1979-2021年中国南海海表风速和大风事件的变化特征

Variation Characteristics of Surface Wind Speed and Gale Events in the South China Sea from 1979 to 2021

利用欧洲中期天气预报中心European Centre for Medium-Range Weather Forecasts(ECMWF)最新的第五代再分析资料ECMWF Reanalysis v5(ERA5),定义了大风事件,使用经验正交分解等方法分析了1979-2021年中国南海海表风速和大风事件的变化特征,并对是否受热带气旋的影响进行了区分。结果发现,南海风速分布呈现出十分明显的季节特征,冬季主要为东北风,夏季为西南风;春、夏季南海东北部与其他地区风速变化存在反向关系,除东北部沿海地区外,春季平均风速变化经历了减小-增大-减小的变化,总体呈较弱的增加趋势;而夏季则是增大-减少-增大,总体呈减小趋势。秋季南海风速呈全区一致的变化,呈减小趋势。冬季变为东南与其余部分反向,除西南部外,风速呈显著增强趋势。大风事件发生在风速较大的区域和时间内,冬季和秋季发生大风事件的频次要高于春季和秋季,冬半年要高于夏半年;在冬季和冬半年,大风事件的发生频次在南海中部长山山脉东侧直到南海东北部台湾海峡附近有显著上升趋势;大风事件频次变化趋势随季节改变有很大的差异,冬季和春季大风事件频次变化趋势与夏季和秋季相反。夏半年大风事件频次变化融合了夏季和秋季的变化趋势特点;类似的冬半年大风事件频次融合了冬季和春季的变化趋势特点。在夏季,秋季和夏半年这些受到南海夏季季风影响的季节内,热带气旋对发生的大风事件频次影响更大;对在冬季,春季和冬半年发生的大风事件则影响较小。

In this paper,the gale events are defined firstly.Using ERA5 reanalysis data,the variation characteristics of the sea surface wind speed and the gale events from 1979 to 2021 were analyzed.The variation characteristics of sea surface wind speed and gale event in the South China Sea from 1979 to 2021 were analyzed using methods such as the empirical orthogonal decomposition.Specifically,the effects of tropical cyclones were distinguished.The results show that the distribution of wind speed in the South China Sea has obvious seasonal characteristics with the northeast wind in winter and in the summer,the wind direction turns to be southwest.Except for the northeast coastal areas,the mean wind speed in the spring time experienced a decreasing-increasing-decreasing character.While in the summer,it turns to a kind of increased-decreasing-increasing trend and the overall trend is decreasing.The consistent change of wind speed in the whole area of the South China Sea in the autumn shows a decreasing trend.In the winter,the wind speed in the southeast of the South China Sea is opposite to the rest aera,with a significant increase in wind speed except for the southwest.The frequency of the gale events that occur in the winter and in the autumn is higher than that in the spring and autumn,and the frequency of the gale events in the winter half year is higher than that in the summer half year.In the winter or winter half year,the frequency of the gale event has a significant increasing trend,especially in the area from the east of the Annamese Cordillera to area near the Taiwan Strait,through the central part of the South China Sea,in the northeast part of the South China Sea.The variation trend of the frequency of gale event in the winter and spring is opposite to that in the summer and autumn.The changes of the frequency of gale event in the summer half year combines the characteristics of the variation trends in the summer and autumn.Similarly,gale event that occur in the winter half year combines the variation trends of winter and spring.During the seasons affected by the South China Sea summer monsoon,such as summer,autumn,and the summer half year,tropical cyclones have a greater impact on the frequency of gale event which is different from the gale event that appearance in the winter,spring and winter half year.