Abstract
Shipborne aerosol lidar observations were performed aboard the research vessel Polarstern in 2009 and 2010 during three north-south cruises from about 50°N to 50°S. The aerosol data set provides an excellent opportunity to characterize and contrast the vertical aerosol distribution over the Atlantic Ocean in the polluted northern and relatively clean southern hemisphere. Three case studies, an observed pure Saharan dust plume, a Patagonian dust plume east of South America, and a case of a mixed dust/smoke plume west of Central Africa are exemplarily shown and discussed by means of their optical properties. The meridional transatlantic cruises were used to determine the latitudinal cross section of the aerosol optical thickness (AOT). Profiles of particle backscatter and extinction coefficients are presented as mean profiles for latitudinal belts to contrast northern- and southern-hemispheric aerosol loads and optical effects. Results of lidar observations at Punta Arenas (53°S), Chile, and Stellenbosch (34°S), South Africa, are shown and confirm the lower frequency of occurrence of free-tropospheric aerosol in the southern hemisphere than in the northern hemisphere. The maximum latitudinal mean AOT of 0.27 was found in the northern tropics (0– 15°N) in the Saharan outflow region. Marine AOT is typically 0.05 ± 0.03. Particle optical properties are presented separately for the marine boundary layer and the free troposphere. Concerning the contrast between the anthropogenically influenced midlatitudinal aerosol conditions in the 30– 60°N belt and the respective belt in the southern hemisphere over the remote Atlantic, it is found that the AOT and extinction coefficients for the vertical column from 0–5km (total aerosol column) and 1–5km height (lofted aerosol above the marine boundary layer) are a factor of 1.6 and 2 higher at northern midlatitudes than at respective southern midlatitudes, and a factor of 2.5 higher than at the clean marine southern-hemispheric site of Punta Arenas. The strong contrast is confined to the lowermost 3km of the atmosphere.
Highlights
[2] Atmospheric aerosols influence the radiation budget of the Earth and the water cycle via aerosol-cloud interactions
Large progress was achieved with the introduction of the handheld Microtops Sun photometer observations that are used aboard research vessels (RV) to determine the aerosol optical thickness (AOT) above the oceans in the framework of Maritime Aerosol Network (MAN) since October 2004 [Smirnov et al, 2009, 2011]
[37] The vertical distribution of aerosols above the North and South Atlantic was analyzed with shipborne multiwavelength Raman/polarization lidar
Summary
[2] Atmospheric aerosols influence the radiation budget of the Earth and the water cycle via aerosol-cloud interactions. Large progress was achieved with the introduction of the handheld Microtops Sun photometer observations that are used aboard research vessels (RV) to determine the AOT above the oceans in the framework of Maritime Aerosol Network (MAN) since October 2004 [Smirnov et al, 2009, 2011]. The situation improved significantly since 2006 when the CALIPSO mission began and the satellite-based lidar (CALIOP) started its operation [Winker et al, 2007] This dual-wavelength backscatter lidar provides worldwide observations of lofted aerosol and cloud layers. Advanced ground-based lidars use various techniques (e.g., Raman scattering) to directly determine profiles of particle extinction coefficients and to allow a much more comprehensive aerosol characterization by means of measured lidar ratios [Ansmann et al, 1992; Müller et al, 2007].
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