Simultaneous detection of medium-scale traveling ionospheric disturbances and ionospheric plasma irregularities over Srinagar, J&K, India

We report some ionospheric phenomena that occurred on September 23, 2019 observed by an airglow imager installed at University of Kashmir, Srinagar, India (34.08°N, 74.79°E, and 25.91°N magnetic latitude). The various phenomena observed on this night are as follows: (1) The wave-like structures near the dusk time having phase fronts aligned along Northwest to Southeast direction and moving southwestward, classified as nighttime medium-scale traveling ionospheric disturbance. (2) Simultaneous observation of northwestward-moving nighttime medium-scale traveling ionospheric disturbances and eastward-drifting plasma irregularity and (3) The westward reversal of field-aligned plasma irregularity and K-shaped depletion structure formation post-midnight. We analyze their characteristics and evolution processes in detail. The plasma irregularity seems to be the signature of locally generated plasma irregularities at low-mid-latitude transition region as the radar observations from a geomagnetic low-latitude station (Gadanki, India; 13.5°N, 79.2°E, Magnetic latitude ~ 6.5°N) do not show any signatures of equatorial plasma bubbles during this night. It is interesting to note that the westward reversal of plasma irregularity occurred even when the geomagnetic conditions were at quiet levels (Kp ~ 0 to 1+). Though the observed nighttime MSTIDs and plasma irregularity bands are two different events, yet the structures appear to interact with each other, the apparent mechanism leading to the quiet time westward reversal of plasma irregularity structures at midnight and the development of complex K-shaped depletion structure. Interaction between these phenomena and their observed characteristic features is also discussed.