This project will investigate in detail the entry of solar wind plasma into Earth's plasma sheet. The investigation will be conducted using a combination of data analysis and model simulations which will be used to track the solar wind plasma throughout the magnetosphere. Periods where the interplanetary magnetic field (IMF) is stable for several hours and there is good satellite coverage in the plasma sheet will be selected to form the core of the study. Thorough model-data comparisons of plasma properties, including magnetic field and topology, flow, density, and temperature, at different locations in the magnetosphere will be performed. The specific locations that will be examined include the plasma sheet, low-latitude boundary layer (LLBL), dayside magnetosphere, and cusp region. The purpose of the model-data comparisons is to reveal the path of the solar wind plasma and subsequently the solar wind plasma entry sites and mechanisms. Special attention will be given to the transitions between the hot tenuous and the cold dense plasma sheet. The research will determine whether such transitions occur in a continuous fashion or whether there are critical IMF orientations at which a discontinuous change in the entry sites occurs. Examining how the plasma parameters change at different locations versus time in the magnetosphere will be particularly helpful when identifying the plasma sheet formation mechanisms. Although the ionosphere certainly contributes to the formation of the plasma sheet, this project will focus on the role of the solar wind. However, because composition measurements will be available from the satellite data, in many cases it will be possible to distinguish between these plasma sources and assess their relative importance. This research will directly impact space weather studies because the plasma sheet is the primary source of plasma for the inner magnetosphere, which in turn is one of the main regions where space weather affects human activity. Two graduate students will perform significant parts of the work and will receive valuable hands-on training. In the course of this study a data base of events that are characterized by sharp transitions in the IMF clock angle and/or the SW density concurrent with cold dense plasma sheet and hot tenuous plasma sheet (CDPS/HTPS) transitions in the tail will be compiled. This data base will be made publicly available.
