Abstract
Abstract. In the present work it is investigated the direct shortwave effect of anthropogenic aerosols on the near surface temperature over Southeastern Europe and the atmospheric circulation during summer 2000. In summer 2000, a severe heat-wave and droughts affected many countries in the Balkans. The study is based on two yearly simulations with and without the aerosol feedback of the regional climate model RegCM3 coupled with a simplified aerosol model. The surface radiative forcing associated with the anthropogenic aerosols is negative throughout the European domain with the more negative values in Central and Central-eastern Europe. A basic pattern of the aerosol induced changes in air temperature at the lower troposphere is a decrease over Southeastern Europe and the Balkan Peninsula (up to about 1.2°C) thus weakening the pattern of the climatic temperature anomalies of summer 2000. The aerosol induced changes in air temperature from the lower troposphere to upper troposphere are not correlated with the respective pattern of the surface radiative forcing implying the complexity of the mechanisms linking the aerosol radiative forcing with the induced atmospheric changes through dynamical feedbacks of aerosols on atmospheric circulation. Investigation of the aerosol induced changes in the circulation indicates a southward shift of the subtropical jet stream playing a dominant role for the decrease in near surface air temperature over Southeastern Europe and the Balkan Peninsula. The southward shift of the jet exit region over the Balkan Peninsula causes a relative increase of the upward motion at the northern flank of the jet exit region, a relative increase of clouds, less solar radiation absorbed at the surface and hence relative cooler air temperatures in the lower troposphere between 45° N and 50° N. The southward extension of the lower troposphere aerosol induced negative temperature changes in the latitudinal band 35° N–45° N over the Balkan Peninsula is justified from the prevailing northerly flow advecting the relatively cooler air from the latitudinal band 45° N–50° N towards the lower latitudes. The present regional climate modeling study indicates the important role of anthropogenic aerosols for the regional climate and their dynamical feedback on atmospheric circulation.
Highlights
Aerosol particles influence climate by modifying both the global energy balance through absorption and scattering of radiation, as well as the reflectance and persistence of clouds and the development and occurrence of precipitation (Hansen et al, 1997; Lohmann and Feichter, 2001; Ramanathan et al, 2001)
The third limitation is that the short length of the simulations presented in the study is not sufficiently long to establish a climatic signal of the aerosol radiative forcing, but this study focuses on the short-term signals rather than the long-term climate signals
The near surface NCEP/National Center for Atmospheric Research (NCAR) Reanalysis 1 project air temcalculated with RegCM3 shortwave surface radiative forcing ranging from 0 to a maximum of about −90 W m−2 over the perature anomalies between summer 2000 and the sum- area of maximum dust loading
Summary
Aerosol particles influence climate by modifying both the global energy balance through absorption and scattering of radiation (direct effects), as well as the reflectance and persistence of clouds and the development and occurrence of precipitation (indirect effects) (Hansen et al, 1997; Lohmann and Feichter, 2001; Ramanathan et al, 2001). The second indirect effect (which is that smaller cloud particles decrease the precipitation efficiency that results in prolonging cloud lifetime) is estimated to be roughly as large as the Twomey effect (Lohmann and Feichter, 2005) These aerosol induced changes of the earth’s radiation budget (negative radiative forcing) cause changes in atmospheric thermal structure, changes in synoptic and regional circulation systems, suppression of rainfall and less efficient removal of pollutants (Ramanathan and Feng, 2009). Lohmann and Feichter (2001) concluded that the absorption of solar radiation by absorbing aerosols (black carbon) can decrease cloud cover and liquid water path locally, but the indirect aerosol effects of increasing cloud lifetime and cloud albedo dominate Aerosols have both natural sources such as desert dust lifting, sea spray, volcanic explosions, biogenic organic emissions and anthropogenic sources such as fossil fuel and biomass burning. In the present work it is investigated the direct shortwave effect of anthropogenic aerosols on the near surface temperatures over Southeastern Europe and the atmospheric circulation during summer (from June to August) 2000 based on simulations performed by the regional climate model RegCM3 coupled with a simplified aerosol model
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