scholarly journals Light reflection and transmission by a temperate snow cover

2007 ◽  
Vol 53 (181) ◽  
pp. 201-210 ◽  
Author(s):  
Donald K. Perovich
Keyword(s):  
Snow Cover ◽  
Optical Measurements ◽  
Optical Observations ◽  
Light Reflection ◽  
Infrared Transmission ◽  
Snow Layer ◽  
Reflection And Transmission ◽  
Light Levels ◽  
Dual Detector ◽  
Air Interfaces

AbstractAn understanding of the reflection and transmission of light by snow is important for snow thermodynamics, hydrology, ecology and remote sensing. Snow has an intricate microstructure replete with ice/air interfaces that scatter light. Spectral observations of light reflection and transmission, from 400 to 1000 nm, were made in temperate snowpacks, under cold and under melting conditions. The optical observations were made using a dual-detector spectroradiometer. One detector was placed above the snow surface to monitor the incident and reflected solar irradiance, and the second detector was placed at the base of snow cover to measure downwelling irradiance. The optical measurements were supplemented by a physical characterization of the snow, including depth, density and an estimate of grain size. In general, transmitted light levels were low and showed a strong spectral dependence, with maximum values between 450 and 550 nm. For example, a 10 cm thick snow layer reduced visible transmission (500 nm) to about 5% of the incident irradiance, and infrared transmission (800 nm) to less than 1%. Extinction coefficients were in the range 3–30 m−1, and tended to decrease slightly as the snow aged and increase as snow density increased.

Towards an Improved Parameter-Free Entrainment Model for Snow Avalanches

2021 ◽  
Author(s):  
Dieter Issler
Keyword(s):  
Snow Cover ◽  
Ad Hoc ◽  
Shear Stresses ◽  
Entrainment Rate ◽  
Snow Layer ◽  
Present Contribution ◽  
Weak Layer ◽  
Model Combining ◽  
The Difference ◽  
The 1960S

<p>On physical grounds, the rate of bed entrainment in gravity mass flows should be determined by the properties of the bed material and the dynamical variables of the flow. Due to the complexity of the process, most entrainment formulas proposed in the literature contain some ad-hoc parameter not tied to measurable snow properties. Among the very few models without free parameters are the Eglit–Grigorian–Yakimov (EGY) model of frontal entrainment from the 1960s and two formulas for basal entrainment, one from the 1970s due to Grigorian and Ostroumov (GO) and one (IJ) implemented in NGI’s flow code MoT-Voellmy. A common feature of these three approaches is their treating erosion as a shock and exploiting jump conditions for mass and momentum across the erosion front. The erosion or entrainment rate is determined by the difference between the avalanche-generated stress at the erosion front and the strength of the snow cover. The models differ with regard to how the shock is oriented and which momentum components are considered. The present contribution shows that each of the three models has some shortcomings: The EGY model is ambiguous if the avalanche pressure is too small to entrain the entire snow layer, the IJ model neglects normal stresses, and the GO model disregards shear stresses and acceleration of the eroded mass. As they stand, neither the GO nor the IJ model capture situations―observed experimentally by means of profiling radar―in which the snow cover is not eroded progressively but suddenly fails on a buried weak layer as the avalanche flows over it. We suggest a way to resolve the ambiguity in the EGY model and sketch a more comprehensive model combining all three approaches to capture gradual entrainment from the snow-cover surface together with erosion along a buried weak layer.</p>

scholarly journals Intercomparison study and optical asphericity measurements of small ice particles in the CERN CLOUD experiment

2017 ◽  
Vol 10 (9) ◽  
pp. 3231-3248 ◽  
Author(s):  
Leonid Nichman ◽  
Emma Järvinen ◽  
James Dorsey ◽  
Paul Connolly ◽  
Jonathan Duplissy ◽  
...  
Keyword(s):  
Light Scattering ◽  
Single Particle ◽  
Optical Measurements ◽  
Optical Observations ◽  
Atmospheric Measurements ◽  
Optical Probes ◽  
Cloud Particle ◽  
Ice Particles ◽  
Cloud Particles ◽  
Ice Fraction

