective zone and below. Title: Measurements of the total and spectral solar irradiance: what do we have and what will we get in future? Authors: Thuillier, G.; Fröhlich, C.; Schmidtke, G. Bibcode: 2004cosp...35.1277T Altcode: 2004cosp.meet.1277T Total and spectral solar irradiance (TSI and SSI) and their variability play a key role as input to the Earth's and - in more general terms - to all planetary atmospheres. Modeling of the properties of these atmospheres in terms of composition, thermal structure and dynamics have been significantly improved in recent years. Thus, the demand for more accurate solar irradiance data has increased accordingly. On the other hand, the solar physics community needs such data in order to improve the understanding of the mechanisms leading to solar variability without which no reliable long-term predictions are possible. The results from 8 years of the ESA/NASA SOHO mission and from the recently launched US satellites TIMED and SORCE demonstrate the present state-of-the-art capabilities for TSI and SSI. We summarize the present knowledge of TSI and SSI together with estimates of the uncertainties involved. We show also what the three instruments of SOLAR to be flown in 2006 on board the International Space Station will contribute to the long-term record with observations of TSI and the solar spectrum between 17 to 3000 nm. Moreover, in 2008 the data will be supplemented by TSI measurements and some spectral channels of PICARD, a French microsatellite. As it looks now, we will have overlapping measurements of total and spectral solar irradiance - at least until about 2010 - which is very promising. Title: Solar irradiance variation during rapid sunspot growth Authors: Zahid, H.; Frohlich, C.; Hudson, H. Bibcode: 2003AGUFMSH32A1102Z Altcode: Large sunspot areas correspond to dips in the total solar irradiance (TSI), a phenomenon associated with the local suppression of convective energy transport in the spot region. Observations show a strong correlation between spot area and TSI. During the growth phase of a sunspot, though, other physics might conceivably affect this correlation. In this study we analyze the growth phase of NOAA active region 8179, in which large sunspots suddenly appeared near disk center at a time when few competing sunspots or plage regions were present on the visible hemisphere. The spot area of AR 8179 increased by a factor of two in less than 12 hours on March 13, 1998. The study makes use of the continuum images from SOHO/MDI and total-irradiance data from SOHO/VIRGO. We find that the area/TSI correlation does not significantly differ from the expected pattern of correlation, a result consistent with high thermal conductivity even at small depths below the photosphere. We have also searched for localized irradiance variations (transient bright rings) associated with the period of rapid growth. We discuss the significance of this lack of irradiance signatures of spot formation. Title: Total Solar Irradiance Variability from 1978 to present Authors: Fröhlich, C. Bibcode: 2003AGUFMSH31C..04F Altcode: Since February 1996 VIRGO radiometers observe total solar irradiance from SOHO at L1, allowing continuous and uninterrupted observations of the Sun. Besides the 3-month gap during the SOHO vacation in summer 1998 and a few other minor gaps the record covers more than 99% of the almost 8 years of operation. This allows a very detailed assessment of the long-term behaviour of the two VIRGO radiometers, PMO6V and DIARAD. The results of this analysis are presented and their implications for other space radiometers discussed. With these data and those from HF/NIMBUS7, ACRIM-I/SMM and ACRIM-II/UARS a composite of total solar irradiance (TSI) is presented (updated and improved from Fröhlich and Lean, 1998), which covers now almost three solar cycles starting in November 1978, just before the maximum of solar cycle 21. Radiometrically the composite is based on ACRIM-I and ACRIM-II, with the latter shifted to the scale of ACRIM-I. During the gap between ACRIM-I and II the results from the HF radiometer are used. These data need to be corrected for a change which was first detected by comparison with ERBS. The inclusion or omittance of this change is the main reason for the discrepancy between this composite and the one presented by Willson and Mordvinov (2003). The discussion concentrates on this change and its determination by comparison of HF with ERBS and a proxy model for interpolation between its 14-day observations. Comparison of the composite with ERBS over the period from 1984-2003 supports very strongly the validity and need of the HF correction and confirms that TSI had no significant trend over the last 25 years of observation from space. References: C. Fröhlich and J. Lean, 1998, The Sun's Total Irradiance: Cycles and Trends in the Past Two Decades and Associated Climate Change Uncertainties, Geophys. Res. Let., 25, 4377--4380 R. C. Willson and A.~V. Mordvinov, 2003, Secular Total Solar Irradiance trend during solar cycles 21-23, Geophys. Res. Let., 30, 1199--1202 Title: Spectral Solar Irradiance Variability from {VIRGO} on {SOHO}: 1996 to present Authors: Fröhlich, C.; Wachter, R.; Wehrli, C. Bibcode: 2003AGUFMSH12A1152F Altcode: Since February 1996 VIRGO filterradiometers on SOHO monitor spectral solar irradiance at 402, 500 and 862nm with a bandwidth of 5nm. SOHO's vantage point at L1 allows uninterrupted observations of the Sun, 24 h a day and 365 days an year. Besides the 3-month gap during the SOHO vacation in summer 1998 and a few other minor gaps the record covers more than 99% of the period up to now of almost 8 years of observations. The long-term behaviour of the operational channels is dominated by instrumental degradation masking the solar variability signature. However, comparisons with the back-up channels allows to take off some of the instrumental long-term variation, and the resulting time series can now provide reliable information about variability with periods up to about 4--500 days. Time series with the long-term variation removed and the corresponding periodogram show many similarities between the three channels and total solar irradiance. Details about the spectral redistribution during changes of TSI are investigated by multivariate spectral analysis. Furthermore, comparison of the spectral analysis of the cleaned 1-minute sampled time series during solar minimum (1996/7) and maximum (2001/2) allows to asses the variation of power with the activity cycle in a range from about 30 nHz (about 1 year period) up to 8 mHz (5-minute oscillations). The variability with activity of the three colours is compared with the one of TSI. Title: Traceable radiometry underpinning terrestrial- and helio-studies (TRUTHS) Authors: Fox, N.; Aiken, J.; Barnett, J. J.; Briottet, X.; Carvell, R.; Frohlich, C.; Groom, S. B.; Hagolle, O.; Haigh, J. D.; Kieffer, H. H.; Lean, J.; Pollock, D. B.; Quinn, T.; Sandford, M. C. W.; Schaepman, M.; Shine, K. P.; Schmutz, W. K.; Teillet, P. M.; Thome, K. J.; Verstraete, M. M.; Zalewski, E. Bibcode: 2003AdSpR..32.2253F Altcode: The Traceable Radiometry Underpinning Terrestrial- and Helio- Studies (TRUTHS) mission offers a novel approach to the provision of key scientific data with unprecedented radiometric accuracy for Earth Observation (EO) and solar studies, which will also establish well-calibrated reference targets/standards to support other EO missions. This paper presents the TRUTHS mission and its objectives. TRUTHS will be the first satellite mission to calibrate its EO instrumentation directly to Sl in orbit, overcoming the usual uncertainties associated with drifts of sensor gain and spectral shape by using an electrical rather than an optical standard as the basis of its calibration. The range of instruments flown as part of the payload will also provide accurate input data to improve atmospheric radiative transfer codes by anchoring boundary conditions, through simultaneous measurements of aerosols, particulates and radiances at various heights. Therefore, TRUTHS will significantly improve the performance and accuracy of EO missions with broad global or operational aims, as well as more dedicated missions. The provision of reference standards will also improve synergy between missions by reducing errors due to different calibration biases and offer cost reductions for future missions by reducing the demands for on-board calibration systems. Such improvements are important for the future success of strategies such as Global Monitoring for Environment and Security (GMES) and the implementation and monitoring of international treaties such as the Kyoto Protocol. TRUTHS will achieve these aims by measuring the geophysical variables of solar and lunar irradiance, together with both polarised and unpolarised spectral radiance of the Moon, Earth and its atmosphere. Published by Elsevier Ltd on behalf of COSPAR. Title: Solar irradiance variations Authors: Fröhlich, C. Bibcode: 2003ESASP.535..183F Altcode: 2003iscs.symp..183F Since November 1978 a set of total solar irradiance (TSI) measurements from space is available, yielding a time series of nearly 25 years. From measurements made by different space radiometers (HF on NIMBUS 7, ACRIM I on SMM, ACRIM II on UARS and VIRGO on SOHO) a composite recored of TSI can be constructed. This leads to a reliable record of TSI with an overall precision of the order of ±0.1 Wm-2 over the 25 years. Within this uncertainty no significant secular trend of TSI can be detected. This contrasts the results of the ACRIM composite which does show a significant trend. This difference is analyzed in detail and it can be demonstrated that the assumptions for the ACRIM composite are incorrect. The variability of TSI over the last cycle is characterized by analyzing the statistics of the time series and the behaviour of the power spectrum. Moreover, the composite TSI is compared to a proxy model based on sunspot darkening and brightening due to faculae and network, both in terms of time series and in frequency space. Since early 1996 spectral measurements by filter-radiometers of VIRGO provide continuous time series of spectral solar irradiance (SSI) at 402, 500 and 862 nm. These time series are analyzed and compared to TSI providing detailed information about the redistribution of energy within the spectrum during changes of TSI. Title: A Small Institute with a Heart as Big as the Sun Authors: Fröhlich, Claus Bibcode: 2002ESASP1261...97F Altcode: 2002ses..book...97F No abstract at ADS Title: Solar irradiance variability and climate Authors: Fröhlich, C.; Lean, J. Bibcode: 2002AN....323..203F Altcode: Since November 1978 a complete set of total solar irradiance (TSI) measurements from space is available, yielding a time series of more than 23 years. From measurements made by different space-based radiometers (HF on NIMBUS 7, ACRIM I on SMM, ACRIM II on UARS and VIRGO on SOHO) a composite record of TSI is compiled with an overall precision of order 0.05 Wm-2 and a secular trend uncertainty of +/-3 ppm/year. This time series is compared with an empirical model of irradiance variability based on sunspot darkening and brightening due to faculae and network. From this comparison the model is calibrated and used to estimate possible changes of TSI in the past, using historical proxies of solar activity. For this purpose, stellar observations provide information about the possible range of solar variability over the last millennium when changes of Earth's climate are well documented. Together, the paleo solar and climate data enable a discussion of the extent of global climate change that can be explained by a variable Sun. Title: Estimation of the ozone and temperature sensitivity to the variation of spectral solar flux Authors: Rozanov, E.; Egorova, T.; Fröhlich, C.; Haberreiter, M.; Peter, T.; Schmutz, W. Bibcode: 2002ESASP.508..181R Altcode: 2002soho...11..181R We have applied a 1-D steady-state radiative-convective model with interactive photochemistry to estimate the sensitivity of temperature and ozone mixing ratio to the observed variability of the extraterrestrial spectral solar irradiance. We have carried out several runs using the spectral solar flux for minimum and maximum solar activity conditions. The results show that the ozone and temperature in the stratosphere are mostly sensitive to the solar flux variations in the spectral area between 200 and 220 nm, where they positively correlate with solar flux intensity. In the upper stratosphere and mesosphere the effects of the solar flux variability in the Lyman-α line and Schumann-Runge band are found to be very important. The obtained results have an implication for the optimal choice of wavelength to be measured from a satellite and for the understanding of what kind of radiation code should be used in a GCM aimed to study solar-climate connections. Title: Total solar and spectral irradiance variations from solar cycles 21 to 23 Authors: Pap, J. M.; Turmon, M.; Floyd, L.; Fröhlich, C.; Wehrli, Ch. Bibcode: 2002AdSpR..29.1923P Altcode: Total solar and UV irradiances have been measured from various space platforms for more than two decades. More recently, observations of the "Variability of solar IRradiance and Gravity Oscillations" (VIRGO) experiment on SOHO provided information about spectral irradiance variations in the near-UV at 402 nm, visible at 500 nm, and near-IR at 862 nm. Analyses based on these space-borne irradiance measurements have convinced the skeptics that solar irradiance at various wavelengths and in the entire spectrum is changing with the waxing and waning solar activity. The main goal of this paper is to review the short- and long-term variations in total solar and spectral irradiances and their relation to the evolution of magnetic fields from solar cycles 21 to 23. Title: A discussion of recent evidence for solar irradiance variability and climate Authors: Pap, Judit; Fröhlich, Claus; Kuhn, Jeff; Sofia, Sabatino; Ulrich, Roger Bibcode: 2002AdSpR..29.1417P Altcode: One of the over-arching questions, among others, to be addressed by studying Sun-Earth connections is: "Is the climate changing in a way we can understand and predict?" The Earth's climate is the result of a complex and incompletely understood system of external