Shi, J. K. and Cheng, Z. W. and Zhang, T. L. and Dunlop, M. and Liu, Z. X. and Torkar, K. and Fazakerley, A. and Lucek, E. and Rème, H. and Dandouras, I. and Lui, A. T. Y. and Pu, Z. Y. and Walsh, A. P. and Volwerk, M. and Lahiff, A. D. and Taylor, M. G. G. T. and Grocott, A. and Kistler, L. M. and Lester, M. and Mouikis, C. and Shen, C. (2010) South-north asymmetry of field-aligned currents in the magnetotail observed by Cluster. Journal of Geophysical Research, 115 (A7): A07228. ISSN 0148-0227
Abstract
We statistically investigated features of the field-aligned current (FAC) distribution in plasma sheet boundary layers between 17 and 19 RE in the magnetotail using the curlometer technique to calculate the current from four-point magnetic field measurements taken in 2001. The results show that the FAC distribution in the plasma sheet boundary layers in the magnetotail has dusk-dawn asymmetry, earthward-tailward (polarity) asymmetry, and north-south asymmetry. The occurrence and polarities of FACs in the Northern Hemisphere are different from those in the Southern Hemisphere. The average density and the standard deviation of the FACs that are most likely to be connected to the Earth are 4.90 nA m−2 and 2.55 nA m−2 in the Northern Hemisphere and 4.21 nA m−2 and 1.80 nA m−2 in the Southern Hemisphere, respectively. For investigating the mechanism of the north-south asymmetry, we mapped the FACs along the field line into the polar region. The footprints of the FACs also show a difference between the Southern and Northern hemispheres (as a function of mapped latitude). These characteristics suggest a north-south asymmetry of the FACs in the magnetosphere. Further investigation is needed to identify the causes of this asymmetry, although the configuration of the magnetosphere, the polar cap boundary, the conductivity in the ionosphere, or the various solar wind-magnetosphere interaction processes all may be contributors. That the FAC densities are different between the hemispheres suggests that an important source of these currents must be a voltage generator.