Abstract
Abstract. The presence of airborne aerosols affects the meteorology as it induces a perturbation in the radiation budget, the number of cloud condensation nuclei and the cloud micro-physics. Those effects are difficult to model at regional scale as regional chemistry-transport models are usually driven by a distinct meteorological model or data. In this paper, the coupling of the CHIMERE chemistry-transport model with the WRF meteorological model using the OASIS3-MCT coupler is presented. WRF meteorological fields along with CHIMERE aerosol optical properties are exchanged through the coupler at a high frequency in order to model the aerosol–radiation interactions. The WRF-CHIMERE online model has a higher computational burden than both models run separately in offline mode (up to 42 % higher). This is mainly due to some additional computations made within the models such as more frequent calls to meteorology treatment routines or calls to optical properties computation routines. On the other hand, the overall time required to perform the OASIS3-MCT exchanges is not significant compared to the total duration of the simulations. The impact of the coupling is evaluated on a case study over Europe, northern Africa, the Middle East and western Asia during the summer of 2012, through comparisons of the offline and two online simulations (with and without the aerosol optical properties feedback) to observations of temperature, aerosol optical depth (AOD) and surface PM10 (particulate matter with diameters lower than 10 µm) concentrations. The result shows that using the optical properties feedback induces a radiative forcing (average forcing of −4.8 W m−2) which creates a perturbation in the average surface temperatures over desert areas (up to 2.6° locally) along with an increase in both AOD and PM10 concentrations.
Highlights
Both the direct and semi-direct aerosol effects refer to the perturbation of the radiation budget induced by the presence of aerosol in the atmosphere along with the induced changes in the meteorology (Jacobson et al, 2007; Hansen et al, 1997)
The impact of the coupling is evaluated on a case study over Europe, northern Africa, the Middle East and western Asia during the summer of 2012, through comparisons of the offline and two online simulations to observations of temperature, aerosol optical depth (AOD) and surface PM10 concentrations
The result shows that using the optical properties feedback induces a radiative forcing which creates a perturbation in the average surface temperatures over desert areas along with an increase in both AOD and PM10 concentrations
Summary
Both the direct and semi-direct aerosol effects refer to the perturbation of the radiation budget induced by the presence of aerosol in the atmosphere along with the induced changes in the meteorology (e.g. surface temperature, wind velocity, cloud coverage) (Jacobson et al, 2007; Hansen et al, 1997). The coupler may perform some operations on the coupling fields, such as interpolations This approach is a manner of sharing new model developments among research groups while allowing each group to continue to administrate their own model. In Péré et al (2011), aerosol radiative effects over Europe are evaluated using both the Weather Research and Forecasting (WRF) meteorological model (Skamarock et al, 2007) and the CHIMERE regional chemistry-transport model (Schmidt et al, 2001; Bessagnet et al, 2004; Menut et al, 2013). A WRF-CHIMERE online coupling was created, allowing the two models to exchange fields at each main physical time step (i.e a few minutes), enabling the possibility of the aerosol effects modelling. The study of cloud–aerosol interactions is currently ongoing and shall be the focus of a forthcoming paper
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