inputs and interacting parts. Climate change can occur over a range of time scales, may be driven by natural variability, including solar variability, and/or anthropogenic causes and may be identified through the study of a variety of measurable parameters. Global climate change in response to human influences is one of the pressing threats facing science today. However, many of the external factors that govern our climate, including solar variability, cannot be adequately determined from existing operational observations. Since the Sun is the fundamental source of energy that sustains life on Earth, establishing its radiation environment, controls its temperature and atmospheric composition, the accurate knowledge of the solar radiation received by the Earth and understanding of its variability are critical for environmental science and climate studies. In this paper we point out the necessity of a new strategy, i.e., to study global solar properties, such as solar irradiance, solar shape, shape oscillations, and radius, to better understand the origin of solar-induced climate changes. Title: ISCS Working Group1 Activities Authors: Pap, J.; Frohlich, C. Bibcode: 2002cosp...34E.493P Altcode: 2002cosp.meetE.493P International Solar Cycle Study,Working Group 1, "Solar Energy Flux Variations: From the Interior to the Outer Atmosphere" is concerned about measuring and analyzing solar irradiance variations and their underlying physical mechanisms. In this paper we report the latest results on WG 1 activities, i.e., the variations of solar total irradiance and spectral irradiance from EUV to infrared. The most interesting result is that while solar cycle 23 was relatively weak compared to the previous two cycles as far as sunspots are concerned, both total and UV irradiances reached about the same maximum level than during cycle 22. The implications of this observation will be discussed. A summary of future irradiance measurements, plans, perspectives and organization efforts will also be presented. Title: Long-term solar irradiance variations: results and perspectives Authors: Pap, J.; Fleck, B.; Frohlich, C.; Jones, H.; Kuhn, J.; Schmutz, W. Bibcode: 2002cosp...34E.553P Altcode: 2002cosp.meetE.553P In this paper we show the recent result on irradiance variations and their relation to solar magnetic activity over solar cycles 21 to 23. Comparison of the multi-decade long irradiance and magnetic field measurements indicates that the shape and magnitude of irradiance variations are different from that of magnetic indices. Specifically, while magnetic indices show that solar cycle 23 is weaker than the two previous cycles, the long-term variation of total solar irradiance over solar cycles 21 to 23 is rather symmetrical, showing that its maximum and minimum levels were about the same within their measuring uncertainties. These results raise questions like: (1) is there a strict linear relationship between solar variability and irradiance variations as the current irradiance models used in climate studies assume?; (2) what is the role of polar magnetic fields in irradiance changes?; (3) is there a significant non-magnetic component in the observed irradiance variations? The results presented in this paper underscore the need to further develop new measurement and analysis techniques to study and predict the climate impact of solar variability. Title: Total solar irradiance variations since 1978 Authors: Fröhlich, Claus Bibcode: 2002AdSpR..29.1409F Altcode: A composite record of solar total irradiance compiled from measurements made by five independent space-based radiometers since 1978 is the basis for an evaluation of the influence of solar activity on total solar irradiance. An empirical model that parameterizes the combined influences of dark sunspots and bright faculae features on solar irradiance is able to explain more than 95% of the variance. After removing the magnetic influence with the model, the remaining 'quiet sun' shows no trend over the whole period, indicating that the sun has not changed over the past two solar cycles. The inclusion of p-mode frequency changes in the model does not explain more than already expained by the magnetic parameters. Title: Preface Authors: Fröhlich, Claus; Pap, Judit M. Bibcode: 2002AdSpR..29.1879F Altcode: No abstract at ADS Title: International Solar Cycle Studies (ISCS), "Solar Energy Flux Study: from the interior to the outer layer" — Working Group 1 report Authors: Pap, Judit; Fröhlich, Claus Bibcode: 2002AdSpR..29.1571P Altcode: The purpose of this report is to describe the research activities and plans of Working Group 1: "Solar Energy Flux Study: From the Interior to the Outer Layer" of the International Solar Cycle Study (ISCS), which is an international research organization operating under the auspices of the Scientific Committee on Solar-Terrestrial Physics (SCOSTEP). As part of the report, we also summarize the status of the measurements and results on the solar energy flux variations. The main objective of ISCS's Working Group 1 is to coordinate and support comprehensive international research of the variations in the solar energy flux during the rising portion and maximum of solar cycle 23. The research activities of ISCS's Working Group 1 will concentrate on the following tasks: (1) to measure and study the variations in the solar radiative and mass output and solar activity indices during the solar activity cycle, (2) to understand why the solar radiative and mass output and the solar activity indices vary during the solar cycle, and (3) to study the role of solar variability in solar-terrestrial changes and its contribution to global change. ISCS WG1 "Solar Energy Flux Study: From the Interior to the Outer Layer" has been divided into three panels: •| Panel 1: Variations in Total and Spectral Irradiance from Infrared to Far UV. Panel leaders: Martin Anklin of the Physikalisch-Meteorologishes Observatorium Davos, Switzerland (total irradiance), Gerard Thuillier of the Service d'Aeronomie-CNRS, Verrieres, France (visible and infrared), and Linton Floyd of the Naval Research Laboratory, Washington, DC, USA (ultraviolet).

•| Panel 2: Variations in EUV, X-ray and Particle Fluxes. Panel leaders: Gerhard Schmidtke of Fraunhofer IPM, Freiburg, Germany and W. Kent Tobiska of FDC/Jet Propulsion Laboratory, Pasadena, CA, USA (EUV/XUV), and David Winningham of the Southwest Research Institute, San Antonio, TX, USA (particles).

•| Panel 3: Solar Indices, Cosmogenic Isotopes, Solar-Stellar Relations. Panel leaders: Gary Chapman of the San Fernando Observatory, CSUN, Northridge, CA, USA (solar indices), Juerg Beer of Institute for Environmental Science and Technology, Dübendorf, Switzerland (cosmogenic isotopes), and Sallie Baliunas of the Harvard Smithsonian Center for Astrophysics, Cambridge, MA, USA (solar-stellar relations).

The first two panels concentrate on solar energy flux measurements, whereas the third panel concentrates on solar indices and alternative ways to model and predict irradiance variations at various wavelengths and their terrestrial/climate effects. Working Group 1 of ISCS has supported and adopted the "Thermospheric-Ionospheric Geospheric Research (TIGER)" program as part of ISCS/WG1/Panel 2. The main objectives of TIGER are to measure, model, and interpret solar EUV/UV and particle fluxes and to study and model their effect on the Earth's thermosphere and ionosphere (see details by Schmidtke et al., 2001, this volume). This approach links ISCS/WG1 activities directly with studies of our space environment. Title: SIM3D: Solar Irradiance Monitor-3D-view Authors: Schmutz, W.; Fröhlich, C.; Rüedi, I.; Roth, H.; Wehrli, Ch.; Wyss, J. Bibcode: 2001ESASP.493..447S Altcode: 2001sefs.work..447S No abstract at ADS Title: Variations of solar spectral irradiance from near UV to the infrared-measurements and results Authors: Fligge, M.; Solanki, S. K.; Pap, J. M.; Fröhlich, C.; Wehrli, C. Bibcode: 2001JASTP..63.1479F Altcode: 2001JATP...63.1479F Solar spectral irradiance variations are known to exhibit a strong wavelength dependence with the amount of variability increasing towards shorter wavelengths. The bulk of solar radiation is emitted at visible and infrared wavelengths. Thus, the spectral radiation length of 300nm accounts for 99% of the total solar radiative output. Deposited in the Earth's troposphere and biosphere, this part of the solar irradiance spectrum determines direct solar radiative forcing and is therefore of particular interest for climate studies. First, measurements of solar irradiance and irradiance variability from near UV to the IR are reviewed with particular emphasis on the results obtained from the Variability of Irradiance and Gravity Oscillations (VIRGO) on SOHO and Solar Spectrum Measurement (SOLSPEC) instruments. In the second part a model is presented which describes solar spectral irradiance variations in terms of the changing distribution of solar surface magnetic features. Title: Low-Order p Modes From Virgo Irradiance Data Authors: Finsterle, W.; Fröhlich, C. Bibcode: 2001SoPh..200..393F Altcode: Several candidates for low-order p modes (n ≤ 5) and possibly g modes were found by applying mode-detection techniques such as multivariate spectral regression analysis and time-frequency analysis to the VIRGO full-disc solar irradiance data. Three out of the candidates for low-order p modes could be confirmed by significant peaks in the un-treated power spectra in good agreement with theoretical predictions. The frequency of a fourth candidate for a low-order p mode lies some 2.8 μHz below the predicted frequency. The candidates found for g modes are less reliable, since none of them could be confirmed neither by significant peaks in the un-treated power spectra nor by the detection of multiplets. Title: VIRGO Radiometry and Total Solar Irradiance 1996-2000 Revised Authors: Fröhlich, C.; Finsterle, W. Bibcode: 2001IAUS..203..105F Altcode: Total solar irradiance (TSI) observations show a very short solar minimum in early 1996. The increase of TSI starts well before those of other activity parameters such as the magnetic field or the MgII index. Thus the onset of solar cycle 23 seems to be quite different from the last one in 1987. Models based on PSI and MgII-Index are unable to explain this behaviour whereas they accounted for over 90% of the variance over the period of the minimum in the 1985-87 time frame followed by the increase into cycle 22. Possible explanations for this behaviour are proposed. Title: Dependence on azimuthal order of the amplitudes of low-degree p modes Authors: Fröhlich, C.; Appourchaux, T.; Gough, D. O. Bibcode: 2001ESASP.464..629F Altcode: 2001soho...10..629F The m-dependence of the amplitudes of the multiplets of low-degree p modes contains information about the latitudinal distribution of the power in the excitation of the oscillations. We present estimates of those amplitudes from 4 years of VIRGO/LOI observations. Variation of the excitation with magnetic activity is studied. Title: Using Precise Solar Limb Shape Measurements to Study the Solar Cycle Authors: Kuhn, J. R.; Floyd, L.; Fröhlich, C.; Pap, J. M. Bibcode: 2000SSRv...94..169K Altcode: Despite 20 years of total solar irradiance measurements from space, the lack of high precision spatially resolved observations limits definitive answers to even simple questions like ``Are the solar irradiance changes caused solely by magnetic fields perturbing the radiative flux at the photosphere?" More subtle questions like how the aspheric structure of the sun changes with the magnetic cycle are only now beginning to be addressed with new tools like p-mode helioseismology. Solar 5-min oscillation studies have yielded precise information on the mean radial interior solar structure and some knowledge about the rotational and thermal solar asphericity. Unfortunately this progress has not been enough to generate a self-consistent theory for why the solar irradiance and luminosity vary with the magnetic cycle. We need sharper tools to describe and understand the sun's global aspheric response to its internal dynamo, and we need to be able to measure the solar cycle manifestation of the magnetic cycle on entropy transport from the interior to the photosphere in much the same way that we study the fundamentally more complex problem of magnetic flux transport from the solar interior. A space experiment called the Solar Physics Explorer for Radius, Irradiance and Shape (SPHERIS) and in particular its Astrometric and Photometric Telescope (APT) component will accomplish these goals. Title: Observations of Irradiance Variations Authors: Fröhlich, Claus Bibcode: 2000SSRv...94...15F Altcode: Since November 1978 a complete set of total solar irradiance (TSI) measurements from space is available, yielding a time series of 21 years. From measurements made by different space radiometers (HF on NIMBUS-7, ACRIM I on SMM, ACRIM II on UARS and VIRGO on SOHO) a composite record of TSI can be compiled. The corrections which are needed for each radiometer, mainly to compensate for degradation, but also for operational influences are described. ACRIM I (1980-1989) and ACRIM II (1992-1995) are taken as reference because their degradation was monitored by inflight comparisons with spare radiometers; since 1996 VIRGO is used as reference. The scale of ACRIM II is adjusted to ACRIM I by comparison with NIMBUS-7 and ERBE. The reliability of this adjustment depends strongly on the stability of the HF and ERBE radiometer during the period of the gap between the ACRIMs which is discussed in detail together with an assessment of the overall precision of the composite. Title: Observational Upper Limits to Low-Degree Solar g-Modes Authors: Appourchaux, T.; Fröhlich, C.; Andersen, B.; Berthomieu, G.; Chaplin, W. J.; Elsworth, Y.; Finsterle, W.; Gough, D. O.; Hoeksema, J. T.; Isaak, G. R.; Kosovichev, A. G.; Provost, J.; Scherrer, P. H.; Sekii, T.; Toutain, T. Bibcode: 2000ApJ...538..401A Altcode: Observations made by the Michelson Doppler Imager (MDI) and Variability of solar IRradiance and Gravity Oscillations (VIRGO) on the Solar and Heliospheric Observatory (SOHO) and by the ground-based Birmingham Solar Oscillations Network (BiSON) and Global Oscillations Network Group (GONG) have been used in a