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| Titel |
Impact of planetary boundary layer turbulence on model climate and tracer transport |
| VerfasserIn |
E. L. McGrath-Spangler, A. Molod, L. E. Ott, S. Pawson |
| 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. 13 ; Nr. 15, no. 13 (2015-07-03), S.7269-7286 |
| Datensatznummer |
250119870
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| Publikation (Nr.) |
 copernicus.org/acp-15-7269-2015.pdf |
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| Zusammenfassung |
| Planetary boundary layer (PBL) processes are important for weather, climate,
and tracer transport and concentration. One measure of the strength of these
processes is the PBL depth. However, no single PBL depth definition exists
and several studies have found that the estimated depth can vary
substantially based on the definition used. In the Goddard Earth Observing
System (GEOS-5) atmospheric general circulation model, the PBL depth is
particularly important because it is used to calculate the turbulent length
scale that is used in the estimation of turbulent mixing. This study analyzes
the impact of using three different PBL depth definitions in this
calculation. Two definitions are based on the scalar eddy diffusion
coefficient and the third is based on the bulk Richardson number. Over land,
the bulk Richardson number definition estimates shallower nocturnal PBLs than
the other estimates while over water this definition generally produces
deeper PBLs. The near-surface wind velocity, temperature, and specific
humidity responses to the change in turbulence are spatially and temporally
heterogeneous, resulting in changes to tracer transport and concentrations.
Near-surface wind speed increases in the bulk Richardson number experiment
cause Saharan dust increases on the order of
1 × 10−4 kg m−2 downwind over the Atlantic Ocean. Carbon
monoxide (CO) surface concentrations are modified over Africa during boreal
summer, producing differences on the order of 20 ppb, due to the model's
treatment of emissions from biomass burning. While differences in carbon
dioxide (CO2) are small in the time mean, instantaneous differences are
on the order of 10 ppm and these are especially prevalent at high latitude
during boreal winter. Understanding the sensitivity of trace gas and aerosol
concentration estimates to PBL depth is important for studies seeking to
calculate surface fluxes based on near-surface concentrations and for studies
projecting future concentrations. |
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