Speed Distribution of 100-year Extreme Winds in Lower-reaches of the Yangtze

In engineering meteorological application the basic wind speed of 100-year return period is commonly confirmed according to the recommend value of national regulation or China basic wind speed distribute map by the method of interpolation. In order to avoid both the potential hazard in engineering design and the higher cost in construction, which may be caused by the low re solution of the basic wind speed distribute map in low er-reaches of the Yangtze and the lacking of actual wind speed data along the river, eight short-term wind observation points are selected along low er-reaches of the Yangtze, and the observation runs synchronously with their neighboring meteorological stations from 2000 to 2006. So the observation pro gram is set up to meet the demand of engineering constructions along low er-reaches of the Yangtze. The observation points are built by on-side investigation to eliminate the extreme terrain effects and can represent the actual wind of the low er-reaches to the largest extent. At every observation point, it is assured that more than one year of simultaneous observation with its adjacent weather station is carried out, although the observational time for each point is not always homology. Based on the short-term synchronous wind data and the annual maximum wind speeds of 40 weather stations of lower-reaches of the Yangtze from 1971 to 2006, the 99% confidence level logistic reconfiguration scheme and extreme value Ⅰ type calculation procedure are referred also a new wind speed distributive status over lower-reaches of the Yangtze is described in detail. Results indicate that along low er-reaches of the Yangtze the 100-year return period maximum wind speed is 25 to 38 m· s^-1 which is 3 m ·s^-1 larger than upper limit and 2 m · s^-1 smaller than lower limit of the result by the general method. lower-reaches of the Yangtze, two gale regions exist both in the Nanjing-Zhenjiang segment and in the Nantong-Chongming segment, where the 100-year return period maximum wind speed is greater than 29 m ·s^-1 and even above 34 m · s^-1 near the entrance. It is also found that on both sides of Changzhou-Jiangyin river segment two lower extreme wind speed regions are symmetrical distribution, where the 100-year return period maximum wind speed is about 23 to 24 m· s^-1. Fully considering the wind data of weather stations and the local wind speed observation, the results are important supplement for the concerned meteorological application works.