Snow Particle Counter Research Articles

Elucidation of spatiotemporal structures from high-resolution blowing-snow observations

Abstract. Systematic observations were conducted to investigate the spatiotemporal structures of blowing snow. Along a line perpendicular to the dominant wind direction on the lee side of a flat field, 15 snow particle counters (SPCs) and ultrasonic anemometers (USAs) were placed 1.5 m apart. Data were recorded at high frequencies of 100 kHz for SPCs and 1 kHz for USAs. The horizontal mass flux distributions, representing the spatiotemporal variability of blowing snow, exhibited non-uniformity in both time and space and manifested periodic changes akin to snow waves. Additionally, the presence of “snow snakes”, meandering near the snow surface, was observed. Quadrant analysis revealed predominant snow fluxes in quadrants Q1 (u′>0, w′>0) and Q4 (u′>0, w′<0). However, a more detailed parametric curve analysis indicated the existence of ejection events in Q2 (u′<0, w′>0) before snow waves and in front of snow snakes, shifting to Q1 and Q4 afterward, implying the consideration of both top-down and bottom-up mechanisms for burst sweep events.

A meteorological and blowing snow data set (2000–2016) from a high-elevation alpine site (Col du Lac Blanc, France, 2720 m a.s.l.)

Abstract. A meteorological and blowing snow data set from the high-elevation experimental site of Col du Lac Blanc (2720 m a.s.l., Grandes Rousses mountain range, French Alps) is presented and detailed in this paper. Emphasis is placed on data relevant to the observations and modelling of wind-induced snow transport in alpine terrain. This process strongly influences the spatial distribution of snow cover in mountainous terrain with consequences for snowpack, hydrological and avalanche hazard forecasting. In situ data consist of wind (speed and direction), snow depth and air temperature measurements (recorded at four automatic weather stations), a database of blowing snow occurrence and measurements of blowing snow fluxes obtained from a vertical profile of snow particle counters (2010–2016). Observations span the period from 1 December to 31 March for each winter season from 2000–2001 to 2015–2016. The time resolution has varied from 15 min until 2014 to 10 min for the last years. Atmospheric data from the meteorological reanalysis are also provided from 1 August 2000 to 1 August 2016. A digital elevation model (DEM) of the study area (1.5 km2) at 1 m resolution is also provided in RGF 93 Lambert 93 coordinates. This data set has been used in the past to develop and evaluate physical parameterizations and numerical models of blowing and drifting snow in alpine terrain. Col du Lac Blanc is also a target site to evaluate meteorological and climate models in alpine terrain. It belongs to the CRYOBS-CLIM observatory (the CRYosphere, an OBServatory of the CLIMate), which is a part of the national research infrastructure OZCAR (Critical Zone Observatories – Application and Research) and have been a Global Cryospheric Watch Cryonet site since 2017. The data are available from the repository of the OSUG data centre https://doi.org/10.17178/CRYOBSCLIM.CLB.all.

Merging a terrain-based parameter with blowing snow fluxes for assessing snow redistribution in alpine terrain

Wind and the associated snow transport are dominating factors determining the snow distribution and accumulation in alpine areas. These factors result in a high spatial variability of snow heights that is difficult to quantify. In this study, we propose an efficient method for estimations of changes in snow heights during blowing snow events. We merge a terrain-based parameter Sx, which characterizes the degree of shelter or exposure of a point provided by the upwind terrain, with estimations of quantity of snow transported by the wind. This estimation is provided by snow particle counters (SPC) that estimate the snow flux, the mass of drifting snow particles per time and area. A modified terrain-based parameter Sxm is then used to distribute snow over the terrain. The results are compared with measured changes in snow heights resulting from blowing snow events, obtained with terrestrial laser scanning (TLS). Data and results are from the Col du Lac Blanc research site in the French Alps. We use a high raster resolution of 1 m, which is required when assessing the snow-redistribution situation in highly structured terrain or in the starting zones of small and medium-sized avalanches. Results show that the proposed method can estimate snow distributions based on a modified terrain parameter Sxm and measured snow flux data. It can reproduce patterns of snow redistribution and estimate changes in snow heights reasonably well, as shown by correlation coefficients (R) of 0.78 to 0.86. The derivation of the modified terrain parameter Sxm and snow flux are specific to the research site and not yet generally applicable. The formulations require the calibration and alteration of two parameters only for use in studies with other terrain and weather characteristics.

