Diagnostic Research Based On The Classification Of Typhoons By Chu Coching

It is of indicative significance in forecasting the tracks of typhoons to set a definite classification of typhoons. So some diagnostic researches are made based on the classification of typhoons by Chu Coching. Firstly, a more strict definition based on Chu’s classification is made, taking the intensity and the area affected of the typhoons into account. Secondly, the interannual and monthly variations, the proportion of six main groups and their sub-groups are concluded from zonal and sequential statistics of 1504 typhoons between 1949 and 2010. Finally, taking fourteen typical typhoons ranging from 2000 to 2009 for instance, we analyze the situation field at 500hpa, the vorticity field at middle and lower atmosphere and the 24h allohypsic field by using 1°×1°NCEP/NCAR reanalysis data. The results are as follows:(1) The typhoon has a significant inter-annual and monthly variations. Although the interval is not very long, typhoons show a 35-year period in the 3-year moving average curve. And the typhoons of Northwest Pacific(The South China) occurs mainly during the summer form July to October, accounting for about 70%, peaking at August and decreasing on both side..(2) The proportion of typhoons of the Pacific in Chu’s classification is the largest, about 33.31% while that of the South China Sea is smallest, about 1.53%. The four remaining groups which landed on China, Japan, Indochina or Philippines are up to 65.16%, including the 507 typhoons landing on China.(3) The typhoons of Japan, Indochina and the South China Sea show no significant inter-annual variations. The period of typhoons of China and Philippines is about 20 years and that of typhoons of Pacific is 35 years roughly.(4) All kinds of typhoons in the classification of Chu, except the typhoons of the South China Sea, show apparent monthly variation. The typhoons of China and Japan mainly appear in summer from July to September while those of Indochina and the Pacific are mainly in September and October. And the typhoons of Philippines always occur between October and December.(5) The following characteristics unfold in the circulation field of the typhoons of four types which landed on or crossed the continent. The strongest steering flow at 500hpa appear in the typhoons which belong to type a, b, c in typhoons of China and Indochina. And typhoons locate to the west or southwest of the subtropical high. Because the westerly belt strengthen or the relative position of the typhoons and the subtropical high change when the typhoons move to high latitudes, resulting in the southeasterly flow tunning into southwesterly one, typhoons usually turn eastward. The typhoons of Philippines are far from the subtropical high which is not very strong, so the typhoons move westward controlled by their inner forces and the tropical systems.(6) The vorticity field at 500hpa and 850hpa and the 24h allohypsic field are of indicative significance in the prediction of the tracks of typhoons.