Effects of a stellar flare on an HD 209458b-type planet, irradiated by the star AU Mic, at an orbital distance of 1 AU. The top panel shows the variation of the intensity of the flare (in blue) and the stellar zenith angle (in red) with time, t = 0 representing the beginning of the flare. The bottom panel shows the ratio of electron density during the flare to that pre-flare, as a function of time and pressure within the planetary atmosphere. Electron densities are determined at 30° latitude and a given longitude (located at 12 LT at t = 0), the planet is considered to rotate with a period of 10 h. The onset of the flare corresponds to 12 LT.