Influence of Liquid Water Content and Temperature on the Form and Growth of Branched Planar Snow Crystals in a Cloud

Takahashi, Tomoki

doi:10.1175/jas-d-14-0043.1

Cited by 29 publications

(36 citation statements)

References 30 publications

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“…We collected snow crystals on a black aluminium plate (40 cm × 40 cm) at about 1 m above the floor of the main terrace of the Sphinx Observatory at Jungfraujoch and analysed the crystals inside a small, naturally cold (−1 to −7 • C) anteroom between the terrace and the laboratory. Among a usually wide variety of shapes and sizes precipitating onto the plate, we selected what we considered to be single, planar, branched or dendritic ice crystals (from here on "dendrites"), which can safely be assumed to have grown within MPCs at temperatures around −15 • C (Nakaya, 1954;Magono, 1962;Magono and Lee, 1966;Takahashi et al, 1991, Takahashi, 2014Libbrecht, 2017). Generally, we exposed the plate for some seconds to the precipitating cloud until at least two den-dritic snow crystals had deposited on it and then analysed those.…”

Section: Single Crystal Selection and Analysismentioning

confidence: 99%

“…First, the growth habit of ice crystals forming in supersaturated conditions between −12 and −17 • C is well and distinctively defined. These are single, planar, branched, sector-type or dendrite-type habits (Nakaya, 1954;Magono, 1962;Magono and Lee, 1966;Takahashi et al, 1991;Takahashi, 2014;Libbrecht, 2017) that grow by vapour diffusional growth into a diameter of several millimetres during a vertical fall of a few 100 m (Fukuta and Takahashi, 1999). Second, Westbrook and Illingworth (2013) observed a longlived supercooled cloud layer with a cloud top temperature around −13.5 • C, which continued to precipitate ice crystals well beyond the expected exhaustion of its INP reservoir.…”

Section: Introductionmentioning

confidence: 99%

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New type of evidence for secondary ice formation at around −15 °C in mixed-phase clouds

et al. 2019

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Ice crystal numbers can exceed the numbers of icenucleating particles (INPs) observed in mixed-phase clouds (MPCs) by several orders of magnitude, also at temperatures that are colder than − 8 • C. This disparity provides circumstantial evidence of secondary ice formation, also other than via the Hallett-Mossop process. In a new approach, we made use of the fact that planar, branched ice crystals (e.g. dendrites) grow within a relatively narrow temperature range (i.e. −12 to −17 • C) and can be analysed individually for INPs using a field-deployable drop-freezing assay. The novelty of our approach lies in comparing the growth temperature encoded in the habit of an individual crystal with the activation temperature of the most efficient INP contained within the same crystal to tell whether it may be the result of primary ice formation. In February and March 2018, we analysed a total of 190 dendritic crystals (∼ 3 mm median size) deposited within MPCs at the high-altitude research station Jungfraujoch (3580 m a.s.l.). Overall, one in eight of the analysed crystals contained an INP active at −17 • C or warmer, while the remaining seven most likely resulted from secondary ice formation within the clouds. The ice multiplication factor we observed was small (8), but relatively stable throughout the course of documentation. These measurements show that secondary ice can be observed at temperatures around −15 • C and thus advance our understanding of the extent of secondary ice formation in MPCs, even where the multiplication factor is smaller than 10.

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Section: Single Crystal Selection and Analysismentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

New type of evidence for secondary ice formation at around −15 °C in mixed-phase clouds

et al. 2019

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“…Between 4 and 4.5 km we observe the highest values of Z DR in the column, followed slightly below by the highest values of K dp . The enhancement of Z DR is often explained by the presence of ice crystals grown by vapor deposition, which promotes anisotropic shape enhancement (Takahashi, 2014;Andric et al, 2013), and that can be particularly efficient if SLW is present and the Wegener-Bergeron-Findeisen (WBF) process takes place (e.g., Pruppacher and Klett, 1997). The en- hancement is in this case moderate, with peak values mostly below 1 dB, suggesting that depositional growth is not the only process taking place and aggregation is initiated.…”

Section: Intermediate Level Of Precipitationmentioning

confidence: 99%

“…The shape, density, and growth rate of individual crystals are mostly a function of temperature and relative humidity of the environment in which they form (Magono and Lee, 1966;Chen and Lamb, 1994;Fukuta and Takahashi, 1999;Bailey and Hallett, 2009;Takahashi, 2014). Individual crystals can clump together (aggregation) and/or collect supercooled liquid water droplets that freeze upon impact on the surface of the crystals (riming).…”

Section: Introductionmentioning

confidence: 99%

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

et al. 2015

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Abstract. 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 liquidphase 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 K dp , associated with large number concentrations and riming of anisotropic crystals. Below this K dp peak there is usually an enhancement in radar reflectivity Z H , proportional to the K dp enhancement and interpreted as aggregation of ice crystals. These signatures seem to be recurring during intense snowfall.

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“…The apparent random orientation of these crystals is due to local accelerations as they were drawn into the probe (Gayet et al, ). Laboratory experiments show that the branch‐like structures observed tend to form when plates crystals grow preferentially at the corners in highly saturated environments, typically between −13.5 and −14.5°C (Takahashi, ; Takahashi et al, ). This is precisely the temperature in which these crystals have grown.…”

Section: Case Study Ii: 17 February 2016—coincident Radar and In Situmentioning

confidence: 99%

Revealing Layers of Pristine Oriented Crystals Embedded Within Deep Ice Clouds Using Differential Reflectivity and the Copolar Correlation Coefficient

Keat

Westbrook

2017

JGR Atmospheres

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Pristine ice crystals typically have high aspect ratios (≫ 1), have a high density and tend to fall preferentially with their major axis aligned horizontally. Consequently, they can, in certain circumstances, be readily identified by measurements of differential reflectivity (ZDR), which is related to their average aspect ratio. However, because ZDR is reflectivity weighted, its interpretation becomes ambiguous in the presence of even a few, larger aggregates or irregular polycrystals. An example of this is in mixed‐phase regions that are embedded within deeper ice cloud. Currently, our understanding of the microphysical processes within these regions is hindered by a lack of good observations. In this paper, a novel technique is presented that removes this ambiguity using measurements from the 3 GHz Chilbolton Advanced Meteorological Radar in Southern England. By combining measurements of ZDR and the copolar correlation coefficient (ρhv), we show that it is possible to retrieve both the relative contribution to the radar signal and “intrinsic” ZDR ( ZDRIP) of the pristine oriented crystals, even in circumstances where their signal is being masked by the presence of aggregates. Results from two case studies indicate that enhancements in ZDR embedded within deep ice clouds are typically produced by pristine oriented crystals with ZDRIP values between 3 and 7 dB (equivalent to 5–9 dB at horizontal incidence) but with varying contributions to the radar reflectivity. Vertically pointing 35 GHz cloud radar Doppler spectra and in situ particle images from the Facility for Airborne Atmospheric Measurements BAe‐146 aircraft support the conceptual model used and are consistent with the retrieval interpretation.

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Influence of Liquid Water Content and Temperature on the Form and Growth of Branched Planar Snow Crystals in a Cloud

Cited by 29 publications

References 30 publications

New type of evidence for secondary ice formation at around −15 °C in mixed-phase clouds

New type of evidence for secondary ice formation at around −15 °C in mixed-phase clouds

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

Revealing Layers of Pristine Oriented Crystals Embedded Within Deep Ice Clouds Using Differential Reflectivity and the Copolar Correlation Coefficient

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