Measurement of snow particle size and velocity in avalanche powder clouds

ABSTRACTParticle size, particle speed and airflow speed have been measured in the powder snow clouds of avalanches to investigate the suspension and transportation processes of snow particles. The avalanches were artificially triggered at the Lautaret full-scale avalanche test-site (French Alps) where an ultrasonic anemometer and a snow particle counter were setup in an avalanche track for measurements. Relatively large particles were observed during passage of the avalanche head and then the size of the particles slightly decreased as the core of the avalanche passed the measurement station. The particle size distribution was well fitted by a gamma distribution function. A condition for suspension of particles within the cloud based on the ratio of vertical velocity fluctuation to particle settling velocity suggests that the large particles near the avalanche head are not lifted up by turbulent diffusion, but rather ejected by a process involving collisions between the avalanche flow and the rough snow surface. Particle speeds were lower than the airflow speed when large particles were present in the powder cloud.

Quantifying Particle Numbers and Mass Flux in Drifting Snow

We compare two of the most common methods of quantifying mass flux, particle numbers and particle-size distribution for drifting snow events, the snow-particle counter (SPC), a laser-diode-based particle detector, and particle tracking velocimetry based on digital shadowgraphic imaging. The two methods were correlated for mass flux and particle number flux. For the SPC measurements, the device was calibrated by the manufacturer beforehand. The shadowgrapic imaging method measures particle size and velocity directly from consecutive images, and before each new test the image pixel length is newly calibrated. A calibration study with artificially scattered sand particles and glass beads provides suitable settings for the shadowgraphical imaging as well as obtaining a first correlation of the two methods in a controlled environment. In addition, using snow collected in trays during snowfall, several experiments were performed to observe drifting snow events in a cold wind tunnel. The results demonstrate a high correlation between the mass flux obtained for the calibration studies ( $$r \geqslant 0.93$$ ) and good correlation for the drifting snow experiments ( $$r \geqslant 0.81$$ ). The impact of measurement settings is discussed in order to reliably quantify particle numbers and mass flux in drifting snow. The study was designed and performed to optimize the settings of the digital shadowgraphic imaging system for both the acquisition and the processing of particles in a drifting snow event. Our results suggest that these optimal settings can be transferred to different imaging set-ups to investigate sediment transport processes.

Evaluation of the FlowCapt Acoustic Sensor for the Aeolian Transport of Snow

AbstractFlowCapt acoustic sensors, designed for measuring the aeolian transport of snow fluxes, are compared to the snow particle counter S7optical sensor, considered herein as the reference. They were compared in the French Alps at the Lac Blanc Pass, where a bench test for the aeolian transport of snow was set up. The two existing generations of FlowCapt are compared. Both seem to be good detectors for the aeolian transport of snow, especially for transport events with a flux above 1 g m−2 s−1. The second-generation FlowCapt is also compared in terms of quantification. The aeolian snow mass fluxes and snow quantity transported recorded by the second-generation FlowCapt are close to the integrative snow particle counter S7 fluxes for an event without precipitation, but they are underestimated when an event with precipitation is considered. When the winter season is considered, for integrative snow particle counter S7 fluxes above 20 g m−2 s−1, the second-generation FlowCapt fluxes are underestimated, regardless of precipitation. In conclusion, both generations of FlowCapt can be used as a drifting snow detector and the second generation can record an underestimation of the quantity of snow transported at one location: over the winter season, the quantity of snow transported recorded by the SPC is between 4 and 6 times greater than the quantity recorded by the second-generation FlowCapt.

Snow particle speeds in drifting snow

AbstractKnowledge of snow particle speeds is necessary for deepening our understanding of the internal structures of drifting snow. In this study, we utilized a snow particle counter (SPC) developed to observe snow particle size distributions and snow mass flux. Using high‐frequency signals from the SPC transducer, we obtained the sizes of individual particles and their durations in the sampling area. Measurements were first conducted in the field, with more precise measurements being obtained in a boundary layer established in a cold wind tunnel. The obtained results were compared with the results of a numerical analysis. Data on snow particle speeds, vertical velocity profiles, and their dependence on wind speed obtained in the field and in the wind tunnel experiments were in good agreement: both snow particle speed and wind speed increased with height, and the former was always 1 to 2 m s−1 less than the latter below a height of 1 m. Thus, we succeeded in obtaining snow particle speeds in drifting snow, as well as revealing the dependence of particle speed on both grain size and wind speed. The results were verified by similar trends observed using random flight simulations. However, the difference between the particle speed and the wind speed in the simulations was much greater than that observed under real conditions. Snow transport by wind is an aeolian process. Thus, the findings presented here should be also applicable to other geophysical processes relating to the aeolian transport of particles, such as blown sand and soil.

