Variation of the curl-free component of ionospheric equivalent current in the Arctic during storms 1.Case analysis
In the Arctic region,a dynamic interplay between field-aligned current and the curl-free component of the ionospheric current forms a current loop.This loop undergoes intricate changes during magnetic storms due to fluctuations in ionospheric conductivity.Understanding these alterations requires a comprehensive analysis of ionospheric equivalent current inversion alongside geomagnetic observations.In this study,we undertake the inversion of ionospheric equivalent current utilizing data from the INTERMAGNET geomagnetic network during two significant storm events on September 20,2015,and November 30,2015.Employing low-rank approximation analysis,we delineate the ionospheric equivalent current into its divergence-free(essential component)and curl-free components.Our findings reveal that during sudden storm commencements(SSC),there's no notable change in the ionospheric current.However,during the main phase of magnetic storms,the divergence-free current exhibits a DP2 structure,consistent with previous research,while the curl-free current predominantly flows from the dawn side to the dusk side.In the subsequent recovery phase,this flow shifts from the dayside to the nightside.Interestingly,in the later stages of the storms,the curl-free current reverses direction,flowing primarily from the dusk side to the dawn side,contrasting with its behavior in the main phase.This reversal suggests a dynamic alteration in the near current of field-aligned current within the ionosphere,particularly in regions 1 and 2.
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