Wind-blown Snow Research Articles

Physical and ecological changes associated with warming permafrost and thermokarst in Interior Alaska

AbstractObservations and measurements were made of physical and ecological changes that have occurred since 1985 at a tundra site near Healy, Alaska. Air temperatures decreased (1985 through 1999) while permafrost warmed and thawed creating thermokarst terrain, probably as a result of increased snow depths. Permafrost, active layer and ground‐ice conditions at the Healy site are the result of the interaction of climatic, ecologic and other factors. The slow accumulation of ground ice in an intermediate permafrost layer formed by upward freezing from the permafrost surface leads to long‐term differential frost heave and microrelief. When ground ice in the permafrost melts, the ground surface settles differentially resulting in thermokarst terrain (pits, gullies). Windblown snow fills the thermokarst depressions causing further warming and thawing of the underlying permafrost — a positive feedback effect that enhances permafrost degradation. Thermokarst‐induced changes in relief alter the near‐surface hydrology and ecological processes. Changes in vegetation included differential tussock growth and mortality and a shift in moss species abundance and relative productivity, depending on microtopographic position created by the thermokarst terrain. Water redistribution towards thermokarst depressions caused adjacent higher areas to become drier and resulted in increased moss mortality and shrub abundance. Copyright © 2009 John Wiley & Sons, Ltd.

Geologically recent gully–polygon relationships on Mars: Insights from the Antarctic Dry Valleys on the roles of permafrost, microclimates, and water sources for surface flow

We describe the morphology and spatial relationships between composite-wedge polygons and Mars-like gullies (consisting of alcoves, channels, and fans) in the hyper-arid Antarctic Dry Valleys (ADV), as a basis for understanding possible origins for martian gullies that also occur in association with polygonally patterned ground. Gullies in the ADV arise in part from the melting of atmospherically-derived, wind-blown snow trapped in polygon troughs. Snowmelt that yields surface flow can occur during peak southern hemisphere summer daytime insolation conditions. Ice-cemented permafrost provides an impermeable substrate over which meltwater flows, but does not significantly contribute to meltwater generation. Relationships between contraction crack polygons and sedimentary fans at the distal ends of gullies show deposition of fan material in polygon troughs, and dissection of fans by expanding polygon troughs. These observations suggest the continuous presence of meters-thick ice-cemented permafrost beneath ADV gullies. We document strong morphological similarities between gullies and polygons on Mars and those observed in the ADV Inland Mixed microclimate zone. On the basis of this morphological comparison, we propose an analogous, top–down melting model for the initiation and evolution of martian gullies that occur on polygonally-patterned, mantled surfaces.

A snow sensor experiment in Dronning Maud Land, Antarctica

AbstractIn January 2000 nine snow sensors were deployed in Dronning Maud Land, Antarctica, along a 355 km transect from Kvitkuven near the shelf edge via the Finnish research station, Aboa, to the Amundsenisen plateau. The purpose was to test a sensor system for spatio-temporal variations in temperature across the snow–air interface and snow accumulation/ablation, which includes atmospheric net balance and migrating snow dunes. In the dry snow conditions, environmental static electricity interfered with data transfer; several sensors were disabled early, while the longest record reached 6 months. Along the main transect, the year 2000 mass balance ranged from 52 to 221 mm w.e., largely following spatial patterns seen by other researchers. The level increased toward the edge of the ice sheet; unloading of drifting snow as the slope flattens, rather than increased snowfall as previously thought, may be responsible for this. At the Högisen ice dome site the mass balance was 897 mm w.e., possibly due to unloading of wind-blown snow, as katabatic winds are locally forced uphill. This mechanism is important to maintain such topographic features along the Antarctic ice sheet margin. Major precipitation events occurred at 3–5 week intervals and much of the precipitation fell before mid-June. The daily signal in temperature disappeared after the autumn equinox, then the spectrum displayed a broad peak at synoptic frequencies. Potential temperature decreased towards the shelf edge, displaying a pattern consistent with strong inversions and suggesting that strong evaporative cooling is associated with the katabatic winds.

