Doppler-polarimetric radar measurements of the melting layer of precipitation

In stratiform precipitation rain results from melting snow. Just below the zero degree isotherm in the troposphere a melting layer occurs, which can extend several hundreds of meters. The impact of the melting layer on the propagation of radio signals is not yet well known. Two radar measurements of the melting layer are presented. They show some similarity, but the differences between the two are significant. One event exhibits a strong bright band with a peak Zdr (reflecting particles mean shape estimator) in the lower part of the melting layer. Ldr (reflecting particle orientation/asymmetry) increases during melting, as does the width of the Doppler spectrum. The other event has a weak bright band, with in the middle and upper part of the melting layer, a Zdr that is larger than the one observed in the previous event. Ldr does not increase during melting. It appears that, in the upper part of the melting layer, Zdr increases when the copolarly measured reflectivity decreases. The existing models of the melting layer do not predict this behaviour