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| Titel |
The lofting of Western Pacific regional aerosol by island thermodynamics as observed around Borneo |
| VerfasserIn |
N. H. Robinson, J. D. Allan, J. A. Trembath, P. D. Rosenberg, G. Allen, H. Coe |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
1680-7316
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| Digitales Dokument |
URL |
| Erschienen |
In: Atmospheric Chemistry and Physics ; 12, no. 13 ; Nr. 12, no. 13 (2012-07-12), S.5963-5983 |
| Datensatznummer |
250011309
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| Publikation (Nr.) |
 copernicus.org/acp-12-5963-2012.pdf |
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| Zusammenfassung |
| Vertical profiles of aerosol chemical composition, number
concentration and size were measured throughout the lower troposphere
of Borneo, a large tropical island in the western Pacific Ocean.
Aerosol composition, size and number concentration measurements (using
an Aerodyne Aerosol Mass Spectrometer, Passive Cavity Aerosol
Spectrometer Probe and Condensation Particle Counter, respectively)
were made both upwind and downwind of Borneo, as well as over the
island itself, on board the UK BAe-146 research aircraft as part of
the OP3 project. Two meteorological regimes were identified – one
dominated by isolated terrestrial convection (ITC) which peaked in the
afternoon, and the other characterised by more regionally active
mesoscale convective systems (MCS). Upwind profiles show aerosol to be
confined to a shallow marine boundary layer below 930 ± 10 hPa
(~760 m above sea level, a.s.l.). As this air mass advects over the
island with the mean free troposphere synoptic flow during the
ITC-dominated regime, it is convectively lofted above the terrestrial
surface mixed layer to heights of between 945 ± 22 (~630 m a.s.l.)
and 740 ± 44 hPa (~2740 m a.s.l.), consistent with a coupling
between the synoptic steering level flow and island sea breeze
circulations. Terrestrial aerosol was observed to be lofted into this
higher layer through both moist convective uplift and transport
through turbulent diurnal sea-breeze cells. At the peak of convective
activity in the mid-afternoons, organic aerosol loadings in the lofted
layer were observed to be substantially higher than in the morning (by
a mean factor of three). This organic matter is dominated by secondary
aerosol from processing of biogenic gas phase precursors. Aerosol
number concentration profiles suggest formation of new particles aloft
in the atmosphere. By the time the air mass reaches the west coast of
the island, terrestrial aerosol is enhanced in the lofted layer. Such
uplift of aerosol in Borneo is expected to increase aerosol lifetimes
in the lower free troposphere downwind, as they are above the boundary
layer and therefore less likely to be lost by wet or dry
deposition. It is also likely to change the role they play in the
semi-direct and direct aerosol effects. The long chain of islands
extending from Malaysia to Australia may all similarly be expected to
present an orographic barrier to low level mean flow. This would lead
to significant transport of aerosol into the tropical free troposphere
across the Western Pacific region. |
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