TEMPORAL AND SPATIAL VARIATIONS OF PLASMA AND NEUTRAL VELOCITIES DURING SUBSTORM PERIODS

This study statistically investigates the temporal and spatial variations of plasma convection velocity (V_y) and thermospheric zonal wind velocity (U_y) in the range of –4 hour (h) and +2 h MLT relative to substorm onsets (MLT onset) with both CHAMP and DMSP (F13, F15) satellites observations from 2001 to 2005. It shows that V_y increase significantly in all MLT sectors and the latitudes of the peak values move equatorward in 1.5 h after substorm onsets. In the subsequent 1.5 h V_y decrease in intensity and the peaks retreat poleward, which shows that the onsets of substorm can enhance the plasma convection velocity dramatically. The relative increase of V_y is largest from –2 h to MLT onset, which indicates that the substorm mainly affects the thermosphere in the westward 0∼2 h MLT sector. U_y increases steadily in 3 hours after substorm onsets, with a 1.5 h delay relative to V_y in response to the substorm onsets.