ANALYSIS OF RAINSTORMS ASSOCIATED WITH SIMILAR TRACK TROPICAL CYCLONES HAITANG (0505) AND BILIS (0604)

It is generally thought that the influence of comparable track typhoons is approximately similar, but in fact their wind and especially their rainstorm distribution are often very different. Therefore, a contrastive analysis of rainstorms by tropical cyclones (TCs) Haitang (0505) and Bilis (0604), which are of a similar track, is designed to help understand the mechanism of the TC rainstorm and to improve forecasting skills. The daily rainfall of TC Haitang (0505) and Bilis (0604) is diagnosed and compared. The result indicates that these two TCs have similar precipitation distribution before landfall but different precipitation characteristics after landfall. Using NCEP/GFS analysis data, the synoptic situation is analyzed; water vapor transportation is discussed regarding the calculated water vapor flux and divergence. The results show that the heavy rainfall in the Zhejiang and Fujian Provinces associated with Haitang (0505) and Bilis (0604) before landfall results from a peripheral easterly wind, a combination of the tropical cyclone and the terrain. After landfall and moving far inland of the storm, the precipitation of Haitang is caused by water vapor convergence carried by its own circulation; it is much weaker than that in the coastal area. One of the important contributing factors to heavy rainstorms in southeast Zhejiang is a southeast jet stream, which is maintained over the southeast coast. In contrast, the South China Sea monsoon circulation transports large amounts of water vapor into Bilis – when a water-vapor transport belt south of the tropical cyclone significantly strengthens – which strengthens the transport. Then, it causes water vapor flux to converge on the south side of Bilis and diverge on the north side. Precipitation is much stronger on the south side than that on the north side. After Bilis travels far inland, the cold air guided by a north trough travels into the TC and remarkably enhances precipitation. In summary, combining vertical wind shear with water vapor transportation is a good way to predict rainstorms associated with landing tropical cyclones.

An Exploration on the Applicability of Several Statistical Similarity Methods

In allusion to the previous various forecasting verification results of each similarity measurement, starting from formulas, the fact that there existed the same features between analog deviation and Hamming distance was analyzed and then proved. The limitations of analog deviation used in similarity forecast were discussed. The data from 96 different stations at 850 hPa in the East Asia during May 1 -30, 2010 were utilized to make similarity selection experiments among several frequently used similarity measurements and the new one proposed by the authors of this essay. The result indicated that analog deviation and Hamming distance were very much similar, with over 80% selected samples being the same. Analog deviation had the biggest difference with similarity coefficient, with over 70% selected samples being different. The new analog quantity was more similar to the related coefficient, with 60% selected samples being the same. Analog deviation and Hamming distance reflected how much the distances of the samples were similar to each other, while related coefficient and the new analog quantity reflected how much the shapes of the selected samples were similar to each other.