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| Titel |
The role of atmospheric boundary layer-surface interactions on the development of coastal fronts |
| VerfasserIn |
D. Malda, J. Vilà-Guerau de Arellano, W. D. Berg, I. W. Zuurendonk |
| 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 ; 25, no. 2 ; Nr. 25, no. 2 (2007-03-08), S.341-360 |
| Datensatznummer |
250015782
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| Publikation (Nr.) |
 copernicus.org/angeo-25-341-2007.pdf |
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| Zusammenfassung |
Frictional convergence and thermal difference between land and sea surface
are the two surface conditions that govern the intensity and evolution of a
coastal front. By means of the mesoscale model MM5, we investigate the
influence of these two processes on wind patterns, temperature and
precipitation amounts, associated with a coastal front, observed on the west
coast of The Netherlands in the night between 12 and 13 August 2004. The
mesoscale model MM5 is further compared with available observations and the
results of two operational models (ECMWF and HIRLAM). HIRLAM is not capable
to reproduce the coastal front, whereas ECMWF and MM5 both calculate
precipitation for the coastal region. The precipitation pattern, calculated
by MM5, agrees satisfactorily with the accumulated radar image. The failure
of HIRLAM is mainly due to a different stream pattern at the surface and
consequently, a different behaviour of the frictional convergence at the
coastline.
The sensitivity analysis of frictional convergence is carried out with the
MM5 model, by varying land surface roughness length (z0). For the
sensitivity analysis of thermal difference between sea and land surface, we
changed the sea surface temperature (SST). Increasing surface roughness
implies stronger convergence near the surface and consequently stronger
upward motions and intensification of the development of the coastal front.
Setting land surface roughness equal to the sea surface roughness means an
elimination of frictional convergence and results in a diminishing coastal
front structure of the precipitation pattern. The simulation with a high SST
produces much precipitation above the sea, but less precipitation in the
coastal area above land. A small increment of the SST results in larger
precipitation amounts above the sea; above land increments are calculated for
areas near the coast. A decrease of the SST shifts the precipitation maxima
inland, although the precipitation amounts diminish. In the situation under
study, frictional convergence is the key process that enhances the coastal
front intensity. A thermal difference between land and sea equal to zero
still yields the development of the coastal front. A lower SST than land
surface temperature generates a reversed coastal front.
This study emphasizes the importance of accurate prescription of surface
conditions as input of the numerical weather prediction model to improve
coastal front predictability. |
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