Atmospheric aerosols play an important role in Earth’s radiative balance, directly interacting with solar radiation or influencing cloud formation and properties. In order to assess their radiative impact, it is necessary to accurately characterise their optical properties, together with their spatial and vertical distribution. The information on aerosol vertical profile is often scarce, in particular in mountainous, complex terrains. This study presents the first attempt to evaluate the shortwave aerosol direct radiative effect in the Aosta Valley, a moun- tainous region in the Northwestern Italian Alps. Ground-based, remote sensing instruments (a sky radiometer and an Automated Lidar Ceilometer) are used to derive two descriptions of the aerosol properties and vertical distribution: a first, more accurate description, which includes the whole spectral information about the aerosol extinction coefficient, phase func- tion and single scattering albedo; a second, more approximate one, which only relies on spectrally constant values of aerosol single scattering albedo and asymmetry factor. This information is used as input for radiative transfer simulations, which allow to estimate, in cloudless conditions, the shortwave aerosol direct radiative effect and the vertical profile of the instantaneous heating rates in the lower layers of the atmosphere. The simulations obtained with the two descriptions do not differ significantly: they highlight a strong surface dimming (between −25 and −50 W m−2) due to the presence of aerosol, with a consid- erable radiative absorption inside the atmospheric column (around +30 Wm−2), and an overall small cooling effect for the Earth-atmospheric system. The absorption of solar radi- ation within the atmospheric column due to aerosol leads to instantaneous heating rates up to 1.5 K day−1 in the tropospheric layers below 6 km a.s.l. These results show that, in some conditions, the shortwave aerosol direct radiative effect can be considerable even in this Alpine environment, usually considered as relatively pristine (yearly average PM10 concentration about 20 μg m−3).

Fasano, G., Diémoz, H., Fountoulakis, I., Cassardo, C., Kudo, R., Siani, A., et al. (2021). Vertical profile of the clear-sky aerosol direct radiative effect in an Alpine valley, by the synergy of ground-based measurements and radiative transfer simulations. BULLETIN OF ATMOSPHERIC SCIENCE AND TECHNOLOGY, 2(1-4) [10.1007/s42865-021-00041-w].

Vertical profile of the clear-sky aerosol direct radiative effect in an Alpine valley, by the synergy of ground-based measurements and radiative transfer simulations

Ferrero, Luca
2021

Abstract

Atmospheric aerosols play an important role in Earth’s radiative balance, directly interacting with solar radiation or influencing cloud formation and properties. In order to assess their radiative impact, it is necessary to accurately characterise their optical properties, together with their spatial and vertical distribution. The information on aerosol vertical profile is often scarce, in particular in mountainous, complex terrains. This study presents the first attempt to evaluate the shortwave aerosol direct radiative effect in the Aosta Valley, a moun- tainous region in the Northwestern Italian Alps. Ground-based, remote sensing instruments (a sky radiometer and an Automated Lidar Ceilometer) are used to derive two descriptions of the aerosol properties and vertical distribution: a first, more accurate description, which includes the whole spectral information about the aerosol extinction coefficient, phase func- tion and single scattering albedo; a second, more approximate one, which only relies on spectrally constant values of aerosol single scattering albedo and asymmetry factor. This information is used as input for radiative transfer simulations, which allow to estimate, in cloudless conditions, the shortwave aerosol direct radiative effect and the vertical profile of the instantaneous heating rates in the lower layers of the atmosphere. The simulations obtained with the two descriptions do not differ significantly: they highlight a strong surface dimming (between −25 and −50 W m−2) due to the presence of aerosol, with a consid- erable radiative absorption inside the atmospheric column (around +30 Wm−2), and an overall small cooling effect for the Earth-atmospheric system. The absorption of solar radi- ation within the atmospheric column due to aerosol leads to instantaneous heating rates up to 1.5 K day−1 in the tropospheric layers below 6 km a.s.l. These results show that, in some conditions, the shortwave aerosol direct radiative effect can be considerable even in this Alpine environment, usually considered as relatively pristine (yearly average PM10 concentration about 20 μg m−3).
Articolo in rivista - Articolo scientifico
aerosol, vertical profile, heating rate, radiative transfer;
English
Fasano, G., Diémoz, H., Fountoulakis, I., Cassardo, C., Kudo, R., Siani, A., et al. (2021). Vertical profile of the clear-sky aerosol direct radiative effect in an Alpine valley, by the synergy of ground-based measurements and radiative transfer simulations. BULLETIN OF ATMOSPHERIC SCIENCE AND TECHNOLOGY, 2(1-4) [10.1007/s42865-021-00041-w].
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Utilizza questo identificativo per citare o creare un link a questo documento: https://hdl.handle.net/10281/355846
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