Measurements of dissipation rate in frontal zones

S U M M A R Y This paper demonstrates that it is possible to use measurements of the Doppler spectrum width from a highresolution radar to obtain quantitative estimates of dissipation rate during the passage of precipitating frontal zones. Using the high-resolution Chilbolton radar, this method has been applied, for the first time, to infer the rate at which kinetic energy is dissipated by turbulence within midand lower-tropospheric frontal zones. Analysis of detailed measurements for one cold-frontal region showed multiple shallow sheets of high dissipation rate, with spatially averaged values around I x m2s-3. Comparable values were also observed i n a warm-frontal zone. The magnitude of the observed dissipation rate supports the hypothesis that mixing played a major role in determining the mean properties of the fronts, in that the turbulence acted to destroy the frontal shear layer on a tirne-scale of several hours. These issues have particular relevance to the representation of fronts within future very high-resolution numerical weather-prediction models.