Electrodynamical Coupling of the Geospace System During Solar Flares

Reduced daytime upward E×B 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. Plain Language Summary The Earth's ionosphere is the ionized part of upper atmosphere and is created due to solar irradiation. Weakened daytime upward plasma drifts were often observed in the equatorial ionosphere in the initial phase of solar flares; however, the cause remains unknown. The magnetosphere‐ionosphere‐thermosphere coupled model, for the first time, is used to interpret the cause of it. Our results indicated that both solar flares induced high‐latitude and local equatorial ionospheric conductance enhancements are important in producing this phenomenon. High‐latitude ionospheric conductance enhancements reduced high‐latitude electric potential that can immediately leak in the equatorial ionosphere and reduce the upward plasma drifts. Increased low latitude ionosphere conductance during solar flares alters the way of current circulation over the equator by reducing low‐latitude zonal electric fields and thus upward plasma drifts to prevent the low‐latitude Cowling closure current from increasing excessively in relation to the global dynamo current source. Key Points Equatorial ionospheric electrodynamics during solar flares are analyzed in the whole geospace context for the first time Both local and global ionosphere conductance changes during solar flares contribute to the daytime reduced ionospheric upward ion drifts