A regional coupled atmosphere-ocean model is being developed to better understand air- sea interactions in the eastern North Pacific Ocean and California coastal region. The atmospheric part of the coupled model is the Experimental Climate Prediction Center (ECPC) Regional Spectral Model (RSM) and the oceanic component is the eddy-resolving Regional Ocean Modeling System (ROMS). A previous ROMS study for this region forced by RSM winds (at 25 km resolution and monthly time scales) clearly showed that the ocean model captured not only the statistics of observed circulation of the Southern California Current System but also the timing and spatial evolution of annually recurrent westward propagating depth anomalies during active upwelling (Di Lorenzo, 2003, Deep-Sea Res.).

Following Di Lorenzo, we have begun one-way coupling experiments in order to understand the characteristic response of RSM to oceanic forcings and ROMS to atmospheric forcings. The RSM used for these studies has spatial resolution of 20 km and provides 3 hourly forcings to ROMS. The momemtum and buoyancy fluxes used to force ROMS at the upper boundary were initially calculated directly from RSM simulations forced with coarse-resolution analysis ocean temperatures. However, preliminary simulations revealed that simulated area-averaged sea surface temperature (SST) with flux correction was warmer than observed SST by around 0.4 degree C for the year 2003. We subsequently discovered that the coupled simulations were more stable if we used a bulk parameterization that computes surface wind stress and net surface turbulent heat fluxes given the atmospheric boundary layer variables from RSM with ROMS SST. The radiation fluxes were also modified to take into account different assumptions about the ocean boundary conditions. Preliminary multi-year RSM-ROMS coupled simulations will be described at the meeting.

Our ultimate goal is to develop an operational regional joint air-sea modeling system that could be imbedded within a coarser resolution, or global coupled atmospheric-oceanic forecasting system. Such a system would provide a better description of the coastal environment on diurnal to seasonal time scales.