Ship-borne aerosol profiling with lidar over the Atlantic Ocean: from pure marine conditions to complex dust–smoke mixtures
<p>The multi-wavelength Raman lidar Polly<span style="position:relative; bottom:0.5em; " class="text">XT</span> has been regularly operated aboard the research vessel <i>Polarstern</i> on expeditions across the Atlantic Ocean from north to south an...
| Main Authors: | , , , , |
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| Format: | Article |
| Language: | English |
| Published: |
Copernicus Publications
2018-07-01
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| Series: | Atmospheric Chemistry and Physics |
| Online Access: | https://www.atmos-chem-phys.net/18/9661/2018/acp-18-9661-2018.pdf |
| Summary: | <p>The multi-wavelength Raman lidar Polly<span style="position:relative; bottom:0.5em; " class="text">XT</span> has been
regularly operated aboard the research vessel <i>Polarstern</i> on
expeditions across the Atlantic Ocean from north to south and vice versa. The
lidar measurements of the RV <i>Polarstern</i> cruises PS95 from
Bremerhaven, Germany, to Cape Town, Republic of South Africa (November 2015),
and PS98 from Punta Arenas, Chile, to Bremerhaven, Germany (April/May 2016),
are presented and analysed in detail. The latest set-up of
Polly<span style="position:relative; bottom:0.5em; " class="text">XT</span> allows improved coverage of the marine boundary
layer (MBL) due to an additional near-range receiver.</p><p>Three case studies provide an overview of the aerosol detected over the
Atlantic Ocean. In the first case, marine conditions were observed near South
Africa on the autumn cruise PS95. Values of optical properties
(depolarisation ratios close to zero, lidar ratios of 23 sr at 355 and
532 nm) within the MBL indicate pure marine aerosol. A layer of dried marine
aerosol, indicated by an increase of the particle depolarisation ratio to
about 10 % at 355 nm (9 % at 532 nm) and thus confirming the
non-sphericity of these particles, could be detected on top of the MBL. On
the same cruise, an almost pure Saharan dust plume was observed near the
Canary Islands, presented in the second case. The third case deals with
several layers of Saharan dust partly mixed with biomass-burning smoke
measured on PS98 near the Cabo Verde islands. While the MBL was partly mixed
with dust in the pure Saharan dust case, an almost marine MBL was observed in
the third case.</p><p>A statistical analysis showed latitudinal differences in the optical
properties within the MBL, caused by the down-mixing of dust in the tropics
and anthropogenic influences in the northern latitudes, whereas the optical
properties of the MBL in the Southern Hemisphere correlate with typical
marine values. The particle depolarisation ratio of dried marine layers
ranged between 4 and 9 % at 532 nm.</p><p>Night measurements from PS95 and PS98 were used to illustrate the potential
of aerosol classification using lidar ratio, particle depolarisation ratio at
355 and 532 nm, and Ångström exponent. Lidar ratio and particle
depolarisation ratio have been found to be the main indicator for particle
type, whereas the Ångström exponent is rather variable.</p> |
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| ISSN: | 1680-7316 1680-7324 |