IMPACT OF TWO TROPICAL CYCLONES ON THE RADIO ATMOSPHERICS OBSERVED USING
VLF RECEIVERS
Abstract
The response of electric field intensity of VLF radio atmospherics
during two tropical cyclones Fani (May 2019) and Amphan (May 2020) has
been presented in this paper. VLF radio atmospherics (or VLF sferics)
received at Coochbehar (CHB) and Kolkata (CUB) at three discrete
frequencies (4 kHz, 7 kHz, and 9 kHz) showed clear amplitude anomalies
with respect to the reference level during the two cyclonic storms. This
is explained using the electrical structure and distribution of
cloud-to-ground lightning associated with the cyclones. Effects of
‘local lightning’ and ‘distant lightning’ have been identified for both
the CUB and CHB receivers. Field intensity of VLF sferics at CUB station
was found to get enhanced for both types of lightning events. But the
intensity of VLF sferics at CHB station was found to be reduced for
‘distant lightning’ and enhanced for ‘local lightning’, possible reasons
of which are also explained.