Abstract. Turbulence parameters in the tropo-stratosphere are analyzed using high-resolution balloon temperature measurements collected during the MUTSI (MU radar, Temperature sheets and Interferometry) campaign which took place near the Middle and Upper atmosphere (MU) radar (Japan, 35 • N, 136 • E) in May 2000. Vertical profiles of the specific dissipation rate of turbulent kinetic energy, ε, and turbulent diffusivity, K, are estimated from the Thorpe lengthscale, L T . The last is obtained by using two methods. The first one consists of measuring directly L T by reordering the potential temperature profiles. The second method is based on estimates of the temperature structure constant, C 2 T . A relationship between L T and C 2 T can be found by assuming either adiabatic vertical displacements or a model based on turbulent energy balance consideration. Analysis shows that the adiabatic assumption gives indirect estimates of L T more consistent with direct measurements. We also found that vertical profiles of analyzed turbulence characteristics show substantial intermittency, leading to substantial scatter of the local, median and average values. General trends correspond to a decrease in ε and K from the boundary layer up to altitudes 20-25 km. Layers of increased turbulence are systematically observed in the tropo-stratosphere, which may be produced by instabilities of temperature and wind profiles. These maxima may substantially increase local values of turbulence diffusivity.

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International audienceThe Thorpe analysis is a recognized method allowing to identify and characterize turbulent regions within stably stratified fluids. By comparing an observed profile of potential temperature or potential density to a reference profile obtained by sorting the data, overturns resulting in statically unstable regions mainly due to turbulent patches and Kelvin-Helmholtz billows can be identified. However, measurement noise may induce artificial inversions of potential temperature or density, which can be very difficult to distinguish from real (physical) overturns. A method for selecting real overturns is proposed. The method is based on the data range statistics, the range being defined as the difference between the maximum and the minimum of the values in a sample. A statistical hypothesis test on the range is derived and evaluated through Monte-Carlo simulations. Basically, the test relies on a comparison of the range of a data sample with the range of a normally distributed population of same size as the data sample. The power of the test, i.e. the probability of detecting the existing overturns, is found to be an increasing function of both trend to noise ratio (tnr) and overturns size. A threshold for the detectable size of the overturns as a function of tnr is derived. For very low tnr data, the test is shown to be unreliable whatever the size of the overturns. In such a case, a procedure aimed to increase the tnr, mainly based on subsampling, is described. The selection procedure is applied to atmospheric data collected during a balloon flight with low and high vertical resolutions. The fraction of the vertical profile selected as being unstable (turbulent) is 47% (27%) from the high (respectively low) resolution data-set. Furthermore, relatively small tnr measurements are found to give rise to a poor estimation of the vertical extent of the overturns

Abstract. It has been recently proposed by Clayson and Kantha (2008) to evaluate the climatology of atmospheric turbulence through the detection of overturns in the free atmosphere by applying a Thorpe analysis on relatively low vertical resolution (LR) profiles collected from standard radiosoundings. Since then, several studies based on this idea have been published. However, the impact of instrumental noise on the detection of turbulent layers was completely ignored in these works. The present study aims to evaluate the feasibility of overturns detection from radiosoundings. For this purpose, we analyzed data of two field campaigns during which high-resolution (HR) soundings (10-20 cm) were performed simultaneously with standard LR soundings. We used the raw data of standard meteorological radiosondes, the vertical resolution ranging from 5 to 9 m.A Thorpe analysis was applied to both LR and HR potential temperature profiles. A denoising procedure was first applied in order to reduce the probability of occurrence of artificial overturns, i.e. potential temperature inversions due to instrumental noise only. We then compared the empirical probability density functions (pdf) of the sizes of the selected overturns from LR and HR profiles.From HR profiles measured in the troposphere, the sizes of the detected overturns range from 4 to ∼1000 m. The shape of the size pdf of overturns is found to sharply decrease with increasing scales. From LR profiles, the smallest size of detected overturns is ∼32 m, a similar decrease in the shape of the pdf of sizes being observed. These results suggestCorrespondence to: R. Wilson (richard.wilson@upmc.fr) that overturns, resulting either from small-scale turbulence or from instabilities, can indeed be detected from meteorological radiosonde measurements in the troposphere and in the stratosphere as well. However they are rather rare as they belong to the tail of the size distribution of overturns: they only represent the 7 % largest events in the troposphere, and 4 % in the stratosphere.

The Shigaraki unmanned aerial vehicle (UAV)-Radar Experiment (ShUREX) is an international (USA-JapanFrance) observational campaign, whose overarching goal is to demonstrate the utility of small, lightweight, inexpensive, autonomous UAVs in probing and monitoring the lower troposphere and to promote synergistic use of UAVs and very high frequency (VHF) radars. The 2-week campaign lasting from June 1 to June 14, 2015, was carried out at the Middle and Upper Atmosphere (MU) Observatory in Shigaraki, Japan. During the campaign, the DataHawk UAV, developed at the University of Colorado, Boulder, and equipped with high-frequency response cold wire and pitot tube sensors (as well as an iMET radiosonde), was flown near and over the VHF-band MU radar. Measurements in the atmospheric column in the immediate vicinity of the radar were obtained. Simultaneous and continuous operation of the radar in range imaging mode enabled fine-scale structures in the atmosphere to be visualized by the radar. It also permitted the UAV to be commanded to sample interesting structures, guided in near real time by the radar images. This overview provides a description of the ShUREX campaign and some interesting but preliminary results of the very first simultaneous and intensive probing of turbulent structures by UAVs and the MU radar. The campaign demonstrated the validity and utility of the radar range imaging technique in obtaining very high vertical resolution (~20 m) images of echo power in the atmospheric column, which display evolving fine-scale atmospheric structures in unprecedented detail. The campaign also permitted for the very first time the evaluation of the consistency of turbulent kinetic energy dissipation rates in turbulent structures inferred from the spectral broadening of the backscattered radar signal and direct, in situ measurements by the highfrequency response velocity sensor on the UAV. The data also enabled other turbulence parameters such as the temperature structure function parameter C 2 T and refractive index structure function parameter C 2 n to be measured by sensors on the UAV, along with radar-inferred refractive index structure function parameter C 2 n;radar . The comprehensive dataset collected during the campaign (from the radar, the UAV, the boundary layer lidar, the ceilometer, and radiosondes) is expected to help obtain a better understanding of turbulent atmospheric structures, as well as arrive at a better interpretation of the radar data.

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