DYNAMICS OF THE SOUTH-AMERICAN COASTAL DESERT

The world's driest coastal desert is in South America along the coasts of Peru and Chile. The desert's maintenance is investigated by studyi ng the local dynamics of the low-level southerly flow along the coast. A linear boundary-layer model is used in which a Boussinesq atmospher e is driven by a surface thermal contrast on a beta plane. The resting basic state is stably stratified. Constant mechanical and thermal dif fusivities are assumed in the momentum and heat equations, respectivel y. The dynamics of the buoyancy field is governed by a three-dimension al eighth-order differential equation in which the meridional dependen ce enters parametrically. Results are shown for different values of th e constants involved as well as for solutions on an f plane and a semi geostrophic beta plane. The results indicate that the effect of nonuni form rotation is responsible for the presence of subsidence along the coast and inland. This coastal subsidence helps maintain the desert by increasing the static stability and suppressing deep convection. The predicted vertical wind profiles agree well with the observations for Lima, Peru. Sensitivity tests indicate that the flow depends on the in terplay between stratification, friction, and the Coriolis parameter a nd its variation (beta). The mechanical frictional effects are mainly constrained to a shallow Ekman layer, whereas the thermal effects are manifested in deeper layers controlled by the beta effect.