NDLI: The influence of the geostrophic wind advection approximation on a well-mixed layer

Content Provider	Springer Nature Link
Author	Fang, Juan Wu, Rongsheng
Copyright Year	2005
Abstract	Numerical results indicate that advection of momentum in the boundary layer may significantly alter both the structure of the planetary boundary layer and its influence on the overlying free atmosphere. However, due to the nonlinearity of the inertial terms, it is always difficult to obtain the analytical solution of the boundary-layer model that retains the flow acceleration. In order to overcome this difficulty, the geostrophic momentum (hereafter GM) approximation has been introduced into boundary-layer models. By replacing the advected momentum with the geostrophic wind, the effect of the flow acceleration is partially considered and the original nonlinear partial differential equation set is converted to ordinary differential equations, the solutions of which can be obtained easily with standard techniques. However, the model employing GM fails to capture the features of the boundary layer when the spatio-temporal variation of the boundary-layer flow cannot be properly approximated by the geostrophic wind. In the present work, a modified boundary-layer model with the inertial acceleration in a different approximate form is proposed, in which the advecting wind instead of the advected momentum is approximated by the geostrophic wind (hereafter GAM).Comparing the horizontal velocity and boundary-layer pumping obtained from the classical Ekman theory, and the model incorporating (i) GM and (ii) GAM, it is found that the model with GAM describes most facets of the steady well-mixed layer beneath a north-westerly flow with embedded mesoscale perturbations that is considered in the present work. Inspection of the solution of the model with GAM shows that, within the limit of the validation of the model (i.e., the Rossby number RO is not very large and the drag coefficient CD is not too small), the horizontal convergence (divergence) is strengthened by the effect of the inertial acceleration in the region of maximum positive (negative) geostrophic vorticity. Consequently, the boundary-layer pumping there is intensified. It is found that the intensification is firstly strengthened and then weakened as RO or CD increases.
Starting Page	31
Ending Page	52
Page Count	22
File Format	PDF
ISSN	00068314
Journal	Boundary-Layer Meteorology
Volume Number	114
Issue Number	1
e-ISSN	15731472
Language	English
Publisher	Kluwer Academic Publishers
Publisher Date	2005-01-01
Publisher Place	Dordrecht
Access Restriction	One Nation One Subscription (ONOS)
Subject Keyword	Boundary-layer model Boundary-layer pumping Ekman theory Geostrophic momentum approximation Geostrophic wind advection approximation Inertial acceleration. Meteorology/Climatology Atmospheric Protection/Air Quality Control/Air Pollution
Content Type	Text
Resource Type	Article
Subject	Atmospheric Science

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