Spatial structure of the cusp/cleft ion fountain: A case study using a magnetic conjugacy between Interball AP and a pair of SuperDARN radars

The spatial structure of low-energy ion outflows associated with heating pr ocesses in the dayside cusp/cleft region is investigated by using a magneti c conjugacy between Interball Auroral Probe (AP) and the Saskatoon-Kapuskas ing pair of the Super Dual Auroral Radar Network (SuperDARN). The interplan etary magnetic field during this event is characterized by B-y < B-z < 0 co mponents, which breaks the symmetry of morning and afternoon convection cel ls relative to the noon meridian. As a result, plasma convection over the a fternoon polar cap is not antisunward, but almost azimuthally oriented. The three-dimensional thermal ion distributions measured by the Hyperboloid ex periment on board Interball AP are used as input of numerical simulations i n order to investigate the spatial structure of the ion heating processes. The simulations include the complete guiding center motion of ions under th e effect of gravity, geomagnetic field, and convection field measured by Su perDARN radars. In contrast to the classical cleft ion fountain picture, we demonstrate that the observed ions originate from a wide latitudinal inter val and that the heating region likely coincides with the polar cusp. The n umerical simulations allow us to reconstruct the downstream (relative to co nvection) boundary of the heating region, as well as ion distributions alon g this boundary. Ions are found to cross this boundary and to exit the heat ing region over a broad range of altitudes (up to at least 15,000 km) with an average altitude increasing with ion mass, their average pitch angle inc reasing with altitude in agreement with altitude cumulative heating scenari os.