Identification of blowing snow particles in images from a multi-angle snowflake camera

Schaer, Mathieu; Praz, Christophe; Berne, Alexis

doi:10.5194/tc-2018-248

Cited by 5 publications

(7 citation statements)

References 33 publications

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“…Furthermore, Grazioli et al () reported that MASC measurements at DDU are contaminated by blowing snow. To solve this issue, Schaer et al () used a Gaussian mixture model to discriminate between precipitation and blowing snow images in MASC data. As Polar WRF does not account for blowing snow in its current set of parameterizations, removing blowing snow from MASC data makes it possible to directly compare precipitation PSDs between the model and the MASC.…”

Section: Methodsmentioning

confidence: 99%

Microphysics of Snowfall Over Coastal East Antarctica Simulated by Polar WRF and Observed by Radar

et al. 2019

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The current assessment of the Antarctic surface mass balance mostly relies on reanalysis products or climate model simulations. However, little is known about the ability of models to reliably represent the microphysical processes governing the precipitation. This study makes use of recent ground‐based precipitation measurements at Dumont d'Urville station in Adélie Land to evaluate the representation of the precipitation microphysics in the Polar version of the Weather Research Forecast (Polar WRF) atmospheric model. During two summertime snowfall events, high‐resolution simulations are compared to measurements from an X‐band polarimetric radar and from a Multi‐Angle Snowflake Camera (MASC). A radar simulator and a “MASC” simulator in Polar WRF make it possible to compare similar observed and simulated variables. Radiosoundings and surface‐meteorological observations were used to assess the representation of the regional dynamics in the model. Five different microphysical parameterizations are tested. The simulated temperature, wind, and humidity fields are in good agreement with the observations. However, the amount of simulated surface precipitation shows large discrepancies with respect to observations, and it strongly differs between the simulations themselves, evidencing the critical role of the microphysics. The inspection of vertical profiles of reflectivity and mixing ratios revealed that the representation of the sublimation process by the low‐level dry katabatic winds strongly influences the actual amount of precipitation at the ground surface. By comparing the simulated radar signal as well as MASC and model particle size distributions, it is also possible to identify the microphysical processes involved and to pinpoint shortcomings within the tested parameterizations.

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Section: Methodsmentioning

confidence: 99%

Microphysics of Snowfall Over Coastal East Antarctica Simulated by Polar WRF and Observed by Radar

et al. 2019

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“…One challenge during measurements of snowflakes in free-fall is the contamination from blowing snow. Schaer et al (2018) developed a method to automatically identify blowing snow particles in MASC images. Despite the presence of a double fence wind shield during ICE-POP 2018, 31 % of the particles were identified as blowing snow and removed for this study.…”

Section: Multi-angle Snowflake Cameramentioning

confidence: 99%

Microphysics and dynamics of snowfall associated to a warm conveyor belt over Korea

Gehring¹,

Oertel²,

Vignon³

et al. 2020

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Abstract. On 28 February 2018, 57 mm of precipitation associated to a warm conveyor belt (WCB) fell within 21 h over South Korea. To investigate how the large-scale circulation influenced the microphysics of this intense precipitation event, we used radar measurements, snowflake photographs and radiosounding data from the International Collaborative Experiments for Pyeongchang 2018 Olympic and Paralympic winter games. The WCB was identified with trajectories computed with analysis wind fields from the Integrated Forecast System global atmospheric model. The WCB was collocated with a zone of enhanced wind speed of up to 45 m s−1 at 6500 m a.s.l., as measured by a radiosonde and a Doppler radar. Supercooled liquid water (SLW) with concentrations exceeding 0.2 g kg−1 was produced during the rapid ascent within the WCB. Vertical profiles of polarimetric radar variables show during the most intense precipitation period a peak and subsequent decrease in differential reflectivity as aggregation starts. Below the peak in differential reflectivity, the specific differential phase shift continues to increase, indicating early riming of oblate crystals and secondary ice generation. We hypothesise that the SLW produced in the WCB led to intense riming. Moreover, embedded convection in the WCB and turbulence at its lower boundary enhanced aggregation by increasing the probability of collisions between particles. This suggests that both aggregation and riming occurred prominently in this WCB. This case study shows how the large-scale atmospheric flow of a WCB provides ideal conditions for rapid precipitation growth involving SLW production, riming and aggregation. Future microphysical studies should also investigate the synoptic conditions to understand how observed processes in clouds are related to the large-scale circulation.

