Marine and continental aerosol effects on the upwelling solar radiation flux in Southern Portugal during the ACE-2 experiment

C. Tomasi, V. Vitale, A. Lupi, A. Cacciari, S. Marani, U. Bonafé

Abstract


An overall number of 447 spectral series of aerosol optical depth were determined in the 0.4-3.7 mm wavelength
range by examining the IR-RAD sun-radiometer measurements carried out at Sagres (Portugal) on six clear-sky
days, during the CLEARCOLUMN (ACE-2) experiment in June and July 1997. These spectral series were then analysed
with the King inversion method to defi ne the size-distribution curves of columnar aerosol particle total number
and volume, assuming values of both real and imaginary parts of the particulate refractive index obtained on the
six days by combining our measurements with simultaneous sky-brightness measurements taken by the Leipzig
University group. For these results, we then calculated the daily time-patterns of the average single scattering
albedo of the columnar aerosols, fi nding instantaneous values ranging between 0.70 and 0.96 on those days, with
daily mean values varying from 0.83 to 0.95. Furthermore, for each spectral series of aerosol optical depth, we
determined the instantaneous change DF^ induced by the columnar aerosols on the upwelling solar radiation
fl ux leaving the atmosphere, over oceanic areas presenting low surface albedo. The 24-h average values of DF^
obtained on the six days were found to increase as a function of the daily mean value of aerosol optical depth at
the 0.55 mm wavelength, following relationship curves whose positive slope coeffi cients decrease gradually with
the single scattering albedo of the columnar aerosols. The said curves can be used to achieve reliable estimates
of change DF^ directly from daily ground-based multispectral measurements of aerosol optical depth and skybrightness
at different angular distances from the Sun.An overall number of 447 spectral series of aerosol optical depth were determined in the 0.4-3.7 mm wavelength
range by examining the IR-RAD sun-radiometer measurements carried out at Sagres (Portugal) on six clear-sky
days, during the CLEARCOLUMN (ACE-2) experiment in June and July 1997. These spectral series were then analysed
with the King inversion method to defi ne the size-distribution curves of columnar aerosol particle total number
and volume, assuming values of both real and imaginary parts of the particulate refractive index obtained on the
six days by combining our measurements with simultaneous sky-brightness measurements taken by the Leipzig
University group. For these results, we then calculated the daily time-patterns of the average single scattering
albedo of the columnar aerosols, fi nding instantaneous values ranging between 0.70 and 0.96 on those days, with
daily mean values varying from 0.83 to 0.95. Furthermore, for each spectral series of aerosol optical depth, we
determined the instantaneous change DF^ induced by the columnar aerosols on the upwelling solar radiation
flux leaving the atmosphere, over oceanic areas presenting low surface albedo. The 24-h average values of DF^
obtained on the six days were found to increase as a function of the daily mean value of aerosol optical depth at
the 0.55 mm wavelength, following relationship curves whose positive slope coeffi cients decrease gradually with
the single scattering albedo of the columnar aerosols. The said curves can be used to achieve reliable estimates
of change DF^ directly from daily ground-based multispectral measurements of aerosol optical depth and skybrightness
at different angular distances from the Sun.

Keywords


aerosol optical depth;aerosol particle size-distributions;aerosol radiative properties;direct aerosol radiative forcing

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References


DOI: https://doi.org/10.4401/ag-3420
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Published by INGV, Istituto Nazionale di Geofisica e Vulcanologia - ISSN: 2037-416X