Abstract. Optical probes are frequently used for the detection of microphysical cloud particle properties such as liquid and ice phase, size and morphology. These properties can eventually influence the angular light scattering properties of cirrus clouds as well as the growth and accretion mechanisms of single cloud particles. In this study we compare four commonly used optical probes to examine their response to small cloud particles of different phase and asphericity. Cloud simulation experiments were conducted at the Cosmics Leaving OUtdoor Droplets (CLOUD) chamber at European Organisation for Nuclear Research (CERN). The chamber was operated in a series of multi-step adiabatic expansions to produce growth and sublimation of ice particles at super- and subsaturated ice conditions and for initial temperatures of −30, −40 and −50 °C. The experiments were performed for ice cloud formation via homogeneous ice nucleation. We report the optical observations of small ice particles in deep convection and in situ cirrus simulations. Ice crystal asphericity deduced from measurements of spatially resolved single particle light scattering patterns by the Particle Phase Discriminator mark 2 (PPD-2K, Karlsruhe edition) were compared with Cloud and Aerosol Spectrometer with Polarisation (CASPOL) measurements and image roundness captured by the 3View Cloud Particle Imager (3V-CPI). Averaged path light scattering properties of the simulated ice clouds were measured using the Scattering Intensity Measurements for the Optical detectioN of icE (SIMONE) and single particle scattering properties were measured by the CASPOL. We show the ambiguity of several optical measurements in ice fraction determination of homogeneously frozen ice in the case where sublimating quasi-spherical ice particles are present. Moreover, most of the instruments have difficulties of producing reliable ice fraction if small aspherical ice particles are present, and all of the instruments cannot separate perfectly spherical ice particles from supercooled droplets. Correlation analysis of bulk averaged path depolarisation measurements and single particle measurements of these clouds showed higher R2 values at high concentrations and small diameters, but these results require further confirmation. We find that none of these instruments were able to determine unambiguously the phase of the small particles. These results have implications for the interpretation of atmospheric measurements and parametrisations for modelling, particularly for low particle number concentration clouds.

scholarly journals The recent developments in cloud removal approaches of MODIS snow cover product

2019 ◽  
Vol 23 (5) ◽  
pp. 2401-2416 ◽  
Author(s):  
Xinghua Li ◽  
Yinghong Jing ◽  
Huanfeng Shen ◽  
Liangpei Zhang
Keyword(s):  
Snow Cover ◽  
Cloud Cover ◽  
Hydrological Cycle ◽  
Global Climate ◽  
Optical Observations ◽  
Optical Remote Sensing ◽  
Spatial Methods ◽  
Fusion Methods ◽  
Spatio Temporal ◽  
Cloud Removal

Abstract. The snow cover products of optical remote sensing systems play an important role in research into global climate change, the hydrological cycle, and the energy balance. Moderate Resolution Imaging Spectroradiometer (MODIS) snow cover products are the most popular datasets used in the community. However, for MODIS, cloud cover results in spatial and temporal discontinuity for long-term snow monitoring. In the last few decades, a large number of cloud removal methods for MODIS snow cover products have been proposed. In this paper, our goal is to make a comprehensive summarization of the existing algorithms for generating cloud-free MODIS snow cover products and to expose the development trends. The methods of generating cloud-free MODIS snow cover products are classified into spatial methods, temporal methods, spatio-temporal methods, and multi-source fusion methods. The spatial methods and temporal methods remove the cloud cover of the snow product based on the spatial patterns and temporal changing correlation of the snowpack, respectively. The spatio-temporal methods utilize the spatial and temporal features of snow jointly. The multi-source fusion methods utilize the complementary information among different sources among optical observations, microwave observations, and station observations.

scholarly journals Snow-Creep Pressure on Masts

1989 ◽  
Vol 13 ◽  
pp. 154-158 ◽  
Author(s):  
Jan Otto Larsen ◽  
Jens Laugesen ◽  
Krister Kristensen
Keyword(s):  
Snow Cover ◽  
Snow Depth ◽  
Ground Level ◽  
Close Correlation ◽  
Late Winter ◽  
Pressure Measurements ◽  
Snow Pack ◽  
Snow Layer ◽  
Western Norway ◽  
Snow Pressure

Snow-pressure measurements have been carried out on two masts at the NGI avalanche station in Grasdalen, western Norway. These two tubular masts have diameters of 0.22 and 0.42 m, respectively, and are situated on a 25° slope with a deep snow cover. The most important conclusions are that within a homogeneous snow-pack there is a close correlation between snow-creep pressure and the product of acceleration due to gravity, g, density, ρ, and snow depth, H, that the highest pressures are recorded in late winter when the snow-pack is at the 0°C isothermal, and finally that a weak 0° C isothermal snow layer at ground level appears to increase snow pressure.

scholarly journals Snow Thickness Estimation on First-Year Sea Ice from Late Winter Spaceborne Scatterometer Backscatter Variance

2019 ◽  
Vol 11 (4) ◽  
pp. 417 ◽  
Author(s):  
John Yackel ◽  
Torsten Geldsetzer ◽  
Mallik Mahmud ◽  
Vishnu Nandan ◽  
Stephen Howell ◽  
...  
Keyword(s):  
Sea Ice ◽  
Snow Cover ◽  
Winter Season ◽  
Late Winter ◽  
First Year ◽  
Snow Layer ◽  
Independent Case ◽  
Brine Volume ◽  
Snow Thickness

