AbstractThis paper investigates the role of coupled E‐ and F‐regions electrodynamics behind the rapid poleward extension of two dark fronts of an electrified medium‐scale traveling ionospheric disturbance (EMSTID). The fronts of EMSTID observed in O(1D) 630.0 nm airglow images extended poleward from the southern edge of the field‐of‐view to the location of the imager at Hanle (32.7°N, 78.9°E; Mlat. 24.1°N), India, on the geomagnetically quiet (Ap = 3) night of 09 June 2021. The existence of the fronts outside the southern edge of field‐of‐view before and during their extension was apparent from temporal fluctuations in the vertical total electron content. Additionally, favorable direction of thermospheric neutral wind to initiate Perkins instability existed beyond the southern edge of field‐of‐view prior to EMSTID's first appearance in the airglow images. Therefore, the observed EMSTID were likely generated outside the southern edge of field‐of‐view. Interestingly, the expected clockwise rotation of fronts with clockwise rotation of thermospheric neutral wind was not observed, although it was necessary to sustain the positive‐growth of Perkins instability. This indicates the involvement of E‐F coupling to sustain the positive‐growth of EMSTID since the presence of sporadic‐E layers was evident from the signal‐to‐noise ratio amplitude of L1 band and zonal wind profiles over the observation region. The enhanced polarization electric field caused due to E‐F coupling produced larger vertical E × B drift, which helped the EMSTID to sustain positive‐growth during the fronts' extension. Additionally, the enhanced northwestward E × B drift helped to maintain the northwest‐southeast orientation of EMSTID fronts, during the rotation of thermospheric neutral wind.
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