Fresh Snow Research Articles

A scaling law for aeolian dunes on Mars, Venus, Earth, and for subaqueous ripples

The linear stability analysis of the equations governing the evolution of a flat sand bed submitted to a turbulent shear flow predicts that the wavelength λ at which the bed destabilises to form dunes should scale with the drag length Ldrag=ρsρfd. This scaling law is tested using existing and new measurements performed in water (subaqueous ripples), in air (aeolian dunes and fresh snow dunes), in a high pressure CO2 wind tunnel reproducing conditions close to Venus' atmosphere and in the low pressure CO2 Martian atmosphere (Martian dunes). The difficulty is to determine the diameter of saltating grains on Mars. A first estimate comes from photographs of aeolian ripples taken by the rovers Opportunity and Spirit, showing grains whose diameters are smaller than on Earth dunes. In addition we calculate the effect of cohesion and viscosity on the dynamic and static transport thresholds. It confirms that the small grains visualised by the rovers should be grains experiencing saltation. Finally, we show that, within error bars, the scaling of λ with Ldrag holds over almost five decades. We conclude with a discussion on the time scales and velocities at which these bed instabilities develop and propagate on Mars.

Modified snow algorithms in the Canadian land surface scheme: Model runs and sensitivity analysis at three boreal forest stands

Version 3.1 of the Canadian Land Surface Scheme (CLASS) contains a number of new algorithms of significance for snow simulations in the boreal forest. In particular, mixed precipitation is now modelled, the density of fresh snow varies with temperature and the maximum snowpack density varies with snow depth. A model for canopy interception and unloading of snow developed in the Canadian boreal forest has also been implemented. In this paper, nine‐month column runs of CLASS 3.1 are compared with CLASS 2.7, the current operational version. The model runs span the winter of 2002–03 at three boreal forest sites: a mature aspen stand, a mature jack pine stand and a mature black spruce stand, all located in central Saskatchewan. The focus is on the winter performance and the representation of snow. More accurate (lower) values of modelled snow density improve the modelled snowpack depth. The accuracy of the canopy interception algorithm could not be tested directly with respect to measured interception, but results suggest that the ability to unload intercepted snow is important for accurate estimates of sublimation loss, and that simulated snow water equivalent is sensitive to perceived canopy gap fraction, interception capacity, and unloading rate. Underestimation of the canopy gap fraction increases canopy interception and sublimation losses, and decreases snow water equivalent in the snowpack, and vice versa. Employing modified gap fraction values improved the modelled snow water equivalent at two of the sites. Modifications to the model are suggested to allow the total albedo to respond to changes in the modelled sub‐canopy albedo.

Relationships between aerosol and snow chemistry at King Col, Mt. Logan Massif, Yukon, Canada

Simultaneous samples of aerosol ( n = 48 ) and recent snow ( n = 193 ) chemistry were collected at King Col (4135 m) in the St. Elias Mountains, Yukon, between 17 May and 11 June 2001. Major ion concentrations in aerosol samples were low with the total ionic burden averaging 5.52 neq m −3 at standard temperature and pressure (STP). Interspecies aerosol relationships indicate the presence of (NH 4) 2SO 4 aerosol at King Col. An aerosol Cl − deficiency relative to seawater suggests volatilization of HCl by reaction with unneutralized SO 4 2 - that is present in half of the samples. Backwards trajectories for select aerosol concentration peaks document the transport of Asian dust and anthropogenic emissions, the eruption plume from the 22 May eruption of Sheveluch, Kamchatka, and sea salt from the marine boundary layer over the Gulf of Alaska to King Col during the sampling period. Fresh snow chemistry generally mimics aerosol chemistry with similar relative abundances and interspecies relationships except for large enrichments in snow Cl − and NO 3 - relative to aerosol due to snow scavenging of gas-phase HCl and HNO 3. Although relatively strong correlations between aerosol and snow concentrations were observed for species associated with accumulation mode aerosols, e.g. NH 4 + ( r = 0.56 ) and SO 4 2 - ( r = 0.43 ), only weak correlations were observed for dust and sea-salt species. These results are influenced by greater variability in concentrations between replicate snow samples for species associated with coarse mode dust and sea-salt particles and by snow scavenging of gas-phase HCl and HNO 3.

