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

Autor: Sivakandan, M.1,2, Mondal, S.3, Sarkhel, S.3 sarkhel@ph.iitr.ac.in, Chakrabarty, D.4, Sunil Krishna, M. V.3, Upadhayaya, A. K.5, Shinbori, A.1, Sori, T.1, Kannaujiya, S.6, Champati Ray, P. K.6
Předmět:
Zdroj: Journal of Geophysical Research. Space Physics. Sep2021, Vol. 126 Issue 9, p1-15. 15p.
Abstrakt: 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. Plain Language Summary: It is well known that the plasma irregularities/depletions in the ionosphere degrade the satellite‐based communication navigation signals, significantly. Thus, understanding the plausible onset condition and characteristics of these depletions are vital for the better space weather forecasting. Occurrence of plasma depletion in the equatorial and high latitude regions are associated with Generalized Rayleigh Taylor instability mechanism and their characteristics are mostly well reported. On the other hand, though the characteristics of the mid‐latitude field aligned irregularities are reported by a few investigators, there is no direct observational evidence for the onset of the mid‐latitude plasma depletion till now. Thus, the present investigation provides first optical observational evidence of in‐situ generation of plasma depletion and provides some insight on the possible background conditions which supported the onset over the geomagnetic low‐mid latitude transition region. Key Points: A remarkable observational evidence of onset of plasma depletions is captured over geomagnetic transition region in a span of 25 minIt is argued that both mid‐latitude sporadic‐E layer and Perkins instabilities are simultaneously needed to explain the growth timeIt is also proposed that reduced flux tube integrated Pedersen conductivity over south of onset location favored the growth of the bubble [ABSTRACT FROM AUTHOR]
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