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

Abstract

Abstract. Air quality models such as the EPA Community Multiscale Air Quality (CMAQ) require meteorological data as part of the input to drive the chemistry and transport simulation. The Meteorology-Chemistry Interface Processor (MCIP) is used to convert meteorological data into CMAQ-ready input. Key shortcoming of such one-way coupling include: excessive temporal interpolation of coarsely saved meteorological input and lack of feedback of atmospheric pollutant loading on simulated dynamics. We have developed a two-way coupled system to address these issues. A single source code principle was used to construct this two-way coupling system so that CMAQ can be consistently executed as a stand-alone model or part of the coupled system without any code changes; this approach eliminates maintenance of separate code versions for the coupled and uncoupled systems. The design also provides the flexibility to permit users: (1) to adjust the call frequency of WRF and CMAQ to balance the accuracy of the simulation versus computational intensity of the system, and (2) to execute the two-way coupling system with feedbacks to study the effect of gases and aerosols on short wave radiation and subsequent simulated dynamics. Details on the development 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 Community Atmospheric 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 the offline WRF-CMAQ system. Once the feedback mechanism is turned on, the execution time increases only slightly with CAM but increases about 60 % with RRTMG due to the use of a more detailed Mie calculation in this implementation of feedback mechanism. This two-way model with radiative feedback shows noticeably reduced bias in simulated surface shortwave radiation and 2-m temperatures as well improved correlation of simulated ambient ozone and PM 2.5 relative to observed values for a test case with significant tropospheric aerosol loading from California wildfires.

Impacts of Aerosol Shortwave Radiation Absorption on the Dynamics of an Idealized Convective Atmospheric Boundary Layer

“…4a shows, we find that the CBL depth is smaller in both the UNI (955 m) and TOP (860 m) experiments, agreeing with the findings of Yu et al (2002) and Wong et al (2012). Equation 5a predicts that, in the absence of the absorption of heat (no aerosols, F = 0) and with the same atmospheric conditions (subsidence and free atmospheric stability), the CBL depth depends only on the surface heat flux and the entrainment rate, in the absence of other large-scale forcing.…”

“…2b) are equivalent. Since meteorological and air-quality experiments are not designed with the same aim in mind (Bierwirth et al 2010;Wong et al 2012), synchronized and reliable measurements of net radiative flux density and actinic flux are difficult to obtain. The results showed in Fig.…”

“…The impact of aerosols on the vertical structure of the CBL has been investigated by means of various methodologies: satellite data (Kaufman et al 2002), observations made in experimental campaigns (Angevine et al 1998;Johnson et al 2008;Masson et al 2008), numerical modelling (Cuijpers and Holtslag 1998;Yu et al 2002) and combinations of these techniques (Liu et al 2005;Wong et al 2012). A process study on how aerosol heating by SW-absorbing aerosols influences the turbulent fluxes, surface forcing, vertical structure and heat budget of the CBL is still lacking, however.…”

Impacts of aerosol-radiation feedback on local air quality during a severe haze episode in Nanjing megacity, eastern China

“…However, the neglect of aerosol-chemistry feedbacks in off-line models is expected to cause noticeable biases in both meteorological and chemical forecasts (Jacobson, 1997;Wong et al, 2012;Kong et al, 2015;Makar, Gong, Milbrandt et al, 2015). Jacobson (1997) was first to develop a fully-coupled on-line model to account for the radiation feedback of size-resolved aerosols on photolysis and temperature profiles.…”

“…Since then, numerous new generations of on-line-coupled models have been developed worldwide, such as Multiscale Climate Chemistry Model (MCCM) (Grell et al, 2000), Weather Research and Forecasting-Chemistry (WRF-Chem) (Grell et al, 2005) and Global Environmental Multi-scale-Modeling Air quality and CHemistry (GEM-MACH) (Moran et al, 2010). These models have been widely used for Europe and North America and they found that the interactions between meteorology and chemistry can be significant during strong air pollution episodes (Grell et al, 2011;Konovalov et al, 2011;Wong et al, 2012;Chen et al, 2014;Kong et al, 2015;Liu et al, 2016).…”