Snow Crust Research Articles

Shoulder Season

Shoulder Season

The Effects of Winter Climate and Intrinsic Factors on Survival of Cyclic Vole Populations in Southeastern Norway

Changes in winter climate is a possible explanation for dampened population cycles in voles. For voles living in the subnivean space for several months of the year, we may expect that winter conditions affect survival. We examined the effect of different winter climate descriptors (snow depth, subnivean temperature, snow crust) and different intrinsic factors (sex, age, physiology, behaviour estimated as the longest distance travelled between traps) on winter survival of bank voles Myodes glareolus in southeastern Norway by live-trapping voles monthly along elevation gradients. We tested whether winter conditions alone (winter hypothesis), intrinsic factors alone (intrinsic hypothesis), or winter conditions in combination with age and sex were more important for winter survival of voles (multiple factor hypothesis). Our results do not support the winter hypothesis as there were no relations between winter survival and snow depth, snow crust and subnivean temperature. We found strongest support for the intrinsic hypothesis, where the distance travelled was positively correlated with survival. We hypothesize that this behavioural descriptor is related to food resources and their importance during winter, where an increased activity range (distance travelled between traps) increase the access to food resources.

Modeling polarized solar radiation from a snow surface for correction of polarization-induced error in satellite data

Snow surfaces can be composed of ice crystals, melt-form snow or melt-freeze snow. Solar radiation scattered by such surfaces is polarized and the amount of polarization depends on the surface composition. This can be a source of measurement errors in satellite data if a non-polarimetric radiometric sensor is sensitive to the polarization state of light. To obtain highly accurate spectral solar radiation data from the Earth-atmosphere system for the space-borne inter-calibration studies as proposed in NASA's Climate Absolute Radiance and Refractivity Observatory (CLARREO) mission and the CLARREO Pathfinder (CPF) mission, the spectral polarization state of the reflected solar light at the top of atmosphere (TOA) must be known with sufficient accuracy. The degree of polarization (DOP) and the angle of linear polarization (AOLP) of the light at the TOA as functions of incident and viewing geometry and scene type construct the Polarization Distribution Models (PDMs) for correction of polarization-induced error of satellite data [3]. In this work, algorithms for modeling the spectral polarization state of reflected sunlight from various types of snow, including particulate snow, melt-form snow, and melt-freeze snow crusts are developed. A particulate snow surface model based on a mixture of spherical and hexagonal-column particle shapes is used. A rough-surface ice/water facet model is introduced to approximate the melt-form snow and melt-freeze snow crusts. The area fraction of facets for typical (mostly particulate) snow, and for melt-form and melt-freeze snow crusts, is estimated by comparing the model results with the PARASOL satellite data and with ground measurements conducted in Hokkaido, Japan, and in the northwest Greenland ice sheet. Our numerical results demonstrate that the model can provide a reliable approach for making the spectral PDMs for wavelengths between 320 and 2300 nm for satellite inter-calibration applications as proposed in the CLARREO and the CLARREO CPF missions for all kinds of snow surfaces.

Sneaking Back Inside, and: We Live on a Foreign Planet This One

Sneaking Back Inside, and: We Live on a Foreign Planet This One Christopher Citro (bio) Sneaking Back Inside And with the new organizational systemfor the closets we're finally going to getour act together. I'm not looking so I'm notseeing all the good stuff—my stuff—you'rethrowing out in ways that make you feelbetter and lighter and like you're livingthe right life and which make me a littlesad because it's just more of things goingaway never to return and if I get any lighterI won't even be able to stay here on this planet.I barely feel like I can right now, which iswhy I love trees and dead cars in driveways.We kept them on the edge of our driveway.I don't know what the neighbors thoughtand I don't care. I knocked a window outby accident (sort of) playing with a slingshotI shouldn't have. I snuck into my bedroomwhen no one was looking and pretendedI'd been there all day. I lived in fear andwhen nothing happened I stopped living in fear—at least about that window. We taped it upand on summer afternoons I'd lay acrossthe back seat reading novels listening tothe rain on the roof and basically what I'msaying is do what you want with the closets.I don't care. But if you see me later at theside of the house going through the trashit's because when I went to pull it downthe drive it felt so unusually heavy. I thoughtthere might be a body in there. Maybe mine. [End Page 121] We Live on a Foreign Planet This One It's sunlight eventually. They figured this outlong ago. The flame on the candle. It all ties in.The trick to relaxing is to accept yourself.After all you can't be that bad can you?Just talk together with friends. Don't also siton top of your head listening to everythingyou say and second guessing it right then,later that night, and here and there the next day.If a good day is simply a state of mind, thenstand naked in your front windows, wave helloto the snow crusts along the drive and resolveto improve. Physically first if you feel up to it.We built a sort of little gym in the basementnext to the cat box. We let go drops of sweatwhich fall onto the concrete which hasn't seenthe elements since this house was built umpteenyears ago. They come from the food we eat,the wine and seltzer and tea we drink. Theycome from rain and the sea before that. Theycome from clouds and those little puffs you seefrom people's faces when the mercury dropsand the air outside our houses wants to kill us. [End Page 122] Christopher Citro Christopher Citro is the author of The Maintenance of the ShimmyShammy (Steel Toe Books). His awards include a 2018 Pushcart Prize for Poetry and the 2015 Poetry Competition at Columbia Journal. His poetry appears in Ploughshares, Crazyhorse, The Missouri Review, and Best New Poets. Christopher lives in Syracuse, New York. Copyright © 2018 University of Wisconsin Board of Regents

