Energetic electron precipitation as a source of ionization in the night-time D-region over the mid-latitude rocket range, South Uist

Abstract

Two Petrel rockets were launched from South Uist, Scotland, one at a magnetically quiet time and the other during a magnetic storm. At the quiet time only low precipitation fluxes ~4 electrons cm −2 ster −1 sec −1 >40 keV were observed while during the storm these fluxes rose to as high as 3 × 10 5 electrons cm −2 ster −1 sec −1 >40 keV. These precipitating energetic fluxes produced <25 per cent of the total night-time D-region ionization at the magnetic quiet time but the storm time precipitation accounted for 99 per cent of the total ionization. A clear correlation is found between particle flux and magnetic activity K p summed over 24 hr for 13 rockets launched from South Uist. This is used with the abundance of the different levels of activity to show that precipitating energetic electrons become a dominant source of the night-time D-region on 15 ± 11 per cent of the nights at solar minimum rising to 35 ± 20 per cent of the nights at solar maximum. When the magnetic field line passing through South Uist lies inside the plasmasphere, the electron precipitation continues up to 3 1 2 days after magnetic storms, in agreement with measured trapping lifetimes in the ‘electron slot’ of the trapping region.