During the FINTUREX experiment at the Neumayer station in 1994 meteorological
data like wind profile, temperature, humidity, and irradiation were measured
in order to determine the energy exchange and their parametrization over
an antarctic ice shelf.
Since the measurements were performed in the stable stratified boundary layer,
our data are composed of waves, turbulence and intermittent bursts. This
means that the determination of the energy exchange requires a powerful tool
that makes it possible to separate (filter) the different contributions (waves
and turbulence) as well as to analyze the localized intermittent bursts.
Due to the lack of locality in the time domain, the Fourier transformation
(FT) has been increasingly substituted by the wavelet transformation (WT)
for the analysis of turbulent data in the last two decades. Because of their
localization in time as well as in frequency domain, the WT is the ideal
candidate for the analysis of such data. Beside the possibility of calculating
global spectra according to the FT, also local quantities like
local energy spectra and a local intermittency measure can
be determined. Additionally, due to the existence of an inverse transformation,
the WT is perfectly suited for filtering.
Because of the variability of our data, it is desirable to find a typification
that describes the main characteristics of a particular timetrace. We present
a method that allows such kind of classification. Since the wavelet spectra
of our data exhibit a well developed local minimum at the
Brunt-Vaisälä frequency fBV (i.e. the maximum frequency
of waves), the ratio of the energy content of the spectra above and below
fBV can be used for a rough classification of the timeseries in
respect to the contributions of waves and turbulence.
Another most challenging question has been the nonlinear interaction between
the waves and the turbulent flow. We present a new method of direct visualization
of the energy transfer from long scales (waves) to the smaller scales of
turbulence (Richardson cascade) by means of the first moment (i. e. center
of mass) of the local energy spectra and its behavior in time. We are quite
confident that on the basis of this analyzing method the energy transfer
rate between the generations of eddies can be determined. For a comparison
data from a cylinder wake in a wind channel are also analyzed.