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

Abstract

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 = . It is shown that the retrieved prefactor am and exponent bm react to changes in prevailing microphysical processes. From the derived microphysical properties, event-specific relations between the equivalent reflectivity factor Ze and snowfall precipitation rate S (Ze = ) are determined. For the studied events, the prefactor of the Ze–S relation varied between 53 and 782 and the exponent was in the range of 1.19–1.61. The dependence of the factors azs and bzs on the m(D) relation and PSD are investigated. The exponent of the Ze–S relation mainly depends on the exponent of the m(D) relation, whereas the prefactor azs depends on both the intercept parameter N0 of the PSD and the prefactors of the m(D) and υ(D) relations. Changes in azs for a given N0 are shown to be linked to changes in liquid water path, which can be considered to be a proxy for degree of riming.

How Does Riming Affect Dual‐Polarization Radar Observations and Snowflake Shape?

“…Additionally, the particle dimension metrics are slightly different. In Tiira et al () the area equivalent diameter is converted to the maximum particle dimension using a single conversion factor, while von Lerber et al () derive the particle maximum dimension from PIP observations. Therefore, the applicability of the unrimed mass‐size relation needs to be verified.…”

“…One with an orifice of 200 cm 2 is referred as OTT Pluvio 2 200 and is located inside the Double‐Fence Intercomparison Reference wind protection, the other, 20 m away from the DFIR, is OTT Pluvio 2 400 with 400 cm 2 orifice (Petäjä et al, ; Tiira et al, ). Every 5 min, the integrated PIP and gauge observations are used to retrieve mass‐size relations (von Lerber et al, ). Typically, the OTT Pluvio 2 200 measurements are used for this retrieval; only in few cases where this gauge was not operational, data from OTT Pluvio 2 400 is utilized.…”

“…To characterize the mean particle size, in addition to the standard PSD parameters, the reflectivity weighted mean diameter is computed as where D max and D min are maximum and minimum recorded particle sizes, respectively, m ob ( D ) and N ( D ) are average mass for a given particle size and measured snowflake size distribution based on the technique proposed by von Lerber et al (), respectively. Similar to Falconi et al (), the particle size here is defined as the observed maximum particle dimension D max,ob derived from PIP only.…”

“…Similar to Falconi et al (), the particle size here is defined as the observed maximum particle dimension D max,ob derived from PIP only. In the study by von Lerber et al (), two particle dimensions are introduced, the observed maximum particle dimension, D max,ob , and true maximum dimension, D max,true . The latter one is the modified particle size tuned to match retrieved and observed precipitation accumulations.…”

10th European Conference on Radar in Meteorology and Hydrology (ERAD 2018) : 1-6 July 2018, Ede-Wageningen, The Netherlands

“…This time-window is selected to average data in order to avoid spurious results and detect changes in the prevailing particle habit or type. Here, we firstly apply a more accurate snowfall classification based on quantification of the riming effect using the retrieval of the rimed mass fraction (FR), as in Moisseev et al, 2017. A particle video imager, the NASA Particle Imaging Package (PIP) is used to compute the particle volume flux to retrieve the FR.…”