A TIEGCM Numerical Study Of The Characteristics Of The Thermospheric Density

Many works have been done to study the response of thermospheric densities to short-term solar activities by using the numerical model of thermosphere,but the effect of long-term variation of solar radiation in a solar cycle or more on thermospheric densities has not been studied in detail by models.By the analysis of the thermospheric densities response characteristics to solar radiation,the evaluation of the model accuracy can be achieved,and these have great significance to the predictions of thermospheric densities and low earth orbit spacecraft orbit using the model.Thermospheric densities at the altitude of 400 km during the 23^rd solar cycle（1996-2008）are calculated using the NCAR-TIEGCM.The modeled responses of thermospheric density to solar radiation index F107 variations are statistically analyzed.The results show that during the23^rdsolar cycle,the variations of thermospheric density are basically consistent with those of F107.However,the responses of thermospheric density to changes in F107 are different in different years and months,these differences are mainly annual and hemispherical.The increase of solar radiation from solar minimum to maximum is more than a factor of 4 in the 23^rd 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 F107 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 F107 index in high solar activity years are larger than those in solar minimum years.At different latitudes,the correlation coefficients between the thermospheric density and the 27-day variation of F107 are greater than those between the 81-day variations of thermospheric density and F107.The differences of correlation coefficients of 27-day variation at different latitudes are relatively small,while those of 81-day variation are larger.In this paper,the responses of the thermospheric densities to solar radiation at the altitude of 400 km calculated by the thermospheric numerical model TIEGCM are analyzed systematically.We have a better understanding of the calculation results of the model.TIEGCM can be applied to the prediction of thermospheric density in the future,to provide in-orbit security services for the operation of low-orbit spacecraft.