Sublimation Losses Research Articles

Slow Release of Menthol Using Sorbents Developed from Microwave Graphene Oxide

Menthol is a key ingredient in many of the traditional Thai aroma products such as potpourri and herbal air freshener. However, it suffers from the rapid evaporation and sublimation loss. In this work, microwave graphene oxide (mGO) has been prepared as sorbent and tested for the slow release of menthol. Menthol was loaded into microwave graphene oxide at loading ratios of 1:0.5 and 1:1. The release performance of the mGO as compared to traditional essential oil reed diffuser and the pure menthol was studied by monitoring the menthol weight loss at the temperature of 80°C until all of the menthol evaporated using thermogravimetric analysis. It was found that mGO can significantly slow down the menthol release rate compared to that of the pure menthol by up to eight times slower. The interaction and adsorption mechanism of the menthol-loaded microwave graphene oxide was also studied using Fourier Transform Infrared Spectroscopy (FTIR) which indicates that menthol adsorbs strongly onto the mGO leading to the slow release rate.

Long-lived contrails and convective cirrus above the tropical tropopause

Abstract. This study has two objectives: (1) it characterizes contrails at very low temperatures and (2) it discusses convective cirrus in which the contrails occurred. (1) Long-lived contrails and cirrus from overshooting convection are investigated above the tropical tropopause at low temperatures down to −88 °C from measurements with the Russian high-altitude research aircraft M-55 Geophysica, as well as related observations during the SCOUT-O3 field experiment near Darwin, Australia, in 2005. A contrail was observed to persist below ice saturation at low temperatures and low turbulence in the stratosphere for nearly 1 h. The contrail occurred downwind of the decaying convective system Hector of 16 November 2005. The upper part of the contrail formed at 19 km altitude in the tropical lower stratosphere at ∼ 60 % relative humidity over ice at −82 °C. The ∼ 1 h lifetime is explained by engine water emissions, slightly enhanced humidity from Hector, low temperature, low turbulence, and possibly nitric acid hydrate formation. The long persistence suggests large contrail coverage in case of a potential future increase of air traffic in the lower stratosphere. (2) Cirrus observed above the strongly convective Hector cloud on 30 November 2005 was previously interpreted as cirrus from overshooting convection. Here we show that parts of the cirrus were caused by contrails or are mixtures of convective and contrail cirrus. The in situ data together with data from an upward-looking lidar on the German research aircraft Falcon, the CPOL radar near Darwin, and NOAA-AVHRR satellites provide a sufficiently complete picture to distinguish between contrail and convective cirrus parts. Plume positions are estimated based on measured or analyzed wind and parameterized wake vortex descent. Most of the non-volatile aerosol measured over Hector is traceable to aircraft emissions. Exhaust emission indices are derived from a self-match experiment of the Geophysica in the polar stratosphere in 2010. The number of ice particles in the contrails is less than 1 % of the number of non-volatile aerosol particles, possibly because of sublimation losses and undetected very small ice particles. The radar data show that the ice water content in convective overshoots is far higher than measured along the flight path. These findings add insight into overshooting convection and are of relevance with respect to hydration of the lower stratosphere.

Regional surface morphology of comet 67P/Churyumov-Gerasimenko from Rosetta/OSIRIS images

