Abstract
Abstract. Observations by the EISCAT Svalbard radar in summer have revealed electron density enhancements in the magnetic noon sector under conditions of IMF Bz southward. The features were identified as possible candidates for polar-cap patches drifting anti-Sunward with the plasma flow. Supporting measurements by the EISCAT mainland radar, the CUTLASS radar and DMSP satellites, in a multi-instrument study, suggested that the origin of the structures lay upstream at lower latitudes, with the modulation in density being attributed to variability in soft-particle precipitation in the cusp region. It is proposed that the variations in precipitation may be linked to changes in the location of the reconnection site at the magnetopause, which in turn results in changes in the energy distribution of the precipitating particles.Key words: Ionosphere (ionosphere-magnetosphere interactions; plasma temperature and density; polar ionosphere)
Highlights
Long-lived enhancements of ionospheric plasma, known as polar patches, drift in the anti-Sunward convectionow across the polar cap
The current study presents observations made by the EISCAT Svalbard radar (ESR) of a succession of three enhancements in electron density found in the magnetic noon sector between 0810 and 0840 UT on 22 August 1998 that have characteristics consistent with polar patches
A sequence of three electron density enhancements that satisfy criteria for polar patches have been observed by the ESR radar in the noon magnetic sector under IMF conditions conducive to equatorial reconnection
Summary
Long-lived enhancements of ionospheric plasma, known as polar patches, drift in the anti-Sunward convectionow across the polar cap. Auroral observations con®rmed that soft precipitation had played an important role in the creation of this structure at an altitude where the enhanced plasma densities would be expected to have suciently long lifetimes to preserve the patch in the cross-polarow. The current study presents observations made by the EISCAT Svalbard radar (ESR) of a succession of three enhancements in electron density found in the magnetic noon sector between 0810 and 0840 UT on 22 August 1998 that have characteristics consistent with polar patches. Simultaneous observations by several instruments, including the CUTLASS and EISCAT mainland radars and DMSP satellite particle detectors, have been used to identify the source of the enhanced ionisation and to deduce a possible mechanism by which the plasma may have been structured into patches
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