Published in

American Geophysical Union, Journal of Geophysical Research, A10(106), p. 21109-21122, 2001

DOI: 10.1029/2001ja900073

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Location of high‐altitude cusp during steady solar wind conditions

Journal article published in 2001 by M. Palmroth, H. Laakso, T. I. Pulkkinen ORCID
This paper is made freely available by the publisher.
This paper is made freely available by the publisher.

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Abstract

We have investigated the high-altitude cusp location and its dependence on the interplanetary magnetic field (IMF) Bz, solar wind Ey, and solar wind dynamic pressure during steady solar wind conditions. We have adopted strict event selection criteria, where we have studied only events during stationary IMF Bz, when the cusp latitude is supposed to be stationary. Prior to this study, the statistical studies have shown a great deal of scatter between the cusp latitude and the IMF Bz; however, with the strict event selection criteria, we have been able to reduce the scatter. The strongest source of scatter comes from large and largely fluctuating IMF By. When the events are selected during small IMF By, the scattering between the cusp latitude and the IMF Bz is reduced. When IMF is southward, also the fluctuation of IMF By has strong influence on the cusp latitude, whereas for northward IMF, the IMF By fluctuation has less influence on the cusp latitude. For larger southward IMF the cusp appears further equatorward than with smaller southward IMF. When the scatter is reduced by introducing the IMF By control, the larger northward IMF brings the cusp to lower latitudes than the smaller northward IMF, i.e., the maximum cusp latitude is obtained for small positive IMF Bz. For increasing solar wind Ey the cusp moves equatorward. Furthermore, with increasing solar wind dynamic pressure, the cusp appears at lower latitudes. This behavior depends on the orientation of the IMF Bz, with southward IMF the cusp moves faster equatorward than with northward IMF.