Aerosol direct radiative effect in the Po Valley region derived from AERONET measurements

M. Clerici (1) , F. Mélin (1)

1 IES - JRC Institute for Environment and Sustainability

The aerosol direct radiative effect (ADRE) affecting the Po Valley and the adjacent North Adriatic Sea is studied using 10-year series of measurements collected at two AERONET sites located in the western part of the Valley (Ispra), and on a platform (AAOT) offshore Venice. This region is characterized by a high, mostly continental, aerosol load with comparable average aerosol optical thickness ?_a at both locations (0.21 at 500 nm) and more absorbing aerosols at Ispra. A dynamic aerosol model accounting for the changes in scattering phase function with ?_a is used for radiative transfer calculations, together with boundary conditions representative of terrestrial and marine surfaces. A sensitivity analysis allows the construction of an error budget for the daily ADRE estimates, found to be of the order of 20% and mostly due to uncertainties on aerosol single scattering albedo and ?_a. The daily radiative efficiencies, normalized by ?_a at 500 nm, increase from December to June, from ?17 to ?24 W m^?2 ?_a^?1 at top-of-atmosphere (TOA) and ?33 to ?72 W m^?2 ?_a^?1 at surface for the Po Valley, and from ?15 to ?32 (TOA) and ?35 to ?65 W m^?2 ?_a^?1 (surface) for the AAOT site. The average of log-transformed ADRE for TOA, surface and atmosphere are ?5.2, ?12.2 and +6.8 W m^?2 for the Po Valley case, and ?6.5, ?13.0 and +6.5 W m^?2 for the AAOT site but these values can be much higher for individual days. Concurrent clear-sky days give indications on the regional atmospheric heating spatial gradients. Differences between the atmospheric ADRE at the two locations average 6.3 W m^?2 with a gradient positive towards the inner valley in 65% of the cases. This study confirms the importance of duly considering the radiative impact of aerosols on the regional climate.

Domaines: Océan, Atmosphère

M. Clerici, F. Mélin. Aerosol direct radiative effect in the Po Valley region derived from AERONET measurements. Atmospheric Chemistry and Physics Discussions, 2008, 8 (1), pp.3227-3285. ⟨hal-00303976⟩