Magnetic field structures of the magnetotail as observed by GEOTAIL

Abstract

Global magnetic field structures of the earth's magnetotail are investigated by using magnetic field data obtained during the first one‐year observation of GEOTAIL. When the effect of the average solar wind aberration and the geomagnetic dipole tilt is taken into consideration, the tail lobe structures appear to be observed around the expected location even beyond −150RE. The flaring angle of magnetic field lines in the tail lobe is statistically larger than the expansion angle of the tail magnetopause, especially in X > −150RE, suggesting that the lobe magnetic field lines are linked with those in the magnetosheath across the magnetopause. Momentum and particles in the magnetosheath could enter the tail region across the magnetopause with high efficiency. The majority of observed Bz in the current sheet that separates the two distant tail lobes shows northward even beyond −150RE. This is contrary to the model of the quasi‐steady reconnection around −100RE but it cannot be readily concluded that the field lines in the plasma sheet are closed since the convection is predominantly directed tailward in the distant magnetotail.