Based on the Backward Four-Dimensional Variational Data Assimilation (Backward-4DVar) system with the Advanced Regional\nEta-coordinate Model (AREM), which is capable of assimilating radio occultation data, a heavy rainfall case study is performed\nusing GPS radio occultation (GPS RO) data and routine GTS data on July 5, 2007. The case study results indicate that the use of\nradio occultation data after quality control can improve the quality of the analysis to be similar to that of the observations and,\nthus, have a positive effect when improving 24-hour rainfall forecasts. Batch tests for 119 days from May to August during the\nflood season in 2009 show that only the use of GPS RO data can make positive improvements in both 24-hour and 48-hour\nregional rainfall forecasts and obtain a better B score for 24-hour forecasts and better TS score for 48-hour forecasts. When using\nradio occultation refractivity data and conventional radiosonde data, the results indicate that radio occultation refractivity data\ncan achieve a better performance for 48-hour forecasts of light rain and heavy rain.
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