The vertical distribution of aerosols, Saharan dust and cirrus clouds in Rome (Italy) in the year 2001

Abstract

Abstract.A set of 813 lidar profiles of tropospheric aerosol and cirrus clouds extinction and depolarization observed in Rome, Italy, between February 2001 and February 2002 is analyzed and discussed. The yearly record reveals a meaningful contribution of both cirrus clouds (38%) and Saharan dust (12%) to the total optical thickness (OT) of 0.26, at 532 nm. Seasonal analysis shows the planetary boundary layer (PBL) aerosols to be confined below 2 km in winter and 3.8 km in summer, with relevant OT shifting from 0.08 to 0.16, respectively. Cirrus clouds maximise in spring and autumn, in both cases with average OT similar to the PBL aerosols one. With the exception of winter months, Saharan dust is found to represent an important third layer mostly residing between PBL aerosols and cirrus clouds, with yearly average OT≈0.03. Saharan dust and cirrus clouds were detected in 20% and in 45% of the observational days, respectively. Validation of the lidar OT retrievals against collocated sunphotometer observations show very good agreement. These results represent one of the few yearly records of tropospheric aerosol vertical profiles available in the literature.

Aerosol characterization in Northern Africa, Northeastern Atlantic, Mediterranean Basin and Middle East from direct-sun AERONET observations

“…From spring to autumn, a decrease of α values (Fig. 6) is associated to an increase of the frequency of long-range transport of Saharan dust to southern and central Italy Gobbi, 2004, Gobbi et al, 2004;Mona et al, 2006).…”

Sunphotometry of the 2006–2007 aerosol optical/radiative properties at the Himalayan Nepal Climate Observatory-Pyramid (5079 m a.s.l.)

“…The CALIOP lidar backscatter signals from the 532 nm cross and parallel-polarized channels are both plotted (left and right columns, respectively). Since spherical aerosols do not depolarize the laser beam they backscatter, the cross-polarized lidar signal is essentially originated by non-spherical particles as ice crystals and mineral dust (e.g., Gobbi et al, 2004). The image pairs of Fig.…”

“…In Fig. 6a we also report the aerosol scale height H a , a parameter used to characterize the commonly observed exponential decrease with height (z) of the aerosol extinction: σ ext (z) = σ ext (0) exp(−z/H a ), (e.g., Guibert et al, 2005;Gobbi et al, 2004). For such a vertical distribution, the integral over z of σ ext (z), i.e., the AOD, is linked to the ground extinction σ ext (0) by the simple relationship (e.g., Tomasi, 1982;Kaufman and Fraser, 1983): It is worth noticing that H a is also the height a vertically mixed aerosol (i.e.…”

“…noaa.gov/HYSPLIT.php) have been computed to identify the near-ground origin of the air-masses reaching the NCO-P during the observational period. In this analysis, Hysplit rather than Lagranto backtrajectories (as in Bonasoni et al, 2010) have been used to exploit codes successfully developed to detect Saharan dust origin by accounting for airmass transits within the planetary boundary layer (PBL), e.g., Gobbi et al (2004). In fact, PBL height is an output of the Hysplit model.…”

Aerosol stratification, optical properties and radiative forcing in Venice (Italy) during ADRIEX

“…The ratio S ⊥ /S // is here referred to as the total depolarization ratio, D. Since non-spherical particles introduce a change in the polarization plane of the backscattered light, the parameter D is particularly efficient in revealing the presence of non-spherical particles such as desert dust, volcanic ash, or cirrus clouds (e.g. Gobbi et al, 2004). The VELIS system is capable of providing tropospheric profiles of depolarization and aerosol optical properties (backscatter and extinction coefficient) in both daylight and night time conditions.…”