Polar cap plasma convection measurements and their relevance to the modeling of the high‐latitude ionosphere

Abstract

Plasma convection measurements, using Digisonde ionospheric sounders, have been conducted in the central polar cap at Thule, Greenland (86° CGL) and more recently at Qaanaaq, Greenland (87° CGL), in the auroral oval at the Air Force Geophysics Laboratory Goose Bay Ionospheric Observatory (65° CGL), and at suboval latitudes at Argentia NAS (57° CGL). The plasma convection or ionospheric drift measurements conducted at Thule and Qaanaaq during campaigns from the 1983–1984 winter to the present provide evidence that antisunward convection dominates in the polar cap with velocities typically between 300 and 900 m s−1. Velocity reversals or shears were observed in association with polar cap F layer auroras during quiet magnetic conditions. Observations of the plasma drift at Goose Bay show, as expected, a drift reversal from westward to eastward around midnight CGLT, indicating the rotation of Goose Bay from the evening into the morning convection cell. Observations at Argentia, typically a suboval/trough station, provide evidence under magnetically disturbed conditions for the midnight reversal of the antisunward flow pattern. However, the data at Argentia are generally less consistent under magnetically quiet conditions. This likely indicates the proximity of Argentia to the boundary between corotating and convecting plasma. Recent theoretical calculations of electron density profiles within the high‐latitude/polar cap ionosphere demonstrate that the diurnal f0 F2 variation observed at Thule is controlled by the plasma convection pattern and the associated drift velocities. The model calculations for Bz < 0 and Bz ≈ 0 show factors of 2 to 3 differences in Nmax over Thule, supporting the stated importance of convection pattern and velocity measurements for the modeling of the high‐latitude ionosphere.