The preliminary application of tropical cyclone targeted singular vectors in the GRAPES global ensemble forecasts
Abstract
The initial perturbation approach based on the subtropical singular vectors has been applied in the GRAPES global ensemble forecast system. However, the tropical cyclone track ensemble spread is not enough for this system. It is found that the initial perturbation near the tropical cyclone is not reasonable, which leads to that the forecast ensemble could not well estiminate the forecast uncertainty of the tropical cyclone, and may be one reason for the small track ensemble spread. Through computing the tropical cyclone singular vectors (TCSVs), and linearly combining the TCSVs and subtropical singular vectors to generate the initial perturbation, the defect that there is nearly zero initial perturbation near the tropical cyclone is made up, and the tropical cyclone ensemble forecasts are improved. Based on the computation scheme for the GRAPES global SVs, the square area around the typhoon center with the side length being 10 degree is determined as the targeted area to constract the computation scheme for TCSVs. The ensemble forecasts experiments are conducted for the typical typhoon BANYAN and other TC cases, and the best typhoon track at the National Meteorological Center of China Meteorological Administration (CMA) and precipitation observation data at National Meteorological Information Center of CMA are used to verify the forecasts. The structure characters of the TCSVs and the initial perturbations are analyzed, and the influence of TCSVs on the tropical cyclone track ensemble forecasts and the 24 hour accumulated precipitation probability forecast skill for the China area is analyzed. The experiments show that TCSVs are localized, and when TCSVs are used to generate the initial perturbations, the tropical cyclone track ensemble spread is increased, the relation between the track ensemble spread and the ensemble mean forecast error is improved, the track ensemble mean forecast error is decreased, and the ensemble members better describe the forecast uncertainty of the tropical cyclone track, the probability forecast skill of 24 hour accumulated precipitation in China for the light rain, moderate rain, heavy rain, and rainstorm is increased. In a word, the use of TCSVs is effective for improving the initial perturbations and may help improve the tropical cyclone track ensemble forecasts, when there exists one or more TCs.
- Publication:
-
AGU Fall Meeting Abstracts
- Pub Date:
- December 2019
- Bibcode:
- 2019AGUFM.A31O2798H
- Keywords:
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- 3329 Mesoscale meteorology;
- ATMOSPHERIC PROCESSES;
- 3354 Precipitation;
- ATMOSPHERIC PROCESSES;
- 3355 Regional modeling;
- ATMOSPHERIC PROCESSES;
- 4313 Extreme events;
- NATURAL HAZARDS