Long-term Trends Of Sea Surface Wind And Its Impacts On The Marine Environment In The Northern South China Sea Under The Background Of Climate Change

Under the background of global climate change,the marine environment is facing severe challenges.As a major driving factor of air-sea interaction,sea surface wind can characterize the characteristics of global climate change and affect the marine environment change.The northern South China Sea(SCS)is an area that is sensitive to climate change and that has the complex marine dynamic environment.The study on the long-term trends of wind in SCS provides an significnat basis for the study of the regional marine environment and utilization of marine resources.Based on the ERA5 data from 1979 to 2019(41 years in total),we analyzed the trend of sea surface wind in SCS.The results showed that the long term trends of sea surface wind in SCS had significant spatial variability.Over the past 41 years,annual mean wind speed in the coastal area has decreased,while that in the open sea has increased.From the change of wind vectors,the u-component of wind vector was weakening remarkably,but the v-component of the wind vector was strengthening.The results of M-K mutation text analysis showed that the wind speed in the Pearl River Estuary(PRE)and its adjacent sea area occurred in 2004 and in the eastern sea area of Leizhou Peninsula occurred in 1994.After the mutation,the wind speed and strong frequency decreased but the wind direction did not change significantly.Wind speed was decomposed by EOF,and its time coefficient was analyzed by wavelet coherence with ENSO and PDO indices respectively.The results showed that the inter-annual variation of wind speed is significantly affected by the ENSO and PDO.Long-term trends of sea surface wind change the marine environment.The upwelling in the east Guangdong and east Hainan coastal waters were intensified over the past 41 years.The strengthening of the wind stress curl and costal wind stress play an important role in the enhancement of coastal upwelling along the coast of the northern SCS.The long-term trends of significant wave height in the northern SCS also showed consistent spatial-temporal variation with the trend of wind speed.The long-term trends of wind speed impacted the trend of significant wave height.Long-term trends of sea surface wind was presented significantly in PRE.Take wind in July as a research object,the hydrodynamic numerical simulation was used in typical meteorological years of southwest wind(1985)and southeast wind(2018)in PRE.The results showed that surface water flows in a southwest direction along coast in PRE and its shelf area when prevailing southwest wind,which promotes the PRE diluted water eastward offshore transport and induces the vertical circulation in the estuary.When prevailing southeast wind,the flow velocity was weakened and the vertical circulation in the estuary was disappeared.The southeast wind causes the flow direction to change from southwest to northeast in the western PRE,which promotes dilute water to expand western.After mutation of wind speed in July,the flow velocity decreased in the PRE and its sea shelf area,meanwhile the flow direction did not change significantly.Long-term trends of wind have important effects on the expansion direction of diluted water and hydrodynamic change between estuary and open sea in PRE.