Estimation of Turbulence Parameters in the Lower Troposphere from ShUREX (2016–2017) UAV Data

Abstract

Turbulence parameters in the lower troposphere (up to ~4.5 km) are estimated from measurements of high-resolution and fast-response cold-wire temperature and Pitot tube velocity from sensors onboard DataHawk Unmanned Aerial Vehicles (UAVs) operated at the Shigaraki Middle and Upper atmosphere (MU) Observatory during two ShUREX (Shigaraki UAV Radar Experiment) campaigns in 2016 and 2017. The practical processing methods used for estimating turbulence kinetic energy dissipation rate ε and temperature structure function parameter C T 2 from one-dimensional wind and temperature frequency spectra are first described in detail. Both are based on the identification of inertial (−5/3) subranges in respective spectra. Using a formulation relating ε and C T 2 valid for Kolmogorov turbulence in steady state, the flux Richardson number R f and the mixing efficiency χ m are then estimated. The statistical analysis confirms the variability of R f and χ m around ~ 0.13 − 0.14 and ~ 0.16 − 0.17 , respectively, values close to the canonical values found from some earlier experimental and theoretical studies of both the atmosphere and the oceans. The relevance of the interpretation of the inertial subranges in terms of Kolmogorov turbulence is confirmed by assessing the consistency of additional parameters, the Ozmidov length scale L O , the buoyancy Reynolds number R e b , and the gradient Richardson number Ri. Finally, a case study is presented showing altitude differences between the peaks of N 2 , C T 2 and ε , suggesting turbulent stirring at the margin of a stable temperature gradient sheet. The possible contribution of this sheet and layer structure on clear air radar backscattering mechanisms is examined.

On the estimation of vertical air velocity and detection of atmospheric turbulence from the ascent rate of balloon soundings

“…1) may be attributed to turbulent layers. McHugh et al (2008) interpreted isolated peaks of V B of several meters per second of amplitude near the tropopause and at the jet-stream level in terms of W disturbances around critical levels associated with mountain waves. The absence of corresponding negative disturbances was explained by the threedimensional nature of the flow.…”

“…Despite balloons' frequent use all over the world, few studies have tried to extract information from V B . Most of these studies have focused on the estimation of the vertical air velocity because this parameter is very important for many meteorological applications (e.g., Wang et al, 2009) and for the characterization of internal gravity waves (e.g., McHugh et al, 2008). Evidence of internal gravity wave fluctuations in balloon ascent rates was reported by Corby (1957), Reid (1972), and Lalas and Einaudi (1980).…”

“…In addition, most studies did not validate their estimations from concurrent measurements of vertical air velocities, making their models and hypotheses uncertain (e.g., McHugh et al, 2008;Gallice et al, 2011). Gallice et al (2011) proposed a model to describe balloon ascent rates in the presence of free-stream turbulence.…”

“…Most profiles revealed oscillations, indicative of gravity waves. McHugh et al (2008) noted large (always positive) variations in balloon ascent rate around the tropopause over Hawaii and interpreted these localized peaks as strong increases in W due to mountain waves around their critical levels. Independent measurements could not validate this interpretation, and possible turbulence effects were not considered when interpreting observations.…”

On the estimation of vertical air velocity and detection of atmospheric turbulence from the ascent rate of balloon soundings

“…In such conditions, turbulence intensity, often quantified by turbulence kinetic energy dissipation rates, can vary over several orders of magnitudes with height and can reach levels similar to those met in the convective atmospheric boundary layers (e.g. Luce et al 2019).…”