Session CD4 - Recent advances in VLF observations of the ionosphere during space weather events

Carine Briand (LESIA, Observatoire de Paris-PSL), Mark Clilverd (British Antarctic Survey), Peter Gallagher (Dublin Institute for Advanced Studies)

Solar eruptions are the source of significant disturbances of the ionosphere through the rapid increase in energetic radiation, particularly the X-ray flux. Radio wave propagation effects and increases in D- and E-region electron density are the main perturbations generated by these events. From the space weather point of view, HF blackouts over extended regions are the major risks linked to solar eruptions. Being too high for balloons and too low for in situ measurements with spacecraft, the lower ionospheric D-layer, a key region of absorption of the HF emission, is mostly surveyed by VLF measurements. Networks of VLF receivers have been deployed by various groups, including the polar regions (AARDDVARK), Latin and South America (LATNET & SAVNET) or spread over the world (SUPERSID & AWESOME). VLF measurements have also proved to be a powerful tool to detect transients linked to thunderstorm regions (Elves, Sprites, and Terrestrial Gamma-ray Flashes). The interest in such events was recently raised for civil aviation since they can be the source of intense ionizing radiations. This session aims to present several aspects of recent achievements for solar flares or thunderstorm luminous events, from instrumentation to observations, and also modelling. We will also discuss the buildup of an international organization to better share and analyze the VLF data during specific space weather events.