Ionospheric convection in the postnoon auroral oval: Super Dual Auroral Radar Network (SuperDARN) and polar ultraviolet imager (UVI) observations

[1] Super Dual Auroral Radar Network (SuperDARN) observations, ultraviolet imaging from the Polar satellite (ultraviolet imager [UVI]), and particle precipitation data from Defense Meteorological Satellite Program (DMSP) satellites have been used to investigate the electrodynamics of the postnoon auroral oval in the Northern hemisphere. We show that: (1) For negative interplanetary magnetic field (IMF) By, the convection reversal (CR) was colocated with the maximum of auroral luminosity, but during positive IMF By, the convection reversal was poleward of the auroral oval up to several degrees in latitude. (2) Postnoon auroral oval was associated with a large-scale upward field-aligned current (FAC) of the order of 6 x 10(-7) A m(-2) in magnitude (the FAC was inferred from the SuperDARN and UVI data). For negative IMF By, the maximum of the auroral intensity coincides in latitude with the maximum of the upward FAC. However, for positive IMF By, the maximum of the upward FAC was shifted to the poleward edge of the auroral oval. (3) In response to the IMF By turning from positive to negative, the maximum of the auroral luminosity did not change its position noticeably, but the position of the CR changed considerably from 80degrees-81degrees to about 76degrees magnetic latitude (MLAT), and the maximum of FAC moved from 77degrees-78degrees to about 76degrees MLAT. Thus, after the IMF By turns negative, both the FAC maximum and CR tend to coincide with the auroral maximum. (4) The IMF Bz positive deflection was followed by a decrease in both FAC intensity and auroral luminosity. However, the decrease in the auroral luminosity lags behind the FAC decrease by about 12 min. Firstly, these observations allow us to suggest that the IMF By-related electric field can penetrate into the closed magnetosphere and produce convection and FAC changes in the region of the postnoon auroral oval. Secondly, we suggest that the interchange instability is a promising mechanism for the postnoon auroras.