Observational Research On Solar Wind Transport Into Magnetosphere

Magnetosphere is the natural shield of our planet from bombard of the solar wind. For the existence of magnetosphere, only small part of energy and particles from solar wind could enter the magnetosphere, which forms the base of space catastrophe such as storms, substorms and aurora. So solar wind transport into magnetosphere is one of the most important problems in magnetosphere research. In this thesis, firstly, the correlations between the parameters in solar wind and those in plasma sheet has been investigated using measurements of ACE at L1 point and measurements of Double Star/TC-1 in plasma sheet; and then the roles of magnetic reconnection processes at different magnetopause regions under different conditions have been talked about, by analyzing two cases under southward and northward IMF respectively. The results and conclusions could be summarized as follows:1. By using the data of two spacecraft TC-1 and ACE, a statistical study on the correlations between plasma sheet and solar wind has been carried out. The results obtained shows that the plasma sheet at geocentric distances of about 9~13.4 Re has apparent driving relationship with solar wind. It is found that, (1) There is a positive correlation between the duskward component of IMF and the duskward component of geomagnetic field in plasma sheet, with a proportionality constant of about 1.09. It indicates that the duskward component of the IMF can effectively penetrate into the near earth plasma sheet, and can be amplified by sunward convection in the corresponding region at geocentric distances of about 9~13.4 Re. (2) The increase of the density or the dynamic pressure of the solar wind will generally lead to the increase of the density of the plasma sheet. (3) The ion thermal pressure in the near earth plasma sheet is significantly controlled by the dynamic pressure of solar wind. (4) Under the northward IMF condition, the ion temperature and ion thermal pressure in plasma sheet decrease as the solar wind speed increases. This feature indicates that plasmas in the near earth plasma sheet can come from magnetosheath through LLBL. Northward IMF is one important condition for the transport of the cold plasmas of magnetosheath into plasma sheet through LLBL, and fast solar wind will enhance such transport process.2. By analyzing hot ion and electron parameters together with magnetic field measurements from Cluster, a case of magnetopause crossing of the spacecraft has been mainly talked about. A transition layer is observed existing inside the magnetopause at the latitude of about 40o and magnetic local time (MLT) of 13:20 during the southward IMF. The transition layer has magnetospheric field configuration while cold dense plasma features of magnetosheath, with the particle energy-time spectrograms similar to but still a little different from those in magnetosheath, obviously indicating the solar wind entry into magnetosphere. The width of the transition layer along the magnetopause normal direction is evaluated as about 657km, as much as 0.1 Re. The direction and magnitude of the accelerated ion flow means reconnection may possibly cause such a solar wind entry phenomena, and the bipolar signal of the normal magnetic component BN in magnetopause coordinates further supports happening of reconnection there. Solar wind plasma flows toward magnetopause, and enters the magnetosphere along the reconnected flux tube. The magnetosphere part of the flux tube is still inside the magnetosphere after reconnection and applies the path for the solar wind entry into dayside magnetosphere. The case analysis gives observational evidence and more details how the reconnection process at dayside low latitude magnetopause causes solar wind transport or entry into magnetosphere.3. An event of Cluster-Double Star conjunction observations of magnetic reconnection at high latitude magnetopause nightside of both cusps and solar wind transport into magnetosphere caused by such reconnection process has been investigated. During northward IMF, Cluster/SC1 observed accelerated flows and ion heating associated with magnetic reconnection at high latitude magnetopause nightside of southern cusp. And Double Star observed cold dense solar wind plasma transported into dayside magnetosphere. The analysis on such conjunction observations shows that: (1) During northward IMF, magnetic reconnection occurs at high latitude nightside of southern cusp, accompanied by accelerated flows that are observed by Cluster/SC1; (2) The direction of the accelerated flows, with its sunward component Vx, dawnward component Vy, northward component Vz, is quite consistent with the theoretical anticipation under the condition of northward IMF with dawnward component By; (3) Reconnection can heat plasma more in parallel direction than in perpendicular direction, to a level of about 4keV; (4) With reconnection taking place at high latitude magnetopause nightside of the southern cusp, TC-1 observed cold and dense plasma transported into magnetosphere; (5) By reconnection at high latitude magnetopause nightside of both cusps, solar wind flux tube can be captured by magnetosphere and pulled into dayside magnetosphere. This event presents further observational evidence for magnetic reconnection at high latitude magnetopause nightside of both cusps as an important mechanism of solar wind transport into magnetosphere.