Vortex Generation And Aurora Responses To The Solar Wind Dynamic Pressure Sudden Change

The Earth's magnetosphere is prominently affected by the abrupt change of solar wind dynamic pressure(SW Payn),whose influence can be further transferred into the ionosphere through field-aligned currents(FACs)accompanying with modulations of the auroral activities.This paper studied the responses of ionosphere(flow vortex and aurora)to the SW Pdyn changes using the data from THEMIS ground-based magnetometers and THEMIS All-Sky Imager(ASI).It has been demonstrated by previous simulation works that the flow vortices can be generated in both magnetosphere and ionosphere after the SW Pdyn sweeping the Earth's magnetopause.The plasma flow vortices generated in the dawn and dusk side magnetosphere were coupled with the current vortices in ionosphere through the FACs.At the same time,previous studies on the aurora have shown that the intensity of aurora sometimes increases and sometimes weakens under the same variation of SW Pdyn.As proposed by Shi et al.(2014),the auroral activities are probably modulated by the transient FACs associated with the vortices generated in magnetosphere and ionosphere.The upward and downward FACs associated with the opposite rotating vortices on dawn and dusk side may be responsible for the opposite variation of the aurora intensity on the two sides of the ionosphere.Aiming to verify this mechanism,four sets(2 sets are increased and 2 sets are decreased)of cases during abrupt change of SW Pdyn are studied.We found that there is a good time correlation between the asymmetrical variation of auroral intensity in dawn and dusk side and the reverse flow vortices on that two sides of ionosphere caused by the sudden change of SW Pdyn.The auroral intensity is reduced in the clockwise vortex region of the dawn side and enhanced in the anti-clockwise vortex region of the dusk side after the sudden increase of the SWPdyn.On the other hand,the auroral intensity is enhanced in the anti-clockwise vortex region of the dawn side and reduced in the clockwise vortex region of the dusk side after the sudden decrease of the SW Pdyn.Therefore,the downward FACs coupled with clockwise vortex and the upward FACs coupled with anti-clockwise vortex may be the one of the reasons for the difference responses of the auroral intensity in dawn and dusk ionosphere.The global response models induced by sudden increase and decrease of S W Pdyn by Shi et al.(2014)and Zhao et al.(2016)is proved by the observational evidence in this paper.This work is important for us to further understand the solar wind-magnetosphere-ionosphere coupling.In this paper,the background of the Earth's magnetosphere and ionosphere response to the sudden change of SW Pdyn is described in Chapter 1.Chapter 2 and 3 presented the current vortices generated in the ionosphere and the auroral response,which caused by the sudden change of SW Pdyn.The summary and prospective of the future work is shown in Chapter 4.