Regional climate feedback of anthropogenic aerosols over Europe using RegCM3

The regional climate model RegCM3 coupled with aerosols is used in this study to investigate the direct shortwave effect of anthropogenic aerosols on the regional European climate over a 12 yr period (1996-2007). Aerosol feedback induced small changes in the yearly averaged near-surface temperature over Europe during this period and the greatest negative temperature difference of -0.2 degrees C was observed over the Balkan Peninsula. The field of aerosol-induced near-surface temperature anomalies is not spatially collocated with the field of aerosol radiative forcing as the spatial correlation coefficient is only 0.24. A characteristic of the aerosol-induced changes on near-surface temperature is a dipole pattern in which cooling occurs south of the latitudinal zone from 50 to 55 degrees N and warming occurs northwards. This characteristic dipole pattern of changes in temperature is also seen at higher atmospheric levels but the signal weakens at higher altitudes. A characteristic in the aerosol-induced changes in atmospheric circulation is a negative anomaly of the zonal westerly wind of 500 hPa in the latitudinal belt between 45 and 55 degrees N, which is consistent with a dipole pattern in geopotential heights that consists of an anticyclonic anomaly north of approx. 55 degrees N and cyclonic anomaly south of approx. 45 degrees N. The greatest aerosol-induced negative lower troposphere temperature anomaly over the Balkan Peninsula is associated with the collocated greatest cyclonic anomaly. This reveals the important role of the aerosol-induced circulation changes for the pattern of the temperature anomalies and explains the poor correlation between the patterns of aerosol-induced temperature changes and aerosol radiative forcing. Because the aerosol-induced changes in temperature and atmospheric circulation are at the limits of statistical significance, the present regional climate modelling study indicates there is a limited feedback on the European climate related to the direct shortwave effect of European anthropogenic aerosols.