Study On The Influence Of Mesoscale Eddies On The Kuroshio And Its Water Masses East Of Taiwan

As one of the strongest western boundary currents,the Kuroshio is an important link connecting the material and energy exchanges between the western Pacific Ocean and China’s offshore waters,and plays an important modulating effect on climate change in the surrounding seas.The Kuroshio at east of Taiwan is affected by large-scale ocean currents,atmospheric forcing,and mesoscale eddies propagating westward from the Subtropical Countercurrent Zone（STCC）area.Previous studies have shown that the Kuroshio at east of Taiwan has significant intraseasonal variation affected by mesoscale eddies.The mesoscale eddies not only modulate the Kuroshio,but also directly affects the intermediate water at east of Taiwan.During the interaction between the mesoscale eddies and the Kuroshio,the relationship among the Kuroshio,the intermediate water and the mesoscale eddies is closely connected,and the three-dimensional structure of the mesoscale eddies and the Kuroshio also changes accordingly.For a long time,limited by the observational data,the deep understanding of these issues is mostly one-sided.The variation process of mesoscale eddies,Kuroshio,intermediate water is not detail known clearly.Based on the long-term mooring and the large-scale CPIES array observation data,this paper focus on the Kuroshio intraseasonal variations,the variations characteristics of the Kuroshio intermediate water,as well as the three-dimensional structure characteristics of the mesoscale eddies and Kuroshio between their interaction.The main innovative conclusions are as follows:The intraseasonal variation characteristics of the Kuroshio at east of Taiwan were studied by using a by a subsurface mooring between January 2016 to May 2017.The results show that the Kuroshio and the mesoscale eddies have an intraseasonal variation period of 70-90 days,and the average westward speed of the eddies is estimated to be about 10 cm/s.This study found that the Kuroshio thickness at east of Taiwan varies within 100-800 m.Combined with the HYCOM data,the mechanism of the mesoscale eddies affecting the Kuroshio is clarified.Cyclonic（anticyclonic）eddies from the STCC cause a negative（positive）sea surface height anomaly,contribute positive（negative）PV,and lead to a decrease（increase）in the northward velocity.Cyclonic（anticyclonic）eddies also lead to stronger（weaker）vertical stratification in the upper ocean.A smaller（larger）angle of the isopycnal slope corresponds to lower（higher）Kuroshio velocity.Using 17-month current and temperature and salinity data of 400～800 m measurement from mooring located at east of Taiwan.It’s first time proved that the periods of intraseasonal variability of Kuroshio intermediate water（KIW）at east of Taiwan caused by mesoscale eddies is about～80 days.The typical average temperature and salinity characteristics of the KIW east of Taiwan are revealed:the minimum salinity is 34.26,the temperature is 7.5°C,and the potential density is 26.8 kg m^-3,and its mainly located at 400-600 m.The mixing proportion of NPIW and SCSIW in KIW and its variability are revealed.The relationship between mesoscale eddies,current and IW is clarified.The anticyclonic eddies（cyclonic eddies）corresponds to the increase（decrease）of the current speed and the increase（decrease）of the salinity of IW.Combined with HYCOM data,the change process of IW in vertical and horizontal movement is analyzed.It is also proved that more SCSIW water mass can be transported to the east of Taiwan during the anticyclonic to increase its salinity,while the relatively fresh salinity NPIW dominates during the cyclonic.Using the CPIES（Current-Pressure Inverted Echo Sounder）array data,the interaction process between the mesoscale eddies and Kuroshio was explained.It’s reveal that anticyclonic（cyclonic）eddies impinging the Kuroshio,the pycnocline depression（heaving）.while the pycnocline present the opposite changes on the Kuroshio side.The impact of the anticyclonic（cyclonic）eddies increases（weakens）the inclination of the isopycnal connecting the Kuroshio and eddy center,and the inclination of the isopycnal corresponds to the isobaric surface,so corresponding to increase（decrease）the Kuroshio velocity.The detailed three-dimensional structural characteristic of the mesoscale eddies and the Kuroshio are both constructed during its interaction by using CPIES data.This study shows that the anticyclonic eddies impinging Kuroshio,the temperature and salinity anomalies are in the opposite phase,while the cyclone eddies acts on the Kuroshio,the temperature and salinity anomalies are in the same phase.During the interaction between the anticyclonic eddies and the Kuroshio,the center water of anticyclonic eddies（Kuroshio）moves downward（upward）,causing the temperature to show a positive（negative）abnormal structure.While the salinity has a positive（negative）anomaly above 600 m,and a negative（positive）anomaly below 600 m.When the cyclone eddies interaction with the Kuroshio,the temperature and salinity anomaly are consistent,showing the temperature appears as an overall negative anomaly,while salinity above and below 600 m have negative and positive anomalies respectively.