Field‐aligned current associated with a distorted two‐cell convection pattern during northward interplanetary magnetic field

Abstract

A systematic study of the influence of the ionospheric conductance on the field‐aligned current associated with a distorted two‐cell convection pattern during northward interplanetary magnetic field (IMF) has been conducted. Our modeling results indicate that the NBZ current can be associated with the distorted two‐cell convection for most of the ionospheric conductivity conditions. It is shown that the conductivity conditions related to the seasonal variation and the aurora activity can significantly influence the basic features of the field‐aligned current associated with a distorted two‐cell convection pattern. It is found that the increase of the field‐aligned current in the polar cap during the summer is mainly due to the increasing contribution from the Pedersen current, and the increase of the field‐aligned current in both the oval region and the evening‐midnight sector during the active aurora period is mainly due to the increasing contribution from the Hall current. It is also found that the conductivity change related to the solar variation has its impact mainly on the intensity of a field‐aligned current system instead of its pattern. On the basis of the modeling results it is suggested that the field‐aligned current system observed by the Magsat satellite (Iijima and Shibaji, 1987) might imply a distorted two‐cell convection pattern, and a four‐cell convection pattern is most likely to occur when the direction of the IMF is due north or very close to the north.