Detection of snowfall occurrence during blowing snow events using photoelectric sensors

There is a strong need to identify blowing snow events with and without concurrent falling snow and to estimate solid precipitation amounts in mountainous areas and polar regions. For these purposes, we first developed a method using the concomitant analysis of an anemometer and a drifting snow sensors (SPC-S7 and Wenglor/YH03PCT8-YH08PCT8). Photoelectric sensors, such as the SPC-S7 (Snow Particle Counter), specially designed for studying drifting snow, or a simpler photoelectric counter manufactured by Wenglor, were chosen because they had already been tested in previous studies for measuring solid precipitation. They were set up at Lac Blanc Pass, an experimental site dedicated to the study of drifting snow in the French Alps. The data set obtained was compared with the independent database of blowing snow events with or without falling snow collected at the same experimental site, i.e. data on the precipitation amount stemming from heated precipitation gauge and SAFRAN modeling output. The analysis of snow flux and mean diameter according to wind speed allowed us to separate blowing snow events with and without precipitation for moderate wind speed. To reduce the uncertainty at high wind speed, the SPC-S7 must be set up at least 4m above the snow surface. Similar preliminary results were obtained with the simpler Wenglor photoelectric counter, despite the minimum observable diameter being 200μm and the particle size distribution unavailable. These results must be confirmed by further experiments. The SPC-S7- estimated precipitation amount is in relatively good agreement with modeled precipitation given the many uncertainties due to the calculation hypotheses. Since the particle size distribution is not available for the simpler photoelectric counter and there are too many uncertainties and hypotheses in calculating solid precipitation, we concluded that the solid precipitation amount cannot be reliably estimated by the simple photoelectric counter.

Drifting snow measurements on the Greenland Ice Sheet and their application for model evaluation

Abstract. This paper presents autonomous drifting snow observations performed on the Greenland Ice Sheet in the fall of 2012. High-frequency snow particle counter (SPC) observations at ~ 1 m above the surface provided drifting snow number fluxes and size distributions; these were combined with meteorological observations at six levels. We identify two types of drifting snow events: katabatic events are relatively cold and dry, with prevalent winds from the southeast, whereas synoptic events are short lived, warm and wet. Precipitating snow during synoptic events disturbs the drifting snow measurements. Output of the regional atmospheric climate model RACMO2, which includes the drifting snow routine PIEKTUK-B, agrees well with the observed near-surface climate at the site, as well as with the frequency and timing of drifting snow events. Direct comparisons with the SPC observations at 1 m reveal that the model overestimates the horizontal snow transport at this level, which can be related to an overestimation of saltation and the typical size of drifting snow particles.

Occurrence of blowing snow events at an alpine site over a 10-year period: Observations and modelling

Blowing snow events control the evolution of the snow pack in mountainous areas and cause inhomogeneous snow distribution. The goal of this study is to identify the main features of blowing snow events at an alpine site and assess the ability of the detailed snowpack model Crocus to reproduce the occurrence of these events in a 1D configuration. We created a database of blowing snow events observed over 10years at our experimental site. Occurrences of blowing snow events were divided into cases with and without concurrent falling snow. Overall, snow transport is observed during 10.5% of the time in winter and occurs with concurrent falling snow 37.3% of the time. Wind speed and snow age control the frequency of occurrence. Model results illustrate the necessity of taking the wind-dependence of falling snow grain characteristics into account to simulate periods of snow transport and mass fluxes satisfactorily during those periods. The high rate of false alarms produced by the model is investigated in detail for winter 2010/2011 using measurements from snow particle counters.

