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Turbulente flukser ved reversert skjær i den geostrofiske vinden

Simonsen, Magne
Master thesis
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Master_MagneSimonsen.pdf (1.782Mb)
Year
2010
Permanent link
http://urn.nb.no/URN:NBN:no-25080

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  • Meteorologi og oseanografi [90]
Abstract
In boundary layer modelling, the Monin-Obukhov theory is widely used

to parmeterize the wind profiles and the momentum fluxes. During the

IPY-THORPEX campaign at Andøya at 3. March 2008, a flight was made

across an arctic front, dropping several sondes to measure atmospheric

parameters from about 7500 meters down to the surface. Due to the

horizontal gradient in potential temperature, the vertical shear in the

geostrophic wind was strongly reversed. This results in a low level jet with

high wind velocities close to the surface. The task of this master thesis is

to investigate the influence of this reversed shear on the momentum fluxes

in the turbulent atmospheric boundary layer. The main parameters are the

wind stress τ , the drag coefficient CD and the stability function φm ( z/ L).

A one-dimensional numerical boundary layer model is developed and run

with different geostrophic wind profiles. Geostrophic wind profiles with

reversed shear from the dropsonde observations are compared to runs with

constant geostrophic wind profiles. Equivalent runs are done with PALM,

a Large Eddy Simulation model (LES).

The simulations with reversed shear in the geostrophic wind gives a wind

stress profile which is curved and is decreasing faster with heigth at the

lowest few hundred meters than the results from the runs with a constant

geostrophic wind. Model runs with reversed shear gives a drag coefficient

which is slightly higher, and a stability function which is reduced compared

to the results from the runs with a constant geostrophic wind profile.
 
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