Ku- and C-band spaceborne scatterometer sigma nought (σ°) backscatter data of snow covered landfast first-year sea ice from the Canadian Arctic Archipelago are acquired during the winter season with coincident in situ snow-thickness observations. Our objective is to describe a methodological framework for estimating relative snow thickness on first-year sea ice based on the variance in σ° from daily time series ASCAT and QuikSCAT scatterometer measurements during the late winter season prior to melt onset. We first describe our theoretical basis for this approach, including assumptions and conditions under which the method is ideally suited and then present observational evidence from four independent case studies to support our hypothesis. Results suggest that the approach can provide a relative measure of snow thickness prior to σ° detected melt onset at both Ku- and C-band frequencies. We observe that, during the late winter season, a thinner snow cover displays a larger variance in daily σ° compared to a thicker snow cover on first-year sea ice. This is because for a given increase in air temperature, a thinner snow cover manifests a larger increase in basal snow layer brine volume owing to its higher thermal conductivity, a larger increase in the dielectric constant and a larger increase in σ° at both Ku- and C bands. The approach does not apply when snow thickness distributions on first-year sea ice being compared are statistically similar, indicating that similar late winter σ° variances likely indicate regions of similar snow thickness.

scholarly journals Variability of light transmission through Arctic land-fast sea ice during spring

2013 ◽  
Vol 7 (3) ◽  
pp. 977-986 ◽  
Author(s):  
M. Nicolaus ◽  
C. Petrich ◽  
S. R. Hudson ◽  
M. A. Granskog
Keyword(s):  
Sea Ice ◽  
Spatial Variability ◽  
Physical Properties ◽  
Snow Cover ◽  
Light Transmission ◽  
Ice Cores ◽  
Arctic Sea Ice ◽  
Optical Measurements ◽  
Light Transmittance ◽  
Seasonal Evolution

Abstract. The amount of solar radiation transmitted through Arctic sea ice is determined by the thickness and physical properties of snow and sea ice. Light transmittance is highly variable in space and time since thickness and physical properties of snow and sea ice are highly heterogeneous on variable time and length scales. We present field measurements of under-ice irradiance along transects under undeformed land-fast sea ice at Barrow, Alaska (March, May, and June 2010). The measurements were performed with a spectral radiometer mounted on a floating under-ice sled. The objective was to quantify the spatial variability of light transmittance through snow and sea ice, and to compare this variability along its seasonal evolution. Along with optical measurements, snow depth, sea ice thickness, and freeboard were recorded, and ice cores were analyzed for chlorophyll a and particulate matter. Our results show that snow cover variability prior to onset of snow melt causes as much relative spatial variability of light transmittance as the contrast of ponded and white ice during summer. Both before and after melt onset, measured transmittances fell in a range from one third to three times the mean value. In addition, we found a twentyfold increase of light transmittance as a result of partial snowmelt, showing the seasonal evolution of transmittance through sea ice far exceeds the spatial variability. However, prior melt onset, light transmittance was time invariant and differences in under-ice irradiance were directly related to the spatial variability of the snow cover.

scholarly journals A systematic review of ecological responses to variation in seasonal snow cover

2020 ◽  
Author(s):  
Rachel Slatyer ◽  
Pieter Andrew Arnold
Keyword(s):  
Snow Cover ◽  
Snow Depth ◽  
Terrestrial Ecosystems ◽  
Ecosystem Change ◽  
Future Research ◽  
Snow Layer ◽  
Spring Phenology ◽  
Ecological Responses ◽  
Seasonal Snow ◽  
Snow Conditions

Seasonal snow is among the most important factors governing the ecology of many terrestrial ecosystems, but rising global temperatures are changing snow regimes and driving widespread declines in the depth and duration of snow cover. Loss of the insulating snow layer will fundamentally change the environment. Understanding how individuals, populations, and communities respond to different snow conditions is thus essential for predicting and managing future ecosystem change. We synthesized 365 studies that have examined ecological responses to variation in winter snow conditions. This research encompasses a broad range of methods (experimental manipulations, natural snow gradients, and long-term monitoring approaches), locations (35 countries), study organisms (plants, mammals, arthropods, birds, fish, lichen, and fungi), and response measures. Earlier snowmelt was consistently associated with advanced spring phenology in plants, mammals, and arthropods. Reduced snow depth also often increased mortality and/or physical injury in plants, although there were few clear effects on animals. Neither snow depth nor snowmelt timing had clear or consistent directional effects on body size of animals or biomass of plants. With 96% of studies from the northern hemisphere, the generality of these trends across ecosystems and localities is also unclear. We identified substantial research gaps for several taxonomic groups and response types, with notably scarce research on winter-time responses. We have developed an agenda for future research to prioritize understanding of the mechanisms underlying responses to changing snow conditions and the consequences of those responses for seasonally snow-covered ecosystems.

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