Precipitation‐induced mesoscale wind perturbations in the melting layer

Doppler radar observations during widespread frontal precipitation in England on 20 February 1967 show significant perturbations of the wind in and near the melting layer. The analysis suggests the following hypotheses: (i) Mesoscale oscillations of the wind near the melting layer are produced by pressure perturbations due to horizontal variations in cooling by melting snow associated with the precipitation pattern. A simple theoretical analysis of the effect is presented. In simple patterns, the perturbed wind has a maximum on the low pressure side of the rainfall. The perturbations propagate with the velocity of the precipitation generators and their magnitude increases with the precipitation rate. This hypothesis is in accord with the finding that the oscillation in the tangential wind across hurricane rain bands is generally a maximum on the low pressure side of the bands. (ii) Smaller scale wind perturbations were also observed in the melting layer with scale of a few kilometers comparable to those reported by Harrold and Browning (1967). However, unlike their observations, these perturbations did not appear to move with the melting layer winds. A tentative suggestion is made that these may represent wave motions.