Interactive coupling of a regional climate model and a chemical transport model: evaluation and preliminary results on ozone and aerosol feedback
Abstract
This study presents an interactive coupling system of the regional climate model RegCM3 and the chemistry transport model CAMx, called RegCMCAMx. This system provides an advancement from offline coupling methods already in use.
In RegCMCAMx, the radiative effects of tropospheric ozone, sulfates and black and organic carbon were considered. A series of annual sensitivity simulations were carried out for the year 2005 over a European domain, where ozone and/or aerosols were interactively coupled (taking their radiative feedbacks into account).
The simulated concentrations of ozone, nitrogen dioxide, sulfur dioxide, sulfate and carbonaceous aerosol were validated against surface measurements. The coupling was evaluated by simulating 2 m temperature as well.
The model satisfactorily reproduced near-surface ozone, especially in summer, and made reasonable predictions for monthly sulfate aerosol concentrations. Deficiencies were identified in simulating nitrogen (underprediction), sulfur oxides (overprediction) and carbonaceous aerosols (underprediction).
The performance of the coupling system compared to non-coupled data was analyzed, and significant improvement of the model was found in terms of reproducing 2 m temperature, mainly for interactively coupled ozone. The short-term climate response of interactively coupled chemistry/aerosol was analyzed for the first time by this coupling model as well.
The seasonally averaged temperature perturbation caused by coupled ozone/aerosols ranged from -1.5 to + 1.5 degrees C, not only near the surface but also at higher altitudes. Despite expectations, the surface radiative forcing due to aerosols did not correlate with the induced temperature changes, reflecting the complexity of the processes when ozone and/or aerosols perturb the overall dynamics of the atmosphere.
The limitations of the newly established coupling system and the potential for future development are discussed.