| The actual impact on vertical transport of small-scale turbulence
in the free atmosphere is still a debated issue.
Numerous estimates of an eddy diffusivity exist,
clearly showing a lack of consensus.
MST radars were, and continue to be,
very useful for studying atmospheric turbulence,
as radar measurements allow one to estimate the dissipation rates
of energy (kinetic and potential) associated with turbulent events.
The two commonly used methods for estimating the dissipation rates,
from the backscattered power and from the Doppler width, are discussed.
The inference methods of a local diffusivity
(local meaning here "within" the turbulent patch)
by using the dissipation rates are reviewed,
with some of the uncertainty causes being stressed.
Climatological results of turbulence diffusivity
inferred from radar measurements are reviewed and compared.
As revealed by high resolution MST radar measurements,
atmospheric turbulence is intermittent in space and time.
Recent theoretical works suggest that the effective diffusivity
of such a patchy turbulence
is related to statistical parameters describing the morphology
of turbulent events:
filling factor, lifetime and height of the patches.
It thus appears that a statistical description
of the turbulent patches' characteristics is required
in order to evaluate and parameterize
the actual impact of small-scale turbulence
on transport of energy and materials.
Clearly, MST radars could be an essential tool in that matter. |