Abstract:

Based on a large dataset of ion drift velocity measurements hoard on DMSP satellite,a study is made on the plasma bulk upflowing in the topside polar ionosphere.The emphasis is put on the storm-time changes in distribution of upflow occurrence and intensity versus MLT (mainly dawn and dusk)in comparison with that during quiet period,as well as the relation- ship between the ion upflow with the plasma convection and its shear.The results show that the storm-time occurrence frequency of upflow events is nearly two times higher than that during quiet period;the dawn-dusk asymmetry for occurrence frequency inversed from favoring dusk- side to favoring dawn-side.On an average,the storm-time velocity of the ion upflow in the dawn sector is larger than that in the dusk,with maximum upflowing velocity much larger than that in dusk sector.The ion upflow is closely related to the plasma convection and its shear, with strong upflow accompanied usually by large convection shear or abnormally large convec- tion itself.