Polarimetric radar and in situ observations of riming and snowfall microphysics during CLACE 2014

This study investigates the microphysics of winter alpine snowfall occurring in mixed-phase clouds in an inner-Alpine valley during January and February 2014. The available observations include high-resolution polarimetric radar and in situ measurements of the ice-phase and liquid-phase components o...

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Main Authors: J. Grazioli, G. Lloyd, L. Panziera, C. R. Hoyle, P. J. Connolly, J. Henneberger, A. Berne
Format: Article
Language:English
Published: Copernicus Publications 2015-12-01
Series:Atmospheric Chemistry and Physics
Online Access:http://www.atmos-chem-phys.net/15/13787/2015/acp-15-13787-2015.pdf
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author J. Grazioli
G. Lloyd
L. Panziera
C. R. Hoyle
P. J. Connolly
J. Henneberger
A. Berne
author_facet J. Grazioli
G. Lloyd
L. Panziera
C. R. Hoyle
P. J. Connolly
J. Henneberger
A. Berne
author_sort J. Grazioli
collection DOAJ
description This study investigates the microphysics of winter alpine snowfall occurring in mixed-phase clouds in an inner-Alpine valley during January and February 2014. The available observations include high-resolution polarimetric radar and in situ measurements of the ice-phase and liquid-phase components of clouds and precipitation. Radar-based hydrometeor classification suggests that riming is an important factor to favor an efficient growth of the precipitating mass and correlates with snow accumulation rates at ground level. The time steps during which rimed precipitation is dominant are analyzed in terms of temporal evolution and vertical structure. Snowfall identified as rimed often appears after a short time period during which the atmospheric conditions favor wind gusts and updrafts and supercooled liquid water (SLW) is available. When a turbulent atmospheric layer persists for several hours and ensures continuous SLW generation, riming can be sustained longer and large accumulations of snow at ground level can be generated. The microphysical interpretation and the meteorological situation associated with one such event are detailed in the paper. The vertical structure of polarimetric radar observations during intense snowfall classified as rimed shows a peculiar maximum of specific differential phase shift <i>K</i><sub>dp</sub>, associated with large number concentrations and riming of anisotropic crystals. Below this <i>K</i><sub>dp</sub> peak there is usually an enhancement in radar reflectivity <i>Z</i><sub>H</sub>, proportional to the <i>K</i><sub>dp</sub> enhancement and interpreted as aggregation of ice crystals. These signatures seem to be recurring during intense snowfall.
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spelling doaj.art-9dd3e1e781994f63a33212d1b1e3ab622022-12-21T19:29:39ZengCopernicus PublicationsAtmospheric Chemistry and Physics1680-73161680-73242015-12-011523137871380210.5194/acp-15-13787-2015Polarimetric radar and in situ observations of riming and snowfall microphysics during CLACE 2014J. Grazioli0G. Lloyd1L. Panziera2C. R. Hoyle3P. J. Connolly4J. Henneberger5A. Berne6Environmental Remote Sensing Laboratory (LTE), École Polytechnique Fédérale de Lausanne (EPFL), Lausanne, SwitzerlandCentre for Atmospheric Science, University of Manchester, Manchester, UKEnvironmental Remote Sensing Laboratory (LTE), École Polytechnique Fédérale de Lausanne (EPFL), Lausanne, SwitzerlandLaboratory of Atmospheric Chemistry, Paul Scherrer Institute (PSI), Villigen, SwitzerlandCentre for Atmospheric Science, University of Manchester, Manchester, UKInstitute for Atmospheric and Climate Science, ETH, Zurich, SwitzerlandEnvironmental Remote Sensing Laboratory (LTE), École Polytechnique Fédérale de Lausanne (EPFL), Lausanne, SwitzerlandThis study investigates the microphysics of winter alpine snowfall occurring in mixed-phase clouds in an inner-Alpine valley during January and February 2014. The available observations include high-resolution polarimetric radar and in situ measurements of the ice-phase and liquid-phase components of clouds and precipitation. Radar-based hydrometeor classification suggests that riming is an important factor to favor an efficient growth of the precipitating mass and correlates with snow accumulation rates at ground level. The time steps during which rimed precipitation is dominant are analyzed in terms of temporal evolution and vertical structure. Snowfall identified as rimed often appears after a short time period during which the atmospheric conditions favor wind gusts and updrafts and supercooled liquid water (SLW) is available. When a turbulent atmospheric layer persists for several hours and ensures continuous SLW generation, riming can be sustained longer and large accumulations of snow at ground level can be generated. The microphysical interpretation and the meteorological situation associated with one such event are detailed in the paper. The vertical structure of polarimetric radar observations during intense snowfall classified as rimed shows a peculiar maximum of specific differential phase shift <i>K</i><sub>dp</sub>, associated with large number concentrations and riming of anisotropic crystals. Below this <i>K</i><sub>dp</sub> peak there is usually an enhancement in radar reflectivity <i>Z</i><sub>H</sub>, proportional to the <i>K</i><sub>dp</sub> enhancement and interpreted as aggregation of ice crystals. These signatures seem to be recurring during intense snowfall.http://www.atmos-chem-phys.net/15/13787/2015/acp-15-13787-2015.pdf
spellingShingle J. Grazioli
G. Lloyd
L. Panziera
C. R. Hoyle
P. J. Connolly
J. Henneberger
A. Berne
Polarimetric radar and in situ observations of riming and snowfall microphysics during CLACE 2014
Atmospheric Chemistry and Physics
title Polarimetric radar and in situ observations of riming and snowfall microphysics during CLACE 2014
title_full Polarimetric radar and in situ observations of riming and snowfall microphysics during CLACE 2014
title_fullStr Polarimetric radar and in situ observations of riming and snowfall microphysics during CLACE 2014
title_full_unstemmed Polarimetric radar and in situ observations of riming and snowfall microphysics during CLACE 2014
title_short Polarimetric radar and in situ observations of riming and snowfall microphysics during CLACE 2014
title_sort polarimetric radar and in situ observations of riming and snowfall microphysics during clace 2014
url http://www.atmos-chem-phys.net/15/13787/2015/acp-15-13787-2015.pdf
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