Fluxropes in the Earth's Magnetosheath

Small scale flux rope structures of duration of 1 - 2 minutes are often observed on Geotail spacecraft in the tail magnetosheath near the magnetopause. In the case of flux ropes observed on 930817 at GSM(x,y,z)=(-70,-21,16.3) Re, the By component showed a bi-polar variation - first positive and then negative, while Bz showed a uni-polar variation - starting from initial negative value to positive value at the center of the flux rope and then back to the negative value. This field variation shows that the current is flowing toward the -z direction along the flux rope structure. The spacecraft potential showed a slightly higher value in the flux rope structure than outside of the structure. This suggests that the density is lower and the temperature is probably higher in the flux rope than in the surrounding sheath plasma. We will discuss the structure of this flux rope from the standpoint of magnetosphere interaction with the solar wind.