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Low‐Latitude VLF Radio Signal Disturbances Due to the Extremely Severe Cyclone Fani of May 2019 and Associated Mesospheric Response
Author(s) -
Pal Sujay,
Sarkar Shubham,
Midya Subrata K.,
Mondal Sushanta K.,
Hobara Yasuhide
Publication year - 2020
Publication title -
journal of geophysical research: space physics
Language(s) - English
Resource type - Journals
eISSN - 2169-9402
pISSN - 2169-9380
DOI - 10.1029/2019ja027288
Subject(s) - daytime , atmospheric sciences , anomaly (physics) , cyclone (programming language) , ionosphere , environmental science , middle latitudes , amplitude , radio wave , meteorology , geology , geophysics , physics , condensed matter physics , field programmable gate array , quantum mechanics , computer science , computer hardware
We present new results of lower ionospheric disturbances due to the extremely severe cyclonic storm Fani over northeastern part of the Indian Ocean. Very low frequency radio signal received at Kolkata, India, and mesospheric temperature and ozone concentration data from the NASA's TIMED satellite are used for this purpose. Significant wave‐like oscillations and strong amplitude anomalies in daytime and nighttime VLF signal were observed when the cyclone center was within ∼700 km from the receiver. Both the mesospheric ozone concentration and temperature showed maximum anomalies beyond 3 σ during the cyclone period. Maximum ozone anomaly and maximum VLF anomaly occurred on the same day when cyclone intensity was maximum, while the maximum temperature anomaly occurred on the next day during landfall. Mesospheric temperature enhancement around VLF reflection heights indicates changes in the chemical composition and electron‐neutral balance in the D region ionosphere. Simulation of VLF signal showed that the D region reflection height decreased by 7.9 km and the D region electron density increased by ∼20 times compared to precyclone midnight values at the maximum perturbed area along the propagation path. Wavelet analysis confirmed significant enhancement of atmospheric gravity waves spectrum with periods 10 min to 2 hr around landfall. Further, a strong anticorrelation between total wavelet power in the wave band of periods 10–30 min and cyclone pressure suggests a possibility of monitoring cyclone intensity from mesospheric gravity waves using VLF radio measurements.