Behavior of A Long-lived Borneo Vortex During March 2023

The Borneo Vortex (BV) is a mesoscale cyclonic circulation centered over the South China Sea (SCS) that typically persists for 1–3 days and significantly influences convective activity in surrounding regions, including Indonesia. However, the behavior and impacts of long-lived BV events remain poorly understood. This study investigates the atmospheric characteristics and convective effects of a strong and long-lived BV event that occurred from March 2–10, 2023. Using ERA5 reanalysis data with high temporal (hourly) and spatial (0.25° × 0.25°) resolution, we analyzed wind, relative vorticity, specific humidity, Outgoing Longwave Radiation (OLR), and precipitation. The event was classified into three phases: pre-BV (February 25–March 1), during-BV (March 2–10), and post-BV (March 11–15), using a composite analysis approach. Results show enhanced convective activity and widespread precipitation over western Kalimantan and western Java during the pre-BV phase, associated with low-level convergence and warm sea surface temperatures (~28 °C) in the central SCS. During the BV phase, convection shifted toward the ocean, with intensified precipitation over the SCS and suppressed rainfall over land, likely influenced by downdraft formation over the Java Sea. In the post-BV phase, a squall line developed over the Java Sea, leading to renewed convective activity and increased precipitation over Kalimantan and western Sumatra. These findings highlight the importance of long-lived BV events in modulating regional weather patterns and suggest implications for short-term weather forecasting and renewable energy planning in Indonesia.Keywords: Borneo Vortex, South China Sea, Indonesian Maritime Continent, convective activity