Simulation of the Partial Reflection by the Critical Latitude with a Linear Model. Part I: Methods of Regulating the Reflectivity

Abstract

In a region with no wave activity sinks or sources, the distribution of the WKB-approximated correlation between the stationary eddy velocity components is determined by the ratio of northward to southward wave activity flux. This offers a method of evaluating the reflection coefficient of the planetary wave critical latitude (CL). The procedure consists of studying the midlatitude response of a steady-state model with weak damping, the forcing being located in high latitudes. The method is applicable even in a baroclinic atmosphere in which the CL is not vertically oriented. In the special cases in which quantitative determination of the reflectivity has been possible thus far, the results obtained with the present method were consistent with earlier ones. For regulating the CL reflectivity, we modified the gradient of the basic-state absolute vorticity (?EFF) in the critical layer. This gave rise to markedly enhanced reflectivities, even overreflection if ?EFF was distinctly negative. In addition to the effect of reflectivity of the CL itself, the amplitude of the reflected wave was strongly affected by the absorption occurring especially in the region of weak westerlies. In our two-layer model the properties of the CL must be specified independently for both layers, since in the tropics the responses at different levels are weakly coupled.