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 a dominant factor leading to an efficient growth of the precipitating mass and to a large snow accumulation on the ground. The time steps during which rimed precipitation is dominant are analysed in terms of temporal evolution and vertical structure. In most cases, riming is the result of a turbulent phase, of limited duration, during which supercooled liquid water (SLW) is available. When this turbulent layer is stable in time and continuously provides SLW, riming can be sustained for many hours without SLW depletion, thus generating large accumulations of snow. The microphysical interpretation as well as the meteorological situation associated with one event with those characteristics are detailed in the manuscript. The vertical structure of polarimetric radar observations during intense rimed precipitation shows a peculiar maximum of specific differential phase shift Kdp, associated with large number concentrations and/or heavy riming of anisotropic crystals. Below this Kdp peak there is usually an enhancement in ZH, proportional to the Kdp enhancement and interpreted as aggregation of ice crystals.
CITATION STYLE
Grazioli, J., Lloyd, G., Panziera, L., Connolly, P. J., Henneberger, J., & Berne, A. (2015). Riming in winter alpine snowfall during CLACE 2014: polarimetric radar and in-situ observations. Atmospheric Chemistry and Physics Discussions, 15(13), 18065–18108. https://doi.org/10.5194/acpd-15-18065-2015
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