Detecting Long-term Characteristics of Marine Heatwaves (1982–2021) in the Indonesian Waters

Abstract

Abstract In this paper, we investigate the characteristics of marine heatwaves (MHWs) (i.e. frequency, maximum intensity, and duration of occurrences) in Indonesian waters and the mechanisms underlying the formation of MHWs generated by local forcing. The study utilizes the remote sensing data from National Oceanic and Atmospheric Administration (NOAA) Optimum Interpolation Sea Surface Temperature (OISST) dataset for SST and the European Centre for Medium-Range Weather Forecasts (ECMWF) reanalysis data (ERA5) for net surface heat flux components (shortwave radiation, longwave radiation, sensible heat flux, and latent heat flux), wind speed, and total cloud cover. The data covered a period within the last 40 years (1982–2021) during the warm (1982–2007) and cold (2008–2021) phases of the Pacific Decadal Oscillation (PDO) and were processed by statistical analysis methods. This study clearly reveals the highest average frequency and duration of MHWs in the Indonesian waters which were around 3–5 times a year and 10–20 days, respectively, occurring during the cold phase of PDO. Meanwhile, the highest maximum intensity of MHWs in the Indonesian waters was around > 1.5°C during the warm phase of PDO (El Niño dominated in Indonesia) generated by the local net surface heat flux. The most dominant contributors of net surface heat flux were high shortwave radiation (heat gain) and low latent heat flux (heat loss) through the evaporation process, thus keeping the ocean warm. Moreover, this study highlights the highest maximum intensity of MHWs which could reach > 3°C along western Sumatra to southern Java and waters around Papua when El Niño and positive Indian Ocean Dipole (pIOD) occur together. In contrast, the lowest maximum intensity of MHWs in the Indonesian waters occurred when La Niña was happening simultaneously with negative IOD (nIOD).