A Two-Layer First-Order Closure Model for the Study of the Baroclinic Atmospheric Boundary Layer

Abstract

A steady-state two-layer model has been developed for the baroclinic boundary layer. The lower layer is the constant flux surface layer (SL) in which the eddy viscosity K varies with height and stability according to the Monin-Obukhov similarity theory; the upper one is the Ekman layer in which K is fixed at the value attained at the top of the SL. The equations of motion in the Ekman layer are solved using the Green's function approach. The lower boundary condition gives two equations from which the nondi-mensionalized friction velocity u*/Vg0 and the cross-isobaric angle α0 can be obtained in terms of the other known parameters. These equations are compared with the resistance laws. The boundary condition also is given a geometrical interpretation. It has been shown that if Vg(z) is linear, the variation of α0 and u*/Vg0 with ?, the angle between Vg(0) (surface isobars) and thermal wind (isotherms), is sinusoidal. Also, there is a phase difference of 90° between the variation of α0 and u*/Vg0, and the amplitude of variation of α0 is found to be proportional to the non-dimensionalized magnitude of thermal wind. ATEX 1969 observations are used to test the wind profiles obtained by the model.