Characteristics Of Upwelling Adjacent To The Tip Of Liaodong Peninsula And Its Influence Mechanisms In Summer

The sea adjacent to the tip of Liaodong peninsula is an important channel for water exchange between the Bohai Sea and the northern Yellow Sea.The existence of upwelling phenomenon at the tip of Liaodong peninsula has a certain influence on the dynamic environment and physical and chemical environment of the sea area where it is located,creating favorable conditions for the formation of sea fog in summer,thus affecting maritime shipping and coastal land traffic.It is of great significance to understand the spatial distribution characteristics,inter-annual variation characteristics and long-term variation trend in the context of global warming of the upwelling at the tip of the Liaodong peninsula for the development of Marine resources,ecological environment protection and the implementation of Marine engineering in the Bohai Sea.The article is based on sea surface temperature and wind field of remote sensing data,combined with the current field,the sea surface net heat flux model data and Ni?o3.4index,analyzed the temporal and spatial distribution characteristics of the summer upwelling at the tip of the Liaodong peninsula,and probed into the summer monsoon and ocean currents affect its spatial distribution characteristics.Then,through the temperature threshold value method and the upwelling edge detection algorithm based on temperature gradient method to calculate sea surface temperature upwelling indices and area of the upwelling at the tip of Liaodong peninsula,using the empirical mode decomposition and regression analysis analyzed the inter-annual variability characteristics and long-term change trend under the background of global warming of the upwelling at the tip of Liaodong peninsula in the last 31 years summer,and using the method of correlation analysis analyzed the effects of net heat flux,wind field,ENSO and other climatic factors on the inter-annual variation and long-term tendency of the upwelling at the tip of the Liaodong peninsula.The main conclusions of this paper are as follows:(1)In summer(from June to August),the upwelling at the tip of the Liaodong peninsula can rise to the ocean surface,presenting in the form of low temperature zone in the south sea area of the Liaodong peninsula.During the whole summer,the upwelling experienced the change of first strengthening and then weakening,and the upwelling was strongest in July.The upwelling always extends southward and northward.In addition,the center of upwelling closes to the tip coast of Liaodong peninsula in July and August.Wind field and ocean current are the two factors that influence the spatial distribution of the upwelling in the tip of Liaodong peninsula in summer.Among them,the strength of upwelling in the study area is mainly determined by the current conditions at the bottom of the ocean,while the location of upwelling center and the distribution range of upwelling are mainly determined by the interaction of wind field and sea surface currents.(2)During the summer of 1988-2018,the strength and extension of upwelling in the tip of Liaodong peninsula showed significant inter-annual variability.The inter-annual oscillation period of the upwelling intensity is roughly the same as that of the upwelling extension.The oscillation period of upwelling intensity and extension is about 3 years and 8 years,and the 3-year oscillation period is the main oscillation period.The inter-annual oscillation of upwelling intensity and its extension is related to net heat flux,wind field and ENSO.When the inter-annual oscillation period of the upwelling is about 3 years,meridional wind,zonal wind and ENSO are negatively correlated with the strength of upwelling.Meanwhile,net heat flux,meridional wind,wind stress curl and ENSO are negatively correlated with the area of upwelling.When the inter-annual oscillation period of the upwelling is about 3 years,net heat flux and ENSO are positively and negatively correlated with the upwelling intensity respectively,while net heat flux and zonal wind are negatively and positively correlated with the area of the upwelling respectively.(3)In the summer of 1988-2018,the strength of upwelling in the tip of the Liaodong peninsula increased significantly,but its extension degree decreased.During the whole study period,the SST upwelling index of upwelling increased at a rate of0.27°C/10a,faster than the global average SST growth rate,and the upwelling intensity increased significantly.However,the area of upwelling decreased at the rate of 216km~2/10a,and the extension of upwelling on the sea surface is obviously weakened.Among them,the change of upwelling intensity and extension were more significant from 1998 to 2018.Under the background of global warming,the variation trend of upwelling intensity is related to the net heat flux and wind field.The increase of net heat flux,the change of latitudinal wind from west wind to east wind and the weakening of meridional wind(south wind)lead to the enhancement of upwelling in the study area,and the increase of net heat flux is the main factor affecting the enhancement of upwelling.However,the long-term variation trend of upwelling extension is only related to the net heat flux.The rapid increase of SST in the non-upwelling area caused by the increase of net heat flux impedes the extension of upwelling in the sea surface,which leads to the weakening of the extension of upwelling.(4)ENSO can affect the extension of upwelling,and can also affect the upwelling intensity through the u component of zonal wind.In the strong El Ni?o development stage(1997 and 2014),the zonal wind(west wind)in the study area has been strengthened,which promotes the onshore movement and coastal accumulation of surface seawater,enhances its inhibition on the upwelling of bottom cold water,and leads to the weakening of upwelling in the study area and the reduction of its intensity and extension.In the years of strong La Ni?a(1998-2001 and 2010-2011),the zonal winds(east wind)in the study area has been strengthened,which reduces the onshore movement and coastal accumulation of surface seawater,promotes the upwelling of bottom cold water,and leads to the upwelling in the study area to be strengthened and its strength and extension degree increase.