Microwave snow emission modeling uncertainties in boreal and subarctic environments

Abstract. This study aims to better understand and quantify the uncertainties in microwave snow emission models using the Dense Media Radiative Theory Multi-Layer model (DMRT-ML) with in situ measurements of snow properties. We use surface-based radiometric measurements at 10.67, 19 and 37 GHz in boreal forest and subarctic environments and a new in situ data set of measurements of snow properties (profiles of density, snow grain size and temperature, soil characterization and ice lens detection) acquired in the James Bay and Umiujaq regions of Northern Québec, Canada. A snow excavation experiment – where snow was removed from the ground to measure the microwave emission of bare frozen ground – shows that small-scale spatial variability (less than 1 km) in the emission of frozen soil is small. Hence, in our case of boreal organic soil, variability in the emission of frozen soil has a small effect on snow-covered brightness temperature (TB). Grain size and density measurement errors can explain the errors at 37 GHz, while the sensitivity of TB at 19 GHz to snow increases during the winter because of the snow grain growth that leads to scattering. Furthermore, the inclusion of observed ice lenses in DMRT-ML leads to significant improvements in the simulations at horizontal polarization (H-pol) for the three frequencies (up to 20 K of root mean square error). However, representation of the spatial variability of TB remains poor at 10.67 and 19 GHz at H-pol given the spatial variability of ice lens characteristics and the difficulty in simulating snowpack stratigraphy related to the snow crust. The results also show that, in our study with the given forest characteristics, forest emission reflected by the snow-covered surface can increase the TB up to 40 K. The forest contribution varies with vegetation characteristics and a relationship between the downwelling contribution of vegetation and the proportion of pixels occupied by vegetation (trees) in fisheye pictures was found. We perform a comprehensive analysis of the components that contribute to the snow-covered microwave signal, which will help to develop DMRT-ML and to improve the required field measurements. The analysis shows that a better consideration of ice lenses and snow crusts is essential to improve TB simulations in boreal forest and subarctic environments.

The winter roosting and diet of Black Grouse Tetrao tetrix in the north-western Italian Alps

The factors influencing the selection of Black Grouse Tetrao tetrix winter roost sites and choice of roosting strategy (open-air roosts vs. snow burrows, or ‘igloos’) were assessed in the Alps, including the influence of winter diet, snow conditions and habitat at different scales. Of 337 roosts detected, 31 % were igloos and 69 % were open-air roosts. At the larger scale (30 × 30 m), ground curvature, altitude, slope, southerly aspect and mountain pine Pinus montana uncinata cover were positively correlated with roost presence. At the smaller scale (10 m radius), roost presence was positively correlated with a northerly aspect, cover of green alder Alnus viridis, and a low cover of vegetation downslope from the roost. Roosting strategy was related to temperature and snow conditions (with more igloos when snow depth was greater, but fewer igloos when a hard snow crust had formed). The winter diet of the Black Grouse mostly comprised mountain pine needles (84 % of droppings). The results suggest that a range of factors influence choice of roost site, including predator avoidance, food availability and topography. The latter showed contrasting effects at different scales, suggesting that Black Grouse select colder sites (with deeper snow) within warmer areas (energetically more favourable). Management to encourage the mountain pine, whilst maintaining scattered green alder in the understorey, is likely to improve Black Grouse winter habitat quality. Choice of roosting strategy is, however, dictated by weather conditions. If the reduction in precipitation and snow cover continues as forecast, open-air roosting might be more frequent in the future. However, open-air roosting might increase predation risk, which could be deleterious for the species’ conservation.