concerted effort to search for solar gravity oscillations. All spectra are dominated by solar noise in the frequency region from 100 to 1000 μHz, where g-modes are expected to be found. Several methods have been used in an effort to extract any g-mode signal present. These include (1) the correlation of data-both full-disk and imaged (with different spatial-mask properties)-collected over different time intervals from the same instrument, (2) the correlation of near-contemporaneous data from different instruments, and (3) the extraction-through the application of complex filtering techniques-of the coherent part of data collected at different heights in the solar atmosphere. The detection limit is set by the loss of coherence caused by the temporal evolution and the motion (e.g., rotation) of superficial structures. Although we cannot identify any g-mode signature, we have nevertheless set a firm upper limit to the amplitudes of the modes: at 200 μHz, they are below 10 mm s-1 in velocity, and below 0.5 parts per million in intensity. The velocity limit corresponds very approximately to a peak-to-peak vertical displacement of δR/Rsolar=2.3×10-8 at the solar surface. These levels which are much lower than prior claims, are consistent with theoretical predictions. Title: Solar Variability and Climate Authors: Friis-Christensen, E.; Fröhlich, C.; Haigh, J. D.; Schüssler, M.; Von Steiger, R. Bibcode: 2000svc..book.....F Altcode: No abstract at ADS Title: Total Solar Irradiance from VIRGO on SOHO Authors: Fröhlich, C.; Finsterle, W. Bibcode: 2000ESASP.463..665F Altcode: 2000sctc.proc..665F No abstract at ADS Title: Using Precise Solar Limb Shape Measurements to Study the Solar Cycle Authors: Kuhn, J. R.; Floyd, L.; Fröhlich, C.; Pap, J. M. Bibcode: 2000svc..book..169K Altcode: No abstract at ADS Title: Influence of snow and clouds on erythemal UV radiation: Analysis of Swiss measurements and comparison with models Authors: Renaud, Anne; Staehelin, Johannes; Fröhlich, Claus; Philipona, Rolf; Heimo, Alain Bibcode: 2000JGR...105.4961R Altcode: Global, direct and diffuse measurements of erythemal UV radiation with UV-Biometer and radiative transfer calculations are used to estimate the influences of (1) a snow-covered surface, (2) an overcast sky, and (3) a joined snow-covered surface and overcast sky at Davos (1610 m asl, Swiss Alps). The influence of total ozone, zenith angle, and aerosol are first investigated. The influence of surface albedo and clouds are then estimated as a function of the zenith angle after normalization of the data to a fixed ozone amount. If the ground is covered with snow on clear-sky days at Davos, erythemal irradiance increases by 15 to 25% due to multiple reflections between the surface and the atmosphere. This relative increase may reach 80% on overcast days. The highly significant dependence of the albedo on solar elevation is most probably due to inhomogeneities in the surrounding terrain leading to a strong non-Lambertian behavior. The impact of clouds on radiation is highly variable: on overcast days with a snow free surface, erythemal UV radiation at Davos is reduced to a level ranging between 8% (very thick cloud cover) and 70% (thin cloud layer) relative to the radiation under clear-sky conditions. Title: Observations of Irradiance Variations Authors: Fröhlich, Claus Bibcode: 2000svc..book...15F Altcode: No abstract at ADS Title: Total Solar and Spectral Irradiance Measured in France during a Stratospheric Balloon Flight Authors: Anklin, M.; Wehrli, C.; Fröhlich, C.; Pepe, F. Bibcode: 1999ESASP.437..537A Altcode: 1999erbp.conf..537A No abstract at ADS Title: Spectral and Total Solar Irradiance Measurements on Board the International Space Station Authors: Thuillier, G.; Fröhlich, C.; Schmidtke, G. Bibcode: 1999ESASP.433..605T Altcode: 1999uiss.conf..605T No abstract at ADS Title: Total solar irradiance variations Authors: Pap, J. M.; Fröhlich, C. Bibcode: 1999JASTP..61...15P Altcode: 1999JATP...61...15P Total solar irradiance has been monitored from space for nearly two decades. These space-borne observations have established conclusively that total solar irradiance changes over a wide range of periodicities-from minutes to the 11-year solar cycle. Since the total energy flux of the Sun is the principal driver for all Earths atmospheric phenomena, the accurate knowledge of the solar radiation received by the Earth and its variations is an extremely important issue. In this paper we review the long-term variations of total solar irradiance during solar cycles 21 and 22. We conclude that, within the current accuracy and precision of the measurements, the minimum level of total solar irradiance is about the same for both solar cycles 21 and 22. Title: What do VIRGO results tell about the solar interior and atmosphere Authors: Fröhlich, Claus Bibcode: 1999AdSpR..24..157F Altcode: The more than two years of observations from VIRGO (Variability of solar IRradiance and Gravity Oscillations) yield a unique data set covering the activity minimum and the rising part of solar cycle 23. This allows not only to determine the influence of varying activity on the solar oscillation frequencies and amplitudes, but also to study the relationship between oscillations and irradiance variability. Title: Variations in total solar and spectral irradiance as measured by the VIRGO experiment on SOHO Authors: Pap, Judit; Anklin, Martin; Fröhlich, Claus; Wehrli, Christoph; Varadi, Ferenc; Floyd, Linton Bibcode: 1999AdSpR..24..215P Altcode: The Variability IRradiance Gravity Oscillation (VIRGO) experiment on SOHO has been observing total solar and spectral irradiances at 402 nm (blue channel), 500 nm (green channel), and 862 nm (red channel) since January 1996. The VIRGO observations have shown that solar active regions influence both total and spectral irradiances in a similar fashion, although the amplitude of the variations seems to be the largest for the near-UV and visible wavelengths. Comparison of the VIRGO total solar irradiance and the UARS/SUSIM Mg II h & k core-to-wing ratio shows that total irradiance started to rise in prior to UV irradiance, as represented by the Mg core-to-wing ratio. In this paper we review the most recent results on the VIRGO irradiance variations related to solar activity. We dedicate this paper to the memory of Dr. Guenther Brueckner, the late Principal Investigator of the UARS/SUSIM experiment, who will always remain in the heart and memory of the authors of this paper. Title: PICARD: simultaneous measurements of the solar diameter, differential rotation, solar constant and their variations Authors: Damé, Luc; Hersé, Michel; Thuillier, Gérard; Appourchaux, Thierry; Crommelynck, Dominique; Dewitte, Steven; Joukoff, Alexandre; Fröhlich, Claus; Laclare, Francis; Delmas, Christian; Boumier, Patrick Bibcode: 1999AdSpR..24..205D Altcode: PICARD is a CNES micro-satellite mission due for flight by the end of 2002, named after the name of a French astronomer who first observed with consistency the solar diameter changes during the Maunder minimum in the 16th century. It consists of two instruments measuring (i) the solar diameter and differential rotation, and (ii) the total solar irradiance. These quantities are fundamental for the understanding of the solar-Terrestrial relations, e.g. the influence of the Sun on the Earth's climate, and of the internal structure of the Sun. The continuous - or nearly continuous - viewing of the Sun from an appropriate orbit, the 5 minutes sampling rate and the very low noise measurements, will allow g-modes detection and precise diameter measurements besides accurately establishing the relationship between irradiance and diameter changes. Providing an absolute measure of the solar diameter to 1 milliarcsecond, PICARD is the first step towards instruments capable of accurate and perennial measurements, for the centuries to come, of the solar-terrestrial influence. The objectives of the mission, instrument capabilities, observing modes and performances are described. Title: Preface Authors: Fröhlich, Claus; Foing, Bernard Bibcode: 1999AdSpR..24..135F Altcode: No abstract at ADS Title: The Sun's total irradiance: Cycles, trends and related climate change uncertainties since 1976 Authors: Fröhlich, Claus; Lean, Judith Bibcode: 1998GeoRL..25.4377F Altcode: A composite record of the Sun's total irradiance compiled from measurements made by five independent space-based radiometers since 1978 exhibits a prominent 11-year cycle with similar levels during 1986 and 1996, the two most recent minimum epochs of solar activity. This finding contradicts recent assertions of a 0.04% irradiance increase from the 1986 to 1996 solar minima and suggests that solar radiative output trends contributed little of the 0.2°C increase in the global mean surface temperature in the past decade. Nor does our 18-year composite irradiance record support a recent upward irradiance trend inferred from solar cycle length, a parameter used to imply a close linkage in the present century between solar variability and climate change. Title: APT: an astrometric and photometric telescope Authors: Kuhn, Jeff R.; Bush, Rock I.; Coulter, Roy; Froehlich, Claus; Gwo, Dz-Hung; Jones, A.; Pap, Judit M.; Scherrer, Philip H.; Sofia, Sabatino; Ulrich, Roger Bibcode: 1998SPIE.3442..203K Altcode: Helioseismic and precise solar photometric measurements reveal that the Sun varies globally as a start during the source of an 11 year solar cycle. To understand the physical mechanisms of the magnetic cycle in the solar interior we must learn how to measure the tiny changes in the Sun's global properties, like its radius, internal temperature distribution and surface luminosity. The SoHO/MDI experimental has proven that exceedingly small solar shape fluctuations are measurable from outside our atmosphere. We describe here an instrument which will not only measure limb shape oscillations with unprecedented accuracy, but it will also detect solar radius changes with heretofore unachieved accuracy and precision. Variations in these parameters are caused by physical changes, both in the photosphere and the deep solar interior. Solar radius and shape observations will teach us how the Sun's convective envelope responds to emergent energy fluctuations. The determination of this outer boundary condition is essential to understand the solar total irradiance and luminosity variations. Title: Asymmetry and Frequencies of Low-Degree p-Modes and the Structure of the Sun's Core Authors: Toutain, T.; Appourchaux, T.; Fröhlich, C.; Kosovichev, A. G.; Nigam, R.; Scherrer, P. H. Bibcode: 1998ApJ...506L.147T Altcode: An accurate determination of the frequencies of low-degree solar p-modes is an important task of helioseismology. Using 679 days of solar oscillation data observed in Doppler velocity and continuum intensity from two Solar and Heliospheric Observatory instruments (the Michelson Doppler Imager and the SunPhotoMeter), we show that fitting the spectra with Lorentzian profiles leads to systematic differences between intensity and velocity frequencies as large as 0.1 μHz for angular degrees l=0, 1, and 2 because of the opposite asymmetry between intensity and velocity. We use a physics-based asymmetrical line shape to fit p-mode lines, and we demonstrate that their asymmetry is statistically significant and that frequency differences are considerably reduced. These measurements provide more accurate estimates of the solar eigenfrequencies. We discuss inferences of the structure of the solar core. Title: A model of solar total and spectral irradiance variations Authors: Fligge, M.; Solanki, S. K.; Unruh, Y. C.; Froehlich, C.; Wehrli, Ch. Bibcode: 1998A&A...335..709F Altcode: We model solar spectral irradiance variations under the assumption that they are produced by sunspots and faculae alone. The model is based on three components, i.e. quiet Sun, assumed to be temporally invariant, sunspots and faculae whose temporal variations are mimicked using time series of sunspot areas and Mg II core-to-wing ratios. The detailed flux spectrum for each component is employed. The results are compared to spectral irradiance measurements at 402 nm, 500 nm and 862 nm obtained between February 22 and December 31, 1996 by the three-channel sunphotometers (SPM) which are part of the VIRGO package onboard SOHO. Our model shows a good correlation with the measured variations of the three colour channels and of the total irradiance. Since it also successfully reproduces changes in the UV spectral irradiance, irradiance variations and observed variations of the faculae-to-spots filling factor ratio since 1978, our model supports earlier suggestions that a large part of the solar irradiance variations is caused by magnetic fields at the solar surface. Finally, we use the model to test whether the difference between the magnitude of solar and stellar brightness variations reported by Lockwood et al. (1992) is due to the particular filters they use for their stellar observations. Our results suggest that this effect can explain only a small part of the discrepancy. Title: Foreword Authors: Fröhlich, C.; Huber, M. C. E.; Solanki, S. K.; von Steiger, R. Bibcode: 1998SSRv...85...11F Altcode: No abstract at ADS Title: Assessment of Degradation of VIRGO Radiometers on Board SOHO Authors: Anklin, M.; Frohlich, C.; Finsterle, W.; Crommelynck, D. A.; Dewitte, S. Bibcode: 1998Metro..35..685A Altcode: No abstract at ADS Title: Line Asymmetry of VIRGO and MDI Low-Degree p Modes Authors: Toutain, T.; Appourchaux, T.; Frohlich, C.; Kosovichev, A.; Rakesh, N.; Scherrer, P. Bibcode: 1998ESASP.418..973T Altcode: 1998soho....6..973T Using continuous time series of 610 days of velocity (MDI, LOI-proxy) and intensity (VIRGO, SPM and LOI) we show that Lorentzian profiles as a model of low-degree p-mode line leads to systematic differences in the determination of intensity and velocity mode frequencies. These differences, as large as 0.1 muHz for degrees l = 0, 1, 2 and 3, are frequency-dependent. The use of a physics-based asymmetrical line shape (Rakesh et al., 1998) to fit the same lines has allowed us to significantly reduce differences in the frequency determination. P-mode lines in velocity exhibit a significant negative asymmetry (excess of power in the left