Neutral density variations in TIE-GCM induced by changes in spatial and temporal profile of eddy diffusivity

Neutral density variations are the largest source of satellite drag variability. Past studies have shown that changes in eddy diffusivity induced by breaking gravity waves in the mesosphere and lower thermosphere can drive variations in thermosphere neutral density on a seasonal scale. In this study, we introduce local time variations in the eddy diffusivity profile at the lower boundary of the Thermosphere Ionosphere Electrodynamics General Circulation Model (TIE-GCM). We have also applied spatial changes in eddy diffusivity based upon similar meridional profiles employed in the Global Scale Wave Model (GSWM), as well as statistical local time variations derived from CHAMP observations. CHAMP neutral density data from 2001-2005 were used in the linear regression analysis to deduce quiet time density diurnal variations at 400 km. Implementing these changes, we have derived an eddy diffusivity model based on the statistical neutral density diurnal variation. TIEGCM results for various diffusivity profiles are presented, and compared with CHAMP observations. The validation study suggests eddy diffusivity is an important parameter for specifying space weather effects on satellite drag due to thermospheric neutral density.