WRF-CMAQ two-way coupled system with aerosol feedback: software development and preliminary results

摘要

Air quality models such as the EPA Community Multiscale Air Quality (CMAQ)require meteorological data as part of the input to drive the chemistry andtransport simulation. The Meteorology-Chemistry Interface Processor (MCIP)is used to convert meteorological data into CMAQ-ready input. Keyshortcoming of such one-way coupling include: excessive temporalinterpolation of coarsely saved meteorological input and lack of feedback ofatmospheric pollutant loading on simulated dynamics. We have developed atwo-way coupled system to address these issues. A single source codeprinciple was used to construct this two-way coupling system so that CMAQcan be consistently executed as a stand-alone model or part of the coupledsystem without any code changes; this approach eliminates maintenance ofseparate code versions for the coupled and uncoupled systems. The designalso provides the flexibility to permit users: (1) to adjust the callfrequency of WRF and CMAQ to balance the accuracy of the simulation versuscomputational intensity of the system, and (2) to execute the two-waycoupling system with feedbacks to study the effect of gases and aerosols onshort wave radiation and subsequent simulated dynamics. Details on thedevelopment and implementation of this two-way coupled system are provided.When the coupled system is executed without radiative feedback,computational time is virtually identical when using the CommunityAtmospheric Model (CAM) radiation option and a slightly increased (~8.5%) when using the Rapid Radiative Transfer Model for GCMs(RRTMG) radiation option in the coupled system compared to theoffline WRF-CMAQ system. Once the feedback mechanism is turned on, theexecution time increases only slightly with CAM but increases about 60%with RRTMG due to the use of a more detailed Mie calculation in thisimplementation of feedback mechanism. This two-way model with radiativefeedback shows noticeably reduced bias in simulated surface shortwaveradiation and 2-m temperatures as well improved correlation of simulatedambient ozone and PM_2.5 relative to observed values for a test casewith significant tropospheric aerosol loading from California wildfires.