wing) whereas p-modes lines in intensity have a positive asymmetry (excess of power in the right wing). The magnitude and sign of this asymmetry are directly related to the location of the source of p-mode excitation and to the correlation between mode and solar noise. Title: Solar Composition and Its Evolution -- From Core to Corona Authors: Fröhlich, C.; Huber, M. C. E.; Solanki, S. K.; von Steiger, R. Bibcode: 1998sce..conf.....F Altcode: No abstract at ADS Title: Total Solar Irradiance: Present Knowledge and Future Needs Authors: Fröhlich, C.; Lean, J. Bibcode: 1998ESASP.417..239F Altcode: 1998cesh.conf..239F No abstract at ADS Title: Importance of Monitoring Solar Global Properties: Luminosity, Radius and Oscillations Authors: Pap, J. M.; Kuhn, J. R.; Fröhlich, C.; Ulrich, R.; Jones, A.; Rozelot, J. P. Bibcode: 1998ESASP.417..267P Altcode: 1998cesh.conf..267P No abstract at ADS Title: Solar irradiance variations during Solar Cycle 22 from ACRIM II, SOVA and VIRGO Radiometry Authors: Froehlich, C.; Anklin, M.; Crommelynck, D.; Finsterle, W.; Willson, R. C. Bibcode: 1998IAUS..185...89F Altcode: The radiometers on UARS (ACRIM II), on EURECA (SOVA) and on SOHO (VIRGO) cover the solar irradiance from the maximum cyle 22 to the minimum. Results from the comparison of the 3 experiments will be presented together with a discussion of the variability during the cycle with special emphasis on the amplitude of the cycle variation. This result will also be compared with the previous cycle. Title: Time Dependence of Solar Noise Observed with VIRGO Authors: Andersen, Bo; Leifsen, Torben; Appourchaux, Thierry; Frohlich, Claus; Jiménez, Antonio; Wehrli, Christoph Bibcode: 1998ESASP.418...83A Altcode: 1998soho....6...83A The effect of non- and quasiperiodic solar surface structures dominate the power spectra of solar irradiance and radiance over a broad range of time scales. Only in the p-mode region above about 2 mHz and in the rotationally dominated region below about 3 μ Hz there seems to be narrow stationary peaks. The solar background signal, or solar noise has clear large scale quasi-stationary structures that seems to be closely correlated to the combination of timescales and contrasts of the solar surface sources. The dominant sources are the solar granulation and supergranulation. The solar noise determines the detection limit in the search for g-modes. Thus an increased understanding of it may be helpfull in this search. In addition this understanding will be usefull to determine the properities of stellar small scale surface structures from the data from future asteroseismology space missions. In this study we use the VIRGO data to study the time variation of the solar noise with timescales from about one day to about one year. Title: Solar Electromagnetic Radiation Study for Solar Cycle 22. Proceedings. SOLERS22 Workshop, Sakramento Peak, Sunspot, NM (USA), 17 - 21 Jun 1996. Authors: Pap, J. M.; Fröhlich, C.; Ulrich, R. K. Bibcode: 1998SoPh..177.....P Altcode: 1998SoPh..177....1P The following topics were dealt with: the prototype RISE-PSPT instrument, solar total irradiance, solar disk spectral intensity, proxy solar activity studies, solar variability, solar UV activity, EUV irradiance, solar-terrestrial relationships, solar magnetic field, spectroheliogram studies, network and plage regions, solar cycle, solar diameter measurements, solar wind, prominences and coronal activity, coronal holes and polar field reversals, magnetograms, reconnection, nanoflares, radio burst chains, and gyrosynchrotron radiation. Title: Statistical Properties of the Amplitude Modulation of Solar p-Modes Authors: Andersen, Bo; Aarset, Magne; Leifsen, Torben; Appourchaux, Thierry; Frohlich, Claus; Hoeksema, J. T.; Jiménez, Antonio; Toutain, Thierry Bibcode: 1998ESASP.418..897A Altcode: 1998soho....6..897A The low degree solar p-modes show amplitude modulation at all observable timescales. For some modes a large fraction of this modulation seems to be correlated to the solar rotation. For other modes there seems to be little or no deterministic component in the modulation. Only intermittent correlation between the modulation of different modes have been observed. This is to be expected if the excitation of modes is completely stochastic. None of the observational methods observe the modes directly. In different ways they all observe the solar atmospheres response to the modes. This implies that the modes may be modulated by this response. By studying the statistical properties of the different observed modes we attempt to discriminate between variations in the modes themselves and the atmospheric response. In this work we study the statistical properties of the mode amplitude variations for radial order p-modes observed with the VIRGO and SOI/MDI instruments on SOHO. The time scales studied span the region from 0.2 μ Hz to 15 muHz. Here, we are modelling the amplitude modulation, utilising the concepts of state space models, as a stochastic process and study the properties of this model as function of radial order and line width of the modes. Title: Characterization of Solar Noise in Irradiance from VIRGO Authors: Anklin, Martin; Frohlich, Claus; Wehrli, Christopf; Finsterle, Wolfgang Bibcode: 1998ESASP.418...91A Altcode: 1998soho....6...91A Power spectral analysis of measurements of total and spectral solar irradiance show a similar general behavior for periods between two minutes to 50 days as found by Frohlich et al. (1997) with a much shorter time series. While the time series are extended, low frequencies become accessible and the influence of the increasing solar activity can be studied. Furthermore, the temporal variation of the influence of supergranulation, mesogranulation, and granulation is investigated. With multivariate spectral analysis the contribution of three spectral channels, blue, green and red, to the variance of the total channel are determined. The difference in gain of the spectral channels is investigated for the frequency range corresponding to magnetic activity or to convection in the range from supergranulation to granulation. Moreover, the temporal variations of the contribution of each channel to the total is studied. Title: VIRGO on SOHO: Status and Future Prospects Authors: Fröhlich, C.; Scherrer, P.; MDI Team; Virgo Team; Gabriel, A.; GOLF Team Bibcode: 1998ESASP.418....7F Altcode: 1998soho....6....7F After two years of nearly uninterrupted operation, the Michelson Doppler Imager (MDI) instrument has produced many unique data sets that are being used to address a wide variety of topics in solar physics. The more than two years of observations from VIRGO (Variability of solar IRradiance and Gravity Oscillations) yield a unique data set covering the activity minimum and the rising part of cycle 23. This allows not only to determine the influence of varying activity on the solar oscillation frequencies and amplitudes, but also to study the relationship between oscillations and irradiance variability. Over 2 years of GOLF data with nearly 100% continuity are yielding the highest ever signal to noise quality, enabling precise measurements of the frequencies, linewidths and power in the p-modes. The precision available for the inversion of the frequencies in terms of sound speed in the solar interior is no longer limited by the quality of the time-series itself, but rather by questions concerning the most correct method of fitting the observed spectrum. Unique measurements from the GOLF p-mode signals include the high-frequency global structure above the acoustic cut-off and the measurement of the global average magnetic field of the Sun. Several different techniques are being employed in searching for the g-mode signals in the GOLF spectrum. Title: Solar Total Irradiance Variations Authors: Lean, Judith; Frohlich, Claus Bibcode: 1998ASPC..140..281L Altcode: 1998ssp..conf..281L No abstract at ADS Title: SOHO/VIRGO Total Solar and Spectral Irradiance Variations Authors: Pap, J. M.; Frohlich, C.; Anklin, M.; Wehrili, Ch.; Varadi, F.; Floyd, L. Bibcode: 1998ESASP.418..951P Altcode: 1998soho....6..951P No abstract at ADS Title: Modelling Spectral Irradiance Variations obtained by VIRGO Authors: Fligge, M.; Solanki, S. K.; Unruh, Y.; Frohlich, C.; Wehrli, Ch. Bibcode: 1998ASPC..140..311F Altcode: 1998ssp..conf..311F No abstract at ADS Title: Observational Upper Limits for Low-Degree Solar g-modes Authors: Fröhlich, C.; Finsterle, W.; Andersen, B.; Appourchaux, T.; Chaplin, W. J.; Elsworth, Y.; D. O. Gough; Hoeksema, J. T.; Isaak, G. R.; Kosovichev, A. G.; Provost, J.; Scherrer, P. H.; Sekii, T.; Toutain, T. Bibcode: 1998ESASP.418...67F Altcode: 1998soho....6...67F No abstract at ADS Title: Amplitude modulation of radial p-modes from Virgo Authors: Leifsen, T.; Andersen, B. N.; Appourchaux, T.; Frohlich, C.; Jimenez, A.; Toutain, T.; Wehrli, C. Bibcode: 1998IAUS..185..113L Altcode: We present results from wavelet analysis of more than one year of data from the VIRGO Sun Photometers (SPM) and the VIRGO Luminosity Oscillation Imager (LOI) onboard the SOHO spacecraft. The temporal behaviour of p-modes with l=0--2 is presented. The analysis of the l=0 modes show a modulation of the mode amplitudes with the solar rotation. This result is quite surprising as the l=0 modes should not be sensitive to the solar rotation. Possible effects of varying solar activity on the modulation of the mode amplitudes is investigated. The effect of the modulation on the fitting of mode lines and determination of the mode frequencies is also studied. Wavelet analysis has a fundamental limitation in the ability to achieve simultaneous high frequency and time resolution. In order to be able to study the rotationally split components of the l=1 modes with good time resolution, we apply a spatial filtering technique on the LOI data to separate the different components. Title: Solar Electromagnetic Radiation Study for Solar Cycle 22 Authors: Pap, J. M.; Frohlich, C.; Ulrich, R. K. Bibcode: 1998sers.conf.....P Altcode: No abstract at ADS Title: Total Solar Irradiance Monitoring Programs Authors: Fröhlich, Claus Bibcode: 1998sers.conf..391F Altcode: No abstract at ADS Title: Solar composition and its evolution - from core to corona. Proceedings. ISSI (International Space Science Institute) Workshop, Bern (Switzerland), 26 - 30 Jan 1998. Authors: Fröhlich, C.; Huber, M. C. E.; Solanki, S. K.; von Steiger, R. Bibcode: 1998SSRv...85.....F Altcode: The following topics were dealt with: solar composition, solar evolution, the solar interior, helioseismology, photosphere, chromosphere, solar corona, solar wind, the Sun as a Sun-like star. Title: Comparative Studies of Low-Order and Low-Degree Solar p Modes Authors: Appourchaux, T.; Andersen, B.; Chaplin, W.; Elsworth, Y.; Finsterle, W.; Frohlich, C.; Gough, D.; Hoeksema, J. T.; Isaak, G.; Kosovichev, A.; Provost, J.; Scherrer, P.; Sekii, T.; Toutain, T. Bibcode: 1998ESASP.418...95A Altcode: 1998soho....6...95A The amplitudes of solar p-modes decrease steeply with decreasing radial order below about 17. The background solar signal (solar noise) in general increases steadily with decreasing frequency. For the irradiance and radiance measurements with VIRGO or SOI/MDI on SOHO this combination makes it difficult to detect low degree modes below about 1.8 mHz. The solar noise as observed in velocity with SOI/MDI or the ground based BISON network is significantly lower in this region than in intensity measurements. This allows low degree modes to be observed close to 1 mHz. We present results of detection and charaterization of the lowest order observable p-modes both in velocity and intensity measurements. Where applicable the properties of the modes observed with the two methods are compared. Title: The Effect of Amplitude Modulation on Asymmetries of Solar p-Modes Authors: Andersen, Bo; Leifsen, Torben; Appourchaux, Thierry; Frohlich, Claus; Hoeksema, J. T.; Toutain, Thierry Bibcode: 1998ESASP.418..893A Altcode: 1998soho....6..893A The low degree solar p-modes show an asymmetry in their line profiles that both depend on the observational technique and on the radial order of the modes. Typically the modes determined from observations with Doppler shift methods show an asymmetry towards lower frequency while the opposite is the case for modes determined from irradiance and radiance observations. The difference in asymmetry is probably caused by near surface effects. If the modes are fitted with symmetric functions this leads to a systematic shift in the frequency determinations for the two data sets. This may lead to systematic differences in the inversions based on the different frequencies. All the mode amplitudes show significant time variation. The typical centroid frequency also varies with timescales from a few days to the solar cycle. These variations may set absolute limits to the observable accuracy of the frequency determination. These time modulations may influence the observed line profiles and thus the frequency determinations. Here we present results of the effect on the mode asymmetry of the amplitude modulation of low degree modes observed with VIRGO and SOI/MDI. The range in timescales is from a few days to a few solar rotations. Title: Automated Recognition and Characterization of Solar Active Regions Based on the SOHO/MDI Images Authors: Pap, J. M.; Turmon, M.; Mukhtar, S.; Bogart, R.; Ulrich, R.; Fröhlich, C.; Wehrli, Ch. Bibcode: 1997ESASP.415..477P Altcode: 1997cpsh.conf..477P No abstract at ADS Title: Total Solar Irradiance Variations: The Construction of a Composite and its Comparison with Models Authors: Fröhlich, C.; Lean, J. Bibcode: 1997ESASP.415..227F Altcode: 1997cpsh.conf..227F No abstract at ADS Title: Wavelength Dependence of Solar Irradiance Variability from VIRGO Onboard SOHO Authors: Wehrli, C.; Fröhlich, C.; Anklin, M.; Fligge, M.; SOlanki, S. K.; Unruh, Y. Bibcode: 1997ESASP.415..497W Altcode: 1997cpsh.conf..497W No abstract at ADS Title: On the Effect of Active Regions on the Solar Irradiance Authors: Domingo, V.; Sanchez, L.; Appourchaux, T.; Fröhlich, C.; Wehrli, C.; Crommelynck, D.; Pap, J. Bibcode: 1997ESASP.415..469D Altcode: 1997cpsh.conf..469D No abstract at ADS Title: Assessment of Degradation of VIRGO Radiometers Onboard SOHO Authors: