Synoptic and Mesoscale Analysis of Extreme Rainfall Event in Cilacap Meteorological Station, Indonesia on December 7, 2018

Abstract

The highest rainfall for the last five years (2016-2020) was recorded at 199.5 mm in twenty-four hours at the Cilacap Meteorological Station. This study examines the dynamics of the atmosphere with a focus on the synoptic scale and the meso scale. This is done because high rainfall with a long duration is usually caused by a wider scale atmospheric circulation than just local convection scale. The rush of cold air masses from the Asian highlands that propagates across the equator is the main cause on the synoptic scale. In addition, the air flow from the south meets the air mass flow from the north right on the island of Java. On the meso scale, numerical simulations have not been able to properly estimate rainfall with values that tend to be underestimated. However, the value of convective available potential energy is high enough to support the growth of convective clouds. Based on himawari-8 satellite imagery, it is clearly observed that the clouds formed due to atmospheric dynamics are meso-scale convective cloud systems with a life span of more than six hours. The cloud growth is quite massive, which is indicated by the cloud top temperature value being lower than -80C in the mature phase. Thus, the resulting rainfall is quite heavy, causing flooding in parts of Cilacap