Hemispheric Asymmetries of the Subauroral Ion Drifts

Abstract:

A large database of subauroral ion drifts (SAID) events from DMSP observations from 1987 to 2012 is used to systematically investigate the features of SAID. SAID occurs mostly at ~ 62° / -60° magnetic latitude (MLAT) and ~ 2215 / 2245 magnetic local time (MLT) for geomagnetically quiet conditions and at ~ 58°/ -56° MLAT and ~ 2215 / 2245 MLT for geomagnetically disturbed conditions in the North Hemisphere (NH) / South Hemisphere (SH), respectively. Significant north-south asymmetries in SAID occurrence, shape, and geomagnetic activity variations are found in this statistical study. The latitudinal width of a SAID is larger in the NH than in the SH. An interesting finding of this work is that the SAID occurrence probability peaks have a ~ 180° difference in longitude between the two hemispheres in the geographic coordinates for both geomagnetically quiet and disturbed conditions. The SAID width peaks in almost the same geomagnetic meridian zone with a geomagnetic longitude of ~ 80°–120° in both hemispheres. Significant hemispheric asymmetries and spike signatures with sharpe dips are found in all the latitudinal profiles of the horizontal velocities of SAIDs.The SAID is highly correlated to geomagnetic activity, indicating that the location and evolution of the SAID might be influenced by global geomagnetic activity, auroral dynamics, and the dynamics of ring currents. The hemispheric asymmetries of SAID may possibly be related with the differences of the hemispheric power, the cross-polar cap potential, and the density of region-2 field-aligned currents in the two hemispheres. Detailed investigations will be presented in future.