Mr. Raupach et Jj. Finnigan, THE INFLUENCE OF TOPOGRAPHY ON METEOROLOGICAL VARIABLES AND SURFACE-ATMOSPHERE INTERACTIONS, Journal of hydrology, 190(3-4), 1997, pp. 182-213
Topography perturbs practically every process and variable relevant to
land-atmosphere interactions, including radiation, air temperature an
d saturation deficit, wind and turbulence, cloudiness and precipitatio
n, and properties of the soil and vegetation. We review progress in un
derstanding some of these influences, concentrating on the wind field
and the exchanges of scalars (especially sensible and latent heat) ove
r low to moderate hills, both without and with flow separation. The tr
eatment of the wind field is based on a physical division of the flow
into inner, outer and wake regions. This framework is used to discuss
modelling approaches, measurements of both the mean flow and the turbu
lence, special processes in the wake region, and the effects of strati
fication. Scalar transfer and the surface energy balance are discussed
first in terms of a linear theory which accommodates radiative, aerod
ynamic, and elevation perturbations on the surface energy balance over
hills. The linear theory provides general scales for determining the
relative magnitudes of these perturbations, but its quantitative predi
ctions are limited to low slopes without separation. Next, wind tunnel
experiments are used to study the aerodynamic perturbations on scalar
transfer caused by hills in situations outside the scope of the linea
r theory, such as flows with separation. Finally, the wind tunnel resu
lts are extrapolated to the atmosphere, using the framework of a conve
ctive boundary layer model. It is found that, for relatively gentle to
pography, the regional surface energy balance (spatially averaged over
several hills) is insensitive to the presence of the topography.