本研究計畫將於中央氣象局未來作業用全球模式系統(FV3GFS)架構下，進行混成資料同化(HGDA)系統的建置與開發，強化具氣象局特色之全球預報系統。計畫第一年已藉由氣象局的FV3GFS-GSI資料同化系統為基礎，利用單點觀測同化實驗測試FV3GFS-GSI內子同化系統的特性。由於HGDA在實作上有兩種同化策略，故亦分就各同化策略進行結合權重的測試與探討，理解結合權重在不同策略中的貢獻。本年度將基於單點觀測實驗的經驗，進行FV3GFS-HGDA的循環同化實驗，並測試出各同化策略的最佳結合權重，評估最合適氣象局的同化策略。第三年將致力於QR-HGDA同化系統的建置，並將正交向量診斷應用於FV3GFS-GSI同化系統，期待可釐清EnVAR同化系統的修正特性。此三年期研究計畫成果預期可完成FV3GFS-HGDA系統的建置與效益評估，並可培養國內自主研發與強化全球模式的維護能力。 ;CWB has advanced its global operational system toward the next-generation system, the FV3GFS, coupled with a Gridpoint Statistical Interpolation (GSI) hybrid ensemble-variational (EnVar) data assimilation system (FV3GFS-GSI). This system is planned to be operational in 2021. Different from hybridizing the background error covariance in EnVar, a three-year project is planned to explore a different possibility of hybrid data assimilation and aims to develop the hybrid gain data assimilation (HGDA) system using the ensemble and variational DA components from the FV3GFS-GSI system. In the first year, single observation experiment had been conducted to investigate the properties of each DA system, including the FV3GFS-GSI, the FV3GFS-HGDA and its component DA systems. In this year, cycling experiments will be conducted to examine the applicability and feasibility for the FV3GFS-HGDA under a semi-operational environment. Since the HGDA has two scenarios for implementation, a series of sensitivity tests are necessary to justify the optimal combination weight for both scenarios. Except for a single weight value, an altitude-dependent combination weight would be a potential option for improving the hybrids if needed. In the last year of this three-year study, we will focus on implementing the QR-HGDA algorithm to evaluate the possibility of removing the ad-hoc determined combination weight in hybrids. The newly derived orthogonal analysis increment through QR-factorization can be used to understand the characteristics of the increments in the current FV3GFS-GSI system. Through the three-year study, we are able to develop a hybrid DA system and such experiences can feedback to the FV3GFS-GSI development. The optimal goal of this study is to enhance CWB’s ability in DA research and global forecast system in Taiwan.
