Reconfiguration and closure of lobe flux by reconnection during northward IMF: possible evidence for signatures in cusp/cleft auroral emissions

Observations are presented of the response of the dayside cusp/cleft aurora to changes in both the clock and elevation angles of the interplanetary ma gnetic field (IMF) vector, as monitored by the WIND spacecraft. The auroral observations are made in 630 nm light at the winter solstice near magnetic noon, using an all-sky camera and a meridian-scanning photometer on the is land of Spitsbergen. The dominant change was the response to a northward tu rning of the IMF which caused a poleward retreat of the dayside aurora. A s econd, higher-latitude band of aurora was seen to form following the northw ard turning, which is interpreted as the effect of lobe reconnection which reconfigures open flux. We suggest that this was made possible in the winte r hemisphere, despite the effect of the Earth's dipole tilt, by a relativel y large negative X component of the IMF. A series of five events then forme d in the poleward band and these propagated in a southwestward direction an d faded at the equatorward edge of the lower-latitude band as it migrated p oleward. It is shown that the auroral observations are consistent with over draped lobe flux being generated by lobe reconnection in the winter hemisph ere and subsequently being re-closed by lobe reconnection in the summer hem isphere. We propose that the balance between the reconnection rates at thes e two sites is modulated by the IMF elevation angle, such that when the IMF points more directly northward, the summer lobe reconnection site dominate s, re-closing all overdraped lobe flux and eventually becoming disconnected from the Northern Hemisphere.