Temporal And Spatial Variations Of Ionospheric Plasma Drift And Thermospheric Zonal Wind During Substorm Periods-Satellite Observation And Model Simulation

The solar wind can transport large amount of energy to the geospace,which can cause strong disturbance in the near Earth space,such as substorm.When substorm occurs,there are large variaitons in the electric field,current and particles.Substorm plays an important role in the magnetosphere-ionosphere-thermosphere coupling system.Substorm has been investigated for over a half century.In the present work the temporal and spatial variations of plasma convection velocity(Vy)and thermospheric zonal wind velocity(Uy)have been investigated in the range of-4 hour(h)and +2h magnetic local time(MLT)relative to substorm onset(MLT onset)with both CHAMP and DMSP satellites observations from 2001 to 2005.Then,we use global ionosphere and thermosphere model(GITM)model to simulate the substorm effect on the thermospheric winds at 400 km height focusing on its related physical mechanism.The main results are summarized as following:1.Using both CHAMP and DMSP satellites observations from 2001 to 2005,the temporal and spatial variations of plasma convection velocity and thermospheric zonal wind velocity have been investigated.It shows that:(1)Vy increase significantly in all MLT sectors and latitudes of the peak values move equatorward in 1.5h after substorm onset.In the subsequent 1.5h yy decrease in intensity and the peaks retreat poleward,which shows that the onset of substorm can enhance the plasma convection velocity dramatically.(2)The relative increase of Vy are largest from-2h to MLTonset,which indicates that title substorm mainly affects the thermosphere in the westward 0-2h MLT sector.(3)Uy increase steadily in 3 hours after substorm onsets,with a 1.5h delay to Vy in response to the substorm onset.2.Using GITM model to simulate and analysis the influence of the substorm on the thermospheric wind.It shows that:(1)The substorm-induced westward disturbance winds at high latitudes are extremely enhanced mainly both in the dusk and dawn sector in the nighttime.(2)The daytime perturbation is due to ion drag,driven by variations in interplanetary magnetic field(IMF)Bz,whereas the nighttime perturbation is due to both the Bz and hemispheric power input.The nightside disturbed winds respond somewhat later than the dayside owing to low background ion density.(3)Ion drag is the dominant driving force in the daytime for zonal disturbed winds.The nighttime zonal winds are driven by a combination of ion drag,Joule heating,and heating of the auroral belt.(4)The viscous force acts to resist the ion drag,whereas the Coriolis force is negligible.