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

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 (?) and radial shears of raw radial velocity (?Vr/?R). 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 ? and ?Vr/?R 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 ? and ?Vr/?R 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 ? maxima were estimated, some with magnitudes exceeding 0.07 m2 s?3.