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| Titel |
Channelling of high-latitude boundary-layer flow |
| VerfasserIn |
N. Nawri, R. E. Stewart |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
1023-5809
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| Digitales Dokument |
URL |
| Erschienen |
In: Nonlinear Processes in Geophysics ; 15, no. 1 ; Nr. 15, no. 1 (2008-01-31), S.33-52 |
| Datensatznummer |
250012552
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| Publikation (Nr.) |
 copernicus.org/npg-15-33-2008.pdf |
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| Zusammenfassung |
| Due to the stability of the boundary-layer stratification, high-latitude winds over complex
terrain are strongly affected by blocking and channelling effects. Consequently, at many low-lying
communities in the Canadian Archipelago, including Cape Dorset and Iqaluit considered in this study,
surface winds for the most part are from two diametrically opposed directions, following the orientation
of the elevated terrain. Shifts between the two prevailing wind directions can be sudden and are associated
with geostrophic wind directions within a well defined narrow range. To quantitatively investigate the role
of large-scale pressure gradients and the quasi-geostrophic
overlying flow, an idealised dynamical system for the evolution of channelled surface winds is derived
from the basic equations of motion, in which stability of stationary along-channel wind directions is
described as a function of the geostrophic wind. In comparison with long-term horizontal wind statistics
at the two locations it is shown that the climatologically prevailing wind directions can be identified
as stationary states of the idealised wind model, and that shifts between prevailing wind directions can
be represented as stability transitions between these stationary states. In that sense, the prevailing
local wind conditions can be interpreted as attracting states of the actual flow, with observed surface
winds adjusting to a new stable direction as determined by the idealised system within 3–9 h. Over these
time-scales and longer it is therefore advantageous to determine the relatively slow evolution of the
observationally well-resolved large-scale pressure distribution, instead of modelling highly variable
surface winds directly. The simplified model also offers a tool for dynamical downscaling of global climate
simulations, and for determining future scenarios for local prevailing wind conditions. In particular, it
allows an estimation of the sensitivity of local low-level winds to changes in the large-scale atmospheric circulation. |
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