Investigation and Future Projection of Warm Rain During Winter Monsoon in Java Sea, Indonesia

This study investigates the characteristics and future trends of warm rain during the winter monsoon season (December, January, February; DJF) over Indonesia, with a focus on the Java Sea. The analysis integrates satellite observations from the Tropical Rainfall Measurement Mission (TRMM), reanalysis datasets (ERA5), and model simulations from the Atmospheric General Circulation Model (AGCM). An analysis of ERA5 data (1950–2009) reveals a pronounced upward trend in SST across the broader Indonesian region (slope 0.0070) and the Java Sea (slope 0.0094), with the most significant increases occurring during DJF. Cloud Liquid Water Content (CLWC), positively correlated with SST and rainfall, is used as a proxy for warm rain. TRMM satellite observations confirm that warm rainfall corresponds spatially with CLWC distribution. AGCM simulations effectively replicate observed CLWC patterns, showing strong alignment with TRMM data, particularly over western Indonesia, including the Java Sea. Convergence patterns derived from ERA5 and AGCM data exhibit similar trends, emphasizing the role of atmospheric convergence in CLWC formation over the Java Sea. An analysis of 95th percentile CLWC values at lower atmospheric levels (1000–700 hPa) highlights a significant increase in CLWC during DJF over the northwestern Indonesian region, including the Java Sea, across 30-year intervals spanning 150 years (1950–2099). These findings underscore the critical influence of the winter monsoon on warm rain processes in the Java Sea and its connection to extreme weather events, such as flooding in Jakarta, located on the southern coast of the Java Sea.