Surprisingly small HONO emissions from snow surfaces at Browning Pass, Antarctica

Abstract. Measured Fluxes of nitrous acid at Browning Pass, Antarctica were very low, despite conditions that are generally understood as favorable for HONO emissions, including: acidic snow surfaces, an abundance of NO3- anions in the snow surface, and abundant UV light for NO3- photolysis. Photochemical modeling suggests noon time HONO fluxes of 5–10 nmol m-2 h-1; the measured fluxes, however, were close to zero throughout the campaign. The location and state of NO3- in snow is crucial to its reactivity. The analysis of soluble mineral ions in snow reveals that the NO3- ion is probably present in aged snows as NaNO3. This is peculiar to our study site, and we suggest that this may affect the photochemical reactivity of NO3-, by preventing the release of products, or providing a reactive medium for newly formed HONO. In fresh snow, the NO3- ion is probably present as dissolved or adsorbed HNO3 and yet, no HONO emissions were observed. We speculate that HONO formation from NO3- photolysis may involve electron transfer reactions of NO2 from photosensitized organics and that fresh snows at our site had insufficient concentrations of adequate organic compounds to favor this reaction.

Lift Mechanics of Downhill Skiing and Snowboarding

This study is conducted to develop a simplified mathematical model to describe the lift mechanics of downhill skiing and snowboarding, where the lift contributions due to both the transiently trapped air and the compressed solid phase (snow crystals) are determined. To our knowledge, this is the first time that anyone has attempted to realistically estimate the relative contribution of the transiently trapped air to the total lift in skiing and snowboarding. The model uses Shimizu's empirical relation to predict the local variation in Darcy permeability due to the compression of the solid phase. The forces and moments on the skier or snowboarder are used to predict the angle of attack of the planing surface, the penetration depth at the leading edge, and the shift in the center of pressure for two typical snow types, fresh and wind-packed snow. We present numerical solutions for snowboarding and asymptotic analytic solutions for skiing for the case where there are no edging or turning maneuvers. The force and moment balance are then used to develop a theory for control and stability in response to changes in the center of mass as the individual shifts his/her weight. Our model predicts that for fine-grained, windpacked snow that when the velocity (U) of the snowboarder or skier is 20 m.s, approximately 50% of the total lift force is generated by the trapped air for snowboarding and 40% for skiing. For highly permeable fresh powder snow, the lift contribution from the pore air pressure drops substantially. This paper develops a new theoretical framework for analyzing the lift mechanics and stability of skis and snowboards that could have important applications in future ski and snowboard design.

Isotopic exchange between snow and atmospheric water vapor: Estimation of the snowmelt component of groundwater recharge in the southwestern United States

The contribution of snowmelt to groundwater recharge at four sites in the southwestern United States was evaluated using stable isotopes of O and H. Paired precipitation collectors were installed at the study sites; data show that (1) there is often a significant difference between the stable isotope composition of fresh snow and the bulk meltwater derived from it (this suggests that using the isotope composition of high‐elevation springs as a proxy for precipitation may not be sound if snow is a recharge source) and (2) collector design can significantly influence the stable isotope composition of collected snow. Because the isotope composition of snow from a given location becomes heavier (i.e., more rain‐like) with increased exposure, using bulk snowmelt compositions to calculate input to groundwater recharge results in significantly increased estimates of snowmelt contributions to recharge (compared to estimates derived from fresh snow signatures). Snowmelt provides at least 40–70% of groundwater recharge at the study sites, although only 25–50% of average annual precipitation falls as snow. On the basis of these results and presently accepted scenarios for alterations in precipitation in the western United States over the next 50 years (significantly decreased snowpack due to increased atmospheric CO2), investigations of how climate change may affect groundwater resources are needed. We also investigated the potential for snow/atmospheric water vapor isotope exchange to influence the isotope signature of snow (which has been a subject of debate); the results of a laboratory experiment suggest that it can drive significant shifts in the isotope signature of snow, even at temperatures below 0°C.

A Science Application of Area and Ratio Concepts

“CAN THERE BE MONSTER INSECTS?” “Are 'human' giants of fables and fiction possible?” “Why do I sink into fresh snow and a rabbit does not?” “Why are my footprints in wet sand deeper than those of a seagull?” Middle school students can readily investigate these questions when mathematics and science are integrated. This article will focus on the last two questions, which provide rich links among animal characteristics, area of footprints, and the use of ratios in proportional reasoning.