Anklin, M.; Fröhlich, C.; Finsterle, W.; Wehrli, C.; Crommelynck, D. A. Bibcode: 1997ESASP.415..459A Altcode: 1997cpsh.conf..459A No abstract at ADS Title: In-Flight Performance of the Virgo Solar Irradiance Instruments on SOHO Authors: Fröhlich, Claus; Crommelynck, Dominique A.; Wehrli, Christoph; Anklin, Martin; Dewitte, Steven; Fichot, Alain; Finsterle, Wolfgang; Jiménez, Antonio; Chevalier, André; Roth, Hansjörg Bibcode: 1997SoPh..175..267F Altcode: The in-flight performance of the total and spectral irradiance instruments within VIRGO (Variability of solar IRradiance and Gravity Oscillations) on the ESA/NASA Mission SOHO (SOlar and Heliospheric Observatory) is in most aspects better than expected. The behaviour during the first year of operation of the two types of radiometers and the sunphotometers together with a description of their data evaluation procedures is presented. Title: Tri-Phonic Helioseismology: Comparison of Solar P Modes Observed by the Helioseismology Instruments Aboard SOHO Authors: Toutain, T.; Appourchaux, T.; Baudin, F.; Fröhlich, C.; Gabriel, A.; Scherrer, P.; Andersen, B. N.; Bogart, R.; Bush, R.; Finsterle, W.; García, R. A.; Grec, G.; Henney, C. J.; Hoeksema, J. T.; Jiménez, A.; Kosovichev, A.; Roca Cortés, T.; Turck-Chièze, S.; Ulrich, R.; Wehrli, C. Bibcode: 1997SoPh..175..311T Altcode: The three helioseismology instruments aboard SOHO observe solar p modes in velocity (GOLF and MDI) and in intensity (VIRGO and MDI). Time series of two months duration are compared and confirm that the instruments indeed observe the same Sun to a high degree of precision. Power spectra of 108 days are compared showing systematic differences between mode frequencies measured in intensity and in velocity. Data coverage exceeds 97% for all the instruments during this interval. The weighted mean differences (V-I) are −0.1 µHz for l=0, and −0.16 µHz for l=1. The source of this systematic difference may be due to an asymmetry effect that is stronger for modes seen in intensity. Wavelet analysis is also used to compare the shape of the forcing functions. In these data sets nearly all of the variations in mode amplitude are of solar origin. Some implications for structure inversions are discussed. Title: Study of the Effect of Active Regions on the Solar Irradiance During Solar Minimum Authors: Domingo, V.; Sanchez, L.; Appourchaux, T.; Froehlich, C.; Wehrli, C.; Hoeksema, T.; Pap, J. Bibcode: 1997SPD....28.0206D Altcode: 1997BAAS...29..893D We have determined both the size of the area that contributes to the solar irradiance increase around an active region and the angular distribution of the radiance excess in it, using data obtained during about one year around solar minimum (April 1996 - April 1997). During the solar minimum and the early raising phase of the new maximum it is possible to study the effect of isolated active regions while there are few of them. The result of this study will be important to separate the contribution of the active regions to the solar irradiance change during the solar cycle from any underlying long term effect, if there is one. The solar radiance measured by the Low-resolution Oscillations Imager (LOI) of the VIRGO instrument and by the MDI instrument aboard SOHO is used to determine the dimension of the radiating area. The increase in irradance is determined by the Sun Photometers (SPM) and Radiometers on the VIRGO instrument. Title: First results from VIRGO on SoHO Authors: Frohlich, C.; Andersen, B. N.; Appourchaux, T.; Berthomieu, G.; Crommelynck, D. A.; Domingo, V.; Fichot, A.; Finsterle, W.; Gómez, M. F.; Gough, D.; Jiménez, A.; Leifsen, T.; Lombaerts, M.; Pap, J. M.; Provost, J.; Roca Cortés, T.; Romero, J.; Roth, H. -J.; Sekii, T.; Telljohann, U.; Toutain, T.; Wehrli, C. Bibcode: 1997IAUS..181...67F Altcode: No abstract at ADS Title: In-Flight Performance of the Virgo Luminosity Oscillations Imager Aboard SOHO Authors: Appourchaux, Thierry; Andersen, Bo N.; Fröhlich, Claus; Jiménez, Antonio; Telljohann, Udo; Wehrli, Christoph Bibcode: 1997SoPh..170...27A Altcode: The Luminosity Oscillations Imager (LOI) is a part of the VIRGO instrument aboard the Solar and Heliospheric Observatory (SOHO). The scientific objective of the LOI experiment is to identify and characterize pressure and internal gravity oscillations of the Sun by observing the radiance variations. The LOI is a low-resolution imager with 12 pixels, for the measurement of the radiance distribution over the solar disk at 500 nm. The low resolution capability of the instrument allows the identification of individual azimuthal orders for l = 0 to 7, without suffering the mixing that affects integrated solar disk instruments. The performance, calibrations and instrumental effects of the LOI are described together with the procedures for extracting the solar p modes. Title: First Results from VIRGO, the Experiment for Helioseismology and Solar Irradiance Monitoring on SOHO Authors: Fröhlich, Claus; Andersen, Bo N.; Appourchaux, Thierry; Berthomieu, Gabrielle; Crommelynck, Dominique A.; Domingo, Vicente; Fichot, Alain; Finsterle, Wolfgang; Gómez, Maria F.; Gough, Douglas; Jiménez, Antonio; Leifsen, Torben; Lombaerts, Marc; Pap, Judit M.; Provost, Janine; Roca Cortés, Teodoro; Romero, José; Roth, Hansjörg; Sekii, Takashi; Telljohann, Udo; Toutain, Thierry; Wehrli, Christoph Bibcode: 1997SoPh..170....1F Altcode: First results from the VIRGO experiment (Variability of solar IRradiance and Gravity Oscillations) on the ESA/NASA Mission SOHO (Solar and Heliospheric Observatory) are reported. The observations started mid-January 1996 for the radiometers and sunphotometers and near the end of March for the luminosity oscillation imager. The performance of all the instruments is very good, and the time series of the first 4-6 months are evaluated in terms of solar irradiance variability, solar background noise characteristics and p-mode oscillations. The solar irradiance is modulated by the passage of active regions across the disk, but not all of the modulation is straightforwardly explained in terms of sunspot flux blocking and facular enhancement. Helioseismic inversions of the observed p-mode frequencies are more-or-less in agreement with the latest standard solar models. The comparison of VIRGO results with earlier ones shows evidence that magnetic activity plays a significant role in the dynamics of the oscillations beyond its modulation of the resonant frequencies. Moreover, by comparing the amplitudes of different components ofp -mode multiplets, each of which are influenced differently by spatial inhomogeneity, we have found that activity enhances excitation. Title: Book Review: The Sun as a variable star ; solar and stellar irradiance variations (IAU colloquium 143) / Cambridge U Press, 1994 Authors: Pap, J. M.; Fröhlich, C.; Hudson, H. D.; Solanki, S. K. Bibcode: 1996SSRv...76..354P Altcode: No abstract at ADS Title: The history of thge SOHO mission. Authors: Huber, M. C. E.; Bonnet, R. M.; Dale, D. C.; Arduini, M.; Fröhlich, C.; Domingo, V.; Whitcomb, G. Bibcode: 1996ESABu..86...25H Altcode: No abstract at ADS Title: Space degradation of SOVA sunphotometers on EURECA. Authors: Wehrli, C.; Fröhlich, C.; Romero, J. Bibcode: 1996Metro..32..653W Altcode: Two sunphotometers with three channels at 862 nm, 500 nm and 335 nm were operated in space for eleven months on board the European Retrievable Carrier (EURECA). Both instruments experienced substantial losses of sensitivity, although the second instrument was exposed 100 times less than the first one. After retrieval of EURECA, the instruments were examined and optically tested. Contamination and degradation of optical components were found, but only small changes in spectral bandpasses. Title: VIRGO: Experiment for Helioseismology and Solar Irradiance Monitoring Authors: Fröhlich, Claus; Romero, José; Roth, Hansjörg; Wehrli, Christoph; Andersen, Bo N.; Appourchaux, Thierry; Domingo, Vicente; Telljohann, Udo; Berthomieu, Gabrielle; Delache, Philippe; Provost, Janine; Toutain, Thierry; Crommelynck, Dominique A.; Chevalier, André; Fichot, Alain; Däppen, Werner; Gough, Douglas; Hoeksema, Todd; Jiménez, Antonio; Gómez, Maria F.; Herreros, José M.; Cortés, Teodoro Roca; Jones, Andrew R.; Pap, Judit M.; Willson, Richard C. Bibcode: 1995SoPh..162..101F Altcode: The scientific objective of the VIRGO experiment (Variability of solar IRradiance and Gravity Oscillations) is to determine the characteristics of pressure and internal gravity oscillations by observing irradiance and radiance variations, to measure the solar total and spectral irradiance and to quantify their variability over periods of days to the duration of the mission. With these data helioseismological methods can be used to probe the solar interior. Certain characteristics of convection and its interaction with magnetic fields, related to, for example, activity, will be studied from the results of the irradiance monitoring and from the comparison of amplitudes and phases of the oscillations as manifest in brightness from VIRGO, in velocity from GOLF, and in both velocity and continuum intensity from SOI/MDI. The VIRGO experiment contains two different active-cavity radiometers for monitoring the solar `constant', two three-channel sunphotometers (SPM) for the measurement of the spectral irradiance at 402, 500 and 862 nm, and a low-resolution imager (LOI) with 12 pixels, for the measurement of the radiance distribution over the solar disk at 500 um. In this paper the scientific objectives of VIRGO are presented, the instruments and the data acquisition and control system are described in detail, and their measured performance is given. Title: Results of solar spectral irradiance measurements by SOVA2 on EURECA Authors: Wehrli, Ch.; Frohlich, C.; Romero, J. Bibcode: 1995AdSpR..16h..25W Altcode: 1995AdSpR..16...25W The solar irradiance has been measured at 3 wavelengths (335, 500 and 862nm) by the experiment SOVA2 from the European Retrievable Carrier (EURECA). The dataset, corrected for instrumental effects and degradation, is examined for solar variability on timescales from minutes to days. Title: The European retrievable carrier (EURECA) as an observing platform from a user's point of view Authors: Wehrli, Ch.; Frohlich, C.; Romero, J. Bibcode: 1995AdSpR..16g..51W Altcode: 1995AdSpR..16...51W The operational environment of EURECA as experienced by the SOVA2 experiment is presented. This experiment has independently measured the solar pointing with a high resolution sun sensor and monitored several temperatures as ancillary parameters to be used in evaluation of the scientific measurements. Results of these measurements are presented and experience with the novel telemetry / telecommand and data retrieval system is commented. Title: Solar total irradiance variability measured by SOVA-2 on board EURECA Authors: Romero, J.; Frohlich, C.; Wehrli, Ch. Bibcode: 1995AdSpR..16h..29R Altcode: 1995AdSpR..16...29R During its 9 months of operation, the experiment SOVA-2 (Solar Constant and Variability) on board the European Retrievable Carrier (EURECA) has measured the total solar irradiance with two radiometers of the type PMO6-R. The solar variability has been investigated by bivariate spectral analysis of the irradiance and the Photometric Sunspot Index (PSI) to account for the sunspot blocking and after removal of the spot influence with the MgII-Index as proxy for the contribution of faculae and other bright magnetic elements. Title: Low Frequency Helioseismology Authors: Fröhlich, C.; Andersen, B. N. Bibcode: 1995ESASP.376a.137F Altcode: 1995heli.conf..137F; 1995soho....1..137F The main objective of low frequency helioseismology is the search for solar g-modes which allows sounding of the core close to the center. The analyses have been based on ground-based observations by the Crimean Astrophysical Observatory, Stanford University, SCLERA, Birmingham University, Instituto Astrofisica de Canarias and on irradiance observations by ACRIM on the US Solar Maximum Mission satellite and IPHIR on the Russian PHOBOS mission. The most intriguing observation from the ground is the 160 minutes oscillation. Its interpretation is still controversial and even the solar origin is questioned. Interpretation of the observed spectra in the range from 45 - 140 μHz is mostly based on asymptotic theory, but the results do not show consistent evidence that g-modes have been unambiguously detected. Title: Virgo: Expriment for Helioseismology and Solar Irradiance Monitoring Authors: Fröhlich, C.; Andersen, B. N. Bibcode: 1995ESASP.376a..83F Altcode: 1995soho....1...83F; 1995heli.conf...83F The scientific objective of the VIRGO experiment (Variability of solar IRradiance and Gravity Oscillations) is to determine the characteristics of pressure and internal gravity oscillations by observing irradiance and radiance variations, to measure the solar total and spectral irradiance and to quantify their variability over periods of days to the duration of the mission. With these data helioseismological methods can be used to probe the solar interior. Certain characteristics of convection and its interaction with magnetic fields, related to, for example, activity, will be studied from the results of the irradiance monitoring and from the comparison of amplitudes and phases of the oscillations as manifest in brightness from VIRGO, in velocity from GOLF, and in both velocity and continuum intensity from SOI/MDI. The VIRGO experiment contains two different active-cavity radiometers for monitoring the solar "constant", two three-channel sunphotometers (SPM) for the measurement of the spectral irradiance at 402, 500 and 862 nm, and a low-resolution imager (LOI) with 12 pixels, for the measurement of the radiance distribution over the solar disk at 500 nm. The scientific objectives of VIRGO are presented, the instruments and the data acquisition and control system are described in detail, and their measured performance is given. Title: VIRGO - the Solar Monitor Experiment on SOHO Authors: Appourchaux, T.; Domingo, V.; Frohlich, C.; Romero, J.; Wehrli, C.; Andersen, B. N.; Berthomieu, G.; Delache, P.; Crommelynck, D.; Jimenez, A.; Roca Cortes, T.; Jones, A. R. Bibcode: 1995ASPC...76..408A Altcode: 1995gong.conf..408A No abstract at ADS Title: Preface Authors: Pap, Judit M.; Fröhlich, Claus; Hudson, Hugh