Statistical study of effect of solar wind dynamic pressure enhancements on dawn-to-dusk ring current asymmetry

摘要

In this paper, we statistically investigate the effect of solar wind dynamic pressure enhancements on the dawn-to-dusk ring current asymmetry by examining disturbances of the ASY-H index and low-latitude and midlatitude ground asymmetric perturbations in the north-south (H) component of the geomagnetic field during 186 events occurring from 1 June 2003 to 30 September 2004. Both storm time and nonstorm time events are included. It is found that a pressure enhancement further intensifies the ring current asymmetry provided that the ring current is already asymmetric at the time of the onset of the pressure enhancement. This effect strongly depends on the IMF Bz conditions prior to the pressure enhancement. Generally, for negative IMF Bz, pressure enhancements further increase the ring current asymmetry. This effect also depends on the strength of the pressure enhancement. Under the same IMF Bz conditions, the stronger the pressure enhancement is, the stronger the intensification of the asymmetric ring current is. The IMF Bz conditions during a pressure enhancement play a similar role to that of the IMF Bz preconditioning. The results further show that midlatitude H perturbations around the local noon or midnight region as well as the ASY-H index often include significant contribution from field-aligned currents, e.g., the region 1 (R1) or region 2 (R2) currents or the substorm current wedge.