2 research outputs found
Segmentation of SED by Boundary Flows Associated With Westward Drifting Partial Ring current
The segmentation mechanism of polar cap patches is agreed to be related to temporal changes of interplanetary magnetic field or transient reconnection. In this letter, using Global Ionosphere Thermosphere Model driven by twoâway coupled BlockâAdaptiveâTreeâSolarwindâRoeâUpwindâScheme and Rice Convection Model, a new segmentation mechanism is proposed. This mechanism works as follows: A strong boundary flow between the Region 1 and Region 2 fieldâaligned currents develops, while a shielding process develops in the inner magnetosphere. As the partial ring current drifts westward, the peak of the boundary flow also moves westward. This strong boundary flow raises the ion temperature through enhanced frictional heating, enhances the chemical recombination reaction rate, and reduces the electron density. When this boundary flow crosses the stormâenhanced density (SED) plume, the plume will be segmented into patches. No external interplanetary magnetic field variations or transient reconnections are required in this mechanism.Key PointsBoundary flows between Region 1 and Region 2 FACs segment SED plume into patchesLocalized plasma loss is due to enhanced frictional heating within boundary flowsNo external IMF direction change is needed in this segmentation scenarioPeer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/151263/1/grl59354.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/151263/2/grl59354-sup-0006-Text_SI-S01.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/151263/3/grl59354_am.pd
Episodic Occurrence of FieldâAligned Energetic Ions on the Dayside
The tens of kiloelectron volt ions observed in the ring current region at L ~ 3â7 generally have pancake pitch angle distributions, that is, peaked at 90°. However, in this study, by using the Van Allen Probe observations on the dayside, unexpectedly, we have found that about 5% time, protons with energies of ~30 to 50 keV show two distinct populations, having an additional fieldâaligned population overlapping with the original pancake population. The newly appearing fieldâaligned populations have higher occurrence rates at ~12â16 magnetic local time during geomagnetically active times. In particular, we have studied eight such events in detail and found that the source regions are located around 12 to 18 magnetic local time which coincides with our statistical result. Based on the ionospheric and geosynchronous observations, it is suggested that these energetic ions with fieldâaligned pitch angle distributions probably are accelerated near postnoon in association with ionospheric disturbances that are triggered by tail injections.Plain Language SummaryProtons of different sources have different pitch angle distributions (PADs). For example, warm plasma cloak protons, which come directly from the ionosphere, have fieldâaligned PADs, while ring current protons that generally originate from tail plasma sheet have pancakeâshaped PADs. In this study, unexpectedly, we have found that about 5% of the time on the dayside, protons of ring current energies show two distinct populations according to their PADs: higher fluxes of fieldâaligned populations overlapping with the original pancake populations. The newly appeared fieldâaligned populations have higher occurrence rates at ~12â16 magnetic local time during geomagnetically active times. In order to find the mechanism that generates these fieldâaligned energetic proton populations, we have studied eight such events in detail by using the lowâaltitude DMSP, POES satellites, and the NOAAâLANL satellite at the geosynchronous orbit. The results imply that these energetic ions with fieldâaligned PADs probably are accelerated by ionospheric disturbances that are triggered by tail injections. These results provide evidence of another possibly important source of the ring current ions.Key PointsWe have found that about 5% of the time on the dayside, protons with energies of ~30 to 50 keV have strong fieldâaligned PADsThe fieldâaligned PADs have higher occurrence rates at ~12â16 MLT during geomagnetically active timesThese energetic fieldâaligned ions possibly are accelerated by ionospheric disturbances triggered by tail injectionsPeer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/153687/1/grl60102_am.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/153687/2/grl60102.pd