Nighttime plasma transport in the topside ionosphere using back-scatter N_h profiles

Abstract

Electron density profiles observed by means of incoherent backscatter technique at Arecibo (18.4°N, 67°W) have been used to study the vertical transport of plasma in the topside ionosphere during night-time. The height profiles of the transport velocity and the charged particle flux are calculated from the F-region continuity equation for the case of an optimum downward flux from the protonosphere, an estimate for which has been arrived at from the consideration of the limiting upward flux during daytime. During the period 06.00-18.00 hr L.M.T. the limiting flux is found to vary in the range 2.5 × 10¹¹ to 6.0 × 10¹¹ m^-2 sec^-1 with an average value of about 4.0 × 10¹¹ m^-2 se^c-1. The night-time downward flux has a maximum value that decreases with height from ~5 × 10¹² to 10¹² m^-2 sec^-1 in the range 400-625 km during the early hours when the plasma temperature is falling at a rate of about 3.5°K min^-1. The magnitude of the downward transport velocity is found to be less than 25 m sec^-1 at 400 km and 80 m sec^-1 at 625 km throughout the night-time. A post-midnight enhancement observed in the F-layer peak electron density has shown a significant dependence on the magnitude of the topside plasma transport velocity.