Ionosphere And Magnetosphere Coupling

There are strong mass and energy couplings between the ionosphere and the magnetosphere since the ionosphere and the magnetosphere are connected by magnetic field lines. Studying how these two regions interact with each other is crucial in the understanding of dynamic processes of magnetosphere-ionosphere couplings. Combining satellite, ground-based observations and current system models, we studied physical processes between magnetosphere and ionosphere. We primarily studied characteristics of current wedges in the high-latitude and middle/low-latitude ionosphere during a sawtooth event, the ionospheric response of a flux rope observed in the magnetotail, and characteristics of auroral kilometric radiations during sawtooth events. Our main results are summarized as followings:Firstly, we introduce a method to reconstruct high-latitude ionospheric horizontal equivalent current model using spherical elementary current systems and ground magnetic data.Secondly, based on this current system model, we studied the response characteristics of ionospheric currents and ground magnetic fields to sawtooth injections. By comparing variations of high-latitude electrojets with variations of middle/low-latitude magnetic bays, we found that current wedges were formed during most of the sawtooth injections; we also obtained the temporal and spatial responses of high-latitude electrojets and middle/low-latitude magnetic bays to current wedges: the local time width of current wedges estimated by variations of high-latitude electrojets and variations of middle/low-latitude magnetic bays were both around 11 hours in magnetic local time, which were wider than widths of current wedges during typical substorms; central positions estimated by the two methods were in good agreements for events that had sufficient stations distributed uniformly at nightside; time durations for high-latitude electrojets to reach maximum variations were generally shorter than those for middle/low-latitude magnetic bays. Our study has important implications for the revealing of response characteristics of high-latitude electrojets and middle/low-latitude magnetic bays to current wedges during sawtooth injections.Thirdly, we utilized data of Cluster satellites and IMAGE ground magnetometers to study an earthward moving flux rope in the magnetotail. Through reconstructing 2-dimensional ionospheric equivalent current systems combined with satellite observations in the magnetosphere, we observed field aligned current accompanied the flux rope, and its footprint in the ionosphere was close to a current vortex. This indicates the current in the flux rope was connected to currents in the ionosphere by field aligned currents.Finally, based on observations of LANL satellites and Geotail satellite, we statistically studied whether there were explosions of auroral kilometric radiations (AKR) during sawtooth events from 1998 to 2005. We found good relationship between these two phenomena. We also studied characteristics of AKR during sawtooth events and found that 22.5% events had similar characteristics as those of AKR during substorms; 55.9% events showed that mid-frequency AKR existed first and continued for more than～30 minutes, and then low-frequency AKR appeared with single or multiple intensifications. According to positions of satellite at which it didn't observe low-frequency AKR explosions, we suggested low-frequency AKR mainly exploded at dusk to pre-midnight region during sawtooth injections.In conclusion, the high-latitude ionospheric equivalent current system we established in the Northern Hemisphere provides an effective tool to study current couplings between the magnetosphere and ionosphere. Using the current system model and ground magnetic data we studied response characteristics at high-latitude and middle/low-latitudes to current wedges during sawtooth injections. The statistical study of AKR during sawtooth events demonstrates the close relationship between these two phenomena and provides characteristics of AKR explosions during sawtooth events. These have important significances for the study of magnetosphere and ionosphere couplings.