Measurements of dissipation rate in frontal zones

This paper demonstrates that it is possible to use measurements of the Doppler spectrum width from a high‐resolution 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 mid‐ and 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 1 x 10 −3 m 2 s −3 . Comparable values were also observed in 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 time‐scale of several hours. These issues have particular relevance to the representation of fronts within future very high‐resolution numerical weather‐prediction models.