Response of a montenegro glacier to extreme summer heatwaves in 2003 and 2007

.The Debeli Namet glacier in the Durmitor massif, Montenegro, is one of the lowest altitude glaciers (2050–2300 m) at this latitude (42–44°N) in the northern hemisphere. The glacier survives well below the climatological equilibrium line altitude because of substantial inputs from avalanching and windblown snow. The glacier survived two of the hottest summers on record in 2003 and 2007, although it experienced significant retreat. However, during the intervening years (2004–2006) the glacier increased in size and advanced, forming a new frontal moraine. This rapid advance was primarily in response to much cooler summer temperatures, close to or cooler than average, and a marked increase in winter precipitation. The rapid growth and decay of the Debeli Namet glacier in response to inter‐annual climate variability highlights the sensitivity of small cirque glaciers to short‐term climate change.

Spruce trees from a melting ice patch: evidence for Holocene climatic change in the Colorado Rocky Mountains, USA

In September, 2006, we found the remains of timber-sized spruce trees ( Picea engelmannii) on the floors of melting ice patches at altitudes of 3465—3480 m in the Mummy Range of north-central Colorado. The ice patches occupy northeast-facing recesses in which windblown snow, scoured from a tundra upland to the southwest, accumulates deeply. We hypothesize that the upland was timbered during the early to middle Holocene. Dense forest vegetation intercepted snow, preventing it from blowing to the recesses, and allowing trees to become established there. Neoglacial cooling led to gradual deforestation of the upland, renewed transport and deposition of snow by wind, and death of the ice-patch trees. Radiocarbon dates show that the trees died between 3860 ± 15 and 3780 ± 20 14C yr BP ( c. 4200 cal. yr BP). The trunks show decay similar to that of historic log structures built above timberline during the late nineteenth and early twentieth centuries, suggesting that they have been protected by ice for all but a small portion of the past 4200 years. A series of warm summers and dry winters led to their recent emergence. The study illustrates the importance of monitoring glaciers and ice patches for floral, faunal and archaeological remains whenever severe melting occurs.

Snow recurrence sets the depth of dry permafrost at high elevations in the McMurdo Dry Valleys of Antarctica

AbstractDry permafrost on Earth is unique to the Antarctic and is found in the upper elevations of the McMurdo Dry Valleys. Despite its widespread presence in the Dry Valleys, the factors that control the distribution of dry permafrost and the ice-cemented ground below it are poorly understood. Here I show, by a combination of theoretical analysis and field observations, that the recurrence of snow can explain the depth of dry permafrost and the location of ice-cemented ground in Antarctica. For data from Linnaeus Terrace at 1600–1650 m elevation in Upper Wright Valley a recurrence intervals of about two years explains the presence of ground ice at 25 cm depth, under 12.5 cm of dry permafrost. Snow recurrence periods longer than 10 years would create only dry permafrost at this site. The snow gradient in University Valley resulting from the windblown snow from the polar plateau creates a corresponding gradient in the depth to ice-cemented ground. On the floor of Beacon Valley, the presence of dry permafrost without underlying ice-cemented ground indicates snow recurrence intervals of more than 10 years and implies that the ancient massive ice in this valley is not stable. Snow recurrence may also set the depth to ground ice on Mars.

The role of thermal contraction crack polygons in cold-desert fluvial systems

AbstractThermal contraction crack polygons modify the generation, transport, and storage of water in Wright Valley gullies. Water generation is contributed to by trapping of windblown snow in polygon troughs. Water transport is modified by changes to the ice-cement table and active layer topography caused by polygon trough formation. Water storage is modified by sediment grain-size distribution within polygons in gully distal hyporheic zones. Patterned ground morphological variation can serve as an indicator of fluvial modification, ranging from nearly unmodified composite-wedge polygons to polygons forming in association with gully channels. Thermal contraction crack polygons may also constrain the gully formation sequence, suggesting the continuous presence of permafrost beneath the Wright Valley gullies during the entire period of gully emplacement. This analysis provides a framework for understanding the relationships between polygons and gullies observed on Mars. If comparable stratigraphic relationships can be documented, the presence of an analogous impermeable ice-cemented layer beneath the gullies can be inferred, suggesting an atmospheric source for Martian gully-carving fluids.

