Electrodynamical Coupling of the Geospace System During Solar Flares

Abstract

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.

The Role of Flare‐Driven Ionospheric Electron Density Changes on the Doppler Flash Observed by SuperDARN HF Radars

“…In order to maintain global current continuity, the low-latitude zonal electric field must weaken during flares. The weakened eastward electric field causes weakened ionospheric vertical drift and weakened fountain effect during flares, as observed (Liu et al, 2020). The weakened ionospheric vertical drift changes the vertical distribution of plasma density, thus changing the radio signal reflection height.…”

“…Liu et al. (2020) examined mechanisms of weakened upward ion drift during the initial phase following an X‐class solar flare. They found that sudden enhancements in electron density following solar flares increase both Hall and Pedersen conductivities.…”

Ionospheric Electrodynamic Response to Solar Flares in September 2017

“…Figure 7 shows that the flare‐induced reduction of daytime zonal electric fields was caused predominantly by conductivity changes. Several studies (Liu, Qian, et al., 2021; Xiong et al., 2014; Zhang et al., 2017, 2019) suggested that this reduction at the dip equator might be associated with an increased that caused an increase in the Cowling conductance. The flare enhanced the equatorial Cowling conductance, which was relatively greater than the increase of global dynamo source currents that is suggested to scale with the Pedersen conductance increase.…”

“…In Figure 10, the comparison of the equatorial zonal electric fields from Run 4 to Run 2 (Run 2–Run 4) show the impacts of the flare‐increased and . Since the conductivity responses decrease with altitudes and the peak height of the Hall conductivity is lower than that of the Pedersen conductivity, is enhanced by solar flares and further induces the electrodynamic variations (Liu, Qian, et al., 2021; Xiong et al., 2014). However, the effects of the enhancement by the flares are much smaller than the influences of the changes caused by the flares (Figure 10), this is different from the previous explanation that the enhancement of equatorial Cowling conductivity, , is the major factor that causes the daytime electric field reduction (Liu, Qian, et al., 2021; Xiong et al., 2014; Zhang et al., 2017, 2019).…”

“…In some flare events, E‐region equatorial counter electrojets (CEJs) occurred, which was accompanied by the occurrence of F‐region westward electric fields in the observations (Manju & Viswanathan, 2005; Mayaud, 1977; Xiong et al., 2014; Yamazaki et al., 2009; Zhang et al., 2019). In addition to CEJ events, a weakening of ionospheric equatorial eastward electric fields during the daytime was also frequently observed and simulated during the initial phase of most solar flares (Liu, Qian, et al., 2021; Qian et al., 2012; Xiong et al., 2014; Zhang et al., 2017, 2019).…”