Abstract :
Earlier studies have revealed mesoscale structures in southwesterly flows over the mountains of southern Norway
(Rossby number ∼1): a left-side jet and an upstream wind minimum as signs of the influence of rotation; a downstream
wind shadow connected to inertio-gravity waves; a weak jet on the right side of the wind shadow and a shallow coastal
wind shadowbetween the left-side jet and the main wind shadow. In the present study, the dynamics of the structures have
been further examined from the results of experiments performed by a mesoscale numerical model and computations
using a linear model with rotation included. Ideal atmospheric conditions for a large-scale wind direction from southwest
have been used to initialize the numerical model. The sensitivity of mesoscale structures was studied with respect to
dissipation from wave breaking and surface friction. Nonlinearity and dissipation in breaking waves are needed to
explain the location, depth and strength of the downstream wind shadow. Increased wind to the right of the shadow was
found to be generated by the effect of the Coriolis force as air was pulled towards the low-pressure perturbation behind
the mountains. The coastal wind shadow was found to be a direct result of differential friction between land and ocean.
Nonlinear experiments and an attempt to include boundary layer effects in linear theory showed that friction is reducing
the effective height of the mountain and the signal of the mesoscale structures.
