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The plasma sheet is fundamentally important for understanding dynamical processes in the magnetosphere such as geomagnetic storms and substorms. It is also important as a source population for ring current, energetic outer radiation belt particles, and auroral precipitation. Plasma sheet populations originate from both the solar wind and the ionosphere depending on solar wind and geomagnetic conditions. For northward interplanetary magnetic field conditions there is massive particle entry of magnetosheath material leading to the formation of a cold, dense plasma sheet that can precondition the magnetospheric response to geomagnetic storms. The most promising mechanisms for plasma entry during northward IMF conditions are reconnection at high latitudes, reconnection associated with Kelvin-Helmholtz modes, and wave-induced diffusion that can be driven externally or associated with reconnection or Kelvin-Helmholtz waves. These processes are not exclusive and all have been demonstrated to be capable to transport plasma across magnetic boundaries. These three mechanisms can also play significant roles in the plasma entry during southward IMF.

Our team plans to address the following central questions: (1) what processes lead to the increased entropy in the cold-dense plasma material that enters the plasma sheet? (2) what signatures of plasma entry are observed (e.g. plasma heating, density profiles, mixing of distributions, dawn-dusk asymmetries) and how are they related to physical entry processes? and (3) what processes lead to the heating of the nominal plasma sheet material? The team will bring together in situ observations from GEOTAIL, CLUSTER, THEMIS, LANL combined with remote measurements of the plasma sheet from low altitude DMSP satellites, which will be compared with global and local MHD simulations, multi-fluid simulations that include ion inertial effects, kinetic-MHD, and hybrid simulations that include gyroradius physics. The results of the project would lead to better understanding of observations from current and future space missions and contribute to the main mission of the International Space Science Institute.