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

• Main Authors: U. Bonafé, S. Marani, A. Cacciari, A. Lupi, V. Vitale, C. Tomasi
• Format: Article
• Language: English
• Published: Istituto Nazionale di Geofisica e Vulcanologia (INGV) 2003-06-01
• Series: Annals of Geophysics
• Subjects: aerosol optical depth; aerosol particle size-distributions; aerosol radiative properties; direct aerosol radiative forcing
• Online Access: http://www.annalsofgeophysics.eu/index.php/annals/article/view/3420
• ISSN: 1593-5213; 2037-416X

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.