Plasmapause effects in the top side ionosphere

Abstract

Values of plasma temperature and O+/H+ ion transition height, obtained from 60,000 Alouette 1 electron density profiles, are used to study changes associated with the plasmapause. An ionospheric plasmapause can be defined by (1) the latitude at which peak temperatures occur, (2) the latitude down to which the ion transition height remains high, showing a near-limiting outflow of protons (the polar wind), and (3) the latitude below which H+ densities start to increase rapidly. All three criteria agree to within the experimental accuracy of about 2° at all times of day. The position of this plasmapause and its movement with magnetic activity agree with the results for the position and movement of the equatorial plasmapause, as defined by whistler measurements. Inside the ionospheric plasmapause the vertical proton flux decreases over a latitude range of about 20°, reaching to about L = 1.7 (day) or 1.9 (night). Thus there is an upflow of protons at all times of day on field lines just inside the plasmapause. Expansion of the equatorial plasmapause near dusk increases this flow and moves the ionospheric plasmapause to lower latitudes.