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Interannual and climatological variations of wind stress drag coefficient (CD) are examined over the global ocean from 1998 to 2004. Here CD is calculated using high temporal resolution (3- and 6-hourly) surface atmospheric variables from two datasets: 1) the 40-yr European Centre for Medium-Range Weather Forecasts (ECMWF) Re-Analysis (ERA-40) and 2) the Navy Operational Global Atmospheric Prediction System (NOGAPS). The stability-dependent CD algorithm applied to both datasets gives almost identical values over most of the global ocean, confirming the validity of results. Overall, major findings of this paper are as follows: 1) the CD value can change significantly (e.g., >50%) on 12-hourly time scales around the Kuroshio and Gulf Stream current systems; 2) there is strong seasonal variability in CD, but there is not much interannual change in the spatial variability for a given month; 3) a global mean CD ≈ 1.25 × 10−3 is found in all months, while CD ≥ 1.5 × 10−3 is prevalent over the North Pacific and North Atlantic Oceans and in southern high-latitude regions as well, and CD ≤ 1.0 × 10−3 is typical in the eastern equatorial Pacific cold tongue; and 4) including the effects of air–sea stability on CD generally causes an increase of >20% in comparison to the one calculated based on neutral conditions in the tropical regions. Finally, spatially and temporally varying CD fields are therefore needed for a variety of climate and air–sea interaction studies.

Subtropical boundary layer clouds have a fundamental role on the radiative budget of the atmosphere and on the modulation of the tropical circulations. The development of realistic parameterizations of these clouds in global atmospheric models is a major challenge. Unfortunately, this has been a difficult problem to solve in an acceptable way. In this paper, new and simple parameterization schemes for subtropical clouds are implemented in the U.S. Navy Operational Global Atmospheric Prediction System's (NOGAPS) forecast model. The parameterizations are partially based on large eddy simulation (LES) results and provide a substantial improvement when compared with observations and with the previous scheme. The global distribution of boundary layer clouds and of surface shortwave radiation is more realistic with this new scheme, particularly over the stratocumulus regions. The transition from stratocumulus to cumulus is well captured, the seasonal and diurnal cycles of stratocumulus are realistic, a...

Cloud radiative effects are represented in simulations with the general circulation model of the Navy Operational Global Atmospheric Prediction System (NOCAPS) using ingested cloud field data from the ISCCP dataset rather than model-diagnosed cloud fields. The primary objective is to investigate the extent to which the high temporal resolution ISCCP data can be used to improve the simulation of cloud radiative effects on the general circulation in GCM simulations much as observed sea surface temperatures (SSTs) have been used to avoid simulation errors resulting from inaccurately modeled SSTs. Experiments are described that examine the degree to which uncertainties in cloud field vertical structure impair the utility of the observed cloud data in this regard, as well as the extent to which unrealistic combinations of cloud radiative forcing and other physical processes may affect GCM simulations. The potential for such unrealistic combinations stems from the lack of feedback to the cloud fields i...