SEA-BREEZE FRONT PROPAGATION OVER THE NORTHERN COAST OF WESTERN JAVA AND ASSOCIATION WITH DEEP CONVECTION IN THE DRY SEASON

• Main Author: Wijaya Yonas, Banu
• Format: Theses
• Language: Indonesia
• Subjects: Ilmu kebumian
• Online Access: https://digilib.itb.ac.id/gdl/view/86377
• Institution: Institut Teknologi Bandung

The sea breeze affects mesoscale weather and local climate through the formation of sea-breeze circulation (SBC) and sea-breeze front (SBF). With numerous islands in the Indonesian Maritime Continent (IMC), the sea breeze phenomenon plays a crucial role in the diurnal convection patterns in IMC. In the western part of Java Island (particularly around Jakarta), the formation of SBC is most clearly observed from July to September or October, when convective activity is at its lowest. However, during the July-August-September (JAS) period, rainfall in western Java is higher than in other parts of Java Island. Previous studies in tropical India have shown that strong sea breezes are associated with more intense deep convection. However, similar research is still limited to the western part of Java. Therefore, it is necessary to study the characteristics of sea breeze and deep convection and how the sea breeze influences the formation of deep convection. By analyzing surface winds and relative humidity observed at two points in Jakarta during the June - September (JJAS) period from 2017 to 2021, the time of sea-breeze intrusion and its propagation speed can be estimated. The spatio-temporal characteristics of deep convection are investigated using the PyFLEXTRKR method based on Blackbody Temperature (TBB) data obtained from Himawari-8 satellite infrared imagery. For a more detailed analysis of the relationship between the sea breeze and deep convection, simulation data from the WRF model are used in this study. In general, the sea breeze occurs at KKP around 9 LT and at LLH around 11 LT. The later the sea-breeze intrusion, the higher the propagation speed tends to be. There is also a variation in sea-breeze propagation speed, ranging from 1.7 km/h to 16.9 km/h. The frequency of convective activity during the JJAS period remains quite high, particularly in southern Jakarta and southwest Banten. Based on detection results, the frequency of Deep Convective Systems (DCS) during JJAS is highest between 17 LT and 18 LT, with the favored formation areas located in southern Jakarta and southwest Banten. The size of the DCS varies from hundreds to tens of thousands of km². When the sea breeze propagates quickly, the DCS reaches its maximum size near the southern coastal area, while when propagation speeds are low to moderate, DCS predominantly forms in the island's interior. Case studies on the relationship between sea-breeze propagation speed and DCS show that strong sea breezes are associated with large DCS, while in weak sea-breeze cases, no DCS formation occurs at the study location. The WRF model simulation results used for analysis effectively represent the sea breeze, as evidenced by the visible circulation and convergence lines that match the observed SBF intrusion times. Further analysis shows that fast-moving sea breezes can penetrate further inland, creating convergence with southern airflows that initiate DCS formation. Additionally, fast-propagating sea breezes are accompanied by atmospheric conditions conducive to DCS formation. This indicates that fast sea breezes promote unstable atmospheric conditions favorable for the development of deep convection.