High-resolution numerical simulation of Younger Dryas glaciation in Scotland

We use a 500 m resolution three-dimensional thermomechanical ice-sheet model forced by a scaled GRIP temperature pattern to retrodict the extent of glaciers during the Younger Dryas episode in Scotland. Using empirical data from sources spanning half a century we systematically perturb temperature depression, precipitation distribution, and the amount of basal sliding to identify the parameter space that most closely reproduces the glacier margins identified from field investigations. Arithmetic comparison of predicted ice cover with empirical glacier extent enables mismatch to be quantified and an ‘optimum-fit’ timeslice to be identified. This ‘best-fit’ scenario occurs with a maximum mean annual temperature depression from present of 10 ∘ C and steep eastward and northward gradients imposed on a modern precipitation distribution, coupled with restricted basal sliding. Even small deviations around these values produce considerably less well-fitting glacier configurations, suggesting that only a narrow range of optimal parameterisation exists. Mismatch between modelled and empirically reconstructed glacier extents occurs as a consequence of local conditions not accommodated by the model, such as wind-blown snow accumulation and lake (loch) bathymetry, and where geological evidence is equivocal. At the domain scale, however, our simulation suggests that inception of Scottish glaciers occurs rapidly, and leads to a coherent ice cap within 400 years of initial climatic cooling. According to our model, the ice cap begins to decay relatively early in the stadial, probably as a result of increasing aridity leading to net thinning and recession of many of its margins, with final and catastrophic collapse of the ice cap occurring largely within a century.

Atmospheric transport and concentration of diatoms in surficial and glacial sediments of the Allan Hills, Transantarctic Mountains

A global climate up to 3 °C warmer than present around 3 Ma is widely accepted, but the response of the Antarctic ice sheets at that time is still debated. The presence of rare Pliocene marine diatoms in the Sirius Group tillites of the Transantarctic Mountains has led some to infer that the warming caused a collapse of the ice sheet, exposing the Antarctic interior to inland seas. Here we document an alternative source for the Sirius Group diatoms through atmospheric transport onto the surface of the East Antarctic Ice Sheet to be carried downslope by katabatic winds flowing over the Allan Hills, one of many nunataks that border the East Antarctic Ice Sheet. Evidence comes from diatom remains recovered in windtraps, surficial sediments and Sirius Group deposits themselves. The abundance and preservation of the diatoms being actively transported and trapped in the Allan Hills far exceeds those observed in the Sirius Group. Melting of wind-blown snow during summer provides a mechanism to transport and concentrate these diatoms into “diatom-rich” layers. This mechanism, along with the extreme sparseness and sporadic occurrence of diatoms previously documented in the Sirius Group, suggests a more likely scenario in which diatoms from the atmosphere contaminated tillites that had been deposited beneath wet-based glaciers in much older and warmer times. In this scenario, Pliocene marine diatoms may have been injected into the troposphere by meteorite impact, or picked up from exposed land around the Ross Embayment following the disappearance of the Ross Ice Shelf in Pliocene times. We conclude that the Pliocene age assigned to the Sirius Group on the basis of rare diatoms should be regarded as unproven, and the inferred collapse of the East Antarctic Ice Sheet at that time unlikely.

