Dayside and nightside contributions to cross-polar cap potential variations: the 20 March 2001 ICME case

We investigate the association between temporal-spatial structure of polar cap convection and auroral electrojet intensifications during a 5-h-long interval of strong forcing of the magnetosphere by an ICME/Magnetic cloud on 20 March 2001. We use data from coordinated ground-satellite observations in the 15:00-20:00 MLT sector. We take advantage of the good latitudinal coverage in the polar cap and in the auroral zone of the IMAGE chain of ground magnetometers in Svalbard - Scandinavia - Russia and the stable magnetic field conditions in ICMEs. The electrojet events are characterized by a sequence of 10 min-long AL excursions to -1000/-1500 nT followed by poleward expansions and auroral streamers. These events are superimposed on a high disturbance level when the AL index remains around -500 nT for several hours. These signatures are different from those appearing in classical substorms, most notably the absence of a complete recovery phase when AL usually reaches above -100 nT. We concentrate on polar cap convection in both hemispheres (DMSP F13 data) in relation to the ICME B-y conditions, electrojet intensifications, and the global UV auroral configuration obtained from the IMAGE spacecraft. The temporal evolution of convection properties such as the cross-polar cap potential (CPCP) drop and flow channels at the dawn/dusk polar cap (PC) boundaries around the time of the electrojet events are investigated. This approach allows us to distinguish between dayside (magnetopause reconnection) and nightside (magnetotail reconnection) sources of the PC convection events within the context of the expanding-contracting model of high-latitude convection in the Dungey cycle. Inter-hemispheric symmetries/asymmetries in the presence of newly-discovered convection channels at the dawn or dusk side PC boundaries are determined.