Microphysical Properties of Snow and Their Link to Ze–S Relations during BAECC 2014

This study uses snow events from the Biogenic Aerosols-Effects on Clouds and Climate (BAECC) 2014 campaign to investigate the connection between properties of snow and radar observations. The general hydrodynamic theory is applied to video-disdrometer measurements to retrieve masses of falling ice particles. Errors associated with the observation geometry and the measured particle size distribution (PSD) are addressed by devising a simple correction procedure. The value of the correction factor is determined by comparison of the retrieved precipitation accumulation with weighing-gauge measurements. Derived mass-dimensional relations are represented in the power-law form m = a(m)D(m)(b). It is shown that the retrieved prefactor a(m) and exponent b(m) react to changes in prevailing microphysical processes. From the derived microphysical properties, event-specific relations between the equivalent reflectivity factor Z(e) and snowfall precipitation rate S (Z(e) = a(zs)S(zs)(b)) are determined. For the studied events, the prefactor of the Z(e)-S relation varied between 53 and 782 and the exponent was in the range of 1.19-1.61. The dependence of the factors a(zs) and b(zs) on the m(D) relation and PSD are investigated. The exponent of the Z(e)-S relation mainly depends on the exponent of the m(D) relation, whereas the prefactor a(zs) depends on both the intercept parameter N-0 of the PSD and the prefactors of the m(D) and nu(D) relations. Changes in a(zs) for a given N-0 are shown to be linked to changes in liquid water path, which can be considered to be a proxy for degree of riming.