Abstract
A precipitation simulation associated with Typhoon Sinlaku using the fifth-generation Pennsylvania State University – National Center for Atmospheric Research Mesoscale Model (MM5) initialized diabatically with the Local Analysis and Prediction System (LAPS) is evaluated over the Taiwan area. Two purposes of this paper are to test the performance of the LAPS diabatic data assimilation technique and investigate the impact of the Doppler radar data on the short-range quantitative precipitation forecasts for the typhoon. Typhoon Sinlaku was selected because Doppler radar is one of the most important data sources for an accurate analysis of typhoons and Sinlaku was located close to the Wu-Fen-Shan (WSR-88D) Doppler radar station at north tip of Taiwan during part of its lifetime on 6-7 September 2002. The observed rainfall distribution associated with Sinlaku was closely related to the topography in northern Taiwan. Simulation results show that the MM5 initialized diabatically with LAPS has higher skill for precipitation simulation than the non-LAPS cold start experiment, especially for the higher thresholds in the early portion of model integration (?10 mm in 0-6 h). The assimilation of the Wu-Fen-Shan Doppler radar data played a key role in the improvement of precipitation simulation owing to improvement in the presentation of typhoon hydrometeorological features, such as clouds and the outer rainband, in the model initial conditions. The presence of these initial hydrometeor species had a beneficial impact on reduced precipitation spin-up time. The use of Doppler radar data also can enhance the forecast definition of typhoon structure and rainband simulations. However, these radar data only play a minor role on the typhoon track simulations. However, these radar data only play a minor role on the typhoon track simulation in this case study. Overall, the mesoscale model initialized diabatically with LAPS data assimilation shows improved capability on the typhoon short-range quantitative precipitation forecasts, especially when the Doppler radar data is included.
Highlights
One of the major forecasting technique developments of the Central Weather Bureau (CWB) in Taiwan has been to improve the quantitative precipitation forecasting (QPF) of tropical cyclones
Two objectives of this paper were to evaluate the performance of the precipitation simu lation associated with Typhoon Sinlaku from MM5 model initialized diabatically with the high-resolution (9 km horizontal grid interval) operational Local Analysis and Prediction System (LAPS) data assimilation system and determine the impact of the Wu-Fen-Shan Doppler radar data on the simulation results
During the period when Typhoon Sinlaku passed to the sea north of Taiwan, observed rainfall analysis from 391 rain gauge stations showed that the precipitation associated with typhoon over Tai wan was, in general, phase-locked with the northern Central Mountain Range and mostly confined to 6 September with two major rainfall episodes
Summary
One of the major forecasting technique developments of the Central Weather Bureau (CWB) in Taiwan has been to improve the quantitative precipitation forecasting (QPF) of tropical cyclones. As a tropical cyclone approaches Taiwan, the steep and high altitude topography over the island - Central Mountain Range (Fig. 1 , hereinafter, CMR) with highest peak close to 4000 m -, is a critical factor for the storm's track deflection, local circulation variations, and many extreme rainfall events (Wu and Kuo 1999). The rainfall distribution for tropical cyclones affecting Taiwan is often phase-locked with the CMR (Wu and Kuo 1999), the mesoscale precipitation distribution associated with a landfalling typhoon is still a difficult task for nu merical weather prediction (Wu 2001). The discussions and conclusions are provided in the final section
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