Validation of spatial variability of snowpack thickness and density obtained with GPR and TDR methods

Abstract We evaluate the reliability of the joint use of Ground Penetrating Radar (GPR) and Time Domain Reflectometry (TDR) to map dry snow depth, layering, and density where the snowpack thickness is highly irregular and the use of classical survey methods (i.e., hand probes and snow sampling) is unsustainable. We choose a test site characterised by irregular ground morphology, slope, and intense wind action (about 3000 m a.s.l., Western Alps, northern Italy) in dry snow conditions and with a snow-depth ranging from 0.3 m to 3 m over a few tens of metres over the course of a season. The combined use of TDR and high-frequency GPR (at a nominal frequency of 900 MHz) allows for rapid high-resolution imaging of the snowpack. While the GPR data show the interface between the snowpack and the ground, the snow layering, and the presence of snow crusts, the TDR survey allows the local calibration of wave speed based on GPR measurements and the estimation of layer densities. From January to April, there was a slight increase in the average wave speed from 0.22 to 0.24 m/ns from the accumulation zone to the eroded zone. The values are consistent with density values in the range of 350–450 kg/m 3 , with peaks of 600 kg/m 3 , as gravimetrically measured from samples from snow pits at different times. The conversion of the electromagnetic wave speed into density agrees with the core samples, with an estimated uncertainty of about 10%.

New Insight To Old Hypotheses: Ruffed Grouse Population Cycles

We examined factors hypothesized to influence Ruffed Grouse (Bonasa umbellus) population cycles by evaluating 13 a priori models that represented correlations between spring counts of male Ruffed Grouse drumming displays and these factors. We used AICc to rank the relative ability of these models to fit the data and used variance components analysis to assess the amount of temporal process variation in Ruffed Grouse spring counts explained by the best model. A hypothesis representing an interaction between winter precipitation and winter temperature was the top-ranked model. This model indicated that increased precipitation during cold winters (soft snow cover for roosting) was correlated with higher grouse population indices, but that increased precipitation during warm winters (snow crust effect) was correlated with lower spring counts. The highest ranked model (AICc weight = 0.45), explained only 17% of the temporal process variation. The number of migrating Northern Goshawks (Accipiter gentilis), which has been correlated with grouse cycles in previous studies, does not adequately explain, by itself, the variation in annual population indices of Ruffed Grouse. Other factors not considered in our analysis, such as endogenous mechanisms, parasites, or interactions among factors may also be important, which suggest that mechanisms mediating the Ruffed Grouse cycle still require investigation.

Winter methane dynamics beneath ice and in snow in a temperate poor fen

AbstractThe influence of winter on methane (CH4) stored in pore water and emitted through snow was investigated in a temperate poor fen in New Hampshire over two winters. Methane accumulated beneath ice layers (1 cm) deposited by freezing rain, resulting in snow‐pore air mixing ratios as high as 140 ppmv during the first winter and 600 ppmv during the second. An early winter snow crust of 300 kg m−3 caused no discontinuity in a linear mixing ratio profile and therefore was not observed to retard snowpack emissions. Methane concentration‐depth profiles in pore water steepened and concentrations increased by as much as 400 μM at the 10 and 20 cm depths as the ice cover formed. This suggests that the peat‐ice cover plays an important part in CH4 build‐up in pore water by limiting the transport of gases between the peat and the atmosphere. Pore water concentrations gradually declined through late winter. The seasonality of dissolved CH4 in pore water over two winters and one summer showed an average annual amplitude of 1.3 gCH4m−2 (25–75cm depth range), with a winter maximum of 4.7gCH4m−2. Emissions during the winter with average snowfall accounted for a larger percentage (9.2% in 1993–1994) of total annual emission than the winter with below‐average snowfall and warmer air temperature (2% in 1994–1995). Emissions averaged 56 and 26mg m−2 day−1 during the first and second winter (December, January and February), respectively.

Microwave signatures of snow crusts Modelling and measurements

Abstract The particle-size dependence of microwave scattering from snow is investigated. Frozen crusts have been analysed, and the microslruclure is described by correlation functions. Relations between the correlation length and various quantities such as ice-intercept lengths or volume-to-surface ratios are checked. The scattering is calculated using the Bom approximation and is linked to the emissivity through the albedo. The model yields good agreement with the microwave data from C to K bands, and the predicted particle-size dependence is verified. The claims that the variance and the correlation length of the permittivity fluctuations are the characteristic parameters are confirmed. Initial uncertainties with respect to the validity of the Born approximation for an air-ice mixture are clarified.