Role of Lightning Activity in Deciphering Atmospheric Gravity Waves (AGWs) Induced D‐Region Ionospheric Perturbations During Extremely Severe Cyclonic Storm (ESCS) Fani

Abstract

The study presents detailed meteorological characteristics of extremely severe cyclonic storm (ESCS) Fani, and subsequent Atmospheric Gravity Waves (AGWs) induced D‐region ionospheric perturbations and the role of lightning activity in it. The cyclone shaped as a weak disturbance over the north Indian Ocean (2.7°N, 89.7°E) on 25 April 2019. The disturbance intensified and evolved into ESCS Fani over Bay of Bengal (BoB) on 30 April, had landfall on 03 May, and dissipated after 04 May 2019. What makes Fani unique is its long life span of ∼10 days, and only ESCS to occur after ∼30 years over the BoB. Fani attained a minimum cloud top temperature of about −80°C, and a corresponding maximum cloud top altitude of about ∼17 km. Such meteorological conditions presented a strong convection process in the towering cumulonimbus in inner and outer rain bands, resulting in intense lightning activity. The peak lightning flash rate observed was ∼375 min−1. SABER observations confirmed the coupling of atmosphere with ionosphere with strong AGWs in middle atmosphere during Fani. NWC (19.8 kHz) Very Low Frequency signal intersecting the track of Fani is used to decipher D‐region ionospheric perturbations induced by AGWs from Fani. The results show the presence of increased AGW activity in D‐region during the cyclone period when compared to that of the pre‐ and post‐cyclone periods. The periods of the observed gravity waves are between ∼13 and 20 min, highlighting the important role of lightning activity and AGWs in atmosphere‐ionosphere coupling.