Global Coupled Atmosphere/Ocean Model for Climate and Seasonal Forecast Applications
Shan Sun(1,2), Rainer Bleck(1,2) and Stan Benjamin (2)
(1) CIRES, (2) NOAA ESRL
A 3-dimensional global ocean circulation model, named iHYCOM, is under development at NOAA’s Earth System Research Laboratory. This ocean model, a version of HYCOM, is the oceanic counterpart of the finite-volume, flow-following, icosahedral atmospheric model FIM (http://fim.noaa.gov). FIM uses an icosahedral horizontal grid and a hybrid-isentropic vertical coordinate. The atmospheric FIM model shares column physics with GFS.
Grid nesting is common in weather modeling, but grid discontinuities are usually kept away from the region of interest. To avoid joining disparate grids at the ocean-atmosphere interface, arguably the region of most interest in coupled modeling, we have recoded HYCOM for an icosahedral grid (hence the name iHYCOM). iHYCOM uses the same 1-d vertical component as HYCOM, and the same set of prognostic variables on the hybrid-isopycnal vertical coordinate. The similarity of FIM and iHYCOM (3-D grid, prognostic variables) allows the two models to share dycore components and software engineering innovations developed for FIM.
Preliminary results from coupled FIM-iHYCOM global model will be discussed. Several performance measures indicate that running HYCOM on an icosahedral mesh is feasible. This paves the way for integrating FIM into a coupled ocean-atmosphere system without the need for an interpolating flux coupler. However, biases in the annual net surface heat flux in coupled as well as atmospheric-only simulations, both global and regional, are large and need to be reduced. The current status on the FIM-iHYCOM coupled model and its latest simulations compared to CFSv2 and ERA reanalysis data will be presented.