The impact of moderately absorbing aerosols on the energy budget over Central Europe is discussed, based on experimental observations and numerical simulations obtained for the summer of 2015. Aerosol events, defined as aerosol optical depth (AOD) at 500 nm greater than 0.15, especially in August, are mostly attributed to transport of biomass burning (BB) from Eastern Europe. Shortwave (SW) aerosol radiative forcings (ARF) at the surface and the top of the atmosphere (TOA) are estimated from ensembles of ten and eight observational and model-based approaches, respectively. Different measuring methods, including unmanned aviation system (UAS) and ground-based measurements, radiative transfer models, including MOTRAN and FuLiou, and parameterisations of aerosol optical properties regarding full vertical profiles, columnar and surface properties, are used in these approaches. The mean ARF is-15.9 +/- 2.1 W/ m2,-9.1 +/- 1.4 W/m2, and 7.0 +/- 1.0 W/m2, respectively, for the Earth's surface, TOA, and atmosphere under clear conditions for June-August 2015. During an aerosol event with AOD peak of about 0.6 at 500 nm, the daily mean surface, TOA, and atmosphere ARF are around-30,-18, and 13 W/m2, respectively. The mean ARF differences between all methods are about 4.0 W/m2 for the surface and about 2.3 W/m2 for the TOA, which correspond to 23% of ensemble means. Aerosols are also shown to have a significant impact on observed surface sensible and latent heat fluxes for the study period. Flux sensitivity to AOD for a solar zenith angle of 45? is-70 +/- 41 W/ m2/tau 500,-112 +/- 56 W/m2/tau 500, and-119 +/- 19 W/m2/tau 500, respectively, for sensible, latent, and net SW and longwave (LW) radiation flux. When averaged over day time, sensitivities of sensible heat, latent heat fluxes, and net radiation fluxes to AOD are reduced by about 50%, 20%, and 70%, respectively.

During June, July and August 2003, an exceptional heat wave affected western and central Europe. In Piedmont, a region located in northwestern Italy at the foot of the Alps, many stations recorded the highest mean summer temperatures since the beginning of their instrumental record. Some consequences of this extraordinary hot summer in Piedmont and in many European countries include severe drought conditions, with strong effects on agriculture and electric production, an acceleration of glacier ablation, and an increase in the frequency of forest fires. This heat wave has been analyzed by running a Soil-Vegetation Atmosphere Transfer scheme for 5 years (1999-2003): the LSPM (Land Surface Process Model). The attention was focused on energy and hydrologic budget components by performing two simulations in climatically different sub-areas of Piedmont. The increment in the observed solar radiation during summer 2003 produced an increment in the net radiation, which in turn generated an increase of sensible (more) and latent (less) heat flux, and soil-vegetation heat flux. The latter caused a consistent warming of soil and vegetation surfaces, which acted partially as a negative feedback increasing the longwave radiation emitted by the terrestrial surface. Latent heat flux showed a small increment in summer 2003, because the evapotranspiration was limited by the soil moisture unavailability, particularly during July and August, due to the scarcity of precipitations during the previous spring. The drought conditions, acting as a positive feedback, caused the effects of the heat wave to be more severe, favored its persistence and enhanced the further reduction of soil moisture. The comparison among the results of the two simulations allowed to highlight the role of two phenomena that concurred to exacerbate the heat wave: the enhancement of the drought conditions and the increment of the adiabatic compression connected with the anticyclonic conditions. A rough estimate allowed us to quantify in about 2 C the contribution of the former.