Statistical Characterization Of Sea Surface Temperature And Heat Flux Over Mesoscale Eddies In The South China Sea

Mesoscale eddies are ubiquitous in the ocean,they induce anomalies on sea surface temperature(SST),influence the turbulent heat flux and the overlaying atmosphere.Studying the role of mesoscale eddies in generating and regulating changes on turbulent heat flux is of significant importance for both ocean and atmospheric circulation.The study focuses on the the characteristics of SST and heat flux over mesoscale eddies in the South China Sea(SCS),aims to figure out the relationship between the sea surface height anomaly(SSHA),SST and heat flux over mesoscale eddies in the SCS.Four tasks are conducted in the study as following:(1)Develop a parallel SSHA-based method for global mesoscale eddies identification.Considering the low computational efficiency of previous eddy identification algorithm,the study proposes a fast and accurate eddy recognition algorithm,which uses the techniques of spatial segmentation and parallel computing to reduce the complexity of algorithm.The eddy identification method not only improves the efficiency of eddy identification,but also ensures the accuracy of identification results.When applying the method to the global SSHA map,the computation is 145 times faster than the previous SSHA-based method.(2)Identifying mesoscale eddies based on multiple SST data.Based on three widely used SST data,mesoscale eddies are identified respectively.SST-based mesoscale eddies are observed to have similar spatial distribution with SSHA-based mesoscale eddies,however,the former have smaller eddy radii and show different seasonal variability.By comparing three SST products,AVHRR-only SST product performed better on describing the shape and size of mesoscale eddies,and help tracking SSHA-based eddies that have splitting or merging activities.(3)Statistical characterization of SST over mesoscale eddies in the SCS.Using SSHA-based mesoscale eddies dataset and AVHRR-only SST data,we investigate the SST characteristics over mesoscale eddies in the SCS during 2000-2015.The results show that SSTA associated with anticyclonic(cyclonic)eddies are not always positive(negative).Positively correlated eddies show different spatial and seasonal variations at different amplitude percentiles.Composite SSTA over eddies are observed to have westward and poleward(equatorward)phase shifts with respect to SSHA-based eddy center of anticyclonic(cyclonic)eddies.The maximum(minimum)SSTA within anticyclonic(cyclonic)eddies is 0.12°C(-0.2°C).There is a linear relationship between SSTA and SSHA,and the coupling strength of them is 0.2°C(-0.2°C)per 10 cm for positively correlated anticyclonic(cyclonic)eddies.(4)Statistical characterization of turbulent heat flux over mesoscale eddies in the SCS.Based on the eddy-resolving turbulent heat flux dataset,the study investigates the characteristics of latent heat flux,sensible heat flux,and their related air-sea variables:wind speed,air-sea humidity difference,air-sea temperature difference,air humidity and air temperature over mesoscale eddies in the SCS during 2000-2015.On average,anticyclonic eddies loss 3.31 W/m~2heat to atmosphere,while cyclonic eddies gain 3.96W/m~2from atmosphere.Except that wind speed shows a dipole pattern over mesoscale eddies,heat flux and other air-sea variables show positive(negative)monopole over anticyclonic(cyclonic)eddies,which is in phase with eddy-induced SSTA,but show westward and poleward(equatorward)phase shift with respect to SSHA-based eddy center of anticyclonic(cyclonic)eddies.Eddy-induced SSTA is positively correlated with heat flux and other air-sea variables over mesoscale eddies.There are 48.4 W/m~2(46.9 W/m~2)changes in heat flux associated with 1°C changes of SSTA over anticyclonic(cyclonic)eddies.It is noteworthy that wind speed and air humidity don’t increase when eddy-induced SSTA larger than 1°C.