Global Coupled Atmosphere/Ocean Models for Climate and Seasonal Forecast Applications

A coupled global 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 based on HYCOM ("iHYCOM"). Both FIM and iHYCOM are 3-dimensional grid point models, laid out on a common icosahedral horizontal grid and using an adaptive hybrid-isentropic/isopycnic vertical coordinate. The atmospheric model shares column physics with NCEP's Global Forecast System (GFS) and Climate Forecast System version 2 (CFSv2).

Initial results using GFS and CFSv2 physics showed that regional biases in cloud cover, and hence shortwave radiation flux, are large in both coupled and uncoupled (FIM-only) global simulations, and needed to be reduced in many geographic regions. For this reason, we have developed and tested modifications for shallow and deep convection and vertical discretization and conducted several 1-year AMIP tests on sensitivity to these changes/parameters.

Results of these tests and optimal configuration so far of the FIM-iHYCOM coupled model and its latest simulations compared to CFSv2 and NASA/GEWEX Surface Radiation Budget data will be presented.