Tiger, Tiger, Burning Bright

The Cassini spacecraft has been touring Saturn's neighborhood since it entered orbit there on 1 July 2004. As well as interrogating the giant planet and its filigree rings, understanding the formation of Saturn's moons is one of the key goals of the mission. Saturn has 35 named moons in its family, as well as a plethora of smaller objects hidden in the rings. The variety of moons is staggering. Some consist of exposed rock; others are enveloped in thick ice. Some are pock-marked with billion-year-old craters; others varnished with fresh snow. Cassini's busy schedule included more than 20 encounters with Saturn's moons in the past year, offering but a sampling of these different worlds. One of the most curious of all Saturn's moons is Enceladus. The sixth largest saturnian satellite—although at a mere 504 km across, its width is smaller than that of Arizona or Spain—Enceladus rides in the middle of Saturn's E ring, a wide and diffuse blue ring of fine particles. Because this ring lacks the bigger shards characteristic of ancient satellite smash-ups, astronomers have long suspected that the E-ring particles emanate from Enceladus itself. Earlier Earth-based and Voyager space probe images revealed that Enceladus' surface is icy and complex. Old cratered terrains butt up against newly resurfaced smooth ice flows. So Cassini scientists hoped to see signs of recent activity and possibly ice volcanism. As the papers in this special issue show, their anticipation was rewarded. In three flybys, in February, March, and July 2005, Cassini trained its instruments on Enceladus. The first two cruises descended to about 1000 and 500 km above the moon's equator. Onboard cameras snapped images of lines of folded mountain ridges and cracked white ice plains streaked with dark green organic material. The magnetometer saw signs of ions leaking out from Enceladus'atmosphere, and it localized, in the second flyby, a strong outflow from the south pole. The trajectory of the third flyby on 14 July 2005 was then adjusted to fly through the emergent gas just 168 km above the south pole. The flybys show that Enceladus' south polar landscape is still active today and is being resurfaced by cryovolcanism and fresh snowfall. Tidal forces have twisted and buckled the surface ice, producing long ridges and fractures. At infrared wavelengths, the south pole actually glows. An underground heat source lies beneath a surface grid of “tiger stripes”: a parallel set of linear trenches stained with dark organic material. From these warm vents, water vapor, ice, and dust particles are lofted in a spectacular plume, like spray from a Yellowstone geyser. Ions are driven further into the atmosphere and out into the magnetosphere of Saturn itself and the E ring. The rate at which water is being blown out is enough to replenish not only the E ring but also oxygen throughout the whole saturnian system. So is the mystery of Enceladus solved? Not at all. Finding such active geology on such a tiny moon is a big surprise. Neptune's Triton and Jupiter's Io have ice and sulfur volcanoes, respectively, but are larger bodies; Europa has experienced plate tectonics but no current activity is seen there. Yet tiny Enceladus produces a plume large enough to drench the whole Saturn system. The origin of Enceladus' internal heating is also still a major puzzle. To produce the plume, water needs to be boiled off or sublimated. Ammonia could act as antifreeze but was not detected by Cassini. Does liquid water, or locked-up ammonia, lie beneath the surface? We may need to wait for future missions to this enigmatic moon to find out for sure, but Enceladus is definitely on the map.

A Stable Isotopic Investigation of a Polar Desert Hydrologic System, McMurdo Dry Valleys, Antarctica

The hydrologic system of the coastal McMurdo Dry Valleys, Antarctica, is defined by snow accumulation, glacier melt, stream flow, and retention in closed-basin, ice-covered lakes. During the austral summers from 1993–1996 and 1999–2000 to 2002–2003, fresh snow, snow pits, glacier ice, stream water, and lake waters were sampled for the stable isotopes deuterium (D) and 18O in order to resolve sources of meltwater and the interactions among the various hydrologic reservoirs in the dry valleys. This data set provides a survey of the distribution of natural water isotope abundances within the well-defined dry valley hydrologic system in Taylor Valley, which extends 20 km inland from McMurdo Sound. The three major Taylor Valley lakes are not connected to one another hydrologically, and their levels are maintained by glacial meltwater inflow and perennial ice-cover sublimation. At the valley scale, glacial ice, snow, stream, and lake waters become more depleted in δD with increasing distance from McMurdo Sound (further inland). Snow pack in glacial accumulation zones is heterogeneous, likely a result of varying storm sources (continental versus coastal), and, in general, snow pits, fresh snow samples, and glacier ice are more depleted than stream waters. Within the lake basins, glacial ice source waters are depleted by as much as 111‰ δD and 20‰ δ18O compared to lake waters. These results demonstrate the importance of in-stream fractionation at the valley scale. In-stream enrichment occurs through direct evaporation fractionation from the channel and hyporheic exchange with isotopically enriched waters in the near-stream subsurface during transport from the glacial source to lake. Furthermore, the results show that lake waters directly reflect their glacial ice sources, despite fractionation during stream transport. Inter-annual comparisons of lake profiles suggest that lake waters are directly influenced by the isotopic composition and amount of stream flow during a season.