S.; Tobiska, W. Kent Bibcode: 1994SoPh..152D...9P Altcode: No abstract at ADS Title: Improvement of the Photometric Sunspot Index and Changes of the Disk-Integrated Sunspot Contrast with Time Authors: Froehlich, Claus; Pap, Judit M.; Hudson, Hugh S. Bibcode: 1994SoPh..152..111F Altcode: 1994IAUCo.143..111F; 1994svs..coll..111F The photometric sunspot index (PSI) was developed to study the effects of sunspots on solar irradiance. It is calculated from the sunspot data published in theSolar-Geophysical Data catalogue. It has been shown that the formerPSI models overestimate the effect of dark sunspots on solar irradiance; furthermore results of direct sunspot photometry indicate that the contrast of spots depends on their area. An improvedPSI calculation is presented; it takes into account the area dependence of the contrast and calculates 'true' daily means for each observation using the differential rotation of the spots. Moreover, the observations are screened for outliers which improves the homogeneity of the data set substantially, at least for the period after December 1981 when NOAA started to report data from a few instead of one to two stations. A detailed description of the method is provided. The correlation between the newly calculatedPSI and total solar irradiance is studied for different phases of the solar cycles 21 and 22 using bi-variate spectral analysis. The results can be used as a `calibration' ofPSI in terms of gain, the factor by whichPSI has to be multiplied to yield the observed irradiance change. This factor changes with time from about 0.6 in 1980 to 1.1 in 1990. This unexpected result cannot be interpreted by a change of the contrast relative to the quiet Sun (as it is normally defined and determined by direct photometry) but rather as a change of the contrast between the spots and their surrounding as seen in total irradiance (integrated over the solar disk). This may partly be explained by a change in the ratio between the areas of the spots and the surrounding faculae. Title: The sun as a variable star: Solar and stellar irradiance variations Authors: Pap, Judit M.; Froehlich, Claus; Hudson, Hugh S.; Tobiska, W. Kent Bibcode: 1994SoPh..152.....P Altcode: 1994svs..coll.....P; 1994IAUCo.143.....P Variations in solar and stellar irradiances have long been of interest. An International Astronomical Union (IAU) colloquium reviewed such relevant subjects as observations, theoretical interpretations, and empirical and physical models, with a special emphasis on climatic impact of solar irradiance variability. Specific topics discussed included: (1) General Reviews on Observations of Solar and Stellar Irradiance Variability; (2) Observational Programs for Solar and Stellar Irradiance Variability; (3) Variability of Solar and Stellar Irradiance Related to the Network, Active Regions (Sunspots and Plages), and Large-Scale Magnetic Structures; (4) Empirical Models of Solar Total and Spectral Irradiance Variability; (5) Solar and Stellar Oscillations, Irradiance Variations and their Interpretations; and (6) The Response of the Earth's Atmosphere to Solar Irradiance Variations and Sun-Climate Connections. For individual titles, see A95-78168 through A95-78218. Title: Poster Proceedings from IAU Colloquium 143: The Sun as a Variable Star: Solar and Stellar Irradiance Variations Authors: Pap, J. M.; Frohlich, C.; Hudson, H. S.; Solanki, S. K. Bibcode: 1994svsp.coll.....P Altcode: 1994IAUCo.143P....P No abstract at ADS Title: Irradiance Observations of the Sun Authors: Frohlich, C. Bibcode: 1994svsp.coll...28F Altcode: 1994IAUCo.143P..28F No abstract at ADS Title: Relationship between solar activity and luminosity Authors: Fröhlich, Claus Bibcode: 1993AdSpR..13i.429F Altcode: 1993AdSpR..13..429F Measurements of the solar constant - the total irradiance at mean Sun-Earth distance - during the last 12 years from satellites show variations over time scales from minutes to years and decades. The most important variance is in the range from days to several months and is related to the photospheric features of solar activity: decreasing the irradiance during the appearance of sunspots, and increasing it by faculae and the bright magnetic network. Modulation by the 11-year activity cycle is now observed conclusively with the irradiance being higher during solar maximum. All these variations can be explained - at least qualitatively - by their manifestation on the photosphere. Whether the short term variations are luminosity changes cannot be deduced from irradiance observations. For the solar cycle variation the situation is different: simultaneous changes of the solar p-mode frequencies are observed and both effects can be explained qualitatively by the same mechanism. This suggests that the solar cycle related irradiance change can be interpreted as a global phenomenon and is the manifestation of a change in luminosity. Longer term variations can be inferred from stellar observations and the possibility for a solar origin of the little ice-age during the Maunder minimum are explored. Title: Prisma - the First Space Mission to See Inside the Stars Authors: Appourchaux, T.; Gough, D. O.; Catala, C.; Frandsen, S.; Frohlich, C.; Hoyng, P.; Jones, A.; Lemaire, P.; Tondello, G.; Weiss, W. W. Bibcode: 1993ASPC...42..411A Altcode: 1993gong.conf..411A No abstract at ADS Title: PRISMA: Probing Stars from Core to Corona Authors: Appourchaux, T.; Catala, C.; Catalano, S.; Fransden, S.; Fröhlich, C.; Gough, D. O.; Hoyng, P.; Jones, A.; Lemaire, P.; Tondello, G.; Weiss, W. Bibcode: 1993ASSL..183..505A Altcode: 1993pssc.symp..505A No abstract at ADS Title: Results from IPHIR as guideline for asteroseismology Authors: Toutain, T.; Fröhlich, C. Bibcode: 1993ASPC...40..713T Altcode: 1993ist..proc..713T; 1993IAUCo.137..713T No abstract at ADS Title: PRISMA: a new space mission for stellar physics. Authors: Appourchaux, T.; Gough, D.; Hyoyng, P.; Catala, C.; Frandsen, S.; Froehlich, C.; Jones, A.; Lemaire, P.; Tondello, G.; Weiss, W. W. Bibcode: 1993ASPC...40..812A Altcode: 1993ist..proc..812A; 1993IAUCo.137..812A This paper mainly focuses on the scientific objectives that can be achieved with a new space mission of the European Space Agency - PRISMA (Probing Rotation and Interior of Stars: Microvariability and Activity). The scientific objectives can be classified into three areas of interest: (1) Stellar structure and evolution. (2) Stellar atmospheres and magnetic fields. (3) Stellar dynamics and stellar dynamos. Title: Multi-Variate Spectral Analysis of Short-Term Irradiance Variations Authors: Pap, J. M.; Frohlich, C. Bibcode: 1992sers.conf...62P Altcode: No abstract at ADS Title: Solar Irradiance Variability Authors: Frohlich, C. Bibcode: 1992sers.conf....1F Altcode: No abstract at ADS Title: Characteristics of solar p-modes - Results from the IPHIR experiment Authors: Toutain, T.; Froehlich, C. Bibcode: 1992A&A...257..287T Altcode: Solar p-modes were observed in irradiance during more than 160 days by the IPHIR experiment on the USSR PHOBOS Mission in 1988. They are characterized by their frequency, splitting, linewidth, and amplitudes, determined by fitting Lorentzians to the lines. Because of the long uninterrupted time series the frequencies are probably the most accurate available at present. They are compared with results from other observations and theoretical models. Very good agreement is observed with a recent standard model, MHD-S2, of Christensen-Dalsgaard (1991), for both the absolute frequencies (less than 3 micro-Hz) and the difference delta (02) = nu(n,0) - nu(n-1,2) (less than 0.15 micro-Hz), which means that the standard solar model is a good approximation to the real sun and that the solution to the 'Neutrino Puzzle' has to be sought from particle physics. From the splittings of the l = 1 and 2 modes the rotation of the core (0.0 - 0.2) is inferred to about 4.6 times the surface rate. The damping of p-modes is determined from the linewidths; lifetimes between 24 and 2 days are found for n = 16...26. Title: Rotation of the Sun's Core Authors: Goode, Philip R.; Frohlich, Claus; Toutain, Thierry Bibcode: 1992ASPC...27..282G Altcode: 1992socy.work..282G No abstract at ADS Title: Multi-Variate Spectral Analysis of Solar Irradiance Variations Authors: Pap, J. M.; Frohlich, C. Bibcode: 1991BAAS...23Q1069P Altcode: No abstract at ADS Title: The helioseismology experiment on the Phobos planetary mission. Preliminary results Authors: Frohlich, C.; Bonnet, R. M.; Bruns, A. V.; Vial, J. C.; Delaboudiniere, J. P.; Domingo, V.; Kollath, Z.; Kotov, V. A.; Rachkovskii, D. N.; Wehrli, Ch.; Toulain, T.; Shumko, S. M. Bibcode: 1991BCrAO..83...18F Altcode: No abstract at ADS Title: The Solar Variations (SOVA) experiment in the EURECA space platform Authors: Crommelynck, D.; Domingo, V.; Fröhlich, C. Bibcode: 1991AdSpR..11d..83C Altcode: 1991AdSpR..11Q..83C The Solar Variations (SOVA) experiment aboard EURECA will measure the total and spectral irradiance of the Sun, and their variations. Aims of the experiment are: - to study the short term (hours to months) variations of the solar irradiance for the investigation of the mechanisms of energy redistribution in the convection zone, - to study periodic fluctuations, with periods between a few minutes and several hours, for helioseismology and, - to measure the absolute value of the solar constant to determine its long term variations when compared with previous and future measurements. Two absolute active cavity radiometers of different design will measure independently the value of the total solar irradiance, one relative radiometer will measure the variations of the total solar irradiance and five photometers will measure the variations of the spectral irradiance in 5-nm wide wavelength bands centred at 335, 480, 500, 546 and 865 nm. The European Retrievable Carrier (Eureca), is an ESA space platform that will be placed in orbit around the Earth by the NASA Shuttle in October 1991, and will be recovered after 6 months of operation. Title: Phase difference between irradiance and velocity in low degree solar p-modes Authors: Schrijver, C. J.; Jiménez, A.; Domingo, V.; Fröhlich, C. Bibcode: 1991AdSpR..11d..77S Altcode: 1991AdSpR..11Q..77S We derive phase differences between irradiance and full-disk velocity variations for l=0, 1, and 2 modes with order ranging from 11 up to 30 (1.8-4.3mHz). We use irradiance measurements from the IPHIR instrument flown on the PHOBOS mission to Mars during the second half of 1988, and simultaneous velocity measurements obtained at Tenerife. The IPHIR instrument measures broad-band irradiance fluctuations and the derived phase differences are therefore typical of the deep layers of the photosphere. We select three one week intervals from the 155 day observing interval of PHOBOS 2 for which simultaneous good quality velocity data are available. We find a smooth variation of the phase difference between irradiance at 500nm (5nm FWHM) and velocity from about 70° at 1.8mHz to 145° at 2.5mHz, while it remains roughly constant at 145° degrees up to at least 3.5mHz, and possibly up to 4.3mHz. We also show that the phase differences between the green (500nm) and red (865nm) channels does not differ significantly from zero below 3mHz, while a small difference of about 10° may exist at higher frequencies. Title: Solar gravity modes. Authors: Hill, H.; Froehlich, C.; Gabriel, M.; Kotov, V. A. Bibcode: 1991sia..book..562H Altcode: The internal gravity modes, or g-modes, of the Sun may be important both in affecting the internal structure of the Sun and in furnishing a diagnostic probe of the solar interior. The internal structure could be altered by core mixing due to unstable g-modes or by nonlinear effects due to large-amplitude g-modes located in the core. On the other hand, small-amplitude g-modes operating in the linear regime offer the possibility of studying in detail the present state of internal solar structure such as the internal rotation rate, the Brunt-Väisälä frequency, the speed of sound and the mean molecular weight. In all of these roles, the solar g-modes may be important. The g-modes may be a contributor to the solar neutrino paradox and/or they may be a source of information leading to a more complete understanding of the physics responsible for the paradox. The observational work on solar g-modes does not exclude any of these possibilities at this time. Title: The helioseismological experiment at the Phobos interplanetary station - Preliminary results Authors: Froehlich, C.; Bonnet, R. M.; Bruns, A. V.; Vial, J. C.; Delaboudiniere, J. P.; Domingo, V.; Kollath, Z.; Kotov, V. A.; Rachkovskii, D. N.; Wehrli, Ch. Bibcode: 1991IzKry..83...22F Altcode: Preliminary results obtained from IPHIR (Interplanetary Helioseismology by Irradiance Measurements), a solar irradiance experiment on board the Soviet planetary mission Phobos-2, are presented. During the spacecraft's flight to Mars, the instrument gathered valuable data on tiny variations of solar irradiance over the course of six months. The data clearly show 5-min oscillations with relative amplitudes of about 10 exp -5 and with a well-defined pattern of discrete peaks in the power spectrum. The data of the red channel (it exhibited the lowest degradation of sensitivity over time) reveal remarkable temporal changes of amplitudes of discrete peaks within a period range of about 5 min, but with excellent frequency stability. Title: Solar Irradiance Variability from Modern Measurements Authors: Froehlich, C.; Foukal, P. V.; Hickey, J. R.; Hudson, H. S.; Willson, R. C. Bibcode: 1991suti.conf...11F Altcode: Direct measurements from satellites of the solar 'constant' (the total irradiance at mean sun-earth distance) during more than ten years show variations over time scales from minutes to years and decades. At high frequencies, solar oscillations contribute to the variance. The most important influences are related to solar activity: during the passage of active regions on the solar disk (sunspots and faculae) changes of a few 0.1 percent lasting for several days are observed. The effects of spots can be well reproduced by the projected sunspot index, whereas the influence of faculae have to be modeled from proxy data like the Ca-K plage index or the He I index. Long-term trends are detected