The Evolution Of The Great Whirl In The Arabian Sea And Its Influence On The Air-Sea Interaction

Based on the Archiving,Validation and Interpretation of Satellite Oceanographic Data(AVISO)satellite altimeter data and Advanced Very High Resolution Radiometer(AVHRR)satellite remote sensing data,the basic properties of the Great Whirl(GW)are investigated.Additionally,the interannual variations characteristics of the center position and other related characteristics are shown.The Tropical Rainfall Measuring Mission Microwave Imager(TMI)satellite data and the European Centre for Medium-Range Weather Forecasts reanalysis data is also used to analyze the response of wind speed,water vapor and other atmospheric variables to the GW.Based on the Regional Ocean Modeling System(ROMS),the three-dimensional structure of the GW,and its generation and dissipation mechanisms are investigated through a series of sensitivity experiments.Finally,the Coupled Ocean–Atmosphere–Wave–Sediment Transport(COAWST)modeling system is used to further analyze the effect of the GW on the atmosphere.The turbulent kinetic energy(TKE)budget analysis and momentum diagnostic analysis are used to study the mechanisms through which the GW affects the atmosphere.By comparing the results of ROMS and COAWST,the influence of the atmosphere on the GW is observed.The main conclusions are as follows:(1)From 1993 to 2015,the average position of the GW center is 7.73°N,53.20°E,the average life cycle is 169 days,the average radius is 116.86 km,the average normalized vorticity is-0.53,the average eddy kinetic energy(EKE)is 0.08m²·s^-2 and the average deformation rate is 0.58.Obvious interannual variation of the center position,Sea Surface Tempertrue(SST),Sea Level Aomaly(SLA),radius,deformation rate,normalized vorticity and EKE of the GW are all observed.(2)The generation and dissipation mechanisms of the GW are as follows: 1.Westward Rossby wave signals can induce a GW,but it is not a necessary factor for the generation of the GW;2.The southwest monsoon is a necessary factor for maintaining the GW and can also stimulate the generation of a GW;3.Without the westward Rossby wave signal and the southwest monsoon,the GW cannot be generated;4.The decline of the southwest monsoon is closely related to the dissipation of the GW.(3)Through the cross-section analysis of temperature and density at the GW center,it is found that the vertical influence of the GW is mainly concentrated above 400 m depth.In addition,by analyzing the structure of the GW at different depths,it is found that the average radius of the GW is the largest at 100m(194.7km),followed by the radius of 173.6km at the sea surface.From 200 m to 400 m,the radius of the GW gradually decreases from 172.2km to134.3km and 125.8km,respectively.The GW is a bowl-like structure.(4)From the analysis of the TKE budget,it can be found that the buoyancy and shear term change the most during the monsoon and non-monsoon periods.However,the magnitude of these two terms is smaller than the TKE vertical transport term and dissipation term.After being affected by the GW,the vertical transport term contributes significantly to the TKE generated in the atmosphere.There are also two larger quantities among the four momentum diagnosis terms: the pressure gradient term and the vertical mixing term.The pressure gradient term is stronger during the southwest monsoon than during the non-monsoon periods,while the vertical mixing term is similar.Therefore,the pressure gradient term plays the most significant role in the process of momentum transport.(5)The intensity of the GW in the coupled model is less than that in ROMS,but the coupled model has a better simulation of the GW.By comparing the changes in the depth of the isotherms and isopycnal,it is found that the GW has a weaker vertical effect on water temperature and density in the coupled model than in ROMS.The reason is that the positive wind stress curl induced by the GW can cause the sea water to move upwards,thereby inhibiting the downward movement of the GW.That is,the feedback of the atmosphere on the GW inhibits the influence of the GW in the vertical direction.