Tropical cyclones as a possible source of lower ionosphere (thermosphere) perturbation: a case study of Amphan Super Cyclone (SuCS) over Bay of Bengal

Abstract

The study investigates Super Cyclone (SuCS) Amphan, which occurred over the Bay of Bengal (BoB) during 16–21 May 2020 as a possible source of lower ionospheric perturbations. INSAT-3D satellite observations confirmed intense convective activity through low Cloud Top Brightness Temperature (∼–80 °C) and suppressed Outgoing Longwave Radiation (below 100 W/m²). Lightning analysis indicated an increase in activity within 500 km of the cyclone center, with cloud-to-cloud (CC) lightning intensifying in the eyewall during the cyclone's peak. Over 60 % of positive CC flashes exceeded 10 kA, highlighting strong convective electrical dynamics. Temperature perturbations observed by the AIRS instrument onboard NASA's Aqua satellite appeared as concentric wave patterns at stratospheric altitudes, indicating atmospheric gravity waves (AGWs) activity in the northeast of the storm center. SABER temperature profiles further revealed enhanced wave amplitudes from May 17–20, confirming AGW propagation into the mesosphere-lower thermosphere (MLT) region. Nightglow emissions observed by the Suomi-NPP/DNB sensor provided additional evidence of concentric gravity waves at the MLT heights. This enhanced AGW activity coincided with Amphan's intensification. This multi-altitude observational analysis highlights the role of intense convection and lightning in AGW generation and their subsequent influence on upper atmospheric dynamics. The observations confirm that tropical cyclones serve as a source of lower ionospheric disturbances through AGW-driven energy and momentum deposition.