High-Resolution Observations of Electric Fields and F-Region Plasma Parameters in the Cleft Ionosphere

Abstract

Details of the high-latitude ionosphere in the vicinity of the noon sector cleft have been examined using the Sondrestrom radar on April 18, 1983. An experiment combining azimuth and elevation scans was used to reveal the patterns of convection and F region temperature and density over a region of 1000 km diameter centered on the radar at 75°Λ. High-resolution line-of-sight observations have been used to produce detailed maps of the convection pattern and plasma transport each 20 minutes as the radar rotated through the noon sector during the 8 hour experiment. Patterns of electrostatic potential across the radar field of view reveal strong poleward and eastward convection in the morning sector several hours pre-noon, a region of low speed convection associated with the velocity convergence region, and high speed poleward and westward plasma transport from the afternoon sector into the region of cleft precipitation and polar cap entry near noon. The divergence of plasma flow at polar latitudes away from the cleft is seen in both the convection velocity and F region density data (poleward flow through the ionospheric cleft populates the polar cap with enhanced plasma density). A topside density trough is associated with the poleward edge of the strong afternoon convection toward noon where flow velocities approach 2000 m/s and a potential drop of 50 kV is seen across a 500 km region. The region of high-speed plasma entry into the polar cap was characterized by predominently northwestward directed flow on this day on which the IMF was directed away from the sun and Bz was near 0. Plasma entered polar latitudes across a rotational convection reversal which spanned at least 3 hours of local time in the noon sector. Low energy particle precipitation and an enhancement in the ionospheric electron temperature and density were observed at this convection reversal. High-resolution redar data revealed a region of multiple soft arcs aligned with the reversal and polar cap boundary in the post-noon sector.