Modeling the solar spectral irradiance

International audienceModeling the solar spectral irradiance is necessary for different fields: solar, atmospheric and climate physics. In general, the reconstructions aim to generate the solar spectral irradiance (SSI) at a time where no measurement exists. Therefore, they are based on different solar indicators (named proxies), which have the property to correlate their variations with the SSI variation. The long term reconstructions are used in Climate science to study some particular epochs such as the Maunder minimum or the optima of the Middle age. However, reconstructions can be also used to fill a gap in a SSI time series due to a temporary interruption of an instrument operation in space. As in this case many proxies are available, it is expected that filling the gap by modeling will produce precise results. Reconstructions are also used in the field of Earth and planetary atmosphere physics as the relevant space missions started in the 60's (e.g. the Orbital Geophysical Observatory series), i.e before the solar space missions were able to produce SSI time series. Here also, using moderm proxies allow production of precise SSI, which are the necessary input to the atmophere models. Then, the output of such models are compared to the measurements permitting validation of the photochemical processes implemented in the models. Solar reconstructions employ different means leading to simulations either theoretical, semi-empirical or fully empirical methods. For the past periods, their inputs are generally the sunspots number, the cosmogenic isotopes concentration variation obtained from tree rings, and ice core soundings. These proxies constitute time series more or less without gaps, and have variable accuracy and precision generally time dependent. These proxies are the basic inputs of most of the models

Les relations entre le Soleil et la Terre

International audienceThe Earth's atmosphere evolution through geological times has induced significant changes in its composition. The properties of today's atmosphere, due in particular to the presence of oxygen, show strong evidence of the Sun–Earth relationship. The influence of solar activity will be presented, concerning the neutral and ionised atmosphere including the magnetosphere, the thermosphere down to the troposphere, and climate as well as the various consequences on our environment (space weather).L'évolution de l'atmosphère terrestre au travers des temps géologiques a entraı̂né des changements importants de sa composition chimique. Les propriétés de l'atmosphère actuelle, en particulier en raison de sa richesse en oxygène, montrent que c'est dans celle-ci que les relations Soleil–Terre y sont les plus marquées. C'est pourquoi l'influence de l'activité solaire sur l'atmosphère neutre et ionisée (incluant la magnétosphère, la thermosphère et jusqu'à la troposphère) ainsi que sur le climat sera présentée, avec ses conséquences sur notre environnement (météorologie de l'espace)

3. L’éclairement spectral absolu du Soleil

La Terre reçoit son énergie de deux sources : la chaleur transmise au travers de sa surface depuis ses couches internes et le Soleil. Cependant, la seconde est environ 8 000 fois plus importante que la première, ce qui fait du Soleil la seule source d’énergie pour la Terre. Le Soleil produit son énergie sous deux formes, les photons et les particules (électrons, protons*…) dont le flux varie en fonction du temps. Les photons solaires agissent sur les surfaces continentales et océaniques, et s..

Optical Payload onboard the International Space Station for Solar Spectral Irradiance Measurements

International audienceThree optical instruments for measuring the solar total spectral irradiance from 16 nm to 2900 nm were selected under an ESA funded mission for study of the solar, atmospheric and climate physics. These three instruments are referred to as SOLAR payload, which is placed as an external platform for the COLUMBUS laboratory launched on 7 February 2008 onboard the International Space Station.The primary objective of this mission is the measurement of the solar total and spectral irradiance and their variability using these three instruments. The first instrument called Solar Variability Irradiance Monitor (SOVIM) is made up of two absolute radiometers and filter-radiometers. The second instrument called Solar Spectrum (SOLSPEC) is composed of three double grating spectrometers, covering the wavelength range from 170 nm to 2900 nm. The third instrument Solar Auto-Calibrating EUV/UV Spectrometers (SolACES) consists of four grazing incidence planar grating spectrometers plus two three-current ionization chambers with 42 narrow-band filters to determine the absolute fluxes from 16 nm to 150 nm. This chapter describes the performances of SOLSPEC and SolACES, as well as their most recent results and future plans

Comparison of OGO 6 measured thermospheric temperatures with the MSIS-86 empirical model

International audienceThe thermospheric temperatures measured by the Fabry-Perod interferometer on the OGO 6 satellite are found to be reasonably represented by the mass spectrometer/incoherent scatter 1986 (MSIS-86) empirical model except for two anomalies, one in the South Atlantic and the other near noon local time. These anomalies are likely due to measurement problems. The OGO 6 temperature data were not used in the generation of the MSIS models, so this is an independent comparison of measured and model temperatures. The measurements were made primarily during daytime at mid to low latitudes and throughout the day at high latitudes. On average, the measured temperatures are 16 K below the MSIS-86 model temperatures. Latitude gradients during solstices as well as for the yearly average are well represented by the model, as are high-latitude longitudinal and magnetic activity variations