Keystones for Success: How Preoperative Sensorimotor Testing and Postoperative Sensorimotor Manipulations Can Save Your Patient (and You)!

This workshop will employ the principles of our prior symposium to utilize the nuances of preoperative and postoperative sensorimotor management to achieve maximal patient outcomes. Scheduled to appear: Monte Del Monte, Ed Buckley, David Weakley, Rich Freeman, Kyle Arnoldi, Erika Castro, Ginny Karlsson. Intraoperative muscle manipulation is often the easiest component in the treatment of strabismus. Careful interpretation and collection of preoperative sensorimotor tests can be the difference between a successful and a failed surgical plan. A detailed understanding of the sensorimotor system and the use of appropriate interventions can snatch victory out of the jaws of postoperative defeat. This multidisciplinary panel will share tips and pearls from previous surgical successes and failures. Topics will include: When is prism adaptation helpful? When is postoperative diplopia desirable and when is it unacceptable? How can you use prisms in free space as well as the synoptophore to help guide surgical plans? What techniques are available to enhance fusional amplitudes in the postoperative patient? When can sensorimotor evaluations assist in the timing and implementation of reoperation? What additional surprises may appear in patients with neurologic disease? These evaluations and interventions go to the heart of where much of strabismus really lies—the complex interaction between the sensory and motor systems. Paying attention to how many millimeters to move a muscle without assessing proper sensory motor data is like Colorado without fresh snow; the results just aren’t as good as they could be. Panel discussion will ensue and audience participation will be encouraged.

Elemental and organic carbon measurements with a two-step heating-gas chromatography system in snow samples from the Tibetan Plateau

AbstractIn this study, an optimized two-step heating-gas chromatography system is used to measure elemental carbon (EC) and organic carbon (OC) content in snow and ice, with the ability to quantify the elemental and organic carbon species in a snow or ice sample of 60−80 g. In this system, OC and EC are transformed into CO2 in a stream of oxygen at 340°C and 650°C, respectively. The resulting CO2 is accumulated in two molecular-sieve traps, and then put into a gas chromatograph equipped with a flame ionization detector by heating the traps to 200°C in a helium stream. Background contamination (mainly caused by impurities in the oxygen stream) and accuracy are dominated by the variability of the blank loads on the pre-cleaned filters, which are 0.50 ± 0.04 (1σ) μgC for OC, and 0.38 ± 0.04 (1σ) μgC for EC. The system is suitable for snow and ice sample measurements, with the same precision as shown for the blank tests. EC and OC concentrations have been measured in snow samples collected from different glaciers on the Tibetan Plateau. The results allow quantification for the first time of the different carbonaceous particle contents on the Tibetan Plateau and other regions. The concentrations of EC and OC particles in snow show a clearly decreasing trend from east to west and from north to south on the plateau, excluding the Pamirs region. The highest mean EC content, 79.2 ngg-1, was found in the northeast region, and the lowest, 4.3 ngg-1, was found in the western Himalaya. We note that even slight surface melting results in fresh snow getting dirtier, especially in regions with higher pollution such as seen on a glacier in the Qilian Shan. Here, the EC and OC concentrations in the fresh snow average 6.6 and 87.5 ngg-1, but after 2 days of surface melting they increased to 52.6 and 195.5 ngg-1. This suggests that surface snow melting can reduce snow albedo due to the accumulation of carbonaceous particles.

