Comparison of Tropical Ocean–Atmosphere Fluxes with the NCAR Community Climate Model CCM3

Abstract

The properties of the marine boundary layer produced by the National Center for Atmospheric Research (NCAR) Community Climate Model version 3 (CCM3) are compared with observations from two experiments in the central and western equatorial Pacific. The main objective of the comparison is determining the accuracy of the ocean?atmosphere fluxes calculated by the model. The vertical thermodynamic structure and the surface fluxes calculated by the CCM3 have been validated against data from the Central Equatorial Pacific Experiment (CEPEX) and the Tropical Ocean Global Atmosphere?Tropical Atmosphere Ocean (TOGA?TAO) buoy array. The mean latent heat flux for the TOGA?TAO array is 92 W m?2, and the model estimate of latent flux is 109 W m?2. The bias of 17 W m?2 is considerably smaller than the overestimation of the flux by the previous version of the CCM. The improvement in the latent heat flux is due to a reduction in the surface winds caused by nonlocal effects of a new convective parameterization. The agreement between the mean sensible heat flux for the TOGA?TAO array and the model estimate has also been improved in the new version of the model. The current version of the CCM overestimates the sensible heat flux by 3.4 W m?2. The atmospheric temperature and water vapor mixing ratio from the lowest model layer are within 0.3 K and 0.4 g kg?1 of measurements obtained from radiosondes. The mean model value of the boundary layer height is within 13 m of the average height derived from a Raman lidar on board a ship in the CEPEX domain. There is some evidence that the biases in the model can be reduced further by modifying the bulk formulation of the surface fluxes.