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| Titel |
Evaluation of high-resolution forecasts with the non-hydrostaticnumerical weather prediction model Lokalmodell for urban air pollutionepisodes in Helsinki, Oslo and Valencia |
| VerfasserIn |
B. Fay, L. Neunhäuserer |
| 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 ; 6, no. 8 ; Nr. 6, no. 8 (2006-06-20), S.2107-2128 |
| Datensatznummer |
250003922
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| Publikation (Nr.) |
 copernicus.org/acp-6-2107-2006.pdf |
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| Zusammenfassung |
| The operational numerical weather prediction model Lokalmodell LM with 7\,km
horizontal resolution was evaluated for forecasting meteorological
conditions during observed urban air pollution episodes. The resolution was
increased to experimental 2.8 km and 1.1 km resolution by one-way interactive
nesting without introducing urbanisation of physiographic parameters or
parameterisations. The episodes examined are two severe winter
inversion-induced episodes in Helsinki in December 1995 and Oslo in January 2003,
three suspended dust episodes in spring and autumn in Helsinki and Oslo, and
a late-summer photochemical episode in the Valencia area. The evaluation was
basically performed against observations and radiosoundings and focused on
the LM skill at forecasting the key meteorological parameters characteristic
for the specific episodes. These included temperature inversions,
atmospheric stability and low wind speeds for the Scandinavian episodes and
the development of mesoscale recirculations in the Valencia area. LM
forecasts often improved due to higher model resolution especially in
mountainous areas like Oslo and Valencia where features depending on
topography like temperature, wind fields and mesoscale valley circulations
were better described. At coastal stations especially in Helsinki, forecast
gains were due to the improved physiographic parameters (land fraction, soil
type, or roughness length). The Helsinki and Oslo winter inversions with
extreme nocturnal inversion strengths of 18°C were not sufficiently
predicted with all LM resolutions. In Helsinki, overprediction of surface
temperatures and low-level wind speeds basically led to underpredicted
inversion strength. In the Oslo episode, the situation was more complex
involving erroneous temperature advection and mountain-induced effects for
the higher resolutions. Possible explanations include the influence of the
LM treatment of snow cover, sea ice and stability-dependence of transfer and
diffusion coefficients. The LM simulations distinctly improved for winter
daytime and nocturnal spring and autumn inversions and showed good skill at
forecasting further episode-relevant meteorological parameters. The
evaluation of the photochemical Valencia episode concentrated on the
dominating mesoscale circulation patterns and showed that the LM succeeds
well in describing all the qualitative features observed in the region. LM
performance in forecasting the examined episodes thus depends on the key
episode characteristics and also the season of the year with a need to
improve model performance in very stable inversion conditions not only for
urban simulations. |
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