IMF B_y and day‐night conductivity effects in the expanding polar cap convection model

Abstract

During southward B z periods the open field line region in the ionosphere (polar cap) expands due to increased dayside merging. Ionospheric plasma flow patterns result which can be classified by the sign of the interplanetary m•ignetic field (IMF) By component. In this paper we construct a time-dependent ionospheric convection model to simulate these flows. The model consists of a spiral boundary with a gap in it. The sign of the IMF By component determines the geometry of the gap. A potential is applied across the gap and distributed around the boundary. A fløw results which enters the polar cap through the gap and uniformly pushes the boundary outward. Results of the model show that By effects are greatest near the gap and virtually unnoticeable on the nightside of the polar cap. Adding a day-night ionospheric conductivity gradient concentrates the polar cap electric field toward dawn. The resulting flow curvature gives a sunward component that is independent of By. These patterns are shown to be consistent with published observations.

Coordinated interhemispheric SuperDARN radar observations of the ionospheric response to flux transfer events observed by the Cluster spacecraft at the high-latitude magnetopause

“…However, it is interesting to note, despite the limited backscatter available, the remarkable consistency of the flow patterns presented with the inferences regarding the motion of newly-reconnected field line footprints based upon lineof-sight data alone and the theoretical predictions of expected flow patterns based upon IMF conditions (Cowley and Lockwood, 1992). The estimated pre-noon location of the throat of the convection pattern in both the Northern and Southern Hemispheres is, at least in part, a consequence of the Ruohoniemi and Greenwald (1996) Moses et al (1987) presented a time dependent model of ionospheric flow patterns that incorporated a realistic day-night ionospheric conductivity gradient. Once this conductivity variation was taken into account, mirror symmetry between positive and negative IMF B Y convection patterns was destroyed, and the model reproduced the main features of ion flow observations made by spacecraft over the polar cap (e.g.…”

An unusual geometry of the ionospheric signature of the cusp: implications for magnetopause merging sites

“…The continual addition and removal of flux across this boundary, as a result of reconnection, is described in the expanding/contracting polar cap model (Siscoe and Huang, 1985;Cowley and Lockwood, 1992). The reconnection location (termed the X-line) on the magnetopause maps to a region in the dayside ionosphere termed the merging gap (Moses et al, 1987) which is a longitudinally-limited region of the PCB through which the ionospheric plasma flows into the polar cap. Identifying the PCB in the dayside ionosphere is crucial for studying the ionospheric signature of magnetic reconnection on the dayside magnetopause.…”

High-time resolution conjugate SuperDARN radar observations of the dayside convection response to changes in IMF B<sub>y</sub>

“…Cowley and Lockwood (1992) discuss the general concepts concerning the excitation of ionospheric convection and consider how patches of newly opened ux and their associated¯ows evolve with time following a burst of magnetopause reconnection. Their model envisages reconnection commencing at the ionospheric footprint of the magnetopause reconnection x-line (sometimes known as the merging gap, Moses et al, 1987) near magnetic local noon and spreading tailward. Observations suggest that the speed of this tailward expansion is between 1 and 10 kms À1 depending on the magnetic local time of observation (e.g.…”