Development of an automatic blowing-snow station

Abstract Blowing snow is a significant component of the mass and energy balance of the Antarctic ice sheet, and is an important factor when predicting the likely effects of global climate change. Nishimura and Nemoto (2005) carried out blowing snow observations at Mizuho Station, Antarctica in 2000 using Snow Particle Counters (SPCs) able to sense particle diameter as well as particle number. However, the SPC requires a large power supply and data are stored on computer. Deployment of an SPC is therefore not always practical for unmanned observations, particularly under the severe conditions in Antarctica. In this study, we developed a simpler device – the automatic blowing-snow station (ABS) – that measures the attenuation of light intensity, which is strongly influenced by the blowing snow flux. A small wind turbine and a cold-proof battery are used as the power source. We tested the performance of the ABS system in a cold wind-tunnel, in comparison with the SPC. We also undertook field testing of the ABS during the winter of 2009–2010 at Ishikari, Japan, which showed that the system performs well.

スノー・パーティクル・カウンターによる飛雪粒子速度の測定

スノー・パーティクル・カウンターによる飛雪粒子速度の測定

Present weather-sensor tests for measuring drifting snow

AbstarctIn Antarctica, blowing snow accounts for a major component of the surface mass balance near the coast. Measurements of precipitation and blowing snow are scarce, and therefore collected data would allow testing of numerical models of mass flux over this region. A present weather station (PWS), Biral VPF730, was set up on the coast at Cap Prud’homme station, 5 km from Dumont d’Urville (DDU), principally to quantify precipitation. Since we expected to be able to determine blowing-snow fluxes from the PWS data, we tested this device first on our experimental site, the Lac Blanc pass. An empirical calibration was made with a snow particle counter. Although the physics of the phenomenon was not well captured, the flux outputs were better than those from FlowCapts. The first data from Antarctica were reanalyzed. The new calibration seems to be accurate for estimating the high blowing-snow flux with an interrogation of the precipitation effects.

Wind and drifting-snow gust factor in an Alpine context

AbstarctWind-transported snow is a common phenomenon in cold windy areas, creating snowdrifts and contributing significantly to the loading of avalanche release areas. It is therefore necessary to take into account snowdrift formation both in terms of predicting and controlling drift patterns. Particularly in an Alpine context, drifting snow is a nonstationary phenomenon, which has not been taken into account in physical modeling carried out in wind tunnels or in numerical simulations. Only a few studies have been conducted to address the relation between wind gusts and drifting-snow gusts. Consequently, the present study was conducted at the Lac Blanc pass (2700ma.s.l.) experimental site in the French Alps using a snow particle counter and a cup anemometer in order to investigate drifting-snow gusts. First, it was shown that the behavior of the wind gust factor was coherent with previous studies. Then the definition of wind gust factor was extended to a drifting-snow gust factor. Sporadic drifting-snow events were removed from the analysis to avoid artificially high drifting-snow gust factors. Two trends were identified: (1) A high 1 s peak and a mean 10 min drifting-snow gust factor, greater than expected, were observed for events that exhibited a gamma distribution on the particle width histogram. The values of drifting-snow gust factors decreased with increasing gust duration. (2) Small drifting-snow gusts (i.e. smaller than or of the same order of magnitude as wind gusts) were also observed. However, in this case, they were systematically characterized by a snow particle size distribution that differed from the two-parameter gamma probability density function.

Back analysis of drifting-snow measurements over an instrumented mountainous site

AbstractThe NEMO numerical model of drifting snow, whose general outlines are presented in this paper, is based on a physical model for saltation and turbulent diffusion. The model needs a set of input parameters including fall velocity, threshold shear velocity, shear velocity, mass concentration and roughness, which are obtained from empirical formulae and wind speed measured at a given height. To better determine the required field data in an alpine context, our experimental site, Col du Lac Blanc (2700ma.s.l.), French Alps, was first equipped with one anemometer and blowing-snow acoustic sensors, which proved not to be accurate enough for research purposes in the current state of development even though a new calibration curve was used. We therefore set up a Snow Particle Counter and we returned to the traditional, robust mechanical traps and a 10 m mast with six anemometers, two temperature sensors and a depth sensor to better determine friction velocity and aerodynamic roughness. Based on the studied drifting-snow events we conclude: (1) the proportionality of the aerodynamic roughness to the square of the friction velocity was confirmed, but with a varying proportionality ratio depending on the snowdrift event; (2) values of σsUF were relatively well approximated by empirical formulae from data originating from Antarctica, and (3) snowdrift concentration profiles obtained by Pomeroy’s semi-empirical formulae for the saltation layer coupled with a theoretical approach for the diffusion layer overestimated the concentration profiles for the studied blowing-snow event.

