  It was discovered several decades ago that eddy covariance measurements
systematically underestimate sensible and latent heat fluxes, creating an
imbalance in the surface energy budget. Since then, many studies have addressed
this problem and proposed a variety of solutions to the problem, including
improvements to instruments and correction methods applied during data
postprocessing. However, none of these measures have led to the complete
closure of the energy balance gap. The leading hypothesis is that not only
surface-attached turbulent eddies but also sub-mesoscale atmospheric
circulations contribute to the transport of energy in the atmospheric boundary
layer, and the contribution from organized motions has been grossly neglected.
The problem arises because the transport of energy through these secondary
circulations cannot be captured by the standard eddy covariance method given
the relatively short averaging periods of time (~30 minutes) used to compute
statistics. There are various approaches to adjust the measured heat fluxes by
attributing the missing energy to the sensible and latent heat flux in
different proportions. However, few correction methods are based on the
processes causing the energy balance gap. Several studies have shown that the
magnitude of the energy balance gap depends on the atmospheric stability and
the heterogeneity scale of the landscape around the measurement site. Based on
this, the energy balance gap within the surface layer has already been modelled
as a function of a nonlocal atmospheric stability parameter by performing a
large-eddy simulation study with idealized homogeneous surfaces. We have
further developed this approach by including thermal surface heterogeneity in
addition to atmospheric stability in the parameterization.
