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 B y causes a twist of the tail plasma sheet. In this study it is assumed that a sign change of IMF B y 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 Tsyganenko 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.