Observation de la figure du soleil (comparaison des mesures au sol et hors atmosphère)

Pour la physique solaire, il existe des grandeurs qui permettent de valider les modèles dont l'objet est la représentation des phénomènes physiques dont le Soleil est le siège. Parmi ces grandeurs, figurent le diamètre, l'asphéricité et la forme du limbe. La mesure du diamètre solaire a été entreprise depuis le milieu du XVIIème siècle. Poursuivis jusqu'à présent par différents instruments placés au sol, sous ballons stratosphériques ou en orbite, l'ensemble des résultats ne présente pas de cohérence. Nous avons analysé les causes possibles de ces désaccords. Parmi celles-ci, outre les caractéristiques instrumentales, les méthodes de traitement sont susceptibles d'introduire des biais dans les résultats. Des algorithmes ont été développés pour traiter les images solaires qui, appliqués aux données de l'instrument Solar Disk Sextant (SDS), ont montré leur précision et leur efficacité. Ce travail a permis de dégager une stratégie de mesure et de traitement qui sera utile à la mission PICARD dont on prévoit la mise en orbite en fin 2008For solar physics, there exist key parameters, which permit validation of the Sun models operation. Among these parameters are, the diameter, the asphericity, and the shape of the limb. The measurement of the solar diameter was undertaken since the middle of the XVIIth century. Continued until now by various instruments placed at the ground, under stratospheric balloons or in orbit, the set of results does not present coherence. We have analyzed the possible sources of these disagreements. Among these are the instrumental characteristics and the processing methods. Algorithms were developed to process the solar images which, applied to the data of the Solar Disk Sextant (SDS) instrument, showed their precision and their effectiveness. This work permitted to define a strategy of measurement and processing useful for the PICARD mission that will be launched in orbit by the of 2008.VERSAILLES-BU Sciences et IUT (786462101) / SudocSudocFranceF

The Mg II index for upper atmosphere modelling

International audienceThe solar radio flux at 10.7 cm has been used in upper atmosphere density modelling because of its correlation with EUV radiation and its long and complete observational record. A proxy, the Mg II index, for the solar chromospheric activity has been derived by Heath and Schlesinger (1986) from Nimbus-7 data. This index allows one to describe the changes occurring in solar-activity in the UV Sun spectral irradiance. The use of this new proxy in upper atmosphere density modelling will be considered. First, this is supported by the 99.9% correlation between the solar radio flux (F10.7) and the Mg II index over a period of 19 years with, however, large differences on time scales of days to months. Secondly, correlation between EUV emissions and the Mg II index has been shown recently, suggesting that this last index may also be used to describe the EUV variations. Using the same density dataset, a model was first run with the F10.7 index as a solar forcing function and second, with the Mg II index. Comparison of their respective predictions to partial density data showed a 3–8% higher precision when the modelling uses the Mg II index rather than F10.7. An external validation, by means of orbit computation, resulted in a 20–40% smaller RMS of the tracking residuals. A density dataset spanning an entire solar cycle, together with Mg II data, is required to construct an accurate, unbiased as possible density model

Simultaneous measurement of the total solar irradiance and solar diameter by the PICARD mission

Gérard Thuilliera, , , Steven Dewitteb, Werner Schmutzc and The PICARD team aService d'Aéronomie du CNRS, Bp 3, 91371 Verrières-le-Buisson, France bRoyal Meteorological Institute of Belgium, 3 Avenue Circulaire, B-1180 Brussels, Belgium cPhysikalisch-Meteorologisches Observatorium Davos, World Radiation Center, CH-7260 Davos Dorf, Switzerland Received 7 February 2005; revised 14 April 2006; accepted 22 April 2006. Available online 18 September 2006. Abstract A mission dedicated to simultaneous measurements of the solar diameter, spectral, and total solar irradiance is presently in development for launch end of the year 2008 on board of a microsatellite under the responsibility of Centre National d'Etudes Spatiales. The payload will consist of an imaging telescope, three filter radiometers with in total twelve channels, and two independent absolute radiometers. The scientific aims are presented as well as the concepts and properties of the instrumentation. This mission is named PICARD after the pioneering work of Jean Picard (1620–1682) who precisely determined the solar diameter during the Maunder minimum

The Sun-Climate Connection Through Measurements and Modeling: The Picard Investigation

International audienc