which are connected to the 11-yr solar activity cycle. Title: Helioseismology with the IPHIR instrument on the U.S.S.R. Phobos mission Authors: Froehlich, C.; Toutain, Th.; Schrijver, C. J. Bibcode: 1991AdSpR..11d..69F Altcode: 1991AdSpR..11...69F We analyze the solar irradiance data gathered by the IPHIR experiment on the USSR planetary mission to Phobos during 160 days of the cruise phase to Mars of PHOBOS II, launched on 12 July 1988. We use two methods to `clean' the data from the unexpected effects caused by the variable pointing. Both methods yield spectra of the green and red passbands in the range of the solar 5-minute p-mode oscillations with a very high signal-to-noise ratio. The consistency of the four spectra demonstrates the effectiveness of the `cleaning' and allows to determine highly accurate p-mode frequencies. For the low-frequency analysis another, independent method is applied which produces reasonable power spectra in the range from 0.1 to 200 μHz. Interesting features of the medium-term variability of the solar spectral irradiance are revealed. No evidence was found for solar g modes, possibly because the solar or the pointing noise prevents their disclosure. Title: Line shape and temporal variation of p-modes from IPHIR data Authors: Toutain, T.; Froehlich, C. Bibcode: 1991AdSpR..11d.213T Altcode: 1991AdSpR..11R.213T The p-mode linewidths, obtained with the data of the space experiment IPHIR, are performed with a likelihood technique, taking into account the χ2 statistics of the power spectrum. A smoothed daily power is also performed for each mode of the IPHIR p-mode spectrum. Title: Irradiance variability of the Sun. Authors: Froehlich, Claus Bibcode: 1990NASCP3086..269F Altcode: 1990cisv.nasa..269F Direct measurements of the solar constant - the total irradiance at mean Sun-Earth distance - during the last ten years from satellite show variations over time scales from minutes to years and decades. At high frequencies the spectral power is determined by granulation, super- and mesogranulation. In the 5-minute range, moreover, it is dominated by power from the solar p-mode oscillations. Their power and frequencies change with time yielding information about changes in the convection zone. Towards periods of several hours the power is steadily increasing and may be partly due to solar gravity modes. The most important variance is in the range from days to several months and is related to the photospheric features of solar activity: decreasing the irradiance during the appearance of sunspots, and increasing it by faculae and the magnetic network. Long-term modulation by the 11-year activity cycle are observed conclusively with the irradiance being higher during solar maximum. All these variations can be explained - at least qualitatively - by their manifestation on the photosphere. For the long-term changes the simultaneous changes of the frequencies of solar p-mode oscillations suggest a more global origin of the variations. Indeed, it seems that the observed irradiance modulation is a true luminosity change with the magnetic cycle of the Sun. Title: Solar Brightness Oscillations - PHOBOS-2 Observations Authors: Bruns, A. V.; Bonnet, R.; Delaboudinier, J. P.; Frohlich, C.; Shumko, S. M. Bibcode: 1990SvAL...16..140B Altcode: No abstract at ADS Title: Results of the Phobos-2 study of solar brightness oscillations Authors: Bruns, A. V.; Bonnet, R.; Delaboudinier, J. P.; Frohlich, C.; Shumko, S. M. Bibcode: 1990PAZh...16..330B Altcode: Phobos-2 observations indicate that the variations in the power spectrum of 5-min oscillations of the sun appear independently for each of the modes and have the character of 4-5-hour amplitude bursts. In general, the power spectrum lines reveal both quiet and active periods. The quiet periods are characterized by a brightness burst amplitude of (1.5-2) x 10 to the -7th and have a lifetime from about 10 hours to a few days. The active spectrum consists of a single burst or a sequence of bursts with an amplitude 30-50 times higher and lasting from a few hours to one day. Title: p-Mode Analysis of the IPHIR Data Authors: Fröhlich, Claus; Toutain, Thierry Bibcode: 1990LNP...367..215F Altcode: 1990psss.conf..215F The results of the IPHIR experiment on the USSR planetary mission to Phobos presented here are from data gathered during 160 days of the cruise phase of PHOBOS II to Mars, launched on 12 July 1988. The long uninterrupted observation produces a spectrum of the solar p-mode oscillations in the 5-minute range with a very high signal-to-noise ratio. Frequency and line shape determination is limited by the lifetime of the modes and the noise from stochastic excitation. The temporal variation of the amplitudes of l = 0... 2 is discussed. Title: Search for g-Modes in the IPHIR Data Authors: Fröhlich, Claus Bibcode: 1990LNP...367..221F Altcode: 1990psss.conf..221F The results of the IPHIR experiment on the USSR planetary mission to Phobos presented here are from data gathered during 160 days of the cruise phase of PHOBOS II to Mars, launched on 12 July 1988. The search for g-modes is based on a cross-spectral analysis of the low frequency spectrum from IPHIR (20 to 120 µHz) with theoretical g-mode spectra. These spectra are calculated using a second order asymptotic theory for the frequencies and a visibility function for the amplitudes which depends on degree and frequency; the basic period spacing of the g-modes and the rotational rate are varied in the ranges 26 < P 0 < 45 minutes and 0.4 < v R < 2.0 µHz respectively. Comparison with artificial noise spectra indicates that the solar g-modes — if they exist — are buried in solar noise with an upper limit for their amplitudes of the order of 1.3 ppm at 20 µHz. More sophisticated methods to extract a possible g-mode signal from noise are proposed. Title: Solar irradiance variability. Authors: Fröhlich, C. Bibcode: 1989AtmRe..23..379F Altcode: The solar "constant" varies over time scales from minutes to years and decades. From direct measurements of the solar "constant" during the last 10 years, one indeed becomes aware of substantial changes on time scales longer than days. The most important influences seem to be related to solar activity. It is indicated that global effects not related to the solar activity produce irradiance variations, which may be modulated by the same mechanism as that producing solar activity. Title: Multi-spectral analysis of total solar irradiance variations Authors: Froehlich, C.; Pap, J. Bibcode: 1989A&A...220..272F Altcode: A multi-variate spectral analysis is used to investigate the influence of sunspots by their area and classified according to their age and bright magnetic elements as shown by the full-disk equivalent width of the 1987 nm He-line on the total solar irradiance during 1980 and 1984/85. Most of the power in the spectrum of the SMM/ACRIM irradiance variance is explained by the effect of the complex sunspots groups showing new activity. The correlation with old sunspots is different and in general much lower. During the solar minimum, when only a few active regions are on the sun, the main contribution to the irradiance variations arises from the active network, which is formed by the breakup and dispersion of active regions. After eliminating the effect of sunspots and bright magnetic elements from the irradiance power spectrum, there are still peaks around 9 and 27 days, the strength of which seems to vary with solar activity. This indicates that other large scale effects produce irradiance variations, which may be modulated by same effect as produces solar activity. Title: VIRGO: The solar monitor experiment on SOHO. Authors: Froehlich, C.; Andersen, Bo Nyborg; Berthomieu, G.; Crommelynck, D.; Delache, Philippe; Domingo, V.; Jimenez, A.; Jones, A. R.; Roca Cortés, Teodoro; Wehrli, Ch. Bibcode: 1988ESASP.286..371F Altcode: 1988ssls.rept..371F The VIRGO Experiment (Variability of solar Irradiance and Gravity Oscillations) contains two types of active cavity radiometers for monitoring of the solar "constant", two three channel sunphotometers (SPM) for the measurement of spectral irradiance at 335, 500 and 865 nm and a low resolution imager (LOI) with 12 pixels. The main scientific objective is probing the solar interior by helioseismology with p- and g-mode solar oscillations determined from spectral irradiance (SPM) and radiance (LOI) variations on time scales of minutes to the mission time. Moreover, the measurements of the variability of the solar "constant" and spectral irradiance over periods of days to the mission time will yield information about the convection zone, as will the comparison of the amplitudes and phases of the oscillations as manifested in irradiance and radiance (from VIRGO) and velocity (from GOLF and SOI). Title: IPHIR: The helioseismology experiment on the PHOBOS mission. Authors: Fröhlich, C.; Bonnet, R. M.; Bruns, A. V.; Delaboudinière, J. P.; Domingo, V.; Kotov, V. A.; Kollath, Z.; Rashkovsky, D. N.; Toutain, T.; Vial, J. C.; Wehrli, C. Bibcode: 1988ESASP.286..359F Altcode: 1988ssls.rept..359F IPHIR (InterPlanetary Helioseismology by IRradiance measurements) is a solar irradiance experiment on the USSR planetary mission PHOBOS to Mars and its satellite Phobos. The experiment is a cooperative effort of PMOD/WRC, LPSP, SSD/ESA, KrAO and CRIP. The sensor is a three channel sunphotometer (SPM) which measures the solar spectral irradiance at 335, 500 and 865 nm with a precision of better than 1 ppm. A two axis solar sensor (TASS) is added to monitor the moderate solar pointing of the spacecraft. A microprocessor based data processing unit controls the sensor operation, acquires the data, and performs the data compression for the transmission at a mean rate of 1 bit/s. The two spacecrafts have been launched on July 7th and 12th, 1988. The experiment on PHOBOS I gathered data during 45 days before the S/C was lost, the one on PHOBOS II is still operating. The data recovery is excellent with virtually 100% coverage. Although the signal is disturbed by the pointing of the spacecraft the results of a preliminary analysis in the range of the 5-minutes oscillations demonstrate the improvement achievable due to the fact that the time series is truly continuous and the instrumental and sampling noise is very low. Title: VIRGO: The solar monitor experiment on SOHO Authors: Froehlich, C.; Andersen, B. N.; Berthomieu, G.; Crommelynck, D.; Delache, Ph.; Domingo, V.; Jimenez, A.; Jones, A. R.; Roca Cortes, T.; Wehrli, Ch. Bibcode: 1988sohi.rept...19F Altcode: The Variability of solar IRradiance and Gravity Oscillations (VIRGO) experiment contains two types of active cavity radiometers for monitoring of the solar constant, two three channel sunphotometers for the measurement of spectral irradiance at 335, 500 and 865 nm and a low resolution imager with 12 pixels. The main scientific objective is probing the solar interior by helioseismology with p and g mode solar oscillations determined from spectral irradiance and radiance variations on time scales of minutes to the mission time. Information about the convection zone is thus obtained. The comparison of the amplitudes and phases of the oscillations as manifested in irradiance and radiance (from VIRGO) and velocity as measured by the GOLF (global oscillations at low frequencies) experiment are also used in analyzing the convection zone. Title: Solar Gravity Modes from Acrim/smm Irradiance Data Authors: Frohlich, C. Bibcode: 1988IAUS..123...83F Altcode: The power spectra of the time series of 270 days in 1980 and of 240 days in 1984 are analysed using a statistical method for the determination of the basic g-mode period separation T0 and the rotational frequency νR. The results of the analysis of both time series in the frequency range from 10 to 40 μHz are best fitted by a T0 of 29.85 minutes. The angular velocity in the center of the Sun inferred from the rotational splitting of the g-modes amounts to 6.6×10-6per sec, which is 2.3 times the photospheric rate. Title: Correlation of solar irradiance variability with evolution of activity Authors: Pap, J.; Froehlich, C. Bibcode: 1988AdSpR...8g..31P Altcode: 1988AdSpR...8...31P Results of multivariate analysis show that most of the total solar irradiance variability is explained by the effect of active and to a less amount by passive sunspots and bright magnetic elements. This paper also demonstrates the limitation of simple analyses, as linear regression or even bivariate analysis which can reveal only the most obvious correlations between the used data sets. Title: Solar oscillations and helioseismology from ACRIM/SMM irradiance data. Authors: Fröhlich, C. Bibcode: 1987nep..conf..397F Altcode: An introduction to solar oscillations, their properties and diagnostic potential, and a review of our present knowledge is presented. The solar irradiance data from the ACRIM (Active Cavity Radiometer for Irradiance Monitoring) solar constant experiment on board the Solar Maximum Mission satellite (SMM) are used to search for solar gravity modes, which yield a direct information on the structure of the solar core. Title: Variability of the solar "constant" on time scales of minutes to years. Authors: Froehlich, C. Bibcode: 1987JGR....92..796F Altcode: The power of the irradiance variability spectrum from about 70 nHz (150 days) to 5 mHz (3.3 min) can be divided into three major domains with the following characteristics: (1) From 70 nHz to 2 μHz (5.8 - 150 days) the spectrum is dominated by solar activity, the power of which changes during the course of the solar cycle by up to 1 order of magnitude. (2) From 2 to 20 μHz (14 hours to 5.8 days) the spectrum follows a 1/ν2 law, which may be due to g modes. (3) From 20 μHz to 5 mHz (14 hours to 3.3 min) the spectrum follows a 1/ν law, with a broad peak around 5 min which is due to p modes yielding amplitudes of several ppm. As to the long-term changes, trends of the order of 0.02% per year seem to exist. The question whether the up and down trends with a peak around 1980 belong to an oscillatory modulation of the solar output can only be answered in the future. Title: Solar oscillations and helioseismology from ACRIM/SMM irradiance data Authors: Fröhlich, C. Bibcode: 1987nep..conf..395F Altcode: No abstract at ADS Title: Long-Term