B(Y)-CONTROLLED CONVECTION AND FIELD-ALIGNED CURRENTS NEAR MIDNIGHT AURORAL OVAL FOR NORTHWARD INTERPLANETARY MAGNETIC-FIELD

Using the Dynamics Explorer (DE) 2 magnetic and electric field and pla sma data, B(y)-controlled convection and field-aligned currents in the midnight sector for northward interplanetary magnetic field (IMF) are examined. The results of an analysis of the electric field data show that when IMF is stable and when its magnitude is large, a coherent B( y)-controlled convection exists near the midnight auroral oval in the ionosphere having adequate conductivities. When B(y) is negative, the convection consists of a westward (eastward) plasma flow at the lower latitudes and an eastward (westward) plasma flow at the higher latitud es in the midnight sector in the northern (southern) ionosphere. When B(y) is positive, the flow directions are reversed. The distribution o f the field-aligned currents associated with the B(y)-controlled conve ction, in most cases, shows a three-sheet structure. In accordance wit h the convection the directions of the three sheets are dependent on t he sign of B(y). The location of disappearance of the precipitating in tense electrons having energies of a few keV is close to the convectio n reversal surface. However, the more detailed relationship between th e electron precipitation boundary and the convection reversal surface depends on the case. In some cases the precipitating electrons extend beyond the convection reversal surface, and in others the poleward bou ndary terminates at a latitude lower than the reversal surface. Previo us studies suggest that the poleward boundary of the electrons having energies of a few keV is not necessarily coincident with an open/close d boundary. Thus the open/closed boundary may be at a latitude higher than the poleward boundary of the electron precipitation, or it may be at a latitude lower than the poleward boundary of the electron precip itation. We discuss relationships between the open/closed boundary and the convection reversal surface. When as a possible choice we adopt a view that the open/closed boundary agrees with the convection reversa l surface, we can explain qualitatively the configuration of the B(y)- controlled convection on the open and close field line regions by prop osing a mapping modified in accordance with IMF B(y).