Land effect on propagating convective systems during the heavy rainfall event of the 2002 Jakarta flood, Indonesia

The movement direction of propagating convective systems originating from both inland and offshore over the north coast of West Java in Indonesia is determined primarily by the prevailing wind. However, the role of land composition over the western part of the Indonesian Maritime Continent (IMC) is also expected to affect the development of propagating convective systems by enhancing upward motion. This hypothesis is tested using a Weather Research and Forecasting model incorporating convection-permitting with 3 km spatial resolution to simulate the heavy rainfall event during the 2002 Jakarta flood. We addressed the influence of land on the local circulation, particularly in the area surrounding Jakarta, by replacing the inland over the western IMC (96°–119°E, 17°S–0°) with a water body with an altitude of 0 m. We then compared the results of model simulations with and without land. The results show that land-sea difference forcing has a significant role in enhancing upward motion and generates a deep convective cloud in response to the land-based convective system, which then continuously and rapidly propagates offshore due to the cold pool mechanism. This land effect mainly triggers gravity waves and also results in early morning convection over coastal regions.