MHD simulations about the influence of the IMF clock angle on tail topology and polar cap boundary

A. Kullen (1) and P. Janhunen (2)

(1) Alfven Laboratory, Royal Institute of Technology, Stockholm, Sweden
(2) Geophysical Research, Finnish Meterological Institute, Helsinki, Finland

Proceedings of 6th International School/Symposium for Space Plasma Simulation (ISSS-6), Garching, Germany, 3-7 September 2001, ed. J. Buechner, C.T. Dum, and M. Scholer, 279-282, 2001

Abstract

From observations it is known that the IMF By component causes a twist of the magnetotail. To which degree this twist varies for different IMF By-Bz clock angles or abrupt changes of IMF By is not very well known. Here, we investigate with help of an MHD model how the the large-scale tail topology and closed field line region in both the tail and the ionosphere develop for different IMF clock angles and for an IMF By sign change during northward IMF. The simulations show that the tail twist is larger and more homogeneously distributed in one tail cross section for small clock angles. An IMF By sign change causes large deformations of the tail. After the IMF By flip the near Earth and far tail regions are oppositely twisted for about an hour which causes a bifurcation of the closed field line region. The bifurcated part of the closed field line region maps to a bar of closed field line inside the polar cap which may be interpreted as the mapped region of a transpolar arc.