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“…Variables derived from the high-resolution images include those describing a hydrometeor's size, shape, fall orientation, and approximate riming degree (Garrett et al, 2012;Garrett and Yuter, 2014;Garrett et al, 2015). As these hydrometeor properties are crucial for accurate numerical modeling and microwave scattering calculations, the MASC has been used at various polar and mid-latitude locations to constrain microphysical characteristics (Garrett et al, 2012;Garrett and Yuter, 2014;Garrett et al, 2015;Grazioli et al, 2017;Kim et al, 2018;Dunnavan et al, 2019;Jiang et al, 2019;Kim et al, 2019;Vignon et al, 2019), improve radar-based estimates of snowfall rates (Gergely and Garrett, 2016;Cooper et al, 2017;Schirle et al, 2019), automatically classify hydrometeors (Praz et al, 2017;Besic et al, 2018;Hicks and Notaroš, 2019;Leinonen and Berne, 2020;Schaer et al, 2020), reconstruct particle shapes (Notaroš et al, 2016;Kleinkort et al, 2017) and size distributions (Cooper et al, 2017;Huang et al, 2017;Schirle et al, 2019), and as ground truth comparisons for radar measurements (Bringi et al, 2017;Gergely et al, 2017;Matrosov et al, 2017;Kennedy et al, 2018;Oue et al, 2018;Matrosov et al, 2019). Unlike more common precipitation gauges, the wind velocity field in the proximity of the MASC has not been simulated for various surface winds speeds, directions, or turbulence kinetic energies (TKE).…”

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confidence: 99%

Numerical simulations and Arctic observations of surface wind effects on Multi-Angle Snowflake Camera measurements

Fitch¹,

Hang²,

Talaei³

et al. 2020

Preprint

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Abstract. Ground-based measurements of frozen precipitation are heavily influenced by interactions of surface winds with gauge-shield geometry. The Multi-Angle Snowflake Camera (MASC), which photographs hydrometeors in free-fall from three different angles while simultaneously measuring their fall speed, has been used in the field at multiple mid-latitude and polar locations both with and without wind shielding. Here we show results of computational fluid dynamics (CFD) simulations of the airflow and corresponding particle trajectories around the unshielded MASC and compare these results to Arctic field observations with and without a Belfort double Alter shield. Simulations in the absence of a wind shield show a separation of flow at the upstream side of the instrument, with an upward velocity component just above the aperture, which decreases the mean particle fall speed by 55 % (74 %) for a wind speed of 5 m s−1 (10 m s−1). MASC-measured fall speeds compare well with Ka-band Atmospheric Radiation Measurement (ARM) Zenith Radar (KAZR) mean Doppler velocities only when winds are light (< 5 m s−1) and the MASC is shielded. MASC-measured fall speeds that do not match KAZR measured velocities tend to fall below a threshold value that increases approximately linearly with wind speed but is generally

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Identification of blowing snow particles in images from a multi-angle snowflake camera

Cited by 5 publications

References 33 publications

Microphysics of Snowfall Over Coastal East Antarctica Simulated by Polar WRF and Observed by Radar

Microphysics of Snowfall Over Coastal East Antarctica Simulated by Polar WRF and Observed by Radar

Microphysics and dynamics of snowfall associated to a warm conveyor belt over Korea

Numerical simulations and Arctic observations of surface wind effects on Multi-Angle Snowflake Camera measurements

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