Field investigation into the diffusion of semi-volatile organic compounds into fresh and aged snow

Empirically derived field diffusivities were determined over a 24 h period for a selection of anthropogenic chlorinated chemicals in both fresh and aged snow at Tromsø, Norway. Diffusivities in fresh snow were 4.91×10 −2, 4.79×10 −1, 4.75×10 −2 and 4.75×10 −2 cm 2 s −1 for PCB-6, HCB and α-/ γ-HCH, respectively. These field diffusivities were compared to theoretical diffusivities (assuming no interaction between the chemical vapour and ice surfaces) and effective diffusivities (assuming sorption of the chemical vapour to the ice surface). Theoretical diffusivities were the highest values and were in good agreement with the empirical diffusivities derived from the field data. This suggests that the test chemicals used in this study have a low affinity for the snow/ice surfaces during diffusion into the snow. Differences in calculated diffusivities between these compounds can be largely accounted for by their physical–chemical properties, notably their snow interfacial-air partition coefficients ( K ia snow). However, using calculated values of K ia snow to describe sorption to the snow surfaces greatly reduced the effective diffusivities of the chemicals relative to the empirical field diffusivities, and calls into question the accuracy of K ia snow and/or its suitability for describing snow/air interactions at the relatively mild temperatures encountered in this study. Comparison of diffusivities between fresh and aged snow revealed similar values (within the same order of magnitude) and may be due to similar porosities between the snow types, although this parameter was not measured. Mass transfer coefficients were determined using the empirical field diffusivities and depth of the snow-layer, allowing chemical fluxes from snow to air to be calculated through use of the Whitman two-film resistance model. Using derived fluxes the chemical half-lives ( t 1/2) in fresh snow were calculated assuming that snow metamorphosis did not occur. The half-lives were in good agreement to half-lives measured in a separate field study for POPs, and serve to validate the empirical diffusivities measured in this study.

A surface mass balance model for the Greenland Ice Sheet

A surface mass balance model aimed at being coupled to a Global Circulation Model (GCM) for future climate prediction is described and tested for the Greenland Ice Sheet. The model builds on previous modeling designed to be forced by automatic weather station data, and includes surface energy balance as well as processes occurring near the surface such as water percolation and refreezing. Surface albedo is calculated with a new scheme that differentiates the timescale for aging of wet and dry snow and incorporates the effect of a thin layer of water and/or fresh snow at the surface. The model was driven with automatic weather station data from two sites located in the ablation zone in the Kangerlussuaq area (West Greenland), and calculated reasonable annual mass balance values (within 10% in seven out of eight cases) for four individual and consecutive years (1998–2001), using both measured and calculated albedo. This implies that the albedo parameterization is adequate and climate feedbacks affecting the mass balance are well captured. The model was then applied to a distributed 20‐km‐resolution grid covering the whole ice sheet, and forced with 10 years of the European Centre for Medium‐range Weather Forecast (ECMWF) reanalysis (ERA‐40) data. With the aim of coupling the model to a GCM, this study focuses on the ability to model the interannual variability in mass balance rather than to assess the present state of balance of the ice sheet. Modeled spatial and temporal wet zone extent compares well with information derived from passive microwave satellite data.

Dynamic compression of highly compressible porous media with application to snow compaction

A new experimental and theoretical approach is presented to examine the dynamic lift forces that are generated in the compression of both fresh powder snow and wind-packed snow. At typical skiing velocities of 10 to 30ms the duration of contact of a ski or snowboard with the snow will vary from 0.05 to 0.2s depending on the length of the planing surface and its speed. No one, to our knowledge, has previously measured the dynamic behaviour of snow on such a short time scale and, thus, there are no existing measurements of the excess pore pressure that can build-up in snow on this time scale. Using a novel porous cylinder–piston apparatus, we have measured the excess pore pressure that would build-up beneath the piston surface and have also measured its subsequent decay due to the venting of the air from the snow at the porous wall of the cylinder. In further experiments, in which the air is slowly and deliberately drained to avoid a build-up in pore pressure, we have been able to separate out the force exerted by the ice crystal phase as a function of its instantaneous deformation. A theoretical model for the pore pressure relaxation in the porous cylinder is then developed using consolidation theory. Dramatically different dynamic behaviour is observed for two different snow types, one (wind-packed) giving a steady continuous relaxation of the excess pore pressure and the other (fresh powder) leading to a piston rebound with negative pore pressure. A feature of the rebound is the apparent debonding of sintered ice crystals after maximum compression. This behaviour is described well by introducing a debonding coefficient where the debonding force is proportional to the expansion velocity of the medium. The experimental and theoretical approach presented herein and the previous generalized lubrication theory for compressible porous media, have laid the foundation for understanding the detailed dynamic response of soft porous layers to rapid deformation.

