Global Joule heating index derived from thermospheric density physics‐based modeling and observations

Abstract

The primary operational impact of upper atmospheric neutral density variability is on satellite drag. Drag is the most difficult force to model mainly because of the complexity of neutral atmosphere variations driven by solar UV and EUV radiation power, magnetospheric energy input, and the propagation from below of lower atmosphere waves. Taking into account the self‐consistent interactions between neutral winds, composition, ion drifts, and ionization densities, first‐principles models are able to provide a more realistic representation of neutral density than empirical models in the upper atmosphere. Their largest sources of uncertainty, however, are the semiannual variations in neutral density and the magnitude, spatial distribution, and temporal evolution of the magnetospheric energy input. In this study, results from the physics‐based coupled thermosphere‐ionosphere‐plasmasphere electrodynamics (CTIPe) model and measurements from the CHAMP satellite are compared and used to improve the modeled thermospheric neutral density estimates. The good agreement between modeled and observed densities over an uninterrupted yearlong period of variable conditions gives confidence that the thermosphere‐ionosphere system energy influx from solar radiation and magnetospheric sources is reasonable and that Joule heating, the dominant source during geomagnetically disturbed conditions, is appropriately estimated. On the basis of the correlation between neutral density and energy injection, a global time‐dependent Joule heating index (JHI) is derived from the relationship between Joule heating computed by the CTIPe model and neutral density measured by the CHAMP satellite. Preliminary results show an improvement in density estimates using CTIPe JHI, demonstrating its potential for neutral density modeling applied to atmospheric drag determination.