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Transfer and Evaluation of the CAM Parameterization Suite to WRF

Principal Investigator: Jerome Fast

CAM5 diagram
Figure 1: Conceptual diagram depicting the CAM5 physics modules ported into WRF. Enlarge Image

ACI Researchers ported the CAM version 5 advanced physics suite (CAM5) into the Weather Research and Forecasting (WRF) model so that the Aerosol Modeling Testbed can be used to evaluate parameterizations at higher spatial resolution that is more compatible with data. This addresses the following issues:

  • There has been relatively little interaction between the cloud-resolving/mesoscale modeling and global-scale modeling communities. These types of models have been optimized for different purposes and the lessons learned on parameterizations are not necessarily shared.
  • Global climate models, including the Department of Energy's Community Atmosphere Model (CAM) will be run at higher spatial resolution (10-20 km) in the future (5-10 years from now). However, the performance of the current suite of physics modules at those scales is not known.
  • Rapid development and evaluation of the next-generation suite for CAM requires the ability to isolate processes as well as the ability to test parameterizations across a range of scales.
  • In addition, current computing capabilities do not allow global model domains to be run at mesoscale resolutions.

The CAM5 physics was compared against more complex and expensive representations, using a systematic and consistent methodology. Performance metrics were used to identify more desirable parameterization choices for both models. This effort enabled coupled downscaling simulations to have consistent physics treatments from global to regional scales.

CAM5 diagram
Figure 2: Compares the total fine particulate matter and aerosol optical depth between CAM5 and two WRF-Chem simulations at a select time for the MILAGRO field campaign.
Enlarge Image

Preliminary downscaling simulations have been performed, in which CAM5 was used to provide the initial and boundary conditions for WRF-Chem. This allows researchers to compare the performance of CAM5 with the higher resolution application of the CAM5 physics suite in WRF-Chem (see Figure 2). One WRF-Chem simulation employs the same IPCC emissions as CAM5, and the other uses high-resolution emissions from a 2006 inventory. The CAM5 and WRF-Chem simulation that employ the same emissions are qualitatively similar in terms of PM2.5 (representing particulates less than 2.5 micrometers in aerodynamic diameter) mass and aerosol optical depth, except that the higher resolution in WRF-Chem permits more spatial variability in the meteorology and consequently, aerosol transport, mixing, and aging. The WRF-Chem simulation that employs the 2006 emissions inventory is significantly different, but most of the differences in PM2.5 and aerosol optical depth are associated with the treatment of dust emissions. In CAM5, the simulated dust is nearly zero, while the online computations in WRF-Chem produce significant concentrations of dust over northwestern Mexico that are transported over the Gulf of Mexico. Additional simulations are being performed to compare the simple treatment of aerosols from CAM5 with more complex representations and measurements of aerosol mass, composition, and size distribution using the Aerosol Modeling Testbed.

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