Validation of A One-Dimensional Snow-Land Surface Model at the Sleepers River Watershed

A one-dimensional land surface model, based on conservations of heat and water substance inside the soil and snow, is presented. To validate the model, a stand-alone experiment is carried out with five years of meteorological and hydrological observations collected from the NOAA-ARS Cooperative Snow Research Project (1966–1974) at the Sleepers River watershed in Danville, Vermont, U.S.A. The numerical results show that the model is capable of reproducing the observed soil temperature at different depths during the winter as well as a rapid increase of soil temperature after snow melts in the spring. The model also simulates the density, temperature, thickness, and equivalent water depth of snow reasonably well. The numerical results are sensitive to the fresh snow density and the soil properties used in the model, which affect the heat exchange between the snowpack and the soil.

Clopidogrel Pretreatment for Percutaneous Coronary Intervention

In trying to explain how balloon angioplasty relieved coronary narrowing, Andreas Gruentzig often displayed a photograph of footprints in fresh snow. He proposed that balloon expansion resulted in gentle, uniform plaque compression. Subsequent histological examination in the porcine coronary model and of postmortem and ultrasound findings in humans indicated more traumatic effects of angioplasty, including deep medial fissuring and adventitial stretching. Such injury causes the release of potent substances from the arterial wall that have profound vasoactive and thrombotic effects. One early response is platelet activation and deposition over the injured arterial surface, creating the substrate for thrombosis. Stent implantation appears to be associated with even greater platelet activation than balloon angioplasty alone. Importantly, the magnitude of platelet activation is associated with an increased risk for adverse clinical events after coronary intervention.1 See p 2099 Aspirin, administered as an agent to inhibit platelet activity, has been a standard component of the angioplasty protocol since the inception of the procedure. More recently, substantial evidence indicates that supplementing aspirin and unfractionated heparin with agents that antagonize the platelet glycoprotein (GP) IIb/IIIa receptor further reduces the incidence of abrupt coronary closure and the magnitude of periprocedural cardiac enzyme elevations and, in certain patient subsets, may enhance survival.2–6 To decrease the risk of stent thrombosis, practice guidelines call for augmented antiplatelet therapy (aspirin and a thienopyridine) for weeks to months after hospital discharge. In this issue of Circulation , Patti et al7 extend our knowledge about antiplatelet therapy and percutaneous coronary intervention (PCI), particularly with regard to the impact of pretreatment clopidogrel dosage and the magnitude of treatment effect that can be achieved. These investigators administered either 300 or 600 mg of clopidogrel 4 to 8 hours before cardiac catheterization to 329 patients who were potential candidates for coronary revascularization. Excluded …

Top‐of‐atmosphere shortwave broadband observed radiance and estimated irradiance over polar regions from Clouds and the Earth's Radiant Energy System (CERES) instruments on Terra

Empirical angular distribution models for estimating top‐of‐atmosphere shortwave irradiances from radiance measurements over permanent snow, fresh snow, and sea ice are developed using CERES measurements on Terra. Permanent snow angular distribution models depend on cloud fraction, cloud optical thickness, and snow brightness. Fresh snow and sea ice angular distribution models depend on snow and sea ice fraction, cloud fraction, cloud optical thickness, and snow and ice brightness. These classifications lead to 10 scene types for permanent snow and 25 scene types for fresh snow and sea ice. The average radiance over clear‐sky permanent snow is more isotropic with satellite viewing geometry than that over overcast permanent snow. On average, the albedo of clear‐sky permanent snow varies from 0.65 to 0.68 for solar zenith angles between 60° and 80°, while the corresponding albedo of overcast scenes varies from 0.70 to 0.73. Clear‐sky permanent snow albedos over Antarctica estimated from two independent angular distribution models are consistent to within 0.6%, on average. Despite significant variability in sea ice optical properties with season, the estimated mean relative albedo error is −1.0% for very dark sea ice and 0.1% for very bright sea ice when albedos derived from different viewing angles are averaged. The estimated regional root‐mean‐square (RMS) relative albedo error is 5.6% and 2.6% when the sea ice angular distribution models are applied to a region that contains very dark and very bright sea ice, respectively. Similarly, the estimated relative albedo bias error for fresh snow is −0.1% for very dark snow scenes and 0.1% for very bright snow scenes. The estimated regional RMS relative albedo error is 3.5% and 5.0% when angular distribution models are applied to a region that contains very dark and very bright fresh snow, respectively. These error estimates are only due to angular distribution model error and do not include the error caused by scene identification.

