Characteristics And Variations Of High Winds Events In The "Two Oceans And One Sea" In Recent 40 Years

The western Pacific-South China Sea-East Indian Ocean（Two oceans and one sea,TOOS）region has an important impact on the weather and climate,national security,as well as social economy of China.However,due to the limitation of data conditions,the existing research on high winds are mainly focused on the offshore,resulting in insufficient understanding of the temporal and spatial distribution,the characteristics of changes and their mechanisms of high sea winds in the TOOS region.There is an urgent need to use new high-resolution data for in-depth research.Therefore,the ICOADS moored buoys observation data are compared with the ERA5 reanalysis data in the TOOS region to discuss the applicability of the ERA5 reanalysis data in the TOOS region.Further more,the characteristics and mechanism of high winds in the TOOS region are analyzed by using ERA5 reanalysis data with higher spatial and temporal resolution.Firstly,the wind fileds derived form the ERA5 reanalysis of 10 m wind speed data and ICOADS anchor buoy observation data are compared.The results show that the ERA5 reanalysis data can well reflect the distribution and change characteristics of the sea surface wind field in the TOOS region.In addition,the ERA5 reanalysis data has high spatial and temporal resolution,long time series and complete data records.It is feasible to use the ERA5 reanalysis data to study the climatic features of high sea winds.However,it should be noted that the ERA5 reanalysis surface wind speed generally has a systematic bias of underestimating the observed wind speed.In particular,the greater the observed wind speed,the greater the deviation of ERA5 from the observed wind speed.Considering the extreme of high winds,the common standards of scientific research and forecast operation,and the systematic deviation of ERA5 reanalysis wind speed underestimating observed wind speed,the threshold was determind as the 90th percentile in ERA5 reanalysis of hourly 10 m wind speed,that is 11.3 m·s^-1,to identify the TOOS high wind events.The number of high winds events（high winds number）,the frequency of high winds events（high winds frequency）,and the corresponding dominant wind direction of high winds events in the TOOS region were statistically analyzed.The results show that there are significant differences in the frequency patterns of high winds in different seasons in terms of intensity,location and range,which can be divided into winter,summer,and transition-period types.However,the annual cycle of frequency pattern is not completely symmetrical.On the whole,the duration of winter type is longer than that of summer type.In addition,the principal components corresponding to the dominant modes of spring,autumn,and winter have significant interannual variation characteristics,indicating that the temporal variations of the frequency of high winds over the TOOS region are mainly on an interannual scale.However,the dominant modes in summer show more characteristics of interdecadal variation.Finnaly,the possible influencing factors of interannual variation of winter and summer high winds events are studied.The interannual variation of high winds events in winter frequent areas（the north-central part of the Northwest Pacific）is mainly related to the intensity of the Siberian High and the location of the Aleutian low,and the strength of cold air and westerlies might be the direct influencing factors.The local air-sea thermal conditions also affect the occurrence and development of high winds to a certain extent.The interannual variation of the frequency of high winds events in summer is mainly affected by the anomlaies of the large-scale circulation and the tropical low pressure systems.When cross-equatorial flow over Somalia is stronger（weaker）than normal,there are south（north）wind anomalies and more（less）high winds events in the Arabian Sea.At the meantime,the west（east）wind anomalies appear in the Bay of Bengal,stronger（weaker）Indian monsoon trough and East Asian monsoon trough,and the western Pacific Subtropical High is weaker（stronger）than normal,with its location further eastward（westward）.Such anomalous pattern is favourable（unfavourable）for the generation and activity of tropical monsoon low pressures,resulting more（less）high winds events in the Bay of Bengal,the South China Sea and the ocean east of the Philippines.