The Surface Gravity Waves Effect On Air-sea Momentum Flux And The Upper Ocean Current Under High Wind Speed

The surface gravity wave,located between the air-sea interface,can indirectly affect the upper ocean through modifying the momentum flux between air and ocean.On the one hand,the surface wave could change the length of the atmospheric underlying surface roughness,and thereby adjust the atmospheric momentum output t_air;On the other hand,the momentum flux t_oc that injected into the ocean column is controlled by the wave evolution process with the momentum absorbing or releasing.In addition,the surface wave can directly influence the dynamic and thermodynamic structure in the upper ocean layer through wave current interaction where the Stokes drift theory plays a core role.The ocean general circulation model currently put more attention on the wave influence.However,the role of wave evolution on air-sea momentum exchange have not been paid enough attention in previous studies,which often used t_airrather than t_oc to driving the current.Additionally,the accurate simulation of the full Stokes drift is still insufficient.Therefore,our study analyzed the effect of wave evolution on the air-sea momentum flux and upper ocean and discussed the influence of the estimation error of Stokes drift on ocean simulation,and thereby provided a reasonable method for estimating Stokes drift under typhoon condition.In this current work,a series of sensitive ideal typhoon experiments were carried out using the improved coupled model COAWST(Coupled Ocean Atmosphere Waves Sediment Transport),the obtaining results included as following:(1)The ocean side stress t_oc on the right side of typhoon track could significantly reduce by the wave evolution process,the maximum decrease achieves 16%of the local wind stress.Therefore,the wave evolution can suppress the response of the mixed layer flow field to typhoon,and significantly reduces the near inertial kinetic energy(more than 10%)at the bottom of the mixing layer,thus reducing the cooling response of the mixed layer to typhoon.Furthermore,the influence of wave evolution on the real complex ocean current is also analyzed through the simulation of the Northwest Atlantic Ocean.The results show that the effect of the wave evolution process on air-sea momentum flux is related to the strength and change rate of wind field((?)U₁₀/(?)t·U₁₀).Moreover,the effect of wave evolution on the different frequency components of wind stress and upper ocean current is significantly different.The higher frequency of flow field and wind stress,the greater effect by wave evolution,and the influence on the near-inertial and super-inertial current reached 15%and 20%,respectively.(2)When the interaction between Stokes drift and mean current(including Coriolis-Stokes force,Stokes pressure correction,and Stokes-vortex force)was considered in the wave-current coupled model butthe Langmuir turbulence was ignored,the surface waves will weaken the entrainment at the bottom of the mixing layer,and suppress the cooling response of the mixed layer to the typhoon.When considering the Langmuir turbulence factor,the surface waves becameto enhance the mixing of the upper ocean,promoting the cooling response of the mixed layer to the typhoon.(3)Under typhoon condition,the exponential method obtained the best simulation results of Stokes drifting which were closed with the Stokes profile integrated from the parametric spectrum.In addition,it had the highest calculation efficiency which is 2.13 times of the full spectrum method.Compare with exponential method,the Phillips spectrum method is more suitable for Stokes drift calculation under the low and medium wind speeds(<25 m s^-1).This method could reduce the overestimation of the surface Stokes drift when using the exponential method.The calculation efficiency of Phillips approximation method is 1.44 times of the full spectrum method.The monochromatic spectrum method had the largest bias,with the error range of-0.2 and 0.1?in the upper ocean.Using both the exponential and Phillips spectrum estimation methods instead of the monochromatic spectrum method can reduce the error range of the temperature simulation to-0.04?0.08?,which was significantly improved compared with the contribution of Stokes drift(-0.2?0.3?)to the temperature change in the upper ocean.