Thermal plasma acceleration and outflows in the Earth's ionosphere

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Ion outflows play an important role in the coupling of the Earth's ionosphere to its thermosphere and its magnetosphere: they constitute a significant source of plasma for the magnetosphere - the region in near-Earth space dominated by the Earth's magnetic field. The overarching long-term goal of the proposed research is (a) to unravel the underlying plasma acceleration and transport processes of the different ion outflows and (b) to determine and quantify the effects of these outflows on the magnetosphere-ionosphere-thermosphere (MIT). Ion outflow populations may be classified into two categories: thermal and suprathermal. Contrary to earlier theoretical expectations, significant fluxes of "heavy" oxygen ions were found in thermal-energy "light ion polar wind" above their expected peak altitude in the presence of the Earth's gravity, and previously "hidden" cold hydrogen ions (due to spacecraft charging) were recently discovered in the distant magnetosphere. These observations underscore the important direct influence of thermal outflows on the dynamics of the magnetosphere, and highlight important gaps in our knowledge on the different outflows and their interconnections. The short-term objectives of the proposed research projects are to fill several specific knowledge gaps by investigating (a) the role or influence of interplanetary magnetic field (IMF) and geomagnetic activity on plasma outflows, (b) the source mechanisms for thermal ion heating or acceleration and (c) the effect of ion-neutral collisions on plasma outflow in the topside polar ionosphere (300-1000 km), and (d) the role of convection electric field in the transport and intermixing of different outflow species and (e) their fates in the high-altitude magnetosphere (>10,000 km). We plan to engage four graduate (2 Masters and 2 PhD) and two postdoctoral students in data analysis and modeling research projects on (1) the influence of the IMF on dayside thermal outflows and polar ion composition distributions, (2) storm-time atomic nitrogen and molecular ion acceleration at F-region and topside altitudes, (3) the effects of ion-neutral collisions on thermal polar wind and auroral bulk flow and the Solar Cycle dependence of these effects, (4) the role of ion convection in plasma intermixing at high altitudes, and (5) centrifugal ion acceleration of low-energy ions at high altitudes. The data analysis projects will entail detailed and statistical analyses of observation data from the CASSIOPE Enhanced Polar Outflow Probe (e-POP) and complementary data from the SuperDARN radar. CASSIOPE was launched successfully on September 29, 2013 and placed into a polar orbit of 325 x 1500 km. Science operation of its eight instruments started sequentially in late October 2013 as the respective instruments completed commissioning. The modeling projects will involve simulation of particle trajectories in time-dependent electric and magnetic fields in the magnetosphere, using recently developed numerical codes. In terms of expected significance, each project will potentially produce an important scientific first on topside ionospheric ion outflow: including composition observation of IMF-driven dawn-dusk outflow asymmetry; molecular ion acceleration and resulting oxygen/nitrogen geo-corona in the topside ionosphere; solar variability of outflow within a solar rotation; co-existing H+ and O+ ions in the nascent polar wind; and "partially" gravitationally trapped oxygen ions capable of reaching centrifugal acceleration altitude, respectively. The research will advance our knowledge in MIT coupling, and our long-term goal to unravel the underlying plasma processes of ion outflows and to determine and quantify their effects on the MIT system.