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Community Multiscale Air Quality Modeling System (CMAQ)

WRF-CMAQ two-way coupled model


The two-way coupled meteorology and air quality model is composed of the Weather Research and Forecasting (WRF) model and the Community Multiscale Air Quality (CMAQ). The new model system (Wong et. al.), WRF-CMAQ two-way coupled model, runs as a single executable with 2-way data communication between the WRF and CMAQ components through memory. Figure 1 depicts an overview of this system.

Figure 1. WRF-CMAQ two-way coupled model system overview.

Direct Aerosol Radiative Feedback Effects

Aerosol information from CMAQ is transferred to the meteological model, WRF. Efficient Mie scattering algorithms have been developed to calculate short-wave aerosol optical properties (aerosol optical depth, single scattering albedo, and asymmetry factor) using aerosol mass, chemical composition, and modal size distributions computed by CMAQ. Black carbon is treated by the core-shell approach developed by Frank Binkowski based on Bohren and Huffman (1983). This has been implemented in shortwave RRTMG radiation scheme in WRF, where aerosol optical properties are calculated for 14 wavelength bands.


The first release was back in 2012 with WRF 3.3 and CMAQ 5.0. The latest two-way model bases on WRF 3.8 and CMAQ 5.2. In each release, it comes with a step by step instruction to construct the two-way model. Table 1 and 2 list all run time model environment variables.

 Table 1. Essential run time environment variable.


turn on CMAQ portion of the twoway model [ F ]


turn on short-wave feedback calculation [ F ]


WRF and CMAQ calling frequency [ 1 ] e.g. setting to 4 would couple WRF and CMAQ every 4th WRF step


WRF west_east_stag dimension size


WRF south_north_stag dimension size


WRF bottom_top_stag dimension size


number of columns in the CMAQ domain


number of rows in the CMAQ domain


distance between the WRF and CMAQ lower left corner in the x-direction [ 5 ]


distance between the WRF and CMAQ lower left corner in the y-direction [ 5 ]


turn on 64bit offset in IOAPI library [ F ]

 Table 2. Optional run time environment variable.


create intermediate meteorological data for diagnostic purposes [ F ]


Lambert conformal reference latitude


time step size of the physical meteorological output file [ 10000 ]


turn on sub-domain monitoring capability [ F ]


sub-domain starting column


sub-domain ending column


sub-domain starting row


sub-domain ending row


sub-domain monitoring species list


Wong, D. C., Pleim, J., Mathur, R., Binkowski, F., Otte, T., Gilliam, R., Pouliot, G., Xiu, A., and Kang, D., “WRF-CMAQ two-way coupled system with aerosol feedback: software development and preliminary results”, Geosci. Model Dev., 5, 299-312, 2012. ( )

For an overview of the 2-way Coupled WRF-CMAQ see: