Evidence for the In‐Situ Generation of Plasma Depletion Structures Over the Transition Region of Geomagnetic Low‐Mid Latitude

Abstract

On a geomagnetic quiet night of October 29, 2018, we captured an observational evidence of the onset of dark band structures within the field‐of‐view of an all‐sky airglow imager operating at 630.0 nm over a geomagnetic low‐mid latitude transition region, Hanle, Leh Ladakh. Simultaneous ionosonde observations over New Delhi shows the occurrence of spread‐F in the ionograms. Additionally, virtual and peak height indicate vertical upliftment in the F layer altitude and reduction in the ionospheric peak frequency were also observed when the dark band pass through the ionosonde location. All these results confirmed that the observed depletions are indeed associated with ionospheric F region plasma irregularities. The rate of total electron content index (ROTI) indicates the absence of plasma bubble activities over the equatorial/low latitude region which confirms that the observed event is a mid‐latitude plasma depletion. Our calculations reveal that the growth time of the plasma depletion is ∼2 h if one considers only the Perkins instability mechanism. This is not consistent with the present observations as the plasma depletion developed within ∼25 min. By invoking possible Es layer instabilities and associated E‐F region coupling, we show that the growth rate increases roughly by an order of magnitude. This strongly suggests that the Cosgrove and Tsunoda mechanism may be simultaneously operational in this case. Furthermore, it is also suggested that reduced F region flux‐tube integrated conductivity in the southern part of onset region created conducive background conditions for the growth of the plasma depletion on this night.

A Rare Simultaneous Detection of a Mid‐Latitude Plasma Depleted Structure in O(1D) 630.0 and O(1S) 557.7 nm All‐Sky Airglow Images on a Geomagnetically Quiet Night

“…During 5 years of airglow observations from a mid-latitude station, Hanle (32.7°N, 78.9°E; Mlat. 24.1°N), Ladakh, India, different types of plasma structures, viz., electrified and non-electrified medium-scale traveling ionospheric disturbances (MSTIDs), mid-latitude spread-F (MSF), and mid-latitude field-aligned plasma depletion, have been observed in 630.0 nm images (Patgiri, Rathi, Yadav, Sarkhel, et al, 2024;Rathi et al, 2021Rathi et al, , 2022Rathi et al, , 2024Sivakandan et al, 2020Sivakandan et al, , 2021Yadav, Rathi, Gaur, et al, 2021).…”

“…During 5 years of airglow observations from a mid‐latitude station, Hanle (32.7°N, 78.9°E; Mlat. 24.1°N), Ladakh, India, different types of plasma structures, viz., electrified and non‐electrified medium‐scale traveling ionospheric disturbances (MSTIDs), mid‐latitude spread‐F (MSF), and mid‐latitude field‐aligned plasma depletion, have been observed in 630.0 nm images (Patgiri, Rathi, Yadav, Sarkhel, et al., 2024; Rathi et al., 2021, 2022, 2024; Sivakandan et al., 2020, 2021; Yadav, Rathi, Sarkhel, et al., 2021; Yadav, Rathi, Gaur, et al., 2021). The present study reports a first of its kind event in which the same plasma‐depleted structure was observed both in 630.0 and 557.7 nm images on a geomagnetically quiet night (Ap = 3) on 26 June of low solar active year 2021.…”

A Case Study on the Interaction Between MSTIDs' Fronts, Their Dissipation, and a Curious Case of MSTID's Rotation Over Geomagnetic Low‐Mid Latitude Transition Region

“…Sivakandan et al. (2020, 2021) reported a rare case of midlatitude spread F with onset of a midlatitude plasma depletion structure within the field of view (FOV) of the imager. Rathi et al.…”

“…Within a short period of 3 years, several interesting events have been observed over this transition region. Sivakandan et al (2020Sivakandan et al ( , 2021 reported a rare case of midlatitude spread F with onset of a midlatitude plasma depletion structure within the field of view (FOV) of the imager. Rathi et al (2021) found simultaneous coexistence of periodic and single dark band MSTIDs.…”