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Community Multiscale Air Quality Modeling System (CMAQ)

WRF-CMAQ two-way coupled model

Overview

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.

History

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.

RUN_CMAQ_DRIVER

turn on CMAQ portion of the twoway model [ F ]

DO_SW_CAL

turn on short-wave feedback calculation [ F ]

WRF_CMAQ_FREQ

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

WRF_COL_DIM

WRF west_east_stag dimension size

WRF_ROW_DIM

WRF south_north_stag dimension size

WRF_LAY_DIM

WRF bottom_top_stag dimension size

CMAQ_COL_DIM

number of columns in the CMAQ domain

CMAQ_ROW_DIM

number of rows in the CMAQ domain

TWOWAY_DELTA_X

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

TWOWAY_DELTA_Y

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

IOAPI_OFFSET_64

turn on 64bit offset in IOAPI library [ F ]

 Table 2. Optional run time environment variable.

CREATE_PHYSICAL_FILE

create intermediate meteorological data for diagnostic purposes [ F ]

WRF_LC_REF_LAT

Lambert conformal reference latitude

FILE_TIME_STEP

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

SD_TIME_SERIES

turn on sub-domain monitoring capability [ F ]

SD_SCOL

sub-domain starting column

SD_ECOL

sub-domain ending column

SD_SROW

sub-domain starting row

SD_EROW

sub-domain ending row

SD_CONC_SPCS

sub-domain monitoring species list

References:

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. ( http://www.geosci-model-dev.net/5/299/2012/ )

For an overview of the 2-way Coupled WRF-CMAQ see: http://www.cmascenter.org/conference/2011/slides/mathur_overview_two-way_2011.pptx