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An Intense, Quasi-Steady Thunderstorm over Mountainous Terrain. Part III: Doppler Radar Observations of the Turbulent Structure

Kevin R. KnuppDepartment of Atmospheric Science, Colorado State University, Fort Collins 80523

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William R. CottonDepartment of Atmospheric Science, Colorado State University, Fort Collins 80523

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Abstract

The evolution of the turbulent structure of an intense, quasi-steady thunderstorm is examined using Doppler radar estimates of turbulent kinetic energy dissipation rates (ε) and radial shears of raw radial velocity (ΔV rR). A comparison of turbulent patterns with mean storm airflow is made.

Observations taken during the quasi-steady mature stage reveal that turbulent intensity and activity peaked at mid to upper storm levels. The primary storm updraft was nearly turbulence-free at low levels, but exhibited increasingly turbulent activity at higher levels indicating a transition from quasi-laminar flow to bubble-like flow. Comparison of ε and ΔV rR patterns with environmental parameters such as equivalent potential temperature and momentum suggests that buoyancy and wind shear acted together to generate turbulent eddies, some greater than 500 m in size, at middle storm levels. At mid to upper storm levels, patterns of ε and ΔV rR exhibited considerable spatial and temporal variability, and maximum estimated dissipation rate estimates approached 0.15 m2 s−3. During one particular time period, 11 local ε maxima were estimated, some with magnitudes exceeding 0.07 m2 s−3.

Abstract

The evolution of the turbulent structure of an intense, quasi-steady thunderstorm is examined using Doppler radar estimates of turbulent kinetic energy dissipation rates (ε) and radial shears of raw radial velocity (ΔV rR). A comparison of turbulent patterns with mean storm airflow is made.

Observations taken during the quasi-steady mature stage reveal that turbulent intensity and activity peaked at mid to upper storm levels. The primary storm updraft was nearly turbulence-free at low levels, but exhibited increasingly turbulent activity at higher levels indicating a transition from quasi-laminar flow to bubble-like flow. Comparison of ε and ΔV rR patterns with environmental parameters such as equivalent potential temperature and momentum suggests that buoyancy and wind shear acted together to generate turbulent eddies, some greater than 500 m in size, at middle storm levels. At mid to upper storm levels, patterns of ε and ΔV rR exhibited considerable spatial and temporal variability, and maximum estimated dissipation rate estimates approached 0.15 m2 s−3. During one particular time period, 11 local ε maxima were estimated, some with magnitudes exceeding 0.07 m2 s−3.

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