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[1] Present-day land surface models rarely account for the influence of both black carbon and dust in the snow on the snow albedo. Snow impurities increase the absorption of incoming shortwave radiation (particularly in the visible bands), whereby they have major consequences for the evolution of snowmelt and life cycles of snowpack. A new parameterization of these snow impurities was included in the catchment-based land surface model used in the National Aeronautics and Space Administration Goddard Earth Observing System version 5. Validation tests against in situ observed data were performed for the winter of [2003][2004] in Sapporo, Japan, for both the new snow albedo parameterization (which explicitly accounts for snow impurities) and the preexisting baseline albedo parameterization (which does not). Validation tests reveal that daily variations of snow depth and snow surface albedo are more realistically simulated with the new parameterization. Reasonable perturbations in the assigned snow impurity concentrations, as inferred from the observational data, produce significant changes in snowpack depth and radiative flux interactions. These findings illustrate the importance of parameterizing the influence of snow impurities on the snow surface albedo for proper simulation of the life cycle of snow cover.

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[1] Snow surface roughness such as sastrugi on the Antarctic ice sheet can be a cause of error for remote sensing of snow parameters. The effect of sastrugi on snow bidirectional reflectance was assessed by a field experiment, model simulations, and satellite measurements. The hemispherical-directional reflectance factor (HDRF) of artificial sastrugi-like linear ridges measured at Nakasatsunai, Hokkaido, Japan, exhibited different patterns from that of a flat surface, with the difference of more than ±50% for some geometries. A 3-D Monte Carlo radiative transfer model (MC model) reproduced both the HDRF measurements for the artificial ideal sastrugi and previous measurements for natural sastrugi at the South Pole. Furthermore, the sastrugi effect was applied to remote sensing. Failure to include the surface roughness in models for developing snow-grain-size lookup tables can lead to order-of-magnitude retrieval errors. Using the MC model and multiangle data derived from the Moderate Resolution Imaging Spectrometer over the South Pole during the 2003-2004 summer, the sastrugi and snow parameters were retrieved. The height-to-width ratio of sastrugi reduced from 0.1 to 0.02, whereas the azimuth angle was nearly constant within the range of 0°-30°during the summer. The snow grain size showed a seasonal variation, which depended on the spectral channel. These retrieved parameters were consistent with existing ground measurements. The results suggest that a combination of multiangle data and a 3-D radiative transfer model can be used to quantitatively estimate surface roughness, along with snow grain size, on ice sheets.Citation: Kuchiki, K., T. Aoki, M. Niwano, H. Motoyoshi, and H. Iwabuchi (2011), Effect of sastrugi on snow bidirectional reflectance and its application to MODIS data,

This paper presents a new method for identifying the type of solid hydrometeor mainly contributing to snowfall from the measured size and fall speed data. The main type is determined from the relationship between measured size and fall speed by considering the contributions of various hydrometeor types to precipitation, including graupel, graupel-like snow, aggregates at different riming stages, and small particles such as single snow crystals. The mass flux of each hydrometeor, defined as the product of its mass and fall speed, is needed to evaluate its contribution; however, it is practically difficult to measure. In this study, we estimate mass flux from the empirical relationships between size and mass and between size and fall speed. The mass flux distribution in the size̶fall speed coordinates for all measured hydrometeors is found to accurately reflect the characteristics of types of hydrometeors and their contribution to observed precipitation. Considering these results, we introduce a new variable, the center of mass flux distribution (CMF), in the size̶fall speed coordinates. The CMF, which is the average of size and fall speed weighted by the mass flux, can be obtained in the same way as the center of gravity in mechanics. We believe that it indicates the size and fall speed of the principal hydrometeors among all particles in the observation period. This new method allows the quantitative identification of the main hydrometeor types from the locations of CMFs in the coordinates of size and fall speed. We verify this method by its application to different types of observed snowfall events. Although there is some ambiguity in estimating the mass flux, the method is expected to be useful for identifying the main hydrometeor types in snowfall events and for quantitatively interpreting returned radar power.

ABSTRACT. Continuous measurements of the radiation budget and meteorological components, along with frequent snow-pit work, were performed in Sapporo, Hokkaido, Japan, during two winters from 2003 to 2005. The measured relationships between broadband albedos and the mass concentration of snow impurities were compared with theoretically predicted relationships calculated using a radiative transfer model for the atmosphere-snow system in which different types (in light absorption) of impurity models based on mineral dust and soot were assumed. The result suggests that the snow in Sapporo was contaminated not only with mineral dust but also with more absorptive soot. A comparison of the measured relationships between broadband albedos and snow grain size for two different layers with the theoretically predicted relationships revealed that the visible albedo contains information about the snow grain size in deeper snow layers (10 cm), and the near-infrared albedo contains only surface information. This is due to the difference in penetration depth of solar radiation into snow between the visible and the near-infrared wavelengths.

Abstract. In countries like Japan, particular solid precipitation particles (PPs), such as unrimed PPs and graupel, often form a weak layer in snow, which triggers slab avalanches. An understanding of weak PP layers is therefore essential for avalanche prevention authorities to design a predictive model for slab avalanches triggered by those layers. Specific surface area (SSA) is a parameter that could characterize the physical properties of PPs. The SSAs of solid PPs in Nagaoka – a city in Japan experiencing the heaviest snowfall in the country – were measured for four winters (from 2013/2014 to 2016/2017). More than 100 SSAs of PP were measured during the study period using the gas absorption method. The measured SSA values range from 42 to 153 m2 kg−1. Under melting conditions, PPs showed comparatively smaller values. Unrimed and slightly rimed PPs exhibited low SSA, whereas heavily rimed PPs and graupel exhibited high SSA. The degree of PP riming depends on the synoptic meteorological conditions. Based on the potential of weak PP layer formation with respect to the degree of riming of PPs, the results indicate that SSA is a useful parameter for describing the characteristics of PP, and consequently predicting avalanches triggered by weak PP layers. The study found that the values of SSA strongly depend on wind speed (WS) and wet-bulb temperature (Tw) on the ground. SSA increases with increase in WS and decreases with increase in Tw. An equation to empirically estimate the SSA of fresh PPs in Nagaoka using WS and Tw was established. The equation successfully reproduced the fluctuation of SSA. The SSA equation, along with the meteorological data, is an efficient first step toward describing the development of weak PP layers in the snow cover models.