Development of Satellite-Based Cloud-Top Height and Convection Nowcasting Products in Support of SIGMET Coordination in the APAC Region

To reduce discontinuity across the Flight Information Region (FIR) boundaries, the Hong Kong Observatory (HKO) has been operating a HKO SIGMET coordination platform for Meteorological Watch Office (MWOs) in the Asia Pacific (APAC) region to harmonize SIGMET since 2017. Objective guidance of cloud top height and actual/forecast position are made available on the platform to facilitate coordination. In view of the much larger coverage and climatic variation, HKO has enhanced research efforts on algorithms to extract cloud top height, including standard atmosphere, climatology, High-resolution Cloud Analysis Information (HCAI) from JMA, METEOSAT SAF cloud top height algorithm and ECMWF model-based algorithm. This paper will discuss the detailed algorithms on cloud top height extraction and the respective performance verified against CALIPSO observations. Besides, HKO has also developed a convection nowcast product based on satellite derived radar reflectivity and the motion vector field between satellite imageries. A technique of artificial neural network (ANN) was developed for deriving simulated radar reflectivity from geostationary satellite by training multiple satellite channel data with radar data. Studies on training the ANN with radars from various regions were also performed. An echo tracking tool will then compute the motion vector field using optical flow between consecutive satellite imageries, then a semi-Lagrangian advection scheme is used for extrapolation of identified convection areas. This paper will report on the performance of the nowcasting algorithm and its limitations. The above cloud top height information and convection nowcast are helpful in improving the accuracy, consistency and the overall effectiveness of coordinated SIGMET, thus improving the aviation weather service in the APAC region as a whole. Some of the above products may also be made available on the Observatory developed electronic flight bag (EFB) mobile app MyFlightWx in the future if the pilots or airlines find them favorable.