Cloud Spectral Characteristics Prior To Convective Initiation Event Based on Himawari-8 Satellite Around Surabaya

Geostationary satellite-based heavy rain prediction algorithm called convective initiation (CI) nowcasting recently becomes a solution in providing an earlier heavy rain forecast. However, this algorithm depends on the threshold value of the interest fields to predict whether a cloud object could potentially produce heavy rain, so it is important to understand the cloud physical characteristics in a particular area if the CI nowcasting algorithm is going to be developed. This research aims to assess the cloud spectral characteristics based on twelve interest fields of Satellite Convection Analysis and Tracking (SATCAST), one of the promising CI nowcasting algorithms, in Surabaya during the June-July-August period in 2018. Six bands of Himawari-8 and Surabaya weather radar data are used to quantify the cloud object spectral characteristics and determine the CI event, respectively. Four main processes conducted in this research include CI detection, cloud masking, backward cloud object tracking, and cloud spectral evaluation. The results show that 4 of 12 interest fields depict a significant change since 30–60 minutes before the CI event with $\mathbf{T}_{\mathbf{b11.2}}$ as the most significant interest field. Meanwhile, five interest fields tend to be constant until a significant change has reached 10 minutes before the CI event.