A statistical study of the observed and modeled global thermosphere response to magnetic activity at middle and low latitudes

International audience[1] From one year (2004) of thermosphere total density data inferred from CHAMP/ STAR accelerometer measurements, we calculate the global thermosphere response to auroral magnetic activity forcing at middle and low latitudes using a method based on a singular value decomposition of the satellite data. This method allows separating the large-scale spatial variations in the density, mostly related to altitude/latitude variations and captured by the first singular component, from the time variations, down to timescales on the order of the orbital period, which are captured by the associated projection coefficient. This projection coefficient is used to define a disturbance coefficient that characterizes the global thermospheric density response to auroral forcing. For quiet to moderate magnetic activity levels (Kp < 6), we show that the disturbance coefficient is better correlated with the magnetic am indices than with the magnetic ap indices. The latter index is used in all empirical thermosphere models to quantify the auroral forcing. It is found that the NRLMSISE-00 model correctly estimates the main features of the thermosphere density response to geomagnetic activity, i.e., the morphology of Universal Time variations and the larger relative increase during nighttime than during daytime. However, it statistically underestimates the amplitude of the thermosphere density response by about 50%. This underestimation reaches 200% for specific disturbed periods. It is also found that the difference between daytime and nighttime responses to auroral forcing can statistically be explained by local differences in magnetic activity as described by the longitude sector magnetic indices. Citation: Lathuillère, C., M. Menvielle, A. Marchaudon, and S. Bruinsma (2008), A statistical study of the observed and modeled global thermosphere response to magnetic activity at middle and low latitudes

Etude locale par diffusion incohérente du comportement moyen et perturbé de la région F1 de l'ionosphère et de la basse thermosphère aurorale : [thèse soutenue sur un ensemble de travaux]

Tiré à part de: Journal of geophysical research.A. - 1983, 88, 12, p. 10137-10144 ; 1981, 86, 6, p. 4721-4730 ; 1986, 91, 2, p. 1619-1626 , 1985, 90, 4, p. 3520-3524. Journal of atmospheric and terrestrial physics. - 1986, 48, 9-10, p. 837-847, p. 857-866. Radio science. - 1983, 18, 6, p. 887-893. Annales geophysicae. - 1985, 3, 5, p. 557-568Dans les zones aurorales, d'importantes quantités d'énergie sont déposées dans la haute atmosphère terrestre par les particules énergétiques et par les champs électriques d'origine magnétosphérique. Ces entrées d'énergie, très variables dans le temps et l'espace, s 'ajoutent à l'énergie déposée par le rayonnement EUV et UV solaire, prlncipale source d'énergie de la thermosphère des moyennes latltudes . Elles peuvent modifier la composition et la circulation de l'atmosphère neutre et ionisée au dessus de 90 Km d'altitude environ. La technique de diffusion incohérente, avec les radars de Chatanika en Alaska et EISCAT en Scandinavie, est utilisée pour étudier la température et la densité neutre à la base de la thermosphère et la composition ionique de la région F1 en zone aurorale, pendant les periodes calmes et perturbéespas de résum

Doppler temperatures from O(¹D) airglow in the daytime thermosphere as observed by the Wind Imaging Interferometer (WINDII) on the UARS satellite

International audienceFrom 1992 to 1997, the WINDII interferometer on board the UARS satellite acquired a large set of thermospheric data from the O(1D) and O(1S) airglows. We report here for the first time on daytime O(1D) Doppler temperatures obtained with version 5.11 of the WINDII data processing software. Using a statistical analysis of the temperatures independently measured by the two WINDII fields of view, we estimate that the temperature variations larger than 40 K can be considered as geophysical. Comparisons of WINDII temperatures measured during magnetically quiet days with temperatures obtained by the MSIS-90 and DTM-94 thermospheric models show a 100 K bias. We demonstrate, however, that the modeled temperature variations represent very well the mean temperature variation observed by WINDII over 4 years. We also show that the observed latitudinal/local time variation is in very good agreement with the two empirical models. Finally, the temperature variations during a magnetically disturbed day are found to be qualitatively well represented in form by the models, but largely underestimated. The presence of non-thermal atoms and instrument related issues are discussed as possible explanations for the 100 K bias between the WINDII Doppler temperatures and the empirical models

Which solar EUV indices are best for reconstructing the solar EUV irradiance ?

The solar EUV irradiance is of key importance for space weather. Most of the time, however, surrogate quantities such as EUV indices have to be used by lack of continuous and spectrally resolved measurements of the irradiance. The ability of such proxies to reproduce the irradiance from different solar atmospheric layers is usually investigated by comparing patterns of temporal correlations. We consider instead a statistical approach. The TIMED/SEE experiment, which has been continuously operating since Feb. 2002, allows for the first time to compare in a statistical manner the EUV spectral irradiance to five EUV proxies: the sunspot number, the f10.7, Ca K, and Mg II indices, and the He I equivalent width. Using multivariate statistical methods such as multidimensional scaling, we represent in a single graph the measure of relatedness between these indices and various strong spectral lines. The ability of each index to reproduce the EUV irradiance is discussed; it is shown why so few lines can be effectively reconstructed from them. All indices exhibit comparable performance, apart from the sunspot number, which is the least appropriate. No single index can satisfactorily describe both the level of variability on time scales beyond 27 days, and relative changes of irradiance on shorter time scales.Comment: 6 figures, to appear in Adv. Space. Re

Dependence of neutral winds on convection E‐field, solar EUV, and auroral particle precipitation at high latitudes

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/94962/1/jgra18137.pd

Les problèmes de l'édition de Rabelais

Lathuillère Roger. Les problèmes de l'édition de Rabelais. In: Cahiers de l'Association internationale des études francaises, 1981, n°33. pp. 129-145

Jacques Allières, La formation de la langue française, Paris, P.U. F. (Que sais-je ? n° 1907), 1982

Lathuillère Roger. Jacques Allières, La formation de la langue française, Paris, P.U. F. (Que sais-je ? n° 1907), 1982. In: L'Information Grammaticale, N. 22, 1984. pp. 44-45