浙江海岛台风和冬季大风阵风特征的对比分析

为了提高阵风预报准确率，利用2006—2016年浙江7个海岛气象站资料和ERA-interim资料，分析了台风和冬季大风的阵风因子与10 m稳定风速、风向、Brunt-Vaisala频率、总体理查逊数、边界层250~1 000 m风速及其与10 m稳定风速比值等的关系，对比两种大风系统阵风的主要成因差异，最后对冬季大风的阵风因子进行拟合。(1)从总体上，台风阵风因子比冬季大风要大0.1~0.2，波动幅度也一般比冬季大风偏大0.3~0.5。有些站点在稳定风速较大时，阵风因子随稳定风速变化不明显，而有的站点变化幅度较大。(2)站点不同方位的地表特征差异明显，导致台风和冬季大风的阵风因子在某个风向上有较统一的最大值和最小值，两者差值一般为0.2~0.3。(3)大气边界层台风样本主要表现为气流辐合上升及正涡度，而冬季大风样本主要表现为辐散下沉及负涡度，台风垂直速度、涡度和散度的强度均明显大于冬季大风样本；从Brunt-Vaisala频率来看，边界层750 m处冬季大风样本总体为静力不稳定，而台风样本总体为静力稳定；从总体理查逊数来看，台风样本和冬季大风样本两者边界层250 m处动力不稳定程度接近。(4)台风和冬季大风的阵风主要形成机制不同，冬季阵风与边界层上层气流向下动量传输引发的辐合辐散有关，而台风阵风可能更多与边界层气流的水平动量输送引发的辐合辐散有关。(5)基于风向、边界层1 000 m处风速和10 m稳定风速的冬季大风阵风因子的拟合模型，比仅考虑10 m稳定风速的拟合模型的绝对误差减少了20%~50%，误差方差也减少了10%~30%。 

COMPARATIVE ANALYSIS OF FACTORS OF TYPHOON GUST AND WINTER GALE AT COASTAL ISLANDS IN ZHEJIANG

In order to improve the accuracy of gust forecast, the relationships between gust factors of typhoon or winter gale and mean wind speed, wind direction, Brunt-Vaisala frequency, Richardson number, the wind speed from 250 m to 1 000 m at the boundary layer, and their ratios with that at 10 m are analyzed, using the wind data of seven weather stations at coastal islands in Zhejiang and corresponding ERA-interim data during 2006—2016. The main causes of gust in two gale systems are compared. Finally the gust factor of winter gale is fitted. The following conclusions are obtained as follows: (1) On the whole the gust factor of typhoon is 0.1~0.2 larger than that of winter gale, and the fluctuation range is generally 0.3~0.5 larger than that of winter gale. In some stations when the steady wind speed is large the variations of gust factor with the steady wind speed are not obvious, but they are contrary to that at some stations. (2) There are obvious differences in surface features at different directions of the stations, which cause the gust factors of typhoon and winter gale to be the largest and smallest values in a direction, and the difference between them is generally 0.2~0.3. (3) In the dynamic fields the typhoon gale samples mainly show convergence and positive vorticity, while the winter gale samples mainly show divergence and negative vorticity. Based on the Brunt-Vaisala frequency the winter samples are statically unstable at the 750 m boundary layer, while the typhoon samples are statically stable. Based on the Richardson number the dynamic instability at the 250 m boundary layer is close to the typhoon and winter gale samples. (4) The main mechanism of winter gust is directly related to the convergence and divergence caused by the downward momentum transfer of the upper layer air flow of the boundary layer, and the typhoon may be related to the convergence and divergence caused by the horizontal momentum transfer of air at the boundary layer. (5) Compared with models fitted by only the 10 m steady wind speed, the absolute errors of the model of winter gust factor, based on wind direction, 1 000 m wind speed and 10 m steady wind speed, are reduced by 20%~50%, and the error variances are reduced by 10%~30%.