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| Titel |
Parametrisation of the orographic enhancement of precipitation and deposition in a long-term, long-range transport model |
| VerfasserIn |
D. S. Lee, R. D. Kingdon, J. A. Garland, B. M. R. Jones |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
0992-7689
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| Digitales Dokument |
URL |
| Erschienen |
In: Annales Geophysicae ; 18, no. 11 ; Nr. 18, no. 11, S.1447-1466 |
| Datensatznummer |
250014093
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| Publikation (Nr.) |
 copernicus.org/angeo-18-1447-2000.pdf |
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| Zusammenfassung |
Orographic enhancement of wet deposition
arising from the 'seeder-feeder' effect is, by necessity, highly parametrised in
long-range transport models of acid deposition that are long-term (i.e. annual
average) and spatially resolved at tens of kilometres. Here, we describe a
mechanistic approach to the incorporation of these mechanisms into such a model.
The model formulation required the following: precipitation rate by direction
and quantification of the fractions that are orographic and non-orographic;
treatment of the fast oxidation of sulfur dioxide in clouds; the directionality
of the seeder-feeder process; and a quantitative basis for increasing wet
deposition factors to account for the seeder-feeder process. The directionality
of non-orographic precipitation was determined from meteorological data at 47
sites across the UK. Orographic precipitation varies on a much finer scale than
can be interpolated from measurements, and thus a modelling approach was
adopted. The directionality of the seeder-feeder effect was taken from
measurements. The enhancement factor of the orographic component of
precipitation, assumed to represent feeder-rain, was determined from a review of
measurements. Fast oxidation of sulfur dioxide is an observed phenomenon in
cap-cloud, but limited in duration. An adjustment was made to the sulfur dioxide
oxidation rate in the model in locations where cap-cloud was assumed to be
present. The results from the model were compared with UK deposition budgets and
enhanced wet deposition maps. The revised parametrisation underestimated the UK
wet deposition budgets of oxidised N and S, but spatial patterns of deposition
were improved for much of the UK. It was concluded that this was a satisfactory
outcome given the constraints of the statistical approach of weighting of
deposition at receptors utilising straight line trajectories. The sensitivity of
the model to directional constraints of seeder-feeder enhancement was tested and
it was concluded that a fairly narrow constraint resulted in similar estimations
to a broader one, and the broader constraint was thus adopted as frontal
conditions which result in the process arrive from a fairly broad band of
directions. When enhancement was allowed to occur from all directions, UK wet
deposition of oxidised N and S was increased by 10%. The sensitivity to the
enhancement factor on wet deposition was tested and found to be relatively
robust. An increase in the enhancement factor from 2 to 6 resulted in increases
in UK wet deposition of oxidised N and S of 9 and 6%, respectively.
Key words: Atmospheric composition and structure
(pollution – urban and regional) – Meteorology and atmospheric dynamics
(precipitation) |
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