CORIOLIS EFFECTS IN MESOSCALE SHALLOW LAYER FLOWS
A general linearised ‘shallow-layer ’ perturbation model, where the approximately neutral lower layer of thick-ness is situated below a stable upper layer or inversion layer, is developed for idealised and steady, but typical, mesoscale atmospheric flows. Significant Coriolis effects and variations...
| Main Authors: | , , , |
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| Format: | Text |
| Language: | English |
| Subjects: | |
| Online Access: | http://citeseerx.ist.psu.edu/viewdoc/summary?doi=10.1.1.605.4502 http://www.cpom.org/research/jcrh-shallow.pdf |
| Summary: | A general linearised ‘shallow-layer ’ perturbation model, where the approximately neutral lower layer of thick-ness is situated below a stable upper layer or inversion layer, is developed for idealised and steady, but typical, mesoscale atmospheric flows. Significant Coriolis effects and variations in surface conditions (surface rough-ness, mountainous elevation, thermal effects on slopes) are considered. The model equations are solved here when the Froude number of the lower layer is small and where the surface drag roughness and surface elevation are modelled as a distributed body force through the lower layer. The results are compared with linear contin-uously stratified idealised model [10] and non-linear model (UK Unified Model) computations for particular flows over the mountains of Greenland and the coast of the Kent Peninsula/northern France. It is demonstrated that the simpler shallow layer model leads to some useful general concepts and quantitative estimates for a wide range of perturbed mesoscale flows, especially where the surface conditions change sharply over scales of order 1-10km. The main results of meteorological interest are that: (i) The upwind extent of the flow perturbation is of order of the Rossby deformation radius , but that if the stratification is constant with height this distance is of order of the width of the surface condition change (if ). For most significant mountain chains the former is the relevant distance. (ii) If the wind direction is parallel to the edge-line separating the change in surface drag roughness or change in elevation, there are marked positive and negative perturbations in the |
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