TIEGCM Numerical Study on the Thermospheric Density Response to Solar F_10.7 Radio Flux Variations during the 23rd Solar Cycle

Thermospheric densities at the altitude of 400km during the 23rd solar cycle (1996—2008) are calculated using the NCAR-TIEGCM. The modeled responses of thermospheric density to solar radiation index F_10.7 variations are statistically analyzed. The results show that during the 23rd solar cycle, the variations of thermospheric density are basically consistent with those of F_10.7. However, the responses of thermospheric density to changes in F_10.7 are different in different years and months. The increase of solar radiation from solar minimum to maximum is more than a factor of 4 in the 23rd solar cycle, and the increase of thermospheric density from solar minimum to maximum is more than a factor of 10 during the same interval. The intra-annual density variations in the solar minimum years are less than a factor of 2 between density minimum and maximum, whereas those in the high solar activity years can be greater than a factor of 2 or even 3. The correlation coefficients between the thermospheric mass density and the F_10.7 index in the middle and high latitudes of the Northern Hemisphere are larger than those in the middle and high latitudes of the Southern Hemisphere, exhibiting an evident norther-south asymmetry. In the low latitudes, the correlation coefficients between the thermospheric mass density and the F_10.7 index in high solar activity years are larger than those in solar minimum years. At different latitudes, the correlation coefficient between the thermospheric density and the 27-day variation of F_10.7 is greater than that between the 81-day variations of thermospheric density and F_10.7.