Low altitude signatures of magnetospheric configuration and dynamics.

摘要

Three problems in the study of the Earth's magnetospheric configuration and dynamics are studied in this thesis with the use of low altitude satellite data supported by computer simulations. During stably southward interplanetary magnetic field (IMF), we study the correlation between the IMF B{dollar}rmsb{lcub}y{rcub}{dollar} and the distribution of the mantle particle precipitation. We find that the mantle particle precipitation appears mainly in the prenoon region of the northern hemisphere for {dollar}rm Bsb{lcub}y{rcub} > 0{dollar} and in the prenoon region of the southern hemisphere for {dollar}rm Bsb{lcub}y{rcub} < 0{dollar}. This result which is in agreement with an open magnetosphere model during southward IMF, has long been expected but not confirmed by data analyses. We also study whether there exist field-aligned currents (FACs) inside the polar cap during southward IMF. We find that part of the region 1 sense current flows on mantle field lines, and therefore is on open field lines. We term this part of region 1 current R1O currents. The location of the R1O currents is also controlled by the IMF B{dollar}rmsb{lcub}y{rcub}{dollar}, as is the mantle particle precipitation. Results from a global MHD simulation also show the existence of the R1O current and the B{dollar}rmsb{lcub}y{rcub}{dollar} dependence of the location of the R1O currents. Thus, the solar wind, the magnetosphere and the ionosphere are coupled directly through the mantle particle precipitation and associated R1O currents. Such a coupling during southward IMF supplements the solar wind-magnetosphere-ionosphere coupling imposed through the convection driven by the solar wind electric field and by viscous interaction on the boundaries of the magnetosphere. During stably northward IMF, we try to understand whether the magnetosphere remains open or becomes closed. We use intense polar rain electrons during solar proton events as test particles, and find that magnetosphere remains open after many hours of stably northward IMF with both {dollar}rm Bsb{lcub}z{rcub}/vert Bsb{lcub}y{rcub}vert > 1 and Bsb{lcub}z{rcub}/vert Bsb{lcub}y{rcub}vert < 1{dollar}. Results from the global MHD simulation also show an open polar cap during stably northward IMF with finite B{dollar}rmsb{lcub}y{rcub}{dollar}. We conclude that the magnetosphere remains open during stably northward IMF.