Downward Trend in Total Solar Irradiance Authors: Willson, R. C.; Hudson, H. S.; Frohlich, C.; Brusa, R. W. Bibcode: 1986Sci...234.1114W Altcode: The first 5 years (from 1980 to 1985) of total solar irradiance observations by the first Active Cavity Radiometer Irradiance Monitor (ACRIM I) experiment on board the Solar Maximum Mission spacecraft show a clearly defined downward trend of -0.019% per year. The existence of this trend has been confirmed by the internal self-calibrations of ACRIM I, by independent measurements from sounding rockets and balloons, and by observations from the Nimbus-7 spacecraft. The trend appears to be due to unpredicted variations of solar luminosity on time scales of years, and it may be related to solar cycle magnetic activity. Title: Internal Structure of the Sun Authors: Frohlich, C.; Gough, D. Bibcode: 1985ESASP.235..241F Altcode: 1985fmsh.work..241F No abstract at ADS Title: Solar gravity modes from ACRIM/SMM irradiance data. Authors: Frohlich, C.; Delache, P. Bibcode: 1984sses.nasa..183F Altcode: 1984sss..conf..183F The record of 280 days of continuous data of the ACRIM radiometer on board the Solar Maximum Mission satellite is analysed in the frequency range from 10 to 80 μHz. Gravity modes of degree one and two with orders from about 10 to several hundreds can be localized. A statistical method to determine the fundamental period T0 and the rate of rotation νR as seen by rotational splitting is described and the results for 33.5 < T0 < 45.5 minutes and 0.4 < νR < 2.0 μHz presented. They indicate a rather high T0 and it cannot be excluded that it is above the upper limit analysed. Title: Global solar oscillations in irradiance and velocity: a comparison. Authors: Frohlich, C.; Vanderraay, H. B. Bibcode: 1984ESASP.220...17F Altcode: 1984ESPM....4...17F The results of 7 hours of solar spectral irradiance measurements from a stratospheric balloon (1983) are analysed for frequencies between 1 ad 5 mHz. Several significant peaks of up to 6 ppm in the red (778 nm) and of up to 15 ppm in the blue (380 nm) can be identified as 5-minute p-mode oscillations of the Sun. From bivariate time series analysis a more or less constant relative phase close to zero and an amplitude ratio between 1.5 and 3.2 with a maximum around 3 mHz is found. By comparing the spectra with velocity measurements a phase difference between the velocity and irradiance signals of 120 to 180° is found and amplitude ratios of 15 and 50 ppm/m s-1 for the red and blue respectively. Title: Solar gravity modes from ACRIM/SMM irradiance data Authors: Froehlich, C.; Delache, P. Bibcode: 1984MmSAI..55...99F Altcode: The record of 280 days of continuous data of the ACRIM radiometer on board the Solar Maximum Mission satellite is analyzed in the frequency range 2-80 microhertz. Gravity modes of degree one and two with orders from about 10 to several hundred can be localized. Due to the complexity of the spectrum of the enormous number of lines in a given frequency interval, the individual identification is very difficult. A statistical method to determine the fundamental period and the rate of rotation as seen by rotational splitting is described, and the results compared with other determinations. Title: The solar and heliospheric observatory, SOHO - A phase-A project of the European space agency Authors: Malinovsky-Arduini, M.; Froehlich, C. Bibcode: 1984AdSpR...4g.383M Altcode: 1984AdSpR...4..383M The Solar and Heliospheric Observatory is designed to address basic questions concerning the Sun and Heliosphere. In this paper our present understanding of coronal heating, solar wind generation and solar oscillations is described. The proposed model SOHO instrument payload is outlined and it is shown how it would contribute to our understanding in the above three fields. Title: Approaches to radiation guidelines for space travel Authors: Froehlich, C.; Eddy, J. A. Bibcode: 1984AdSpR...4h.121F Altcode: 1984AdSpR...4..121F There are obvious risks in space travel that have loomed larger than any risk from radiation. Nevertheless, NASA has maintained a radiation program that has involved maintenance of records of radiation exposure, and planning so that the astronauts' exposures are kept as low as possible, and not just within the current guidelines. These guidelines are being reexamined currently by NCRP Committee 75 because new information is available, for example, risk estimates for radiation-induced cancer and about the effects of HZE particles. Furthermore, no estimates of risk or recommendations were made for women in 1970 and must now be considered.

The current career limit is 400 rem to the blood forming organs. The appropriateness of this limit and its basis are being examined as well as the limits for specific organs. There is now considerably more information about age-dependency for radiation effects and this will be taken into account. In 1973 a committee of the National Research Council made a separate study of HZE particle effects and it was concluded that the attendant risks did not pose a hazard for low inclination near-earth orbit missions. Since that time work has been carried out on the so-called microlesions caused by HZE particles and on the relative carcinogic effect of heavy ions, including iron. A remaining question is whether the fluence of HZE particles could reach levels of concern in missions under consideration. Finally, it is the intention of the committee to indicate clearly the areas requiring further research. Title: Solar variability for periods of days to months Authors: Froehlich, C. Bibcode: 1984AdSpR...4h.117F Altcode: 1984AdSpR...4..117F The time series of total solar irradiance determinations from ACRIM on the Solar Maximum Mission satellite (SMM) of 270 days and from the ERB experiment on NIMBUS 7 of 1445 days are analysed for periods greater than a few days. Comparison of the spectra of both with the spectrum of projected sunspot area over the corresponding time periods show high coherence for periods of 7 to about 25 days and for periods longer than about 30 to 35 days. In the vicinity and at the 27-day rotational period of the Sun, however, the coherence between sunspot area and irradiance is small, although both spectra show significant power at and around this period. This means that there is a signal in the irradiance which cannot be due to the sunspot area and the assumption of a straight forward sunspot blocking seems to be over simplified. This irradiance signal at 27 days has an amplitude of about +/-0.012 per cent and is an enhancement. Title: Solar radiometry from high-altitude balloons Authors: Brusa, R. W.; Froehlich, C.; Wehrli, C. Bibcode: 1983ESASP.183..429B Altcode: 1983erbp.conf..429B A balloon experiment was devised to determine the solar constant and the spectral solar irradiance at selected wavelengths. New methods of characterization substantially improved the state of the art of absolute radiometers and sunphotometers. The solar constant was determined during flights in 1979 and 1980 as 1366.2 and 1367.8 W m-2. A time series analysis of the sunphotometer data showed several peaks in the 5 minutes range. The high coherence with simultaneous measurements from the SMM satellite indicates the solar origin of the peaks, which are likely to be low degree p-mode oscillations of the Sun. Title: Determination of aerosol optical depth from ground measurements Authors: Fröhlich, C. Bibcode: 1982AdSpR...2e.139F Altcode: 1982AdSpR...2..139F The methods used to determine the aerosol optical depth as a function of wavelength are briefly described and discussed. Some results from the operational network of the World Meteorological Organization and other, more research oriented studies, are reviewed and critically analysed to assess the reliability and accuracy of such determinations and their value as ground truth measurements for space applications. Title: Solar radiometry: Total irradiance measurements Authors: Froehlich, C. Bibcode: 1982AdSpR...2d.191F Altcode: 1982AdSpR...2..191F The operating principles of modern absolute radiometers are discussed and the methods of their characterization, that is the accurate determination of the uncertainties, are described. In view of this analysis, the results of the solar constant determinations of the last 6 years are reviewed and an estimate of their uncertainties given. Procedures for the strategy of future experiments are recommended. Title: The variability of the solar output Authors: Frohlich, C. Bibcode: 1981NASCP2191...37F Altcode: 1981vsc..conf...37F A review of solar constant determinations and measurements of its spectral distribution is presented. For the period from 1966 to 1980 a mean value of 1367 Wm-2 was determined. Within the corresponding uncertainty, no significant change of both the integral value and the spectral distribution can be detected. However, short term solar variations and their spectral dependence were deduced from measurements during four hours on June 20, 1980 from 34 km altitude with amplitudes of + or - 500 ppm at 368 nm, of 200 ppm at 500 nm and + or - 150 ppm at 778 nm. Comparison with simultaneous total irradiance data of the Solar Maximum Mission (SMM) shows a high correlation which indicates the solar origin. The power spectrum shows a weak peak at about 3.2 mHz, which corresponds to the frequency of the 5 minutes solar oscillation. Title: Solar Radiation and its Variation in Time Authors: Froehlich, C.; Brusa, R. W. Bibcode: 1981SoPh...74..209F Altcode: In order to assess the variability of the solar radiation, the record of determinations of the total and spectral solar irradiance of the last 15 years is analysed. Although the datapoints for the period before 1969 suggest a slight decrease, the uncertainties of these determinations are too large to render this statement significant. Together with the results of the following period (1969-1980) which show that within the uncertainty no change is detectable, it can be concluded, that the solar constant has not changed during the last 15 years. The same result is found from the spectral distribution record, though not as conclusive as for the solar constant, due to the much larger uncertainties of the spectral data. Title: New determination of Rayleigh scattering in the terrestrial atmosphere Authors: Froehlich, C.; Shaw, G. E. Bibcode: 1980ApOpt..19.1773F Altcode: New Rayleigh-scattering optical thickness values for the terrestrial atmosphere in the 260-1500-nm wavelength range have been calculated using updated data on atmospheric optical parameters. The calculations include molecular scattering from water vapor and take into account varying atmospheric composition with altitude. The new Rayleigh-scattering coefficients average 4.5% lower than those listed by Penndorf in 1955. Title: Field measurements of penetrator seismic coupling in sediments and volcanic rocks Authors: Nakamura, Y.; Latham, G. V.; Frohlich, C.; Blanchard, M. B.; Murphy, J. P. Bibcode: 1979STIN...7921977N Altcode: Field experiments were conducted to determine how well a seismometer installed using a penetrator would be coupled to the ground. A dry-lake bed and a lava bed were chosen as test sites to represent geological environments of two widely different material properties. At each site, two half-scale penetrators were fired into the ground, a three-component geophone assembly was mounted to the aft end of each penetrator, and dummy penetrators were at various distances to generate seismic signals. These signals were detected by the penetrator-mounted geophone assembly and by a reference geophone assembly buried or anchored to surface rock and 1-m from the penetrator. The recorded signals were digitized, and cross-spectral analyses were performed to compare the observed signals in terms of power spectral density ratio, coherence, and phase difference. The analyses indicate that seismometers deployed by penetrators will be as well coupled to the ground as are seismometers installed by conventional methods for the frequency range of interest in earthquake seismology. Title: Contemporary Measures of the Solar Constant Authors: Fröhlich, C. Bibcode: 1977soiv.conf...93F Altcode: No abstract at ADS Title: The Solar Constant: A Critical Review Authors: Fröhlich, C. Bibcode: 1977raat.conf..589F Altcode: No abstract at ADS Title: 1. Upper mantle structure beneath the Fiji plateau: Seismic observations of second P-arrivals from the olivine spinel phase transition zone. 2: Strainmeter and tiltmeter measurements from the Tonga Island arc. 3: The case for four-component strainmeters Authors: Frohlich, C. A. Bibcode: 1976PhDT........22F Altcode: Large and impulsive second P-arrivals (4-12 second after the intial P-arrivals) from intermediate depth earthquakes located in the New Hebrides island arc are observed at distances of 7 deg. to 14 deg. on the records produced by short-period seismographs in Fiji. This conclusion is consistent with: (1) the observed onset distance of the travel time cusp, (2) the change with distance of Delta t (the time difference between the first and second P-arrivals), (3) the change of Delta t with the depth of the events, (4) the slowness of the first and second P-arrivals, and finally, (5) comparisons with the predicted arrival times from other published velocity models which contain a rapid P-velocity increase in the upper mantle. A four-component quartz tube strainmeter with capacitance transducers was installed in a surface site on the small coral island of Tongatapu in Tonga and 30 days of data was analyzed. Semidiurnal lunar tidal strains with peak-to-peak amplitudes were observed on all components. Title: Measurement of the Solar Constant, A Critical Review Authors: Fröhlich, C.; Brusa, R. W. Bibcode: 1975scea.conf..111F Altcode: No abstract at ADS Title: The relation between the IPS now in use and Smithsonian scale 1913, Angstrom scale and Absolute scale Authors: Frohlich, C. Bibcode: 1973srmi.symp...61F Altcode: Radiation scales used as references for meteorological radiation measurements are discussed. Specific radiation scales included are: the Angstrom scale, the Smithsonian scale, the Absolute scale, and the International Pyrheliometer Scale. The relations between the radiation scales are stated along with the estimated mean differences between the scales.