Low‐latitude ionospheric effects of energetic electrons during a recurrent magnetic storm

Abstract

Abstract We study a magnetosphere‐ionosphere coupling at low latitudes during a moderate (corotating interaction regions/high‐speed solar wind streams‐driven) geomagnetic storm on 22 July 2009. Recently, it has been shown that during major (coronal mass ejection‐driven) storms, quasi‐trapped >30 keV electrons largely enhance below the radiation belt in the forbidden zone and produce an additional ionization in the topside ionosphere. In this work, we examine a case of the recurrent storm when the magnetosphere‐ionosphere coupling through the quasi‐trapped electrons also may take place. Data from NOAA/Polar‐orbiting Operational Environmental Satellite and Japanese Greenhouse gases Observing Satellite were used to identify the forbidden electron enhancement (FEE). We find a positive vertical gradient of the electron fluxes that indicates to the radiation belt as a source of FEE. Using global ionospheric maps, radiotomography reconstructions from beacon data and COSMIC/FORMOSAT‐3 radio occultation measurements, we have observed an unusually large area in the nighttime ionosphere with increased total electron content (TEC) and prominent elevation of the F layer at low latitudes that coincides with FEEs spatially and temporarily. Ionizing particles are considered as an addition source of ionization along with generally accepted mechanisms for storm time TEC increase (a positive ionospheric storm). We discuss relative contributions of the FEE and disturbance dynamo electric field in the TEC increases during the storm recovery phase.