Simultaneous observations of tropospheric turbulence from radiosondes using Thorpe analysis and the VHF MU radar
Résumé
This paper deals with the detection and quantification of refractivity turbulence in the
troposphere from radiosonde and very high frequency (VHF) band radar data. Balloon data processing
methods based on Thorpe sorting and recently developed by Wilson et al. (2010, 2011, and 2013) can be
applied for a direct identification of turbulent layers from the in situ profiles. The VHF band mid and upper
atmosphere radar (MUR) can be operated in range-imaging mode for detecting and monitoring turbulent
layers at high time and range resolutions (of the order of 10 s and a few tens of meters, respectively). For cross
validating the techniques, concurrent MUR and RS92-SGP Vaisala radiosonde observations were made at the
Shigaraki Middle and Upper atmosphere (MU) observatory (34.85°N, 136.15°E; Japan) during a field campaign
of 3 weeks in September 2011. The radar signature, in terms of echo power and aspect ratio, of the turbulent
layers identified from balloon data analyses is investigated from case studies and statistics. The deep
(>~100 m) layers are very often associated with echo power maxima and weak aspect ratios suggesting that
the same events of isotropic turbulence were detected by both instruments. Some others are associated with
relative minima of isotropic echo power, possibly indicating a later stage of turbulence. The ranges of
strong aspect ratios are generally not associated with turbulent events in the balloon data supporting the
hypothesis that anisotropic turbulence is not the cause of vertically enhanced radar echoes. Quantitative
comparisons are made between radar echo power and refractive index constant structure C2n estimated from
temperature variance and additional parameters in the selected layers. Despite a large scatter between the radar
and balloon estimates, the results are statistically significant (correlation coefficients ~0.5–0.88) even when the
causes of systematic decrease with height of C2n (humidity and density) are removed. Our studies therefore
demonstrate that radar and balloon observations of turbulence are consistent between each other and that new
insights on tropospheric turbulence can be obtained by the two techniques as stand-alone systems.
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