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| Titel |
Observations of the temporal variability in aerosol properties and their relationships to meteorology in the summer monsoonal South China Sea/East Sea: the scale-dependent role of monsoonal flows, the Madden–Julian Oscillation, tropical cyclones, squall lines and cold pools |
| VerfasserIn |
J. S. Reid, N. D. Lagrosas, H. H. Jonsson, E. A. Reid, W. R. Sessions, J. B. Simpas, S. N. Uy, T. J. Boyd, S. A. Atwood, D. R. Blake, J. R. Campbell, S. S. Cliff, B. N. Holben, R. E. Holz, E. J. Hyer, P. Lynch, S. Meinardi, D. J. Posselt, K. A. Richardson, S. V. Salinas, A. Smirnov, Q. Wang, L. Yu, J. Zhang |
| 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 ; 15, no. 4 ; Nr. 15, no. 4 (2015-02-19), S.1745-1768 |
| Datensatznummer |
250119442
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| Publikation (Nr.) |
 copernicus.org/acp-15-1745-2015.pdf |
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| Zusammenfassung |
| In a joint NRL/Manila Observatory mission, as part of the Seven
SouthEast Asian Studies program (7-SEAS), a 2-week, late September 2011
research cruise in the northern Palawan archipelago was undertaken to
observe the nature of southwest monsoonal aerosol particles in the South
China Sea/East Sea (SCS/ES) and Sulu Sea region. Previous analyses suggested
this region as a receptor for biomass burning from Borneo and Sumatra for
boundary layer air entering the monsoonal trough. Anthropogenic pollution
and biofuel emissions are also ubiquitous, as is heavy shipping traffic.
Here, we provide an overview of the regional environment during the cruise,
a time series of key aerosol and meteorological parameters, and their
interrelationships. Overall, this cruise provides a narrative of the
processes that control regional aerosol loadings and their possible
feedbacks with clouds and precipitation. While 2011 was a moderate El Niño–Southern Oscillation (ENSO) La Niña year, higher burning activity and
lower precipitation was more typical of neutral conditions. The large-scale
aerosol environment was modulated by the Madden–Julian Oscillation (MJO) and
its associated tropical cyclone (TC) activity in a manner consistent with
the conceptual analysis performed by Reid et al. (2012). Advancement of the MJO from
phase 3 to 6 with accompanying cyclogenesis during the cruise period
strengthened flow patterns in the SCS/ES that modulated aerosol life cycle.
TC inflow arms of significant convection sometimes span from Sumatra to
Luzon, resulting in very low particle concentrations (minimum condensation
nuclei CN < 150 cm−3, non-sea-salt PM2.5 < 1 μg m−3). However, elevated carbon monoxide levels were occasionally
observed suggesting passage of polluted air masses whose aerosol particles
had been rained out. Conversely, two drier periods occurred with higher
aerosol particle concentrations originating from Borneo and Southern Sumatra
(CN > 3000 cm−3 and non-sea-salt PM2.5 10–25 μg m−3). These cases corresponded with two different mechanisms of
convection suppression: lower free-tropospheric dry-air intrusion from the
Indian Ocean, and large-scale TC-induced subsidence. Veering vertical wind
shear also resulted in aerosol transport into this region being mainly in
the marine boundary layer (MBL), although lower free troposphere transport
was possible on the western sides of Sumatra and Borneo. At the hourly time
scale, particle concentrations were observed to be modulated by integer
factors through convection and associated cold pools. Geostationary
satellite observations suggest that convection often takes the form of
squall lines, which are bowed up to 500 km across the monsoonal flow and 50 km wide. These squall lines, initiated by cold pools from large
thunderstorms and likely sustained by a veering vertical wind shear and
aforementioned mid-troposphere dry layers, propagated over 1500 km across
the entirety of the SCS/ES, effectively cutting large swaths of MBL aerosol
particles out of the region. Our conclusion is that while large-scale flow
patterns are very important in modulating convection, and hence in allowing long-range transport of smoke and pollution, more short-lived phenomena can
modulate cloud condensation nuclei (CCN) concentrations in the region,
resulting in pockets of clean and polluted MBL air. This will no doubt
complicate large scale comparisons of aerosol–cloud interaction. |
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