Friction Mechanisms in Global Geophysical Flows; Quasi-geostrophic Equation for Transformation of Potential Vorticity
One of the main features of the dynamics of viscous global geophysical flows is that the dissipation of their kinetic energy is mainly due to friction of free atmosphere over so-called geophysical boundary layers (GBL). Under free atmosphere one understands the atmosphere’s areas that are remote from solid boundaries or from sharp fluctuations of horizontal velocity. The friction is caused by the exchange of momentum between these boundary layers and the free atmosphere. In the GBL themselves velocity gradients are intensified, and hence the internal friction is strengthened. This leads to disruption in quasi-hydrostatic and quasi-geostrophic equilibria. Moreover, the effects of internal friction manifest differently in neighborhoods of the horizontal and vertical GBLs. Based on this it is convenient to adopt the following definition of GBLs. A geophysical boundary layer (GBL) is a region in which the conditions of quasi-hydrostatic and quasi-geostrophic equilibria are violated under the influence of viscosity forces.
KeywordsPlanetary Boundary Layer Potential Vorticity Geostrophic Wind Free Atmosphere Ekman Layer
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