Energetics of persistent turbulent layers underneath mid-level clouds estimated from concurrent radar and radiosonde data

Abstract

Two Japanese-French field campaigns devoted to studying small-scale turbulence and instabilities in the lower atmosphere were conducted in September 2011 and November 2012 at the Shigaraki Middle and Upper atmosphere (MU) Observatory (34.85°N, 136.15°E; Japan). The Very High Frequency Middle and Upper atmosphere radar (MUR) was operated with a time resolution of the order of 10s in range imaging mode allowing echo power measurements at fine range-resolutions (typically, a few tens of meters). In addition, balloons instrumented with RS92G Vaisala radiosondes were launched from the observatory during the radar operations. From the raw data of temperature, pressure and humidity, temperature turbulent layers can be identified from the detection of overturns by using the Thorpe (1977) method. During the two campaigns, both radar and balloon data revealed turbulent layers of about 1.0km in depth, underneath mid-level clouds and meteorological frontal zones. They persisted for about 10h in the radar data. The balloon data collected were undoubtedly representative of the conditions met by the radar. Turbulence parameters associated with stably stratified flows were tentatively estimated by using different methods involving both radar and balloon observations for 4 balloon flights. These parameters included the Thorpe, buoyancy, and Ozmidov scales LT, LB and LO, potential and kinetic turbulent energies TPE and TKE, potential kinetic energy dissipation rates εP and εK and turbulent diffusivities Kθ. The turbulence scales were found to be consistent between each other within a factor of about 2. Energy dissipation rates of 0.6mW/kg were found for 3 cases and 0.06mW/kg for one case.