Numerical experiments on the genesis of Sharav cyclones: idealized simulations

A three‐level channel flow model is used to investigate the generation of Sharav cyclones in the lee of the Atlas mountains through “idealized” numerical experimentation. A typical initial state consists of a barotropic high–low system, embedded in baroclinic shear flow and centered to the north of the Atlas mountains. If this “perturbation” is of sufficient strength, a cold‐air outbreak occurs in the rear of the low as well as a southward excursion of the trough at upper levels. The cold air is blocked by the Atlas mountains, if the initial location of the low is chosen properly. The upper‐level trough intensifies slightly when crossing the mountain range and induces then a low‐level cyclone in the lee. The trough turns eastward later on and the new cyclone is staying close to this upper‐level centre. A simple two‐dimensional three‐layer model is used to explain salient features of this type of lee cyclogenesis. Moreover, additional experiments are conducted in order to elucidate details of the cyclogenetic process.