Auroral signature of lobe reconnection

We report specific changes in the dayside auroral morphology in the winter hemisphere which occur in response to sharp transitions between northward and southward - directed interplanetary magnetic fields (IMF). In two case examples we show how a switch between large negative and large positive IMF BZ component was accompanied by a corresponding switch in the location of the 630.0 nm aurora: the cusp aurora situated at approximate to 74 degrees MLAT disappeared and another form this time situated at approximate to 77 - 78 degrees MLAT appeared simultaneously (within 1 min.). We suggest that the lower- and higher-latitude auroras correspond to injections of magnetosheath plasma associated with, respectively, magnetic reconnection at low and high magnetopause latitudes. They may be called cusp/LLBL and cusp/mantle auroras, respectively. According to this interpretation the cusp/mantle aurora thus corresponds to reconnection tailward of the cusp, the so-called lobe reconnection. The auroral signature is observed to last for a few tens of minutes, indicating that lobe reconnection can occur in a quasi-steady mode. During the 17 December 1992 case event sunward plasma convection in the polar cap was inferred from magnetometer records obtained during the period when the high-latitude aurora occurred.