Sang-ki Lee, CIMAS/Univ. of Miami, and David Enfield and Chunzai Wang, NOAA/AOML
A series of ocean general circulation (OGCM) model experiments is carried out using the Hybrid Coordinate Ocean Model (HYCOM) to assess the model's sensitivity to surface heat flux data and to the parameterizations of light attenuation and vertical turbulent mixing for simulating the seasonal development and decay of the Western Hemisphere Warm Pool (WHWP). Based on the sensitivity analysis, we have arrived at the following major conclusions. (1) When monthly averaged heat flux data are used, the surface turbulent heat fluxes need to be adjusted to compensate for biases arising from nonlinearities at the unresolved shorter time scales. (2) Among the eight surface heat flux data sets assessed in this study, we find that the simulated SST and the WHWP depth are closest to the observations when the Southampton constrained (SHC) and Oberhuber (OBH) heat flux data are used. (3) The model's performance is optimal in reproducing the WHWP depth and the thermocline structure in the WHWP region if the light attenuation depth is derived realistically from space-based ocean color measurements, for a regional average attenuation depth of 17m. (4) The simulated WHWP SST does not appear to be sensitive to the choice of critical Richardson number as long as it is set within the range of 0.25 ~ 1.00. (5) The fine-tuned accuracy; the WHWP SST bias ranges between -0.21 and 0.39oC, and the WHWP depth bias between -5.8m and 0.8m.