Solar wind effect on Joule heating in the high-latitude ionosphere

摘要

The effect of solar wind on several electrodynamic parameters, measured simultaneously by the European Incoherent Scatter (EISCAT) radars in Troms? (TRO, 66.6? cgmLat) and on Svalbard (ESR, 75.4? cgmLat), has been evaluated statistically. The main emphasis is on Joule heating rate Q_J, which has been estimated by taking into account the neutral wind. In addition, a generally used proxy Q_E, which is the Pedersen conductance times the electric field squared, has been calculated. The most important findings are as follows. (i) The decrease in Joule heating in the afternoon-evening sector due to winds reported by Aikio et al. (2012) requires southward interplanetary magnetic field (IMF) conditions and a sufficiently high solar wind electric field. The increase in the morning sector takes place for all IMF directions within a region where the upper E neutral wind has a large equatorward component and the F region plasma flow is directed eastward. (ii) At ESR, an afternoon hot spot of Joule heating centered typically at 14–15 magnetic local time(MLT) is observed during all IMF conditions. Enhanced Pedersen conductances within the hot spot region are observed only for the IMF B_z + ∕B_y? conditions, and the corresponding convection electric field values within the hot spot are smaller than during the other IMF conditions. Hence, the hot spot represents a region of persistent magnetospheric electromagnetic energy input, and the median value is about 3 mW/m~2.(iii) For the southward IMF conditions, the MLT-integrated Q_E for B_y? is twice the value for B_y+ at TRO. This can plausibly be explained by the higher average solar wind electric field values for By?.