Dependencies of high-latitude plasma convection: Consideration of interplanetary magnetic field, seasonal, and universal time factors in statistical patterns

The database of the nine radars of the Super Dual Auroral Radar Network ( SuperDARN) in the northern hemisphere has been analyzed for information on factors that influence the convection of plasma in the high-latitude ionosphere. The velocity measurements were collected over the period 1998-2002. The data were first used to derive a new statistical model of convection that improves upon the earlier one-radar model of Ruohoniemi and Greenwald (1996) in its specification of the dependence of the convection pattern on the magnitude and direction of the IMF in the GSM Y-Z plane. We then derived average patterns for secondary sortings by season, year, and radar. Such dependencies as emerged were most clearly seen by contrasting the results for B-y+ and B-y-. The seasonal effect in the convection pattern is found to have similarities to that of the sign of B-y. In particular, the combination of B-y+/summer (B-y-/winter) reinforces the tendency of the B-y sign factor to sculpt the dusk and dawn cells into more round/crescent (crescent/round) shapes and to shift the crescent cell across the midnight MLT meridian. However, these combinations are associated with lower estimates of the total cross polar cap potential drop, Phi(PC), while the nonreinforcing combinations produce elevated Phi(PC), especially B-y-/summer. There is an overall tendency for Phi(PC) to increase from winter to summer, although the pure seasonal effect on the potential drop is weaker than that of the B-y-sign/season factor. We did not find pronounced differences among the patterns derived for the 5 individual years, which spanned the most recent interval of solar cycle maximum. Sorting by radar, we found few differences among the patterns for B-y+, but for B-y-, variations emerged that are consistent with a possible dependence on universal time (UT). The impacts of season and UT on convection in the high-latitude ionosphere thus depends on the IMF, especially the sign of B-y. We speculate that variability in the ionospheric conductivity has a greater effect on magnetosphere-ionosphere coupling under B-y- conditions.