Abstract

The sudden increase of X-ray and extreme ultra-violet irradiance during flares increases the density of the ionosphere through enhanced photoionization. In this paper, we use model simulations to investigate possible additional contributions from electrodynamics, finding that the vertical E × B d... Show moreThe sudden increase of X-ray and extreme ultra-violet irradiance during flares increases the density of the ionosphere through enhanced photoionization. In this paper, we use model simulations to investigate possible additional contributions from electrodynamics, finding that the vertical E × B drift in the magnetic equatorial region plays a significant role in the ionosphere response to solar flares. During the initial stage of flares, upward E × B drifts weaken in the magnetic equatorial region, causing a weakened equatorial fountain effect, which in turn causes lowering of the peak height of the F₂ region and depletion of the peak electron density of the F₂ region. In this initial stage, total electron content (TEC) enhancement is predominantly determined by solar zenith angle control of photoionization. As flares decay, upward E × B drifts are enhanced in the magnetic equatorial region, causing increases of the peak height and density of the F₂ region. This process lasts for several hours, causing a prolonged F₂-region disturbance and TEC enhancement in the magnetic equator region in the aftermath of flares. During this stage, the global morphology of the TEC enhancement becomes predominantly determined by these perturbations to the electrodynamics of the ionosphere. Show less