Estimating length scales for tropospheric turbulence from MU radar and balloon data
Résumé
Recently, Wilson et al. (2011, 2013) showed that the application of Thorpe sorting on vertical
profiles of dry or moist potential temperatures estimated from Vaisala (RS92G) balloon data
makes it possible to identify turbulent layers or patches in the troposphere. The Thorpe
processing provides a turbulence length scale, the so-called Thorpe length, found to be closely
related to outer scales of turbulence according to studies for oceanic turbulence (e.g., Dillon,
1982). The deepest layers, detected from balloon data, can be monitored by the Middle and
Upper atmosphere radar (MUR) in range imaging mode so that additional information on the
characteristics of the layers can be obtained. In addition, Wilson et al. (2014) showed that
buoyancy and Ozmidov scales of turbulence (and energetic parameters such as energy
dissipation rates and diffusion coefficients) can be retrieved from the width of Doppler spectra
(after careful removal of the non turbulent contributions) and the local stability N2 provided
by the sorted potential temperature profiles. The first comparisons made from selected
turbulent events revealed a close relationship between the Thorpe and the buoyancy (or
Ozmidov) scales in agreement with the studies for oceanic turbulence (Wilson et al., 2014).
The present study aims at showing results from additional events met during three radarballoon
campaigns in 2011, 2012 and 2013 at Shigaraki MU observatory. A preliminary
statistics and estimates for turbulence in (cirrus) clouds and clear air will be presented.
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