Global Coupled Atmosphere/Ocean Modeling for Seasonal Forecast Applications at NOAA/ESRL

A global coupled model aimed at intra-seasonal and interannual prediction is under development at NOAA's Earth System Research Laboratory. It uses the FIM atmospheric model and an ocean model "iHYCOM", basically an icosahedral grid version of HYCOM. Both components are 3-dimensional grid point models, laid out on a common icosahedral horizontal grid, and using an adaptive hybrid-isentropic/hybrid-isopycnic vertical coordinate in FIM and iHYCOM, respectively. The fact that FIM and iHYCOM share a horizontal grid allows us to couple the atmosphere and ocean model directly without the need for an interpolating flux coupler and without coastline ambiguities.

The atmospheric model uses column physics from the U.S. Weather Service's GFS/CFS. Initial results showed large regional biases in cloud cover, and hence shortwave radiative flux, in both coupled and uncoupled (AMIP style) global simulations. In an attempt to reduce these biases, we have modified the model to use the Grell-Freitas scheme for shallow and deep convection. A number of 1-year AMIP tests at different horizontal and vertical resolutions have been performed exploring the sensitivity to these changes/parameters.

Results of these tests and an optimal configuration of the FIM-iHYCOM coupled model are presented. We will evaluate MJO patterns and other model performance indicators on seasonal time scales against observations and model output from CFSv2.