Abstract
Quantification and hemispheric asymmetry of low-latitude geomagnetic disturbances caused by solar wind pressure enhancements
Haystack Observatory, Massachusetts Institute of Technology, Westford, Massachusetts, USA
Space Environment Research Center, Kyushu University, Fukuoka, Japan
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(
−
), 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.
Citation: (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.
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