Features of Atmospheric Dynamics During Tropical Cyclone AMPHAN Observed Using ST Radar and Doppler Weather Radar

A very severe cyclonic storm (CS) AMPHAN struck the eastern coast of Indian subcontinent adjoining northern parts of Bay of Bengal (BoB) on May 20, 2020. Pilot version of an active phased-array radar operating at 53 MHz implemented by University of Calcutta was used to measure zonal, meridional, and vertical velocities, resultant wind speed and direction before and during this cyclone. It is important to note that this was the first super cyclone which could be tracked using very high frequency (VHF) active phased-array radar in India. One of the striking features of this cyclone was its rapid development over a short period of time with wind speeds increasing from 12 m/s on May 19, 2020, to 41 m/s on May 20, 2020. The wind directions were found to reverse from westerly to easterly direction in the lower troposphere. Intense turbulence layers and vorticity were found on May 20, 2020, which may be attributed to strong wind shear. Although satellite images corresponding to such severe weather conditions are usually available, ground-based radar measurements with very high resolution of 37.5–75 m in altitude are considered invaluable when trying to characterize the atmospheric winds and other parameters within an altitude range of 0–10 km, these being some of the first such results for AMPHAN from this region using VHF stratosphere troposphere (ST) radar. The analysis obtained from this radar has also been supported by the S-band Doppler weather radar (DWR) and European reanalysis (ERA) reanalysis data during the cyclonic period.