Satellite Observation And Numerical Simulation Of The Coupling Between Solar Wind, Magnetosphere And Ionosphere

Solar-terrestrial relation is an important aspect of space plasma research. The interplanetary magnetic field (IMF) and plasma, driven by the solar wind, interacts with the dipole field of the earth and generates the observed magnetosphere. The solar wind, carrying the plasma and IMF, is slowed down by the magnetosphere, produce the bow shock region and the magnetosheath. In fact, the solar wind, as well as the IMF carried by it, could be considered as direct or indirect cause of the fine structures of magnetosphere and also the various physical phenomenons of magnetosphere. Therefore, the study of the solar wind and the interaction between the solar wind and the bow shock and/or magnetopause can improve our understanding of the coupling of the solar wind and magnetosphere and then perfect the prediction model of space weather to make the earth to be a better place to live in for human being.Numerous previous observation indicate that there are many discontinuities existed in the solar wind. These discontinuities, carried by the solar wind, will go across the bow shock and then interact with the magnetopause. Such a process will lead to the evolution of the structure of these discontinuities. For the certain discontinuities with specific initial configuration, the magnetosheath magnetic reconnection, as an important consequence of such evolution, has been confirmed by simulation and observation. Unlike the magnetopause reconnection, the magnetosheath reconnection can only lead to the topology change of IMF and the acceleration and heating of the magnetosheath plasma. So the magnetosheath reconnection provides an alternative way of convection of near-earth plasma and field, will affect the interaction between the magnetosheath and magnetosphere, and to some degree, change the coupling of the magnetosheath and the magnetosphere.It has long been recognized that the magnetopause reconnection is the most important pattern of solar wind-magnetosphere coupling, because it involves both the magnetosphere and the magnetosheath. Especially, in a long period of southwaUd'M) Fondition, the magnetoSause will Ee "eUoded" Ey the magnetopause reconnection continually. The "Flose" Ilux oI the magnetoSause Eepome "oSen", and dUagged Ey the solar wind, move towards the magnetotail. These fluxes will accumulate in the magnetotail, and cause the thinning of the magnetotail current sheet. t hen such accumulation and thinning process reach some points, near-tail reconnection will happen and so is the substorm, which could be considered as an intense magnetospheric convection and also a very important issue of space physics.1 ne of the important consequences of the magnetopause reconnection is the generation of flux transfer events (FTEs). The FTEs driven by the high speed flow (generated by reconnection) and the magnetosheath flow, move poleward, and then realize the exchange of mass, momentum, energy between the magnetosheath and the magnetosphere. Meanwhile the) T(s'FuUUent system will transfer information to the ionosphere, cause various physical phenomenons, such as:polar geomagnetic disturbance, aurora and vortex convection of polar ionosphere and so on. Clearly, such process also could be considered as the coupling between magnetopause and ionosphere.The laUge sFale Fhanging oI the eaUth's convection electric field is also controlled by the solar wind. Such changing will cause the modification of convection pattern of inner magnetosphere and so are the boundary layers of different region in the inner magnetosphere, leads to the exchanges of mass, momentum and energy between these regions. Therefore, it is expected that various wave phenomenon will be generated by the exchanges.In this thesis, we utilize the observation data of ACE and Cluster II spacecrafts, IMAd E geomagnetic station, CUTi USS e F coherent radar and computer simulations, studying the multi-level coupling process between the solar wind, the magnetosheath, the magnetosphere and ionosphere. The main results are listed as below1, s ia computer simulation, we study the interaction between the solar wind discontinuities with different initial configurations and the bow shock/magnetopause, analysis the effect of initial configuration on the magnetosheath reconnection:1) t hile the Ta is transmitted through the bow shock into the magnetosheath, it is narrowed by a two-step compression process, the shock compression and the convective compression. The degree of compression by the former one is proportional to the compression ratio of the bow shock, while the latter may play a dominant role in the thinning of the current sheet. Magnetosheath reconnection occurs in the narrowed, thin current sheet.2) The magnetosheath reconnection is of a patchy type for cases with a relatively thin Ta in the solar wind. In cases with either a north-to-south or a south-to-north field direction change across the Ta, the patchy reconnections are initiated before the Ta reaches the magnetopause. In the cases with a south-to-north field change, both the magnetopause reconnection and magnetosheath reconnection may take place simultaneously. The two reconnection processes will compete with each other to consume the southward magnetic field. 3) For cases with a relatively wide initial Ta, the north-to-south and south-to-north field rotations lead to drastically different results. In the north-to-south case, a dominant u line appears at the nose in front of the magnetopause, and some weaker reconnection u lines off the equator are convected tailward before they are fully developed. In the south-to-north case, however, reconnection may cease to exist in the transmitted Ta in the magnetosheath because the removal of the southward component of magnetosheath field by the magnetopause reconnection is faster than the contraction of the transmitted Ta4) The scale lengths of the magnetosheath flux ropes are comparable to those of the magnetopause flux ropes in both the latitudinal and radial directions, but larger than the sizes of magnetopause ropes in the dawn-dusk direction. In particular, in the south-to-north case, the reconnected magnetosheath field lines can re-reconnect with the geomagnetic field lines at the magnetopause, creating newly-reformed closed field lines. Such process leads to the capture of magnetosheath plasma in the magnetosphere, which provides an additional mechanism to transfer the solar wind mass and momentum into the magnetosphere, and contributes to the formation of the magnetopause boundary layer.2, the magnetopause reconnection is an important way to realize the coupling of magnetosphere and ionosphere. By analyzing the observation data of ACE and Clusterâ…¡spacecraft, the geomagnetic field disturbance of IMAd E geomagnetic station and the data from CUTi ASS e F coherent radar. t e study the case of April 15th 2MM3, and we find:1) t hile Cluster 1 (located at the magnetopause) observed 2 FTEs, the CUTi ASS radar also detected the enhanced ionospheric convection.2) The backscatter power spectrum of UadaU showed 4 "SolewaUd moving auUoUal IoUm (3 MA) s)", that have a good "one-to-one" Uelation with the 4 geomagnetic field disturbance observed by MAd E stations.3) the 2 FTEs matched well with the first two nMAFs and geomagnetic field disturbance.4) t ith the help of Cooling model, we suggest that a possible reason for the last two mMAFs and geomagnetic disturbance without corresponding FTEs observed by Cluster 1 is:the unsteady solar wind condition may affect the trajectory of FTEs and it is relative hard to detected the last two FTEs by the spacecraft.3, the convection pattern of plasmaspheric plasma is controlled by both convection electric field and corotation electric field. After convection electric field has been changed, the plasmashpeUe will geneUate a "tail"---- 31ume. These cold plasma will interact with the hot plasma of ring current, and geneUate "eleFtUomagnetiF ion FyFlotUon ((M'C) waves". SuFh a Shenomenon has not been confirmed directly by spacecraft observation. t e study the case of guly 18th 2MM, and find:1) EMIC waves have been detected by Cluster 1 spacecraft when it was located inside the plume.2) The frequency of these waves is close to local gyro frequency of O+ions, while strong linear polarization is shown. This feature is consistence with the linear wave theory of multi-ion plasma, shows that heavy ions in the plasmasphere will affect the characteristics of EMIC waves.