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

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 degrees N, 89.7 degrees 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 similar to 10 days, and only ESCS to occur after similar to 30 years over the BoB. Fani attained a minimum cloud top temperature of about -80 degrees C, and a corresponding maximum cloud top altitude of about similar to 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 similar to 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 similar to 13 and 20 min, highlighting the important role of lightning activity and AGWs in atmosphere-ionosphere coupling. A unique tropical cyclone "Fani" of the ESCS category from the Bay of Bengal with a life span of similar to 10 days is examined to understand the atmospheric gravity waves (AGWs) induced atmosphere-ionosphere coupling. The role of lightning discharges is specifically examined in the generation of AGWs in the lower atmosphere. These AGWs travel upwards from the lower atmosphere and play a significant role in transferring mass and energy during upward propagation through mesosphere to couple with ionosphere. The VLF data is used to understand the D-region ionospheric modulations by AGWs from Fani. Our analysis revealed increased AGW activity in the ionosphere during the cyclone period compared to pre- and post-cyclone days, which is strongly correlated with the lightning activity during the observational period. The findings contribute to a better understanding of how extreme weather events can affect the ionosphere. A unique extremely severe cyclonic storm Fani over the Bay of Bengal with 10-day life span is analyzed to understand the atmosphere-ionosphere coupling due to Atmospheric Gravity Waves (AGWs) Understand role of lightning activity in generation of AGWs, propagation via mesosphere, and consequent coupling with the ionosphere The results presented highlight the important role of lightning activity associated with AGWs in atmosphere-ionosphere coupling