Abstract

Reduced daytime upward ExB drifts and weakened fountain effects in equatorial ionosphere have been frequently observed during the initial stage of solar flares. The cause of this phenomenon, however, remains unresolved. The latest state-of-art whole geospace model provides an unprecedented opport... Show moreReduced daytime upward ExB drifts and weakened fountain effects in equatorial ionosphere have been frequently observed during the initial stage of solar flares. The cause of this phenomenon, however, remains unresolved. The latest state-of-art whole geospace model provides an unprecedented opportunity to explore the origin of this response. We show that both prompt penetration electric fields (PPEFs) and internal changes in the wind dynamo process are responsible for the reduced upward ion drifts. Solar-flare-induced PPEFs are caused by a reduced high-latitude potential as a result of flare-enhanced ionospheric conductances which are distinct from traditional PPEFs that respond to changes in solar wind conditions or magnetosphere dynamics. The neutral wind dynamo source is mainly a reduction in the background low-latitude eastward electric field. This reduction occurs to maintain current continuity in response to the flare enhancement of low-latitude Cowling conductance that is relatively greater than the enhancement of the dynamo current source. Show less