Abstract. The all-sky direct radiative effect by anthropogenic aerosol (DRE a ) is calculated in the solar (0.3-4 µm) and infrared (4-200 µm) spectral ranges for six Mediterranean sites. The sites are differently affected by pollution and together reflect typical aerosol impacts that are expected over land and coastal sites of the central Mediterranean basin. Central to the simulations are aerosol optical properties from AERONET sun-/sky-photometer statistics for the year 2003. A discussion on the variability of the overall (natural + anthropogenic) aerosol properties with site location is provided. Supplementary data include MODIS satellite sensor based solar surface albedos, ISCCP products for high-mid-and low cloud cover and estimates for the anthropogenic aerosol fraction from global aerosol models. Since anthropogenic aerosol particles are considered to be smaller than 1 µm in size, mainly the solar radiation transfer is affected with impacts only during sun-light hours. At all sites the (daily average) solar DRE a is negative all year round at the top of the atmosphere (ToA). Hence, anthropogenic particles produce over coastal and land sites of the central Mediterranean a significant cooling effect. Monthly DRE a values vary from site to site and are seasonally dependent as a consequence of the seasonal dependence of available sun-light and microphysical aerosol properties. At the ToA the monthly average DRE a is −(4±1) W m −2 during spring-summer (SS, AprilSeptember) and −(2±1) W m −2 during autumn-winter (AW, October-March) at the polluted sites. In contrast, it varies between −(3±1) W m −2 and −(1±1) W m −2 on SS and AW, respectively at the less polluted site. Due to atmospheric absorption the DRE a at the surface is larger than at the ToA. At the surface the monthly average DRE a varies between the most and the least polluted site between −(7±1) W m −2 and −(4±1) W m −2 during SS, and between −(4±3) W m −2Correspondence to: M. R. Perrone (perrone@le.infn.it) and −(1±1) W m −2 during AW. The DRE a at infrared wavelengths is positive but negligible, especially at the ToA (<0.3 W m −2 ). The average of DRE a monthly-means referring to all sites has allowed getting a ToA-and sfc-DRE a yearly-mean value of −(3±2) and −(5±3) W m −2 , respectively at solar wavelengths. Last data, even if refer to a particular year, indicate that the radiative energy-balance of Central Mediterranean land and coastal sites is quite affected by anthropogenic particles.
Abstract. The all-sky direct radiative effect by anthropogenic aerosol (DREa) is calculated in the solar (0.3–4 μm) and infrared (4–200 μm) spectral ranges for six Mediterranean sites. The sites are differently affected by pollution and together reflect typical aerosol impacts that are expected over land sites of the central Mediterranean basin. Central to the simulations are aerosol optical properties from AERONET sun-/sky-photometer statistics for the year 2003. A discussion on the variability of the overall (natural+anthropogenic) aerosol properties with site location is provided. Supplementary data include MODIS satellite sensor based solar surface albedos, ISCCP products for high- mid- and low cloud cover and estimates for the anthropogenic aerosol fraction from global modelling. Since anthropogenic aerosol particles are considered to be smaller than 1 μm in size, mainly the solar radiation transfer is affected with impacts only during sun-light hours. At all sites the (daily average) solar DREa is negative all year round at the top of the atmosphere (ToA). Hence, anthropogenic particles produce over land sites of the central Mediterranean a significant cooling effect. Monthly DREa values vary from site to site and are seasonal dependent as a consequence of the seasonal dependence of available sun-light and microphysical aerosol properties. At the ToA the monthly average DREa is −(4±1) W m−2 during spring-summer (SS, April–September) and −(2±1) W m−2 during autumn-winter (AW, October–March) at the polluted sites. In contrast, it varies between −(3±1) W m−2 and −(1±1) W m−2 on SS and AW, respectively at the less polluted site. Due to atmospheric absorption the DREa at the surface is larger than at the ToA. At the surface the monthly average DREa varies between the most and the least polluted site between −(7±1) W m−2 and −(4±1) W m−2 during SS, and between −(4±3) W m−2 and −(1±1) W m−2 during AW. The DREa at infrared wavelengths is positive but negligible, especially at the ToA (<0.3 W m−2. DREa monthly-means referring to all sites have been averaged to evaluate the yearly-mean value of the DREa. The ToA- and sfc-DREa yearly-mean value is −(3±2) and −(5±3) W m−2, respectively at solar wavelengths. Last data further more reveal that the radiative energy-balance of the Central Mediterranean land sites is quite affected by anthropogenic particles.
Abstract. The clear-sky, instantaneous Direct Radiative Effect (DRE) by all and anthropogenic particles is calculated during Sahara dust intrusions in the Mediterranean basin, to evaluate the role of anthropogenic particle's radiative effects and to get a better estimate of the DRE by desert dust. The clear-sky aerosol DRE is calculated by a two stream radiative transfer model in the solar (0.3–4 μm) and infrared (4–200 μm) spectral range, at the top of the atmosphere (ToA) and at the Earth's surface (sfc). Aerosol optical properties by AERONET sun-sky photometer measurements and aerosol vertical profiles by EARLINET lidar measurements, both performed at Lecce (40.33° N, 18.10° E) during Sahara dust intrusions occurred from 2003 to 2006 year, are used to initialize radiative transfer simulations. Instantaneous values at 0.44 μm of the real (n) and imaginary (k) refractive index and of the of aerosol optical depth (AOD) vary within the 1.33–1.55, 0.0037–0.014, and 0.2–0.7 range, respectively during the analyzed dust outbreaks. Fine mode particles contribute from 34% to 85% to the AOD by all particles. The complex atmospheric chemistry of the Mediterranean basin that is also influenced by regional and long-range transported emissions from continental Europe and the dependence of dust optical properties on soil properties of source regions and transport pathways are responsible for the high variability of n, k, and AOD values and of the fine mode particle contribution. Instantaneous net (solar+infrared) DREs that are negative as a consequence of the cooling effect by aerosol particles, span the – (32–10) W m−2 and the – (44–20) W m−2 range at the ToA and surface, respectively. The instantaneous net DRE by anthropogenic particles that is negative, varies within −(13–8) W m−2 and −(17–11) W m−2 at the ToA and surface, respectively. It represents from 41 up to 89% and from 36 up to 67% of the net DRE by all particles at the ToA and surface, respectively. A linear relationship to calculate the DRE by natural particles in the solar and infrared spectral range is provided.
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