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JOURNAL OF GEOPHYSICAL RESEARCH, VOL. 111, A10216, doi:10.1029/2005JA011532, 2006

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

Y. Shi

Department of Atmospheric and Oceanic Sciences, University of California, Los Angeles, California, USA


E. Zesta

Department of Atmospheric and Oceanic Sciences, University of California, Los Angeles, California, USA


L. R. Lyons

Department of Atmospheric and Oceanic Sciences, University of California, Los Angeles, California, USA


K. Yumoto

Department of Earth and Planetary Sciences, Kyushu University, Fukuoka, Japan


K. Kitamura

National Institute of Information and Communications Technology, Space Weather Group, Tokyo, Japan


Abstract

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.

Received 14 November 2005; accepted 11 July 2006; published 19 October 2006.

Keywords: asymmetric ring current; solar wind dynamic pressure enhancement.

Index Terms: 2784 Magnetospheric Physics: Solar wind/magnetosphere interactions; 2730 Magnetospheric Physics: Magnetosphere: inner; 2778 Magnetospheric Physics: Ring current; 2788 Magnetospheric Physics: Magnetic storms and substorms (7954).

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Citation: Shi, Y., E. Zesta, L. R. Lyons, K. Yumoto, and K. Kitamura (2006), Statistical study of effect of solar wind dynamic pressure enhancements on dawn-to-dusk ring current asymmetry, J. Geophys. Res., 111, A10216, doi:10.1029/2005JA011532.