| The influence of islands on local ocean dynamic processes can be divided into two categories:(1)due to blockage from an island's mountains,wind intensity decreases thus weakening upper ocean mixing,and the ocean is affected indirectly by atmospheric parameters;(2)when a current passes an island,island wakes are formed downstream and consequently,the island directly affects the ocean.Through a usage of remotely sensed data,laboratory experiments and numerical model results,this paper analyzes the physical processes in these two types of island influences on the ocean.With regard to indirect processes,islands can produce warm pools on their leeward sides.The size of the island and differences in atmospheric factors have important effects on the warm pool.This study uses satellite remotely sensing data and numerical modeling results to analyze warm pools and their formation mechanisms induced by tow islands: Madagascar island(located under stable Trade Winds)and Sri Lanka island(affected by monsoons).(1)As Madagascar is located in the southwest Indian Ocean and is strongly affected by easterly Trade Winds,when the wind blows through the island,the wind speed on the west side of Madagascar is significantly reduced,weakening upper ocean mixing and thus making the mixed layer shallower.Under these conditions,the bottom cold water is not easy to reach the sea surface.Simultaneously,the precipitation and the cloud coverage on the east side of the island are significantly larger than those the west side,increasing the net sea surface heat flux on the west.The combined effects of the wind and heat flux make the sea surface temperature on Madagascar's western coast much higher than that the eastern coast throughout the year.(2)With regards to the monsoon-dominated island of Sri Lanka,seasonal warm pools appear on the east(west)side of the island in summer(winter).When the monsoon blows over the island,wind intensity decreases,upper ocean mixing weakens,inducing the ocean temperature leeward higher than that on the surrounding sea area.Oceanic interannual signals such as El Ni?o and the Indian Ocean Dipole both affect the intensity of the Sri Lankan seasonal warm pools by modulating the monsoon intensity.Regarding direct impact processes,when a current bypasses an island,island wakes appear downstream.In this study,a rotating platform experiment and a numerical model are used to analyze the instability of anticyclonic eddies in the island wake.Based on the island wake experiments conducted on the French CORIOLIS rotating platform,the entire life evolution process of an anticyclonic eddy is analyzed.The decay process of this anticyclonic eddy is divided into two periods: slow and rapid decay periods.These two processes are influenced by two different factors: the slow decay process is mainly caused by the anticyclonic eddy's centrifugal instability;the rapid decay process is mainly caused by eddy-eddy interactions causing the damage to the eddy's structure.As laboratory experimental data cannot provide information on the eddy's three-dimensional structure,numerical models can make up for this limitation.Numerical model experiments results suggest that the anticyclonic eddy decay rate is faster than that of the cyclonic eddy due to its own unstable processes.Further analysis shows that instability-induced vertical mixing is the main reason for the eddy's rapid intensity decay.The innovations of this paper are as follows: 1)the seasonal warm pools on the east and west sides of Sri Lanka island are discovered for the first time by using satellite remote sensing data;2)two mechanisms causing the decay of the anticyclonic eddy are revealed by using the rotating platform experiment results: the centrifugal instability and the eddy-eddy interaction mechanism;3)the vertical mixing induced by the instability of the anticyclone is revealed by using the high-resolution numerical model. |
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