Interaction Among Cold Surge and Cross-Equatorial Northerly Surge in Influencing Rainfall on Java Island During the Presence of Tropical Cyclone Dujuan in the Philippines and the Vortex in Northern Australia (Case Study, February 18–20, 2021)

On February 18–20, 2021, extreme rainfall occurred, which caused major flooding in several areas on the island of Java, one of which was the Jakarta area. A cold surge (CS) and a cross-equatorial northerly surge (CENS) were detected on that date, which were also followed by tropical cyclone (TC) Dujuan in the Philippines, as well as vortices in northern Australia. This paper examines the interaction mechanism of CS and CENS in influencing rainfall on Java Island at that time, which also coincided with the presence of TC Dujuan and water vortices, using analytical methods. This study uses several datasets in the form of temperature brightness data from Himawari, rainfall data from GSMaP, and several atmospheric parameters from ECMWF ERA5, as well as ASCAT data to identify CENS. The research results show that the impact of CENS and CS occurring simultaneously on rainfall was very significant on February 18–20, 2021, causing flooding in the western part of Java, especially Jakarta. This study highlights the strengthening of CS and CENS winds from TC Dujuan, which are pushing, and vortices in northern Australia, which are pulling. However, the vortex’s pull causes a weakening of the impact of CS and CENS on rainfall in West Java, which causes the release of water vapor along the CS and CENS paths. The impact of CENS and CS occurring simultaneously on rainfall causes persistent and even continuous rainfall throughout the day. This vortex not only brought a lot of water vapor along the CENS + CS route but also from the Indian Ocean, causing strong westerly winds that caused the vortex to pass along the south of Java Island.