Pierrehumbert, R. T., 1985: A theoretical model of orographically modified cyclogenesis. Journal of the Atmospheric Sciences, 42 (12), 1244-1258.
Abstract: The modification of baroclinic instability by low-level orographic blocking
of cold advection is considered within a simple model. In this model, the
meridional flow in the lower layer of a two layer quasi-geostrophic model
is blocked by a semi-infinite knife edge barrier extending eastward from
the origin. The stability problem for a vertically sheared current parallel
to the barrier is solved by means of the Wiener-Hopf technique, and a number
of properties of the eigenmodes are determined. The barrier is found to
have an inhibitory effect on cyclogenesis, in the sense that the magnitude
of the pressure perturbation in the lower layer is reduced in the vicinity
of the barrier. However, the barrier also distorts the flow in such a manner
as to lead to the formation of low-level cutoff low south of the barrier,
which is characterized by intense easterly winds on the barrierward side
of the low. It is also found that at certain phases of the development,
the lower-layer velocities have square root singularities near the tip of
the barrier, leading to a discontinuous turning of air flowing around the
tip. Air impinging on the barrier from the northwest develops a split jet
pattern; the splitting point moves eastward along the barrier with time.
The upper layer flow is almost unaffected near the tip of the barrier, but
the pressure perturbations in both layers decay algebraically to zero sufficiently
far downstream of the tip.
Despite the extreme simplicity of the model, some of the features of the
solution were found to be suggestive of features found in observations and
numerical simulations of cyclogenesis in the lee of the Alps.