LIR-ACheM: Modelling of the D-Region Response to Solar Flares

A significant fraction of the HF waves is absorbed by the lowest ionospheric layer, the D-region. This region is perturbed by solar flares, which notably cause fast increases in the Sun’s X-ray flux. We present here a new chemistry model, the Lower Ionosphere Region — Absorption and Chemistry Modelling (LIR-ACheM), to study the D-region behaviour. It is based on the Mitra-Rowe [] scheme, and takes into account four distinct sources (EUV, Lyman-α, X-rays and cosmic rays) and seven species (electrons, NO+, O2+, O4+, positive cluster ions, O2− and other negative ions). It thus offers a compromise between accuracy and computing time. The D-region sluggishness and its recovery time after a flare are analysed, highlighting the importance of detachment at low altitudes and soft X-ray fluxes above 80 km.