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| Titel |
Local Characteristics of the Nocturnal Boundary Layer in Response to External Pressure Forcing |
| VerfasserIn |
Steven van der Linden, Peter Baas, Antoon van Hooft, Ivo van Hooijdonk, Fred Bosveld, Bas van de Wiel |
| Konferenz |
EGU General Assembly 2017
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| Medientyp |
Artikel
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| Sprache |
en
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 19 (2017) |
| Datensatznummer |
250144019
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| Publikation (Nr.) |
 EGU/EGU2017-7797.pdf |
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| Zusammenfassung |
| Geostrophic wind speed data, derived from pressure observations, are used in combination
with tower measurements to investigate the nocturnal stable boundary layer at Cabauw, The
Netherlands. Since the geostrophic wind speed is not directly influenced by local nocturnal
stability, it may be regarded as an external forcing parameter of the nocturnal stable boundary
layer. This is in contrast to local parameters such as in situ wind speed, the Monin-Obukhov
stability parameter (z∕L) or the local Richardson number. To characterize the stable boundary
layer, ensemble averages of clear-sky nights with similar geostrophic wind speed are
formed. In this manner, the mean dynamical behavior of near-surface turbulent
characteristics, and composite profiles of wind and temperature is systematically
investigated.
We find that the classification results in a gradual ordering of the diagnosed variables in
terms of the geostrophic wind speed. In an ensemble sense the transition from the weakly
stable to very stable boundary layer is more gradual than expected. Interestingly, for very
weak geostrophic winds turbulent activity is found to be negligibly small while
the resulting boundary cooling stays finite. Realistic numerical simulations for
those cases should therefore have a a solid description of other thermodynamic
processes such as soil heat conduction and radiative transfer. This prerequisite poses a
challenge for Large-Eddy Simulations of weak wind nocturnal boundary layers. |
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