Westward Drift of Ionospheric Plasma Irregularities over a Low to Mid-latitude Transition Region in Indian Sector

Manzoor A Malik Manzoor A Malik,T K Ramkumar T K Ramkumar,Aashiq Hussain Bhat Aashiq Hussain Bhat,P Pavan Chaitanya P Pavan Chaitanya,Bilal Ahmad Ganaie Bilal Ahmad Ganaie

doi:10.4401/ag-8510

Abstract

We report the observation of plasma depletions/plumes in the F region ionosphere over a low to middle latitude transition region in the Indian sector. The observation of these plasma depletions is based on the data obtained in May 2019 through the all-sky airglow CCD imager installed in the campus of University of Kashmir, Srinagar (34.12 °N, 74.83 °E, magnetic latitude 25.91 °N). The depletions on the two consecutive nights of 05 and 06 May 2019 are aligned along the North-South (N-S) direction and drift westward. Several depletion bands along with some enhancement bands are seen in the 630-nm airglow images throughout the two nights. The observed structures show certain characteristics similar to Medium Scale Traveling Ionospheric Disturbances (MSTIDs) but these airglow features are not completely periodic. Further, in the observed depletion bands some East-West asymmetries are observed along with the structured tree-like branches of the airglow depletions. Some depletion bands even bifurcate leading to the inference that the structures are signatures of plasma irregularities rather than the usual MSTIDs observed in low-mid latitude transition region. The westward drift of the depletions especially during geomagnetic quiet times over this region makes this study significant since it offers a possible evidence that shows extension of spread F irregularities from the mid latitude region to the low-mid latitude transition region. In this paper, we point out some possible mechanisms related to the occurrence of plasma depletions at this region and their westward movement during geomagnetic quiet times.

Highlights

The frequently observed features in the F-region ionosphere are the Medium-scale traveling ionospheric disturbances (MSTIDs) over mid-latitudes and plasma bubbles (EPBs) in the equatorial and low geomagnetic latitudes
The plasma irregularities at the equatorial ionosphere are generated through Rayleigh–Taylor instability (RTI), but are not confined to the equatorial region as these may extend both altitudinally and latitudinally during the generation [Makela, 2006] the consequences of these irregularities do not have to be limited to the equator as the density depletions caused by equatorial Spread-F (ESF) can extend to higher altitudes and to the equatorial anomaly latitudes
The observations provide an insight of the extension of plasma depletion bands generated in middle latitudes towards the low-mid latitude transition region

Summary

Introduction

The frequently observed features in the F-region ionosphere are the Medium-scale traveling ionospheric disturbances (MSTIDs) over mid-latitudes and plasma bubbles (EPBs) in the equatorial and low geomagnetic latitudes. Since the post-midnight FAIs’ zonal propagation velocities are similar to that of MSTIDs at middle latitudes, some post midnight FAIs may be mid-latitude FAIs simultaneously existing with MSTIDs [Otsuka, 2012] Taori et al [2015] found EPBs and MSTIDs in the lower latitudes of the Indian sector at the same time, suggesting that MSTIDs may be one of their seeding mechanisms. Both the EPB and the MSF are capable of producing FAIs [Saito et al, 2008]. The position of the all sky imager in this study is intriguing because it is surrounded by Himalayan mountain ranges, where wind flows can produce a lot of lee waves, causing secondary instabilities in the upper atmosphere

Results

Discussion

Conclusion