One of the traditional uses of scintillation
measurements is to infer path-averaged values of the turbulent surface fluxes
of momentum (tau) and sensible (H_{s}) and latent (H_{L})
heat. Many scintillometer set-ups, however, measure only the path-averaged
refractive index structure parameter, C_{n}^{2}; the wind information
necessary for inferring the fluxes comes from point measurements or is entirely
absent. In this latter case, H_{s} and H_{L} can be obtained
only under the assumption of free convection; and a path-averaged tau is not
available. The Scintec SLS20 surface-layer scintillometer system, on the other
hand, measures both C_{n}^{2} and the inner scale of
turbulence, l_{0},
where l_{0} is
related to the dissipation rate of turbulent kinetic energy, epsilon. As a
result, the SLS20 is presumed to provide path-averaged estimates of both tau
and H_{s}.

I have used an SLS20 in two experiments: one
over Arctic sea ice during SHEBA (the experiment to study the Surface Heat
Budget of the Arctic Ocean), and a second over a mid-latitude land site during
spring (the so-called Rapid Forcing Experiment). In each deployment, we also
made eddy-covariance measurements of tau, H_{s}, and H_{L} near
the scintillometer path. In this presentation, I will compare the
scintillometer and eddy-covariance measurements of tau and H_{s} for
these two diverse sites. For both tau and H_{s}, the correlation
between eddy-covariance and scintillometer-derived values is reasonable, but
the scintillometer results tend to be biased low. Moreover, estimates of both tau
and H_{s} degrade as C_{n}^{2} decreases. Essentially,
the signal-to-noise ratio for the scintillometer-derived fluxes decreases as C_{n}^{2}
decreases.

An essential question that arises during these
comparisons is what similarity functions to use for nondimensionalizing C_{n}^{2}
and epsilon. From the combined scintillation and eddy-covariance measurements,
I will evaluate which of several candidate similarity functions are consistent
with the data.

Supplementary URL: