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| Titel |
Mesoscale modeling of smoke transport over the Southeast Asian Maritime Continent: coupling of smoke direct radiative effect below and above the low-level clouds |
| VerfasserIn |
C. Ge, J. Wang, J. S. Reid |
| 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 ; 14, no. 1 ; Nr. 14, no. 1 (2014-01-06), S.159-174 |
| Datensatznummer |
250118249
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| Publikation (Nr.) |
 copernicus.org/acp-14-159-2014.pdf |
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| Zusammenfassung |
| The online-coupled Weather Research and Forecasting model with Chemistry
(WRF-Chem) is used to simulate the direct and semi-direct radiative impacts
of smoke particles over the Southeast Asian Maritime Continent (MC,
10° S–10° N, 90–150° E) during October 2006 when
a significant El Niño event caused the highest biomass burning activity
since 1997. With the use of an OC (organic carbon) / BC (black carbon)
ratio of 10 in the smoke emission inventory, the baseline simulation shows
that the clouds can reverse the negative smoke forcing in cloud-free
conditions to a positive value. The net absorption of the atmosphere is
largely enhanced when smoke resides above a cloud. This led to a warming
effect at the top of the atmosphere (TOA) with a domain and monthly average
forcing value of ~ 20 W m−2 over the islands of Borneo and
Sumatra. Smoke-induced monthly average daytime heating (0.3 K) is largely
confined above the low-level clouds, and results in a local convergence over
the smoke source region. This heating-induced convergence transports more
smoke particles above the planetary boundary layer height (PBLH), hence
rendering a positive effect. This positive effect contrasts with a decrease
in the cloud fraction resulting from the combined effects of smoke heating
within the cloud layer and the more stable boundary layer; the latter can be
considered as a negative effect in which a decrease of the cloud fraction
weakens the heating by smoke particles above the clouds. During the
nighttime, the elevated smoke layer lying above the clouds in the daytime is
decoupled from the boundary layer, and the enhanced downdraft and shallower
boundary layer lead to the accumulation of smoke particles near the surface.
Because of monthly smoke radiative extinction, the amount of solar input at
the surface is reduced by as much as 60 W m−2, which leads to a
decrease in sensible heat, latent heat, 2 m air temperature, and PBLH by a
maximum of 20 W m−2, 20 W m−2, 1 K, and 120 m, respectively.
During daytime, the cloud changes over continents mostly occur over the
islands of Sumatra and Borneo where the low-level cloud fraction decreases
more than 10%. However, the change of local wind, including sea breeze,
induced by the smoke direct radiative effect leads to more convergence over
the Karimata Strait and the south coastal area of Kalimantan during both
daytime and nighttime; consequently, the cloud fraction there is increased up
to 20%. The sensitivities with different OC / BC ratios show the
importance of the smoke single-scattering albedo for the smoke semi-direct
effects. Lastly, a conceptual model is used to summarize the responses of
clouds, smoke, temperature, and water vapor fields to the coupling of smoke
direct effect below and above clouds over the Southeast Asian Maritime
Continent. |
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