A rare simultaneous detection of a mid-latitude plasma depleted structure in O(^1D) 630.0 nm and O(^1S) 557.7 nm all-sky airglow images on a geomagnetically quiet night

In general, nighttime thermospheric 557.7 nm emission over mid-latitudes is predominantly masked by significantly larger mesospheric component, and hence, F-region plasma structures are rarely observed in this emission. This paper reports the first rare simultaneous detection of F-region plasma depleted structure in O(^1D) 630.0 nm and O(^1S) 557.7 nm airglow images from Hanle, India, a mid-latitude station (32.7N, 78.9E; Mlat.  24.1N) on a geomagnetically quiet night (Ap=3) of 26 June 2021. This indicates significant enhancement of thermospheric 557.7 nm emission. Interestingly, thermospheric 557.7 nm emission was not significant on the following geomagnetically quiet night as MSTID bands were only observed in 630.0 nm images. We show that enhanced dissociative recombination caused by descent of F-layer peak over the observation region coupled with the significant increase of the electron density at thermospheric 557.7 nm emission altitude enabled the detection of the plasma depleted structure on 26 June 2021.