Abstract
Abstract. Stratospheric turbulence is important for the mixing of trace species and the energy balance, but direct measurements are sparse due to the required resolution and accuracy. Recently, turbulence parameters such as the energy dissipation rate ε were inferred from standard radiosonde data by means of a Thorpe analysis. To this end, layers with vertically decreasing potential temperature are analysed, which is expected to indicate turbulence. Such an application assumes a proportionality between the Thorpe length LT and the Ozmidov scale LO. While this relation is accepted for the ocean, experimental evidence for such proportionality in the stratosphere is sparse. We have developed a high-resolution (8 kHz) turbulence measurement system called LITOS (Leibniz Institute Turbulence Observations in the Stratosphere), which for the first time resolves the inner scale of turbulence in the stratosphere. Therewith the energy dissipation rate ε can be determined by spectral analysis. This independent value for ε enables us to check the relation LO ∝ LT. In our measurements no such proportionality can be seen, although the mean of the ratio LO/LT is close to what is assumed in radiosonde analyses. Dissipation rates for individual layers obtained from radiosondes deviate up to a factor of ~3000 from those obtained by spectral analysis. Some turbulent layers measured by LITOS are not observed by the radiosonde at all, and vice versa. However, statements about the statistical mean seem to be possible by Thorpe analysis.
Highlights
The stratosphere is mostly stably stratified, breaking of gravity waves and instabilities cause turbulence and energy dissipation
With our new high-resolved instrument LITOS (Leibniz Institute Turbulence Observations in the Stratosphere) (Theuerkauf et al, 2011), the energy dissipation rate ε is obtained independent of LT by means of spectral analysis of wind fluctuations
We concentrate on results from high-resolved spectral analysis and low-resolved Thorpe analysis
Summary
The stratosphere is mostly stably stratified, breaking of gravity waves and instabilities cause turbulence and energy dissipation. With our new high-resolved instrument LITOS (Leibniz Institute Turbulence Observations in the Stratosphere) (Theuerkauf et al, 2011), the energy dissipation rate ε is obtained independent of LT by means of spectral analysis of wind fluctuations. We concentrate on results from high-resolved spectral analysis (as a very precise method of ε determination) and low-resolved Thorpe analysis Such a Thorpe evaluation of radiosonde data has been proposed for extensive use (Clayson and Kantha, 2008; Love and Geller, 2012). A kind of spectral analysis can be used to determine dissipation rates from low-resolution wind data (Barat, 1982), but this method depends on the absolute value of the wind velocity, which is not available for our measurements (see section).
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