Estimation of the advection effects induced by surface heterogeneities in the surface energy budget

The effect of terrain heterogeneities in one-point
measurements is a continuous subject of discussion. Here
we focus on the order of magnitude of the advection term
in the equation of the evolution of temperature as generated
by documented terrain heterogeneities and we estimate its
importance as a term in the surface energy budget (SEB),
for which the turbulent fluxes are computed using the eddycorrelation
method. The heterogeneities are estimated from
satellite and model fields for scales near 1 km or broader,
while the smaller scales are estimated through direct measurements
with remotely piloted aircraft and thermal cameras
and also by high-resolution modelling. The variability
of the surface temperature fields is not found to decrease
clearly with increasing resolution, and consequently the advection
term becomes more important as the scales become
finer. The advection term provides non-significant values to
the SEB at scales larger than a few kilometres. In contrast,
surface heterogeneities at the metre scale yield large values
of the advection, which are probably only significant in the
first centimetres above the ground. The motions that seem
to contribute significantly to the advection term in the SEB
equation in our case are roughly those around the hectometre
scales.