Abstract
Abstract. High-time resolution data from the two Iceland SuperDARN HF radars show very strong nightside convection activity during a prolonged period of low geomagnetic activity and northward interplanetary magnetic field (IMF). Flows bursts with velocities ranging from 0.8 to 1.7 km/s are observed to propagate in the sunward direction with phase velocities up to 1.5 km/s. These bursts occur over several hours of MLT in the 20:00–01:00 MLT sector, in the evening-side sunward convection. Data from a simultaneous DMSP pass and POLAR UVI images show a very contracted polar cap and extended regions of auroral particle precipitation from the magnetospheric boundaries. A DMSP pass over the Iceland-West field-of-view while one of these sporadic bursts of enhanced flow is observed, indicates that the flow bursts appear within the plasma sheet and at its outward edge, which excludes Kelvin-Helmholtz instabilities at the magnetopause boundary as the generation mechanism. In the nightside region, the precipitation is more spot-like and the convection organizes itself as clockwise U-shaped structures. We interpret these flow bursts as the convective transport following plasma injection events from the tail into the night-side ionosphere. We show that during this period, where the IMF clock angle is around 70°, the dayside magnetosphere is not completely closed.Key words. Ionosphere (Auroral ionosphere; Ionospheremagnetosphere interactions; Particle precipitation)
Highlights
During prolonged periods of northward interplanetary magnetic field (IMF) and low geomagnetic activity, observations indicating an active nightside auroral zone have been reported in the past
Using incoherent scatter radar and DMSP satellite data, De la Beaujardiere et al (1994) have reported strong southward flow bursts in the night sector associated with velocity dispersed ion precipitation that are believed to be the manifestation of reconnection in the tail
We report here SuperDARN observations of large flow bursts in the evening and night ionosphere during a prolonged period of northward IMF on 17 December 1998, between 20:00 and 24:00 UT, when the radars were operating in a high spatial and temporal resolution mode, together with coincident satellite observations of auroral emissions by the POLAR UVI instrument and particle precipitation by the DMSP satellite
Summary
During prolonged periods of northward interplanetary magnetic field (IMF) and low geomagnetic activity, observations indicating an active nightside auroral zone have been reported in the past. In the Northern Hemisphere and for negative By, the convection tends to be westward at the lower latitudes and eastward at higher latitudes.
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