Abstract
Ten 5-day forecasts have been performed to compare the error characteristics of the global spectral models of the Japan Meteorological Agency (JMA) and the Australian Bureau of Meteorology Research Center (BMRC). Operational global analyses for July 1983 obtained from the European Center for Medium Range Weather Forecasts (ECMWF) are used as initial conditions for both models. Differences in the hydrological cycle in the two models are found to be evident. Strong precipitation and evaporation in the BMRC model integrations are associated with the parameterization of cumulus convection and also the initializing of the model moisture field; strong heating due to cumulus convection results in a positive bias of the upper troposphere in the BMRC model. The hydrological cycle of the JMA model is less intense than that of the BMRC model and more in accord with the climatic estimates. Details in the application of the connective parameterization based on Kuo's scheme and the radiative parameterization appear to explain some of these differences between the two models. Sensible heat flux from the surface is considered to be too small in both models.
The diagnosis of cloud amount in the JMA model has introduced some systematic error in cooling rates in the upper troposphere in the arctic region. This problem is not evident in the simpler scheme used in the BMRC model where climatological cloud amounts are prescribed.
The characteristics of the errors in the wind field prediction are similar in the two models with the major exception being the excessive upper tropical easterlies in the BMRC model. The JMA model includes a parameterization of gravity wave drag which is not included in this version of the BMRC model; this appears to be relevant to the generally more intense zonal flow in the winter hemisphere.
