Research On The Spatiotemporal Distribution And Variation Patterns Of Mesoscale Eddies In The Hawaiian Islands Sea

Mesoscale eddies are widely present in the ocean and have significant impacts on the transport of oceanic matter and energy,global climate change,underwater reconnaissance and anti-reconnaissance.The western windward reversing zone of Hawaiian Islands is a region with complex flow systems and high occurrence rates of mesoscale eddies.The activities of mesoscale eddies in this area have important implications for large-scale circulation changes,air-sea exchange,and distribution of marine organisms.Therefore,in-depth research on the characteristics and formation mechanisms of mesoscale eddies in this area is of great significance for understanding the mechanism of oceanic eddies action and predicting its long-term trends.In order to explore the spatiotemporal distribution and variation patterns of mesoscale eddies near the Hawaiian Islands,a statistical analysis of the spatiotemporal distribution characteristics of mesoscale eddies in the Hawaiian Islands Sea was conducted using the eddy dataset.There is strong horizontal and vertical shear in the lee of the island of Hawaii,which leads to more active mesoscale eddy activity compared to surrounding areas.A total of 4,809 cyclonic eddies and 4,445 anticyclonic eddies were detected in this study,with slightly more cyclonic eddies than anticyclonic eddies.The cyclonic eddies and anticyclonic eddies move westward in the sea off the Hawaiian Islands as a whole,with the largest number of eddies in the radius range of75 km to 100 km,and eddy numbers decreasing as their lifecycles increase.There are pronounced seasonal and interannual variations in mesoscale eddies in this region,with both cyclonic and anticyclonic eddies showing similar seasonal variation patterns,with the highest eddy numbers occurring in winter and the lowest eddy numbers occurring in autumn.Combining the reanalysis data from 1993 to 2020,the lee of the Hawaiian Islands was divided into two areas(off-island and near-island),and the annual variation characteristics and mechanisms of mesoscale eddy kinetic energy in the lee were studied.Based on the eddies energy balance equation and the topography and flow characteristics of the Hawaiian Islands,this study found that baroclinic instability,barotropic instability,transport,and wind stress work were the main factors affecting mesoscale eddy kinetic energy.The study found the following conclusions:(1)Both off-island and near-island showed significant annual variations in mesoscale eddy kinetic energy,with the near-island region leading the off-island region.At a lead time of 12 months,the maximum correlation coefficient between near-island and off-island mesoscale eddy kinetic energy was 0.57.(2)The off-island region was primarily controlled by baroclinic instability,while the near-island region was mainly controlled by wind stress work.(3)Annual variations in mesoscale eddy kinetic energy were regulated by large-scale annual signals.The annual variation in off-island mesoscale eddy kinetic energy was significantly correlated with the PDO index,with a maximum correlation coefficient of 0.85 at a lead time of 10 months.The annual variation in near-island mesoscale eddy kinetic energy was significantly correlated with PDO index at a lead time of 2 months,with a maximum correlation coefficient of 0.4.Overall,this paper presents a statistical analysis of the spatiotemporal distribution characteristics of mesoscale eddies near the Hawaiian Islands,and explores the energy sources of eddies in the Hawaiian leeward countercurrent region using the eddy kinetic energy income and expenditure analysis method,further deepening the understanding of the characteristics of mesoscale eddies in the lee of Hawaii,and providing an important reference for understanding and predicting the changes of mesoscale eddies in the region.