The energy conversion rates from eddies and mean fl ow into internal lee waves in the global ocean

Internal lee waves play an important role in transferring energy from eddies to small scale mixing.However,the energy conversion from eddies into lee waves in the global ocean remains poorly understood.Conversion rates from eddies and from mean fl ow in the global ocean were diff erentiated using single beam sounding data,stratifi cation from climatology,eddy velocity,and mean fl ow from a global ocean model.The global integral energy conversion from eddies is estimated to be 0.083 TW and is almost twice as that from the mean fl ow.A new method was developed to study the uncertainties of energy conversion caused by dealing with the topographic data.Results show that diff erent data processing procedures,and the resolution and accuracy of topographic data have a signifi cant impact on the estimated global energy conversion.

Analysis of a simplification strategy in a nonhydrostatic model for surface and internal wave problems

This paper examines the simplification strategy of retaining only the nonhydrostatic effect of local acceleration in a three-dimensional fully nonhydrostatic model regarding the submesoscale wave phenomenon in the ocean.Elaborate scale analysis of the vertical component of the Reynold-averaged Navier-Stokes(RANS)equation was performed,confirming the rationalization of this simplification.Then,the simplification was implemented in a RANS equation-based nonhydrostatic model NHWAVE(nonhydrostatic WAVE)to make a simplified nonhydrostatic model.Numerical examples were taken to test its performance,including surface sinusoidal waves propagating on an idealized East China Sea topography,tidally induced internal lee waves and small-scale solitary waves.The results show that in a considerably wide range of nonlinear strengths,the simplified nonhydrostatic model can obtain similar results as those in the fully nonhydrostatic model,even for smaller-scale solitary waves.Nonlinearity influences the applicability of the simplification.The stronger the nonlinearity is,the worse the simplified model describes the nonhydrostatic phenomenon.In general,the simplified nonhydrostatic model can simulate surface waves better than internal waves.Improvement of computational efficiency in the simplified nonhydrostatic model is reasonable,reducing the central processing unit time duration in the fully nonhydrostatic model by 16.4%–20.6%.The specially designed algorithm based on the simplified nonhydrostatic equation can remarkably reduce the computational time.