The Connection between Transpolar Arcs and Magnetotail Rotation

Abstract

Recent observations show that the evolution of transpolar arcs (TPA's) are often associated with a sign change of the dawn-dusk component of the interplanetary magnetic field (IMF). It is known that a nonzero IMF By causes a twist of the tail plasma sheet. In this study it is assumed that a sign change of IMF By causes the magnetotail to rotate until the entire tail is twisted in the opposite direction. To examine a possible connection between TPA's and tail rotation the Tsyga-nenko 1989 model is modified such that the near-Earth tail and the far tail are twisted in opposite directions. Mapping from the tail current sheet to the ionosphere shows a separated region of closed field lines that extends into the polar cap. This separated part may be interpreted as the mapped region of a TPA. Copyright 2000 by the American Geophysical Union.