Effects of a stellar flare on planet HD 189733b, irradiated by the star HD 189733 (using ϵ Eri as a proxy). 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 middle and bottom panels show the ratio of electron density during the flare to that pre-flare, as a function of time and of pressure within the planetary atmosphere. The density ratio in the middle panel is for a planet irradiated by the solar-type flaring spectral shape and in the bottom panel, the planet irradiated by the AU-Mic flaring spectral shape. Electron densities are determined at 30° latitude and 12 LT; the planet is considered phase-locked with its star.