A dual‐wavelength radar technique for measuring the turbulent energy dissipation rate ε

Abstract

We used the ratio of simultaneous observations of radar reflectivity by S‐ and UHF‐band radars together with Hill's model of refractivity fluctuations due to turbulence to infer ε, the rate of viscous dissipation of turbulent kinetic energy per unit mass. Observations were made for 25 days from November 13 to December 7, 1995, at 11.4°S, 130.4°E (about 100 km northwest of Darwin, Australia) during the Maritime Continent Thunderstorm Experiment (MCTEX). The 500 m pulse length data covered the height range 872 to 3032 m MSL. The observed distribution of ε has a strong diurnal variation, with mean daytime and nighttime values of ε of the order of 10−3 and 10−5 m²s−3, respectively. With the dual‐wavelength technique most non‐turbulent echoes (including particulate echoes) are identified and filtered out, since the ensemble of turbulent observations is identified by its conformity to Hill's model. The technique is self‐calibrating, requiring only the relative calibration of the two radars using observations during rain, and does not require precise absolute calibration of either radar.