Unraveling the Generation Mechanism of a Mid-Latitude Plasma Blob and the Evidence of Its Rare Interaction with a MSTID Phase Front

Abstract

We report observations of two distinct nighttime F-region irregularities, plasma blob (localized density enhancement) and medium-scale traveling ionospheric disturbance (MSTID), in O(1D) 630.0 nm all-sky airglow images from Hanle (32.7°N, 78.9°E; Mlat~24.1°N), Ladakh, India, during the geomagnetically quiet (Ap=6) night of 06 July 2021. Global vertical total electron content (VTEC) maps revealed that the plasma blob developed beyond the southern edge of imager's field-of-view before appearing in airglow images and propagated predominantly westward, as confirmed from both the airglow and VTEC datasets. The existence of the plasma blob and MSTID outside the imager field-of-view was further confirmed by temporal VTEC fluctuations recorded by multiple GNSS receivers. Additionally, FORMOSAT-7/COSMIC-2 signal-to-noise ratio and ICON/MIGHTI wind profiles indicated the presence of sporadic-E (ES) layers at E-region near both the plasma blob and the MSTID. We propose that polarization electric field associated with either MSTID or ES-layers mapped along magnetic field lines to lower latitudes, driving upward plasma transport from F-peak region through vertical uplift of the F-layer. This F-layer uplift was confirmed by simultaneous in-situ O+/H+ density enhancements/reductions at LEO altitudes measured by FORMOSAT-7/COSMIC-2. Upward-transported plasma experienced reduced chemical loss at higher altitudes, producing localized VTEC enhancements (plasma blob). The plasma subsequently diffused along magnetic field lines to higher/lower latitudes/altitudes (~250 km), entering imager's field-of-view, where enhanced dissociative recombination of O2+ produced high intensity airglow region. Interestingly, interaction between the plasma blob and MSTID's plasma-depleted front caused gradual decay and bifurcation of the front due to plasma influx from the high-density blob region.