The Role of Double Vortex in the Indian Ocean in Influencing Rainfall Distribution Over Sumatra Island During May 6–9, 2022

On May 6–8, 2022, a double vortex occurred in the Indian Ocean, which caused heavy rainfall in several areas on Sumatra Island. This paper examines the role of the double vortex in increasing rainfall and even causing flooding in several areas on the island of Sumatra using analytical methods. This research used brightness temperature (TBB) data from Himawari, rainfall estimation data from GSMaP, and several meteorological parameters from ECMWF ERA5 data. The research results report that there are strong westerly equatorial winds and easterly winds along the latitude 10–15°S, as well as strong easterly winds near the Malaysian peninsula due to an increase in SST anomalies around the location of the two vortexes. The very high SST anomaly at the vortex 1 location triggers a deflection of strong equatorial westerly winds rotating counterclockwise at the vortex 1 location. There is a strengthening of vortex 1 when a strong northeast wind from the South China Sea moves toward the vortex 1 location. At the location of vortex 2, the high SST anomaly causes strong equatorial westerly winds to rotate clockwise at the location of vortex 2, which is then followed by a strong deflection of easterly winds along the 10–15°S latitude to the north, causing vortex 2. The presence of high anomalies of zonal and meridional wind and the center of low pressure at the location of the two vortices also support the double vortex development. Vortex 1 influences increased rainfall on the northern equator of Sumatra Island, while Vortex 2 causes increased rainfall in the southern part of Sumatra. The decrease in rainfall from 2°S latitudes to equatorial latitudes is due to being in an area where the second wind of the vortex is deflected so that there is no water vapor heading toward that area.