Thermospheric response to solar activity during the descending phase of cycle 23, as observed by the CHAMP/STAR accelerometer
Résumé
Total thermospheric density inferred from the STAR accelerometer measurements made onboard CHAMP provide the opportunity to study the atmospheric variability spanning the entire descending phase of solar cycle 23. Our specific interest here is not the thermosphere response to solar irradiance variability, but to the highly variable auroral energy inputs associated to the solar wind forcing of the magnetosphere-ionosphere-thermosphere system. For this purpose we have defined a disturbance coefficient that provides a quantification of the increase of the total thermospheric density observed by CHAMP at low and mid latitudes. The disturbance is calculated relative to a reference thermosphere that we have chosen to describe using the NRLMSISE-00 model without magnetic activity forcing and driven by the MgII index. We will describe the statistical behavior of the disturbance coefficient from January 2002 to the end of 2005. The planetary magnetic indices ap and am, as well as longitude sector indices and new alpha indices with the same or higher time resolution, are used as proxy of the auroral energy input.