How Do Aerosol Radiative Effects Influence Wind? a Sensitivity Study of the Aerosol Impact on the Spatially-Distributed Wind over Europe

Abstract:

Atmospheric aerosols affect the Earth’s climate through their radiative effects, being one of the most uncertain areas in climate modeling. Radiative effects depend mainly on the aerosol optical properties and can be divided into direct and semi-direct effect, produced by the scattering and absorption of radiation; and indirect effect, which influences the aerosols-cloud interactions. Aerosols are widely known to affect radiation, temperature, stability, clouds, and precipitation. However, scientific literature about their effects on wind is scarce.

In this sense, the effects of aerosol particles on spatially-distributed winds over Europe are examined. The methodology carried out consists of two WRF-Chem simulations for Europe for the entire year 2010 differing only in the inclusion (or not) of aerosol radiative feedbacks. These simulations have been carried out under the umbrella of the second phase of the AQMEII (Air Quality Model Evaluation International Initiative, http://aqmeii.jrc.ec.europa.eu/). A Euro-CORDEX compliant domain at 0.22º and 23 km resolution has been used. The first simulation does not take into account any aerosol feedbacks (NFB) and the second simulation differs from the base case by the inclusion of direct and indirect radiative feedbacks (FB).

Results show that the presence of aerosol generally reduces the wind over Europe. The absorption and scattering of solar radiation by the aerosol particles heat the air and cool the ground temperature leading to an atmospheric stability. This increases the atmospheric stability and decreases the turbulence, as consequence the vertical transfer of momentum diminishes and the surface winds are slower. In addition, the decrease of solar radiation to the ground weakens the thermal circulations, such as land-sea breezes which is more noticeable in the southern of Europe in summer. On the other hand, the indirect effect of the aerosols through their enhancement of clouds also favors a decline of winds evidenced by the spatial correlations between the cloud optical depth and wind speed reductions.

Despite these results further investigation is necessary in order to reduce the uncertainties of the aerosol effects over meteorological variables.