Enhancements in electron content at Arecibo during geomagnetic storms

Abstract

A phenomenon has been observed at Arecibo, Puerto Rico in which the total electron content of the ionosphere, in a column nearly parallel to the geomagnetic field, is enhanced in the afternoon or night during a magnetic disturbance. The enhancement is associated with the large negative excursion in the H component of the local geomagnetic field induced by the ring current. The enhancements which occur at night begin simultaneously with a downward motion of the F layer. This motion however is not a disturbance phenomenon as it is observed on 85 per cent of all nights at Arecibo regardless of magnetic activity. The downward motion and the enhancement in electron content which accompanies it on disturbed nights commence later in local time at higher latitudes. Neither north-south nor east-west motions of ionization appear to be able to explain the nighttime enhancements unless in the latter case eastward winds with velocities greater than 500 m/sec exist. Diffusion of ionization from the protonosphere and direct ionization have also been excluded as possible mechanisms.