Summertime Convective Initiation Nowcasting over Southeastern China Based on Advanced Himawari Imager Observations

Abstract

12 Convective initiation (CI) nowcasting often has a low probability of detection (POD) and 13 a high false-alarm ratio (FAR) at sub-tropical regions where the warm-rain processes often 14 occur. Using the high spatial- and temporal-resolution and multi-spectral data from the 15 Advanced Himawari Imager (AHI) on board Japanese new-generation geostationary satellite 16 Himawari-8, a stand-alone CI nowcasting algorithm is developed in this study. The 17 AHI-based CI algorithm utilizes the reflectance observations from channels 1 (0.47 μm ) and 7 18 (3.9 μm ), brightness temperature observations from infrared window channel 13 (10.4 μm ), the 19 dual-spectral differences between channels 10 (7.3 μm ) and 13, 13 and 15 (12.4 μm ), as well as 20 a tri-spectral combination of channels 11, 15 and 13, as CI predictors without relying on any 21 dynamic ancillary data (e.g., cloud type and atmospheric motion vector products). The 22 proposed AHI-based algorithm is applied to CI cases over Fujian province in the 23 Southeastern China. When validated by S-band radar observations, the CI algorithm 24 produced a POD as high as 93.33%, and a FAR as low as 33.33% for a CI case day that 25 occurred on 1 August 2015 over Northern Fujian. For over 216 CI events that occurred in a 26 three-month period from July to September 2015, the CI nowcasting lead time has a mean 27 value of ~64 minutes, with a longest lead time over 120 minutes. It is suggested that 28 false-alarm nowcasts that occur in the presence of capping inversion require further 29 investigation and algorithm enhancements.