European High Mountain (Alpine) Vegetation and its Suitability for Indicating Climate Change Impacts

European High Mountain (Alpine) Vegetation and its Suitability for Indicating Climate Change Impacts

Steering Errors May Result from Non-Rigid Transparent Optical Flow

Transparent, non-rigid optical flow can result from environmental factors (e.g., wind-blown snow) or technological factors (e.g., superposition of sensor imagery flow on the environmental flow viewed directly through the windscreen) and can produce systematic errors in judgments of the direction of heading and control of yaw. Here, we examined whether these systematic errors generalize to control of heading in a more realistic scenario, driving across a textured ground plane through falling snow. Simulated crosswinds caused the snow to move at varying angles (0-32°) relative to the simulated direction of translation. Participants were instructed to steer such that they maintained a straight path relative to the ground plane. For non-zero angles, a pattern of systematic steering errors was found that was consistent with the pattern of errors previously observed with judgments of heading. These results suggest that motion transparency occurring in more realistic simulations can introduce systematic errors in controlling vehicles.

Positive Feedback Between Tree Establishment and Patterns of Subalpine Forest Advancement, Glacier National Park, Montana, U.S.A.

The development and maintenance of several types of visually striking vegetation patterns are controlled by positive feedback between pattern and process. These patterns are particularly common at ecotones, where the influence of positive feedback may affect the position and dynamics of the boundary between the adjacent biotic communities. In this study, I use dendrochronology to examine the role of feedback between existing trees and the establishment and survival of seedlings in the advancement of linear, finger-like strips of subalpine forest in Glacier National Park, Montana. A general upslope, windward to leeward pattern of older trees followed by progressively younger trees was evident in all sample transects, although in some cases this pattern repeated several times along the length of a transect, with each repetition originating leeward of boulders. Overall advancement rates varied from 0.28 to 0.62 m yr−1. The oldest trees established in the early to mid-1700s, but establishment and advancement increased rapidly after 1850, and peaked in the early 1900s. In addition, almost all seedlings established within 5 m downwind of existing trees between 1700 and 1850, while establishment beyond this distance was common after 1850. These patterns suggest that existing trees facilitate leeward seedling establishment and survival, by depositing wind-blown snow. These seedlings in turn modify their leeward environment, thus allowing forest advancement in a linear pattern. Feedback was critical for the survival of seedlings before 1800, and strongly controlled advancement between about 1800 and 1850, but appears to have had little effect on establishment patterns since that time. The importance of feedback between pattern and process may change over time and space as a result of changes in climatic conditions or biotic surroundings.

Application of Snowfall and Wind Statistics to Snow Transport Modeling for Snowdrift Control in Minnesota

Abstract Models were utilized to determine the snow accumulation season (SAS) and to quantify windblown snow for the purpose of snowdrift control for locations in Minnesota. The models require mean monthly temperature, snowfall, density of snow, and wind frequency distribution statistics. Temperature and precipitation data were obtained from local cooperative observing sites, and wind data came from Automated Surface Observing System (ASOS)/Automated Weather Observing System (AWOS) sites in the region. The temperature-based algorithm used to define the SAS reveals a geographic variability in the starting and ending dates of the season, which is determined by latitude and elevation. Mean seasonal snowfall shows a geographic distribution that is affected by topography and proximity to Lake Superior. Mean snowfall density also exhibits variability, with lower-density snow events displaced to higher-latitude positions. Seasonal wind frequencies show a strong bimodal distribution with peaks from the northwest and southeast vector direction, with an exception for locations in close proximity to the Lake Superior shoreline. In addition, for western and south-central Minnesota there is a considerably higher frequency of wind speeds above the mean snow transport threshold of 7 m s−1. As such, this area is more conducive to higher potential snow transport totals. Snow relocation coefficients in this area are in the range of 0.4–0.9, and, according to the empirical models used in this analysis, this range implies that actual snow transport is 40%–90% of the total potential in south-central and western areas of the state.

