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| Titel |
Impacts of Amazonia biomass burning aerosols assessed from short-range weather forecasts |
| VerfasserIn |
S. R. Kolusu, J. H. Marsham, J. Mulcahy, B. Johnson, C. Dunning, M. Bush, D. V. Spracklen |
| 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. 21 ; Nr. 15, no. 21 (2015-11-05), S.12251-12266 |
| Datensatznummer |
250120141
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| Publikation (Nr.) |
 copernicus.org/acp-15-12251-2015.pdf |
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| Zusammenfassung |
| The direct radiative impacts of biomass burning aerosols (BBA) on
meteorology are investigated using short-range forecasts from the
Met Office Unified Model (MetUM) over South America during the South
American Biomass Burning Analysis (SAMBBA). The impacts are
evaluated using a set of three simulations: (i) no aerosols, (ii)
with monthly mean aerosol climatologies and (iii) with prognostic
aerosols modelled using the Coupled Large-scale Aerosol Simulator
for Studies In Climate (CLASSIC) scheme. Comparison with
observations show that the prognostic CLASSIC scheme provides the
best representation of BBA. The impacts of BBA are quantified over
central and southern Amazonia from the first and second day of
2-day forecasts during 14 September–3 October 2012. On average,
during the first day of the forecast, including prognostic BBA
reduces the clear-sky net radiation at the surface by 15 ±
1 W m−2 and reduces net top-of-atmosphere (TOA) radiation by 8 ±
1 W m−2, with a direct atmospheric warming of 7 ±
1 W m−2. BBA-induced reductions in all-sky radiation
are smaller in magnitude: 9.0 ± 1 W m−2 at the
surface and 4.0 ± 1 W m−2 at TOA. In this modelling
study the BBA therefore exert an overall cooling influence on the
Earth–atmosphere system, although some levels of the atmosphere are
directly warmed by the absorption of solar radiation. Due to the
reduction of net radiative flux at the surface, the mean 2 m
air temperature is reduced by around 0.1 ±
0.02 °C. The BBA also cools the boundary layer (BL)
but warms air above by around 0.2 °C due to the
absorption of shortwave radiation. The overall impact is to reduce
the BL depth by around 19 ± 8 m. These differences in
heating lead to a more anticyclonic circulation at 700 hPa,
with winds changing by around 0.6 m s−1. Inclusion of
climatological or prognostic BBA in the MetUM makes a small but significant
improvement in forecasts of temperature and
relative humidity, but improvements were small compare with model error
and the relative increase in forecast skill from the prognostic aerosol
simulation over the aerosol climatology was also small. Locally, on a 150 km scale,
changes in precipitation reach around 4 mm day−1 due to
changes in the location of convection. Over Amazonia, including BBA
in the simulation led to fewer rain events that were more
intense. This change may be linked to the BBA changing the vertical
profile of stability in the lower atmosphere. The localised changes
in rainfall tend to average out to give a 5 %
(0.06 mm day−1) decrease in total precipitation over the
Amazonian region (except on day 2 with prognostic BBA). The change
in water budget from BBA is, however, dominated by decreased
evapotranspiration from the reduced net surface fluxes (0.2 to
0.3 mm day−1), since this term is larger than the
corresponding changes in precipitation and water vapour convergence. |
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