Application of a snow particle counter to solid precipitation measurements under Arctic conditions

Abstract To develop a more reliable means for measuring precipitation in the Arctic, daily solid precipitation in Barrow, Alaska, was measured from October 24, 2002 to January 14, 2003 using a Double-Fence Intercomparison Reference (DFIR), which is the World Meteorological Organization (WMO) reference standard for solid precipitation measurements. Furthermore, a new approach using a snow particle counter (SPC) that outputs the number flux of snow particles without directly catching them was introduced. The correction procedures for wind, wetting, evaporation losses, and trace amounts were applied on a daily basis to the DFIR precipitation. The total corrected DFIR precipitation (61.35 mm) was found to be 1.47 times the uncorrected measurement (41.65 mm). The SPC-estimated precipitation measurements correlate well (r2 = 0.72) with the corrected DFIR measurements, suggesting that precipitation gauges that do not directly catch snow particles are effective in low-precipitation areas such as the polar regions.

On the saltation of fresh snow in a wind tunnel: Profile characterization and single particle statistics

We present experimental results on the snow drift in a turbulent boundary layer over a flat fresh snow‐covered surface. Vertical profiles of mass flux and of the distribution of particle diameters were obtained by means of a pair of Snow Particle Counters parallel with measurements of the stream‐wise velocity profile. The aim of the paper is to discuss current parameterizations of the vertical mass flux profile for fresh snow and to investigate the range of timescales involved in a developing saltation layer occurring in a turbulent boundary layer. The novelty of the work consists of using an intact fresh snow cover as an erodible surface able to provide realistic snow crystals as drifting particles. Results show that (1) the parameters scaling the vertical mass flux profiles of fresh snow can significantly differ from those given in the literature for ice or compacted snow particles; (2) though drifting snow covers an extremely wide range of temporal scales, the mean time interval between saltating particles 〈Δt〉 is the key timescale of the saltation process; (3) 〈Δt〉 allows for the optimal reconstruction of the mass flux as a continuous signal and for neglecting the effects related to the heterogeneous distribution of particle size on the mass flux. Implications on the modeling of snow drift and on the processing of field observations are discussed.

スノー・パーティクル・カウンター（SPC）による飛雪流量測定に及ぼす飛雪粒子の形状の影響

スノー・パーティクル・カウンター（SPC）による飛雪流量測定に及ぼす飛雪粒子の形状の影響

Blowing snow at Mizuho station, Antarctica

Blowing snow observations were carried out at Mizuho station, Antarctica, from October to November 2000. A blowing snow observation system including snow particle counters, which can sense not only the number of snow particles, but also their diameters, was situated on a 30 m tower. All instruments worked correctly and the data obtained revealed profiles of mass flux and particle size distributions as a function of the friction velocity. Measurements were compared with a blowing snow model that accounted for most physical processes including aerodynamic entrainment, grain/bed collisions, wind modification, particle size distribution and turbulent fluctuations on the particle trajectories. Simulated and measured results showed close agreement, and the validity of the model was demonstrated. Vertical profiles of horizontal mass flux from saltation to suspension, as well as the particle size distributions were expressed precisely, which could not be achieved using the previous models.

Field measurements of snow-drift threshold and mass fluxes, and related model simulations

Field measurements were carried out to calculate the threshold friction velocity for snow saltation, and mass fluxes during snow drift. The wind was measured in three components by an ultrasonic anemometer, and the mass fluxes were determined using an optical sensor (‘snow particle counter’), acoustic sensors (‘Flowcapt’) and mechanical traps. The threshold friction velocity was found to be correlated to the grain size (R2=0.75). The mass flux measurements were compared with numerical simulations of snow drift, and it was demonstrated that the maximum snow transport takes place at shear stress values of roughly two times the average shear stress over 20 min. By implementing a probability distribution for the shear stress the mass flux was simulated with only the mean measured value of the shear stress as input. This procedure enables the future use of the numerical model for operational applications.