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JOURNAL OF GEOPHYSICAL RESEARCH, VOL. 111, A09316, doi:10.1029/2006JA011831, 2006

Quantification and hemispheric asymmetry of low-latitude geomagnetic disturbances caused by solar wind pressure enhancements

Chao-Song Huang

Haystack Observatory, Massachusetts Institute of Technology, Westford, Massachusetts, USA


Kiyohumi Yumoto

Space Environment Research Center, Kyushu University, Fukuoka, Japan


Abstract

The solar wind dynamic pressure has significant influence on the magnetic field of the Earth. When the magnetosphere is compressed by a solar wind pressure enhancement, the dayside magnetopause current is enhanced, resulting in an increase in the magnetic field inside the magnetosphere and on the ground. In this paper we present the statistical results of low-latitude geomagnetic disturbances caused by solar wind pressure enhancements under different interplanetary magnetic field (IMF) orientations, including northward, southward, and fluctuating IMF. One of the prominent features of the geomagnetic disturbances revealed in this study is the hemispheric asymmetry and its seasonal dependence. Geomagnetic disturbances in the Northern Hemisphere summer are in general larger than those found simultaneously in the Southern Hemisphere and are smaller in the Northern Hemisphere winter than in the corresponding southern stations. The ratio of the average geomagnetic disturbance at magnetic latitude 36°S to that at magnetic latitude 36°N in winter is 1.36 for northward IMF, 1.64 for fluctuating IMF, and 1.79 for southward IMF. The corresponding ratio at 24° magnetic latitude is 1.49, 1.64, and 2.0, respectively. We suggest that the hemispheric asymmetry is caused by the tilt of the Earth's magnetic axis. Our statistics includes a large data set (160 cases in total), and we derive an empirical formula between the solar wind pressure enhancement and geomagnetic disturbances: ΔH = k(inline equation − inline equation), where ΔH is the change of the low-latitude geomagnetic field and measured with nT, P sw is the solar wind pressure and measured with nPa, and k is a constant. The value of k depends on seasons and is 18.4 if all data are included.

Received 4 May 2006; accepted 21 June 2006; published 28 September 2006.

Keywords: geomagnetic field; geomagnetic disturbances; solar wind pressure; hemispheric asymmetry.

Index Terms: 2435 Ionosphere: Ionospheric disturbances; 2415 Ionosphere: Equatorial ionosphere; 2431 Ionosphere: Ionosphere/magnetosphere interactions (2736); 2784 Magnetospheric Physics: Solar wind/magnetosphere interactions.

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Citation: Huang, C.-S., and K. Yumoto (2006), Quantification and hemispheric asymmetry of low-latitude geomagnetic disturbances caused by solar wind pressure enhancements, J. Geophys. Res., 111, A09316, doi:10.1029/2006JA011831.