Analysis Of Temporal Evolution Characteristics Of Thermospheric Density Measured By CHAMP And Geomagnetic Storms

With the data of thermospheric neutral mass density normalized to 400 km measured by CHAMP satellite,the geomagnetic disturbance of horizontal component(35)H obversed by multiple ground observatories from China and INTERMAGNET,the geomagnetic index of SYM-H,ASY-H and AE provided by International geomagnetic data center,and the parameters of the solar wind and interplanetary magnetic field from the OMNI data system,we stydied the temporal evolution characteristics of the disturbance of the(35)H and the thermospheric density correlating the local solar time(LT)and latitude within large geomagnetic storms during 2001-2006.In the other hand,we made a comparative analysis with the storm-time disturbances of the thermospheric density,geomagnetic(35)H and index,and the parameters of solar wind and interplanetary magnetic field,in order to establish the response relationship within the atmospheric density,the geomagnetic storm and the solar activity,and deepen the understanding of the solar-terrestrial energy coupling.During the large geomagnetic storm,the disturbance of(35)H depends on storm-time variation(Dst)due to the ring current.The disturbace amplitude of(35)H recorded by ground observatories which varied latitude and longitude is quite different.Through the analysis of the UT_MLT and UT_MLAT contour maps of the zonal(30°N)and meridian(120°E)geomagnetic disturbance(35)H,it is shown that the disturbace of(35)H exhibit strong day-night asymmetry during the main phase of the large magnetic storm.And with the increase of latitude,the amplitude of magnetic disturbance decreases.During the great geomagnetic storms,The large deviations of thermospheric density exhibits uneven distribution of the local solar time(LT)and latitude from the climatological behavior upon on the conjunct effect of Jouoole/partical heating,Lorentz force,thermal expansion,upwelling,and horizontal wind circulation.The UT_MLAT contour map shows that the density disturbance of the dayside is stronger and earlier than the nightside,and it’s seasonal(hemispherical)effect is more significant than that on the night side.Cross correlation analysis of thermospheric density at different latitudes indicates that the disturbance propagated from high latitudes to low latitudes during magnetic storms.The response of thermospheric density to geomagnetic index is analyzed by linear regression and cross correlation analysis too.It is found that the correlation between atmospheric density and ring current indexes(SYM-H and ASY-H)is better than the AE index,and the delay time of the two exponents varied with different latitude regions.By analyzing the temporal characteristics of the thermospheric density,(35)H component,geomagnetic index,and the parameters of the solar wind and interplanetary magnetic field during the large magnetic storm,it is found that there is a good correlation between them.The real component of wavelet transform coefficient of the thermospheric density shows the orbit cycle of the CHAMP satellite.In addition,the periodicity of the other parameters is not obvious because of the relatively short duration of the magnetic storm.By the analysis of the 1-3 step details’ superposition of all parameters,we found that the disturbance trends of the thermospheric density,(35)H component and the ring current index are consistent with the parameters of the solar wind and interplanetary magnetic field,while the aurora electric collector index(AE)disturbs many times,and the amplitude is more than 50 nT.The result suggests that the influence of solar activity to the thermospheric density and the magnetic field of low latitudes is larger than the magnetic field of high latitudes.