Vegetation and Topographic Control of Wind-Blown Snow Distributions in Distributed and Aggregated Simulations for an Arctic Tundra Basin

A finescale model of blowing snow is used to simulate the characteristics of snow cover in a low-Arctic catchment with moderate topography and partial shrub cover. The influence of changing shrub characteristics is investigated by performing a sequence of simulations with varying shrub heights and coverage. Increasing shrub height gives an increase in snow depth within the shrub-covered areas, up to a limit determined by the supply of falling and blowing snow, but increasing shrub coverage gives a decrease in snow depths within shrubs as the supply of blowing snow imported from open areas is reduced. A simulation of snow redistribution over the existing topography without any shrub cover gives much greater accumulations of snow on slopes in the lee of the prevailing wind than on windward slopes; in contrast, shrubs are able to trap snow on both lee and windward slopes. A spatially aggregated, or tiled, model is developed in which snow is relocated by wind transport from sparsely vegetated tiles to more densely vegetated tiles. The vegetation distribution is not specified, but the simulation is parameterized using average fetch lengths along the major transport axis. The aggregated model is found to be capable of matching the average snow accumulation in shrub and open areas predicted by the distributed model reasonably well but with much less computational cost.

Modeling Snow-Cover Heterogeneity over Complex Arctic Terrain for Regional and Global Climate Models*

The small-scale (10 to 100 m) and local-scale (100 m to 10 km) effects of topography (elevation, slope, and aspect) and snow redistribution by wind on the evolution of the snowmelt are investigated. The chosen study area is the 142 km2 Upper Kuparuk River basin located on the North Slope of Alaska. Two land surface models (LSMs) designed for regional and global climate studies apply different techniques to resolve these additional processes and features and their effects on snowmelt. One model uses a distributed approach to simulate explicitly the effects of topography on snowmelt at a 131-m resolution across the entire Upper Kuparuk watershed. By contrast, the other LSM employs a simple parameterization to implicitly resolve the effects of wind-blown snow on the hydrology of the Upper Kuparuk basin. In both cases, the incorporation of these local- and small-scale features within the LSMs leads to significant heterogeneity in the 1997 end-of-winter spatial distribution of snow cover in the Upper Kuparuk watershed. It is shown that the consideration of subgrid-scale snow-cover heterogeneity over complex Arctic terrain provides a better representation of the end-of-winter snow water equivalent, an improved simulation of the timing and amount of water discharge of the Upper Kuparuk River, and an alteration of other surface energy and water budget components.

Developments in the MOSES 2 land-surface model for PILPS 2e

Improved representations of snow processes in vegetation canopies and snow hydrology are implemented in the Met Office Surface Exchange Scheme 2 (MOSES 2) land-surface model. Snow falling on forests is partitioned between interception and throughfall; the intercepted snow is removed by sublimation, melt and unloading. A reduction in sublimation of wind-blown snow through trapping by shrubs is simply represented by reducing the scalar roughness length for shrubs with snow cover. Melt water may be retained and refrozen within snow packs. By reducing the amount of snow lost through sublimation and delaying the runoff of melt water, these modifications are found to improve the simulations of runoff for two Swedish catchments used in the PILPS 2e intercomparison project.

A theoretical approach to glacier equilibrium-line altitudes using meteorological data and glacier mass-balance records from southern Norway

Based on a close exponential relationship between mean ablation-season temperature and winter precipitation at the equilibrium-line altitude (ELA) of 10 Norwegian glaciers, three equations are derived. The first equation enables calculation of the minimum altitude of areas climatically suited for glacier formation, and is termed the altitude of instantaneous glacierization (AIG). Equation (2) is derived based on the ‘principle of terrain adaptation’, enabling quantification of the glacial buildup sensitivity (GBS) in presently non-glaciated areas. The theoretical climatic temperature-precipitation ELA (CTP-ELA) in presently non-glaciated areas is calculated in equation three by combining GBS with terrain altitude. Mass-balance records from four modern glaciers (Ålfotbreen, Nigardsbreen, Storbreen and GrÅsubreen) situated in maritime to continental climate regimes in southern Norway are used to test these equations. Correlation between AIG and net balance measurements (bn) yielded correlation coefficients of r=-0.80 to r=-0.84. Calculated AIGs correspond well with observed ELAs on Ålfotbreen, Nigardsbreen and GrÅsubreen, while it deviates from the observed ELA on Storbreen; the latter is probably due to leeward accumulation of wind-blown snow on this cirque glacier. Based on this approach, regional representative climatic ELAs can be calculated for non-glaciated areas with instrumental records of ablation-season temperature and winter precipitation.

