Globally averaged exospheric temperatures derived from CHAMP and GRACE accelerometer measurements

Abstract

Neutral densities (ρ) inferred from accelerometer measurements on the polar‐orbiting Challenging Minisatellite Payload (CHAMP) and Gravity Recovery and Climate Experiment (GRACE) satellites are used to compile exospheric temperatures (T∞) during extended periods in 2003 and 2004 when their orbital planes were nearly parallel and at quadrature, respectively. Exospheric temperatures were first estimated using ρ‐h‐T∞ relationships implicit within the Jacchia models, then averaged over individual orbits. We found good agreement between the orbital‐averaged T∞ obtained from CHAMP and GRACE accelerometer data as well as with globally averaged exospheric temperatures derived from drag measurements from the constellation of satellites used in the High‐Accuracy Satellite Drag Model. Our analysis corrects a critical conjecture by Burke (2008) that globally averaged T∞ is essentially the same as orbit‐averaged values obtained by polar‐orbiting satellites, independent of the local time of their orbital planes. Unlike the symmetric 0200–1400 LT distribution of T∞ minima and maxima found in early Jacchia models, presented data indicate that the minima are located closer to the dawn meridian. We also demonstrate that the averaging technique used to estimate T∞ affects the outcomes. Statistical analyses provide an empirical basis for improving estimates of the thermosphere's total energy budget.