Relations between radar reflectivity, liquid‐water content, and rainfall rate during the MAP SOP

Raindrop size distribution data obtained from two Joss–Waldvogel disdrometers located at Locarno‐Monti, Switzerland during the Mesoscale Alpine Programme (MAP) Special Observation Period are analysed to obtain appropriate relationships of radar reflectivity, Z , with both water content, W , and surface rainfall, R , for use in MAP applications. The disdrometer data are accumulated into 10‐minute samples to reduce sampling error associated with the ∼ 1 m 3 sample volume of the instruments. Based on previous studies, relations of the form W = qZ (4/7) and Z = aR 1.5 are assumed and the coefficients q and a are estimated from the data. The combined dataset of 10‐minute samples from the two disdrometers and the 10‐minute data divided into two independent subsets yielded similar mean values of the coefficients. The recommended relationships are W =3.4 Z (4/7) and Z =216 R 1.5 . The uncertainties in these mean relationships as expressed in terms of ±1 standard deviation are approximately equivalent to a ±4.4 dBZ error for the Z–W relationship, and to a ±2.4 dBZ error for the Z–R relationship.