Measurements of dissipation rate in frontal zones

This paper demonstrates that it is possible to use measurements of the Dopp ler spectrum width front a high-resolution radar to obtain quantitative est imates of dissipation rate during the passage of precipitating frontal zone s. Using the high-resolution Chilbolton radar, this method has been applied , for the first time, to infer the rate at which kinetic energy is dissipat ed by turbulence within mid- and lower-tropospheric frontal zones. Analysis of detailed measurements for one cold-frontal region showed multiple shall ow sheets of high dissipation rate, with spatially averaged values around I 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 hypothes is that mixing played a major role in determining the mean properties of th e fronts. in that the turbulence acted to destroy the frontal shear layer o n a time-scale of several hours. These issues have particular relevance to the representation of fronts within future very high-resolution numerical w eather-prediction models.