Evaluation of a global ocean general circulation model; The Lat-Lon-Cap (LLC90) configuration of the MITgcm

Abstract

An evaluation of a general circulation model from Massachusetts Institute of Technology (MITgcm) with Lat – Lon – Cap (LLC90) configuration was done. Simulation of 100 years yields the annual means of potential temperature, salinity, meridional overturning stream function and transport of several throughflows. A reference run with widened Davis strait from the model was used to compare with observational WOA09 data, and the MITgcm has reproduced reasonably reliable data. The patterns of potential temperature can resemble the WOA09, however not so for the salinity fields. An experiment to simulate the model in 5 different tuning set were then proceeded. For the potential temperature and salinity fields, the North Pacific and the Southern Ocean still has significant difference to the WOA09. The difference was in the range of -6 to 5 °C for the potential temperature and -0.5 to 3 psu for the salinity field. The meridional overturning circulation stream function was still lower than the observational (± 17 Sv); the MITgcm simulates it 10 ± 1Sv in the experiment. The root mean square (RMS) of the difference were calculated, the surface layer has the largest magnitude of difference due to the forcing dynamics. The best simulation, which has the least difference to WOA09, was the one with the original bathymetry and smallest vertical diffusivity coefficient, 1 x 10-5 m2 s-1.