Preliminary Study On The Wind Distribution Of Typhoons Affecting Wenzhou And Typical Case Analysis

Wenzhou is located in the southeast coast. It has 2 to 3 typhoons affecting Wenzhou every year.The strong wind which caused by typhoons is especially serious.Based on the historical data of Wenzhou, the automatic station data of Zhejiang Province, Typhoon Yearbook and Tropical Cyclone Yearbook etc., typhoons which affected Wenzhou from 1949 to 2012 were surveyed. There are 178 typhoons that caused strong wind, and 33 typhoons with no strong wind. The annual and monthly variation of the 178 typhoon was analyzed. It is founded that the frequency of typhoons which caused strong wind in Wenzhou has obvious interannual variation. From 1949 to 2012, there were three stages when typhoons affected Wenzhou more frequently than the other stages: from the end of 1950 s to the middle of 1960 s, from the end of 1970 s to middle of 1980 s and from the beginning of the new century to 2012..The intraseasonal variation of the frequency of the typhoons which impacted Wenzhou has a single peak characteristic, peaking in August. 33 of the typhoons which can’t cause strong wind occurred in July, August and Septemper. The typhoons move along these paths can’t cause strong wind:(1) the typhoons landed south of Xiamen or north of Jiaojiang,(2) the typhoons turned at the east of 124°E, and(3) the typhoons weakened over the southernTaiwan or over the ocean east of Taiwan.Secondly, 178 typhoons which caused strong wind to Wenzhou were divided into six categories according the landing point: class D1 includes the ones that landed from Fuzhou to Jiaojiang, class D2 includes the ones that landed from Fuzhou to Xiamen, class D3 includes the ones that landed south of Xiamen, class D4 includes the ones that landed north of Jiaojiang, class Z includes the ones that steered offshore and class X includes the ones that weakened in the warning area.Then, the typhoons in each category were further clarified by the moving direction after landed. The distribution of strong wind in each category when the typhoons affected Wenzhou was analyzed. It is founded that the typhoons in class D1 and class D2 could cause serve wind, and the typhoons in class D3 and class D4 cause the weaker wind than the ones in class D1 and class D2. The effect of the typhoons in class Z on Wenzhou depends on the turning point, the strength of typhoon and the distance from Wenzhou. The effect of class X typhoons was weak; however, it is necessary to notice the change of the typhoons in their strength when they are in the warning area.Thirdly, the surface pressure field of each typhoon was calculated using the NCEP/NCAR data and was compared between each other. It is founded that there were three classical weather conditions that could strengthen or weaken the wind : the continental high pressure type, the Bohai and Yellow sea high pressure type and the ground low-pressure type. The continental high pressure type and the Bohai and Yellow sea high pressure type would cause the strong wind early and extend the time during which strong wind took effect, while the ground low-pressure type would cause the delay of the time when strong wind took effect. Lastly, the effects of the three classical weather conditions were further confirmed by five typhoons in recent year which caused strong wind in Wenzhou.