SAPS in the 2013 March 17 Storm Event: Initial Results from 1 the Coupled Magnetosphere-Ionosphere-Thermosphere Model

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Thursday, October 31, 2019

Subauroral polarization stream (SAPS) are latitudinally narrow flow channels of large westward plasma drifts in the subauroral ionosphere. In this study, the global structure and dynamic evolution of SAPS are investigated by using the Coupled Magnetosphere-Ionosphere-Thermosphere (CMIT) model with Ring Current extension, namely the LFM-TIEGCM-RCM (LTR) model, to simulate the 2013 St. Patrick’s Day storm event.

Figure of LTR simulation results of the ionospheric states
LTR simulation results of the ionospheric states at three UTs when SAPS peak velocity are identified by the virtual DMSP F18 satellite. (a-c) MIX outputs of electron precipitation energy flux (EnFlux) into the ionosphere and zonal ion drift velocities (black arrows). The zonal drifts are sampled at 24 MLT hours from magnetic latitude of 40 to 80 degrees in every 1 degree interval. The thick black curves show the trajectories of the virtual DMSP F18 during these 10-min intervals. The red crosses indicate the positions of the virtual satellite at the times shown here, which correspond to the maximum westward drift velocities of SAPS in these time intervals. (d-f) MIX outputs of FAC density (background color) and electrostatic potential (black contours) in the northern hemispheric ionosphere. Positive FAC flows into the ionosphere. Positive potential is shown with the solid lines and negative with the dashed. The numbers on the left are the min and max of FAC and potential (bottom). (g-i) TIEGCM outputs of ionospheric TEC.

This is the first time that the global distribution and temporal evolution of SAPS are investigated using first-principle models. The model shows a strong westward ion drift channel formed equatorward of the auroral electron precipitation boundary on the duskside, which is identified as the SAPS structure. The simulated ion drift velocity and auroral electron precipitation sampled along the trajectory of the DMSP F18 satellite are in good agreement with the satellite measurements. SAPS initiate in the pre-dusk sector when the interplanetary magnetic field (IMF) turns southward. SAPS latitude generally decreases with magnetic local time (MLT) from dusk to midnight. The SAPS channel shows wedge, inverse wedge, and crescent morphologies during the storm, and becomes discontinuous when the IMF is weakly southward. The SAPS mean latitude has a correlation coefficient of 0.77 with the Dst index. The mean latitude moves equatorward and the flow channel broadens in the storm main phase. The simulation results illustrate both the global distribution and highly dynamic behavior of SAPS that are not readily apparent from the observation data.

Publication Name: J. Geophys. Res. Space Physics
First HAO Author's Name: Wenbin Wang

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