CONTRAST OF ATMOSPHERIC TRIGGER MECHANISMS IN EXTREME MARINE HEATWAVE EVENTS IN THE SOUTHERN JAVA UPWELLING SYSTEM

Abstract

Marine Heatwaves (MHWs) pose a substantial threat to marine ecosystems, with the physical mechanisms initiating these events in specific coastal regions potentially varying over time due to the prevailing phase of climate anomalies. This study seeks to compare the influence of surface wind stress and net solar radiation flux in initiating extreme MHW events within the Southern Java Upwelling System during 2016 and 2019. Sea surface temperature data were sourced from NOAA OISST version 2.1 satellite imagery, while wind and solar radiation components were derived from ECMWF ERA5 reanalysis data. MHW detection was based on the 90th percentile threshold of daily climatology, persisting for a minimum of five consecutive days. The findings indicate that the 2016 event was characterized by persistence, with absolute temperature peaks surpassing 30°C from March to April. This was triggered by a weakening of the southeast monsoon winds to an average of 2.3 m/s, which interrupted Ekman transport and diminished the influx of cold water from the thermocline layer. In contrast, the pronounced temperature increase in December 2019 was instigated by elevated net solar radiation, reaching 275 W/m² due to clear-sky conditions, while winds remained relatively calm following an earlier strengthening of upwelling. These findings underscore the necessity of comprehensive monitoring of atmospheric variables, beyond merely sea temperature, to enhance the reliability of marine early warning systems in Indonesia.