Response of the magnetospheric convection to a sudden change in the solar wind magnetic field

*Kumiko Hashimoto[1] ,Takashi Kikuchi [1]
Communications Research Laboratory[1]

We found that the magnetic field at the geosynchronous orbit in the evening sector changed from the dipole- to tail-like configuration a few minutes after the enhancement of the ionospheric convection in the dayside polar cap. The PRC signatures followed this tail-like configuration in a few minutes. These results suggest that the electric field responsible for the convection in the near-Earth magnetotail propagated from the nightside polar ionosphere after having propagated from the magnetosphere to the polar ionosphere on the dayside.

It has been reported by many autors that magnetometer and SuperDARN observations showed the instantaneous reaction of ionospheric convection on the dayside and nightside. The AMIE analyses revealed that the potential pattern did not move but remained nearly at fixed locations. SuperDARN observations demonstrated that the plasma motion in the nightside ionosphere was intensified immediately after the motion of dayside ionospheric plasma was intensified within a resolution of the measurement (2 min). The quick response of the convection in the night-side polar ionosphere poses an important issue whether the ionosphere plays a major role in development of the plasma convection in the inner magnetosphere and in the near-earth magnetotail. The plasma convection in the near-earth magnetosphere would cause development of partial ring currents (PRCs) in the evening to afternoon magnetosphere. Development of the PRC is recognized as a decrease in the H component of ground magnetic field at low latitudes. A time l g of the onset of the PRC from the growth of the polar cap potential could give us an idea about the propagation of the convection electric fields to the near-earth magnetotail. In this paper, we examined the onset of the ground magnetic signatures of the growth of the polar cap potential and the PRC for three PRC events caused by sudden southward turning of the IMF. Magnetometer observations in the polar cap showed that ionospheric convection started to enhance simultatously on the dayside and nightside. We estimated the time lag of the onset of the PRC development from the growth of the polar cap potential. We found that ground magnetic changes due to the PRC started to develop simultaneously at all local times with a time lag of 6-10 minutes from the enhancement in the polar cap potential. These results suggest that the magnetospheric convection in the near-earth magnetotail started to develop in several minutes after the enhancement of the polar cap potential. In another event we show that the magnetic field at the geosynchronous orbit in the evening sector changed from the dipole- to tail-like configuration a few minutes after the enhancement of the polar cap potential. Furt ermore, the PRC signatures followed this tail-like configuration in a few minutes. Consequently, the electric field responsible for the convection in the near-Earth magnetotail propagated from the night-side polar ionosphere after having propagated from the magnetosphere to the polar ionosphere on the dayside.