Effect of ocean waves on ocean circulation Peter A.E.M. Janssen ECMWF Shinfield Park Reading, U.K. p.janssen@ecmwf.int ABSTRACT Ocean waves play an important role in processes that govern the fluxes accross the air-sea interface and in the upper-ocean mixing. Equations for current and heat are presented that include effects of ocean waves on the evolution of the properties of the upper ocean circulation and heat budget. The turbulent transport is modelled by means of the level-2 1 2 Mellor-Yamada scheme (Mellor and Yamada (1982)), which includes an equation for the production and destruction of Turbulent Kinetic Energy (TKE). The TKE equation in this work includes production due to wave breaking, production due to wave-induced turbulence and/or Langmuir turbulence, effects of buoyancy and turbulent dissipation. As a first test, the model is applied to the simulation of the daily cycle in Sea Surface Temperature (SST) at one location in the Arabian sea for the period of October 1994 until October 1995. For this location, the layer where the turbulent mixing occurs, sometimes called the Turbocline, is only a few metres thick and fairly thin layers are needed to give a proper representation of the diurnal cycle. The dominant processes that control the diurnal cycle turn out to be buoyancy production and turbulent production by wave breaking, while in the deeper layers of the ocean the Stokes-Coriolis force plays an important role. 1 Introduction Apart from the traditional benefits of sea state forecasting (e.g. for shipping, fisheries, offshore opera- tions and coastal protection) it is now known that knowledge of the sea state is also important for a more accurate description of air-sea interaction, e.g. the sea state affects • the momentum transfer, • the heat transfer and • the ocean surface albedo. Here, I will briefly study sea state effects on the upper ocean dynamics and upper ocean mixing. Start- ing point is the Mellor-Yamada scheme where the turbulent velocity is determined from the turbulent kinetic energy equation. The turbulent velocity is then used to determine the eddy viscosities in the equations for momentum and heat. The turbulent kinetic energy equation describes the balance between the production of turbulent kinetic energy by work against the shear in the current and the Stokes drift (produces wave-induced and Langmuir turbulence), production by gravity wave dissipation, buoyancy and dissipation of turbulence. Note that momentum transport is also directly affected by the waves through the so-called Stokes-Coriolis force. The mixed layer model has been run for a one year period from the 16th of October 1994 for a location in the Arabian Sea where extensive observations of temperature profile, current profile, solar insola- tion, wind speed, etc. were collected during the Arabian Sea mixed layer dynamics Experiment (ASE) ECMWF Workshop on Ocean waves, 25-27 June 2012 71