Dartmouth Events

Abstract: In this talk I present analysis of in situ measurements of the thermal ion particle distribution functions from the MICA nightside auroral sounding rocket. MICA made observations at altitudes below 325 km of the thermal ion kinetic particle distributions which are the origins of ion outflow. This is a difficult measurement to make because of the plasma physics parameter regime. We observe heating of the bulk ion distribution function at altitudes lower than is typically reported. This study divides the flight into two distinct regions based on the geophysical processes driving the thermal ion behavior. I will focus on the second half of the flight during which MICA observes a mostly isotropic thermal ion population inside and poleward of an auroral arc. Joule heating is the primary driver of the ion temperature here, as we observe a direct proportionality between the ion temperature Ti and the electric field power E^2. We observe bulk ion upflows of several hundred m/s inside the arc, ExB convection away from the arc (poleward), and downflows of tens of m/s in the downward current region poleward of this arc, indicating plasma circulation in these low-altitude regions. These in situ measurements of upflows and downflows are more localized and structured than previously reported.