Rapid Changes in PCB and OC Pesticide Concentrations in Arctic Snow

The short-term fate of polychlorinated biphenyl (PCB) and organochlorine (OC) pesticides in the surface snowpack was investigated by taking consecutive air and snow samples over a 12 day period at Tromsø in the Norwegian Arctic. A wide range in PCB and OC pesticide concentrations was observed in snow and was attributed to the systematic decrease in concentrations that occurred over the study period. For example, sigmaPCB concentrations ranged from 2500 to 300 pg L(-1) (meltwater) with a rapid decrease observed during the first 96 h. Rates of decline (ks) conformed to first-order kinetics, with similar rates observed for all compounds measured in this study (k5 = 0.01 +/- 0.001 h(-1)). Because the particle bound fraction accounted for <10% of the individual PCB and OC burden in the snow, then the fraction lost may be accounted for by desorption, following notable increases in snow density (and presumably, decreases in snow surface area). The fraction of chemical present in the fresh snow (phis) was found to be exponentially related to changes in snow density (deltarho). Relatively small increases in p following snowfall result in a large loss of sorbed chemical, presumably due to decreases in snow surface area. Later sampling of the same snow layer, but buried under fresh snowfall, revealed a notable increase in both PCB and OC concentrations. This would indicate a possible downward migration of these chemicals from the fresh snow into deeper snow layers, suggesting that re-emission of desorbed chemical from the interstitial pore spaces to the overlying atmosphere may be complicated by this process.

CHEMICAL COMPONENTS IN RIME ON MT. MORIYOSHI IN NORTHERN JAPAN

In order to shed light on the long-range transport of atmospheric pollutants in the Northeast Asian regions, we studied the chemical components in rime and fresh surface snow on Mt. Moriyoshi (altitude: 1454 m), located on the Sea of Japan side of northern Honshu, Japan, near Northwest China and Southwest Russia. Rime and fresh surface snow samples were collected at Juhyou-Daira (near the summit; altitude: 1200 m) in February 2004. The pH range of rime samples was 4.2 – 4.9, and the electric conductivity (EC) range was 52 – 282 μS/cm. On the other hand, the pH range of snow samples was 4.5 – 4.9, and the EC range was 17 – 77 μS/cm. The elemental compositions, ionic species and particle shapes of these samples were determined and/or observed by PIXE, ion chromatography and SEM-EDX analysis. PIXE analysis of the rime and snow samples revealed 24 elements, of which Na , Mg , Al , Si , K , Ca , Ti and Fe were found to be the major components. Comparing the determined values of rime and snow sample elements, rime samples were several times to several dozen times higher than snow samples for almost all the elements. For determined values of ionic species, rime samples were several times to several dozen times higher than snow samples. With the aid of SEM-EDX analysis, many small silicon-rich spherical particles were observed in the rime samples. Small silicon-rich spherical particles were also found in the snow samples. The existent forms of chemical components in rime will be an important factor when we consider the origin of air pollutants transported over long distances in the Northeast Asian regions.

Transport and modification of humic substances present in Antarctic snow and ancient ice

We performed a study of fulvic acids extracted from fresh and aged snow, and from recent and ancient ice in Antarctica. The fresh snow samples were collected in coastal and inland sites to evaluate the influence of the distance from the sea on organic matter transport. Moreover, in a site (Melbourne Mountain) samples were collected at different heights to study the influence of altitude on transport. The obtained results showed that dissolved fulvic acid concentrations are influenced neither by distance nor by height while particulate fulvic acid concentrations are influenced by both parameters. Moreover, the results showed that fulvic acids transported for a long distance can undergo chemical modifications. Chemical modifications are better evidenced by the analysis of samples taken in trenches at different depth, which showed structural changes attributable to the loss of nitrogen-containing compounds and to an increase in aromatic character of the structures due to reduction and/or condensation processes. With ageing, the humification process proceeds with heavy carbon losses as demonstrated by results obtained from fulvic acids isolated from ice aged between twenty-five thousand and seventy thousand years.