Modeling Thermosphere Density and Temperature Variations L Qian

Modeling Thermosphere Density and Temperature Variations L. Qian 1, S. C. Solomon 1, R. G. Roble 1, B. R. Bowman 2, and F. A. Marcos 3 1 High Altitude Observatory, National Center for Atmospheric Research 2 Air Force Space Command 3 Air Force Research Lab Abstract The NCAR Thermosphere-Ionosphere-Electrodynamics General Circulation Model (TIEGCM) is employed to quantify thermospheric neutral density and its variations, focusing on the global seasonal variation and the solar activity dependence. Solar X-ray, extreme-ultraviolet (EUV), and far-ultraviolet (FUV) spectral irradiance measurements from the Solar EUV Experiment (SEE) on the TIMED satellite are used to drive the model. Density measurements derived from the atmospheric drag on a set of 5 low-earth orbiting satellites are compared to TIEGCM results, and to the MSIS-00 empirical model. Comparison of Modeled Density to Satellite-Drag Derived Density Modeling the Annual/Semiannual Density Variation Satellite drag data showed that thermospheric neutral density exhibits a global annual/semiannual variation that maximizes in April and October and minimizes in July with a secondary minimum in January. TIEGCM simulations indicated that an annual/semiannual variation in eddy diffusion, together with annual insolation variation and largescale circulation, caused annual/semiannual variation in thermospheric neutral density. Annual/semiannual density variation detected by satellite drag data [Bowman, 2004] Comparison of TIEGCM and MSIS 00 to satellite drag-derived density. Left: solar rotational variation during early 2003. Right: geomagnetic variation during the October. November “Halloween” storms of 2003. Solar-Cycle Variation of Thermospheric Density It has been observed that empirical models of thermosphere based on the F 10. 7 index overestimate neutral density at low solar activity. Density simulated using the TIEGCM using measured solar irradiance from TIMED/SEE as input eliminated this solar-activity dependence. An annual/semiannual variation of eddy diffusion, comparable to observations and gravity-wave breaking theory, were imposed at lower boundary of the TIEGCM. Comparison of TIEGCM and MSIS 00 to satellite drag-derived density for the entire year of 2003. Top: density at perigee location. Bottom: ratio of model to measured densities. Ratio averages for all five satellites: Mean MSIS-00 TIE-GCM 1. 03 0. 99 Std. Dev. 0. 20 Ratio of satellite drag derived density to the Jacchia 70 empirical model as a function of F 10. 7, [Marcos et al. , 2005]. (a) Thermospheric neutral density near 400 km from 2001 to 2006. The density is daily-averaged density at satellite perigee locations. (b) The TIMED/SEE integrated (5 nm to 105 nm) solar EUV flux. (c) F 10. 7 index and Ap index. Average ratio of satellite drag-derived density to the TIEGCM simulated neutral density, for all 5 satellites. Green: with effects from annual insolation variation and large-scale circulation, but with constant eddy diffusion; Red: added an annual/semiannual variation of eddy diffusion. Ratio of satellite drag derived density to the TIEGCM and MSIS-00 models, from 2002 -2004, as a function of F 10. 7. Center for Integrated Space Weather Modeling • Annual Site Visit • 0. 14 5 June 2007