Snowfall retrieval at X, Ka and W bands : consistency of backscattering and microphysical properties using BAECC ground-based measurements

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Falconi , M T , von Lerber , A , Ori , D , Marzano , F S & Moisseev , D 2018 , ' Snowfall retrieval at X, Ka and W bands : consistency of backscattering and microphysical properties using BAECC ground-based measurements ' , Atmospheric Measurement Techniques , vol. 11 , no. 5 , pp. 3059-3079 . https://doi.org/10.5194/amt-11-3059-2018

Title: Snowfall retrieval at X, Ka and W bands : consistency of backscattering and microphysical properties using BAECC ground-based measurements
Author: Falconi, Marta Tecla; von Lerber, Annakaisa; Ori, Davide; Marzano, Frank Silvio; Moisseev, Dmitri
Contributor: University of Helsinki, Institute for Atmospheric and Earth System Research (INAR)
Date: 2018-05-30
Language: eng
Number of pages: 21
Belongs to series: Atmospheric Measurement Techniques
ISSN: 1867-1381
URI: http://hdl.handle.net/10138/237040
Abstract: Radar-based snowfall intensity retrieval is investigated at centimeter and millimeter wavelengths using co-located ground-based multi-frequency radar and video-disdrometer observations. Using data from four snowfall events, recorded during the Biogenic Aerosols Effects on Clouds and Climate (BAECC) campaign in Finland, measurements of liquid-water-equivalent snowfall rate S are correlated to radar equivalent reflectivity factors Z(e), measured by the Atmospheric Radiation Measurement (ARM) cloud radars operating at X, Ka and W frequency bands. From these combined observations, power-law Z(e)-S relationships are derived for all three frequencies considering the influence of riming Using microwave radiometer observations of liquid water path, the measured precipitation is divided into lightly, moderately and heavily rimed snow. Interestingly lightly rimed snow events show a spectrally distinct signature of Z(e)-S with respect to moderately or heavily rimed snow cases. In order to understand the connection between snowflake microphysical and multi-frequency backscattering properties, numerical simulations are performed by using the particle size distribution provided by the in situ video disdrometer and retrieved ice particle masses. The latter are carried out by using both the T-matrix method (TMM) applied to soft-spheroid particle models with different aspect ratios and exploiting a pre-computed discrete dipole approximation (DDA) database for rimed aggregates. Based on the presented results, it is concluded that the soft-spheroid approximation can be adopted to explain the observed multifrequency Z(e)-S relations if a proper spheroid aspect ratio is selected. The latter may depend on the degree of riming in snowfall. A further analysis of the backscattering simulations reveals that TMM cross sections are higher than the DDA ones for small ice particles, but lower for larger particles. The differences of computed cross sections for larger and smaller particles are compensating for each other. This may explain why the soft-spheroid approximation is satisfactory for radar reflectivity simulations under study.
Subject: RADAR REFLECTIVITY
SIZE SPECTRA
SCATTERING
PARTICLE
MODELS
ACCUMULATION
HYDROMETEORS
CALIBRATION
SNOWFLAKES
SIGNATURES
1172 Environmental sciences
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