GRAPES_TCM2.6(GT2.6), the updated version of the numerical model GRAPES_TCM2.1(GT2.1), is used to post-forecast tracks of TCs occurred over the Northwestern Pacific and the South China Sea during 2005. A series of detailed performance verifications for the numerical prediction of tropical cyclone tracks is presented. The results show that GT2.6 has a good performance on TC track prediction. The total mean forecast errors (MFE) at 24, 48 and 72h are 135.8, 230.7and 336.0km, respectively. The result also shows that the MFE at 12h is somewhat large (about 100km). The significant improvement of GT2.6's track prediction for the turning TC can be obtained through the modification of the forecast tracks with systematic bias. The model is found to have very good forecast skill for the cases that occurred in the west of 130E, especially for those close to the southeast of China. In general, the forecast track of GT2.6 is faster (slower) before (after) 48 hours than the optimal track, and the speed bias at 12 hour is larger during the forecast period (approximately 1m/s). In comparison with GT2.1, GT2.6 has similar performance stability and MFE characteristics on 0-48h TC track prediction, except that the 48h forecast of GT 2.6 is significantly better than that of GT 2.1.
Primary results indicate that several essential measures should be taken to further improve the track forecast skill of GT2.6. They are replacing the vortex-environment separation scheme with a stricter one, adding persistence vector to improve the initial motion and an asymmetric bogus vortex in the initial time, as well as enlarging the forecast domain and properly setting its position.
中国气象局气象数值预报创新基地开发了多尺度的同化与数值预报系统(简称GRAPES, Global Regional Assimilation and Prediction System)[6]。该系统采用全可压原始方程组,集常规与非常规变分同化、静力平衡与非静力平衡、全球与区域模式、科研与业务应用、串行与并行计算、标准化与模块化程序、理想试验与实际预报为一体,中小尺度与大尺度通用的数值预报系统[7]。现有的结果表明,GRAPES对天气形势和中尺度天气系统有较好的预报能力[8]。基于GRAPES的GRAPES_TCM[9]于2004年6月开始准业务预报试验。经过准业务试验和实际运行的结果看,它对热带气旋路径具有良好的预报精度和预报稳定性。
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