A FAST study of quasi-static structure ("Inverted-V") potential drops and their latitudinal dependence in the premidnight sector and ramifications for the current-voltage relationship

Utilizing FAST satellite electron measurements, we present the first reported investigation of the dependency on latitude of quasi-static structure ("inverted-V") potential drop magnitude (Φ). A trend of lower Φ at lower latitudes in the premidnight sector on field lines with dark foot points was observed. This trend is supported both statistically and in individual satellite crossings. The existence of two distinct peaks in occurrence probability for Φ was also observed: one between ~2 kV and 10 kV and the other at somewhat less than 1 kV. The relative occurrence of structures with Φ in the higher (>2 kV) peak is significantly reduced with decreasing latitude. This partially accounts for the statistical trend of lower potential drop magnitudes at lower latitudes. The two Φ occurrence frequency peaks correspond to two different regimes (one with eΦ/kT_e ~ or > 1 and one with eΦ/kT_e < 1). In the lower Φ (<1 kV, eΦ/kT_e < ~1) regime which constitutes the vast majority of midlatitude events, these results are consistent with a voltage source configuration or more complex current-voltage relation where source electron density rather than Φ is most directly controlled by the field-aligned current density. These observations and their ramifications represent a significant step forward in the understanding of field-aligned currents, auroral acceleration, and magnetospheric-ionospheric coupling. Key Points Lower potential with lower latitude statistical and often single crossing trendTwo distinct occurrence frequency peaks in structure potentialsOccurrence probability of peaks and potentials in each peak vary with latitude