Morphology and significance of some Loch Lomond Stadial moraines in the south-central Lake District, England

At three sites (Widdygill Foot, Blindtarn Moss and Cotra) in the south-central Lake District, moraine ridges and mounds have been mapped. It is inferred, on the basis of their positions within the Lake District mountains and their gross morphology, that the moraines were constructed by glaciers of Loch Lomond Stadial (LLS) age (12.9–11.5 cal. ka BP) and therefore represent additions to the growing body of evidence for a more extensive LLS glaciation of the Lake District than previously envisaged. Map-based reconstructions of the three glaciers indicate their surface areas were similar to many of the previously recognized LLS ice masses but their equilibrium line altitudes (283–340 m OD) were towards the lower end of the established range (284–785 m OD). Site aspects and the nature of surrounding terrain suggest that glacier nourishment may not have been the result of consistent site factors, particularly with respect to the directions from which wind-blown snow could have made significant contributions to glacier mass. The pattern of moraines at each site indicates that the glaciers underwent active retreat over distances of 0.2–0.8 km during their withdrawal.

CHARACTERIZATION OF ALPINE SOILS, EAGLE CAP, WALLOWA MOUNTAINS, OREGON

This study examines alpine soil development along a toposequence on Eagle Cap, Wallowa Mountains, northeast Oregon. Soils studied are from Wind Blown (WB) and Minimal Snow Cover (MSC) sites in the Ridge-Top Tundra geomorphic province. The soils are predominantly loamy sands, and exhibit minimal structural development. Soil pH ranges from 6.5 to 7.3 increasing with depth, and organic carbon ranges from 3.9% in the A horizon to 0.8% in the C horizon. The soils display significant input from Cascade volcanic ash infall and eolian influx from the weathered marble nearby. It is postulated that the ash content in the soils originates from Mazama Ash deposits. Though Eagle Cap soils have developed for the most part on granodiorite, the strong influence of the volcanic ash on pedogenesis leads to a preliminary classification of Andisols, most probably Typic and Lithic Haplocryands. [Key words: Alpine soils, Andisols, Wallowa Mountains.]

Ice-shelf dynamics near the front of the Filchner—Ronne Ice Shelf, Antarctica, revealed by SAR interferometry

AbstractFifteen synthetic aperture radar (SAR) images of the Ronne Ice Shelf (also referred to as the Filchner-Ronne Ice Shelf), Antarctica, obtained by the European remote-sensing satellites ERS-1 and -2, are used to study ice-shelf dynamics near two ends of the iceberg-calving front. Interferograms constructed from these SAR images are used to resolve the ice-shelf displacement along several directions in response to both ocean tide and long-term creep flow. Tidal motion is separated from creep flow using differential interferometry, i.e. two or more interferograms in which fringe patterns common to all are predominantly associated with creep flow. Creep-flow velocities thus determined compare well with prior ice-shelf velocity surveys. Using these data, we studied the influence of large-scale rifts, ice rises and coastal separation on the ice-shelf flow. Many of the large rifts that appear to form the boundaries where tabular icebergs may eventually detach from the ice shelf are filled with a melange of sea ice, ice-shelf debris and wind-blown snow. The interferograms show that this melange tends to deform coherently in response to the ice-shelf flow and has sufficient strength to trap large tabular ice-shelf fragments for several decades before the fragments eventually become icebergs. In many instances, the motion of the tabular fragments is a rigid-body rotation about a vertical axis that is driven by velocity shear within the melange. Tfhe mechanical role of the rift-filling melange may be to bind tabular ice-shelf fragments to the main ice shelf before they calve. This suggests two possible mechanisms by which climate could influence tabular iceberg calving. First, spatial gradients in oceanic and atmospheric temperature may determine where the melange melts and, thus, the location of the iceberg-caking margin. Second, melting or weakening of ice melange as a consequence of climate change could trigger a sudden or widespread release of tabular icebergs and lead to rapid ice-shelf disintegration.