Climate Process Team (CPT): Projects at NCAR

Comparison of the NCAR and GFDL models in subsidence regions

The focus of this research is on the role of low tropical clouds in affecting climate sensitivity. A comparison of climate simulations between the Community Atmosphere Model (CAM3) and the GFDL Atmospheric Model (AM2) indicates that these models have very different responses to warming due to increased carbon dioxide. Low clouds in regions off the west coast of tropical continents play a particular important role in modulating sea surface temperatures in these regions. Stratiform cloud cover off the coasts of southern California, northern South America, north and south Africa reduce shortwave radiation reaching the sea surface by order of 50 to 80 Wm-2.


• Project Description and results overview
• CAM3 and AM2 diagnostics
• Comparison of the NCAR and GFDL models versus observations and reanalysis I
• Comparison of the NCAR and GFDL models versus observations and reanalysis II

GCSS Pacific Cross-section Intercomparison (GPCI)

Weather and climate prediction models are analyzed along a cross-section in the Pacific Ocean, from California to the Equator. The cross-section over the Pacific Ocean encompasses several fundamental cloud regimes such as stratocumulus, shallow cumulus and deep cumulus, as well as the transitions between them. The model outputs are collected every 3 hours (JJA 1998 and 2003), which allows for a better understanding of issues associated with the diurnal cycle of clouds and cloud related processes in the tropics and subtropics. Presently, GPCI has collected output from 6 models from GFDL, NCAR, UKMO, MeteoFrance, JMA and KNMI.


• Project description
• CAM3 simulation for the GCSS Pacific Cross-Section Intercomparison
• Diurnal cycle results
• Forecast runs

Subgrid scale cloud variability: subcolumn generator and McICA method implementation

Collaboration with Robert Pincus (CDC), Mike Iacono (AER)

To take into account the subgrid scale cloud variability in CAM, we have implemented a subcolumn column generator. The idea of the cloud generator is that the Subgrid scale cloud variability can be represented by a set of subcolumns that are generated randomly.
We are testing the subcolumn generator on radiation calculations using the Monte Carlo Independant Column Approximation (McICA). The McICA is a method developed to improve the treatment of cloud variability in climate models. This method is essentially a sampling strategy that yields unbiased estimates of heating rate profiles with respect to the full ICA, but that speeds the calculation up compared to the full ICA.


• Project description

Forecast runs with the UW scheme

Collaboration with Dave Williamson (NCAR), Jerry Olson (NCAR), Dani Coleman (NCAR), Steve Klein (LLNL), Jim Boyle (LLNL)

We are testing the UW atmospheric boundary layer scheme with CAM3 runs in forecast mode. The goal is to provide insight into parameterization errors which ultimately could lead to model improvements. Our effort follows the CAPT protocol. In the CAPT protocol, we realistically initialize CAM3 with NWP analyses, and we then run the model in forecast mode to determine the drift from the NWP analyses and/or from available field data. This method allows us to diagnose model parameterization deficiencies. This project is a collaboration with the LLNL.


• Runs status

Acknowledgments