[A-AS03] Extreme Events and Mesoscale Weather: Observations and Modeling

[AAS03-06] Warm Rain Dynamics and Future Projections During the Winter Monsoon in the Western Java Sea, Indonesia

*wendi harjupa¹, Eiichi Nakakita¹ (1.Disaster Prevention Research Institute, Kyoto University, Kyoto, Japan)

Keywords:Climate Changes, Sea Surface Temperature, Warm Rain, TRMM, Himawari-8

This study investigates the characteristics and future projections of warm rain during the winter monsoon (December–February; DJF) over the western part of the Java Sea (WJS), Indonesia, using satellite observations (Himawari-8 and TRMM), reanalysis data (ERA5), and model simulations (Atmospheric General Circulation Model; AGCM). The Western Java Sea (WJS), influenced by the winter monsoon, shows a significant upward trend in sea surface temperature (SST) based on ERA5 data analysis from 1950 to 2009, with the highest SST increases occurring during DJF. By combining SST and Cloud Liquid Water Content (CLWC) observed by TRMM, the correlation coefficient (R) during DJF shows positive correlations along the winter monsoon pathway, including the WJS. The R value between cloud particles (CLWC, graupel, and Cloud Ice Water Content; CIWC) and rainfall during DJF in the WJS shows a stronger correlation for CLWC and rainfall, highlighting the crucial role of CLWC in rain formation. Warm rain processes, driven by CLWC, align with TRMM shallow rainfall observations and Himawari-8 Brightness Temperature Difference (BTD) data, both reflecting CLWC spatial distributions. AGCM simulations successfully replicate the observed CLWC patterns, showing strong agreement with TRMM data in the western region of Indonesia including WJS. The study also compares convergence patterns from ERA5 and AGCM data at 925 hPa, revealing similar trends in WJS, where convergence facilitates CLWC formation. An analysis of CLWC percentiles averaged between 1000-700 hPa reveals a notable rise in CLWC along the winter monsoon’s path, including the WJS, during DJF over 30-year periods. CLWC trends for both the Indonesia region and WJS also show an upward trend. These results emphasize the important role of the winter monsoon in influencing warm rain processes in the WJS, with significant implications for extreme weather events like flooding in areas such as Jakarta.