Pre- and post-noon asymmetry in dayside auroral activity and convection related to solar wind-magnetosphere interactions Original Research Article

The complex chain of mechanisms involved in the transfer of solar wind energy, momentum and particles into magnetosphere-ionosphere system manifests itself in the aurora as a rich spectrum of activities. Systematic work on cusp/cleft auroral morphology, however, has provided us a rather comprehensive description of one particular class of activity. That is the poleward moving auroral forms near magnetic noon of which location and motion pattern are strongly regulated by the IMF orientation. Since it was first suggested by Sandholt in the mid-eighties, it has been an ongoing debate on whether or not this event class actually is a footprint of pulsed magnetopause reconnection. Ambiguity problems pertain mainly due to the limited longitudinal coverage of optical observations. In this paper, we will use multi-instrument data from Svalbard and Greenland to illustrate the IMF BY effect on the occurrence probability of poleward moving auroral transients on either side of noon, the IMF BY effect on the cusp location, and the relationship between moving auroral forms and excitation of polar cap flow. The data presented indicate a clear IMF BY control of cusp/cleft activities consistent with magnetopause reconnection, and time-varying magnetic reconnection appears to be an efficient driver of large-scale convection.