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 define 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, finding 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 coefficients 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 sky-brightness at different angular distances from the Sun.
Marine and Continental aerosol effects on the upwelling solar radiation flux in Southern portugal during the Ace-2 Experiment
Tomasi C;Vitale V;
2003
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 define 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, finding 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 coefficients 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 sky-brightness at different angular distances from the Sun.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
