A phytoplankton bloom with a cyclonic eddy enhanced by the tropical cyclone Phethai in eastern Sir Lanka

Strong tropical cyclone (TC) Phethai occurred in the Bay of Bengal (BoB) in December 2018. A phytoplankton bloom within the area of 8.5°N–10°N, 81.9°E–83.4°E was studied in eastern Sri Lanka. The dynamic mechanisms of the chlorophyll-a (Chl-a) bloom was investigated with high-resolution satellite remote sensing data, reanalysis data and buoy data. Before the passage of Phethai, there was a weaker cyclonic eddy in eastern Sri Lanka. After the passage of Phethai, the cyclonic eddy vorticity was enhanced to 0.6445 and lasted for five days. With the passage of Phethai, the thermocline deepened to 49.12 m, causing nutrient upwelling into the mixed layer. The Chl-a flux below the thermocline accelerated from December 13 and reached 0.047 mg • m−2 • s−1 on December 17, when the average Chl-a concentration at the sea surface was 0.6445 mg • m−3. This study can help evaluate the ecological impacts of TCs in eastern Sri Lanka.