Bifurcation and merging of low mid-latitude plasma irregularities seeded by Medium Scale Traveling Ionospheric Disturbances over Srinagar, Jammu and Kashmir, India

Abstract:

We report the observation of propagating wave-like structures in the OI 630 nm airglow images obtained by an all sky imager installed in University of Kashmir, Srinagar, India( 34.08° N, 74.79° E, and 25.91° N magnetic latitude). These southwestward moving structures were observed during the night of 17th August, 2017. Their average horizontal wavelength was observed to be about 330 km and moved with average phase velocity of 92 m/s. These periodic structures are classified as Medium Scale Traveling Ionospheric Disturbances (MSTIDs) based on their observed parameters like wavelength, time period and propagating speed. The presence of gravity waves in the mesosphere during this night suggests that the gravity waves from below might have propagated to the ionospheric F-region leading to the generation of the observed MSTIDs. A peculiar characteristic of one of the dark bands of this MSTID, is the clockwise rotation of its lower latitude portion which became more eastward unlike its higher latitude part and ultimately got bifurcated. In addition, a merging process of two dark bands also occurred near the midnight. Some plasma depletion irregularity structures developed near midnight because of the bifurcation of a dark band of MSTID and its merging with other dark bands providing a direct evidence of plasma irregularities being seeded by MSTIDs-the first such results at this location. These signatures of field aligned irregularities drift westward unlike the MSTID bands which moved southwest. Further, the alignment of the depletion bands is also different from the observed MSTIDs. A minor geomagnetic sub-storm had occurred during the observation time of the development of the plasma irregularity structure and we suggest that this sub-storm might have triggered the development of the westward drifting irregularity from the MSTIDs and its different morphological structure. The eastward rotation of a dark band and its merging with other dark bands to seed the plasma depletion structures from MSTIDs, providing a direct observational evidence of generation of plasma depletion structures seeded by MSTIDs for the first time over Srinagar, will be presented in detail.