The OSIRIS camera onboard the Rosetta spacecraft has been acquiring images of the comet 67P/Churyumov-Gerasimenko (67P/C-G)’s nucleus at spatial resolutions down to ~0.17 m/px ever since Aug 2014. These images have yielded unprecedented insight into the morphological diversity of the comet’s surface. This paper presents an overview of the regional morphology of comet 67P/C-G. Methods. We used the images that were acquired at orbits ~20–30 km from the center of the comet to distinguish different regions on the surface and introduce the basic regional nomenclature adopted by all papers in this issue that address the comet’s morphology and surface processes. We used anaglyphs to detect subtle regional and topographical boundaries and images from close orbit (~10 km from the comet’s center) to investigate the fine texture of the surface. Results. Nineteen regions have currently been defined on the nucleus based on morphological and/or structural boundaries, and they can be grouped into distinctive region types. Consolidated, fractured regions are the most common region type. Some of these regions enclose smooth units that appear to settle in gravitational sinks or topographically low areas. Both comet lobes have a significant portion of their surface covered by a dusty coating that appears to be recently placed and shows signs of mobilization by aeolian- like processes. The dusty coatings cover most of the regions on the surface but are notably absent from a couple of irregular large depressions that show sharp contacts with their surroundings and talus-like deposits in their interiors, which suggests that short- term explosive activity may play a significant role in shaping the comet’s surface in addition to long-term sublimation loss. Finally, the presence of layered brittle units showing signs of mechanical failure predominantly in one of the comet’s lobes can indicate a compositional heterogeneity between the two lobes.

Modeling the effects of martian surface frost on ice table depth

Ground ice has been observed in small fresh craters in the vicinity of the Viking 2 lander site (48°N, 134°E). To explain these observations, current models for ground ice invoke levels of atmospheric water of 20 precipitable micrometers – higher than observations. However, surface frost has been observed at the Viking 2 site and surface water frost and snow have been shown to have a stabilizing effect on Antarctic subsurface ice. A snow or frost cover provides a source of humidity that should reduce the water vapor gradient and hence retard the sublimation loss from subsurface ice. We have modeled this effect for the Viking 2 landing site with combined ground ice and surface frost models. Our model is driven by atmospheric output fields from the NASA Ames Mars General Circulation Model (MGCM). Our modeling results show that the inclusion of a thin seasonal frost layer, present for a duration similar to that observed by the Viking Lander 2, produces ice table depths that are significantly shallower than a model that omits surface frost. When a maximum frost albedo of 0.35 was permitted, seasonal frost is present in our model from Ls=182° to Ls=16°, resulting in an ice table depth of 64cm – which is 24cm shallower than the frost-free scenario. The computed ice table depth is only slightly sensitive to the assumed maximum frost albedo or thickness in the model.

Snowpack sensitivity to perturbed climate in a cool mid‐latitude mountain catchment

AbstractThere is great interest in ascertaining the degree of climate change necessary to induce substantial changes in snow accumulation and ablation processes in mountain headwater catchments. Therefore, the response of mountain snow hydrology to changes in air temperature and precipitation was examined by simulating a perturbed climate in Reynolds Mountain East (RME), a headwater catchment with a cool mountain climate in Idaho, USA. The cold regions hydrological model was used to calculate snow accumulation, wind redistribution by blowing snow, interception by forest canopies, sublimation and melt for 25 seasons in RME. The uncalibrated simulations of the highly redistributed snow water equivalent compared well to measurements. Results showed that with concomitant occurrence of warming (5 °C) and precipitation change (±20%) in RME, the peak seasonal snow accumulation decreased by 84–90%, snowmelt decreased 51–79%, rainfall to total precipitation ratio increased from 30% to 78%, and overwinter blowing snow transport and sublimation losses from intercepted snow, the snow surface and blowing snow decreased dramatically. Warming causes an increase in inter‐water year snowcover variability but a decrease in spatial snow accumulation variability. When warming exceeded 1 °C and a precipitation increased by less than 20%, the peak snow accumulation declined dramatically. The results contrast with those from further north along the North American Cordillera in Yukon, Canada, where the impacts of similar warming on alpine snow can be partly compensated for by concomitant increases in precipitation of less than 20%. Copyright © 2015 John Wiley & Sons, Ltd.

Snowpack-climate manipulation using infrared heaters in subalpine forests of the Southern Rocky Mountains, USA

Effects of infrared heaters on snow accumulation, snowmelt, and snow–atmosphere energy exchange were examined at Niwot Ridge, Colorado (CO) and compared to a naturally warmer, but otherwise similar subalpine site in the Valles Caldera National Preserve, New Mexico (NM). Observed snow accumulation was 30% lower on average and snow melted out 16 days earlier in the heated plots compared to the controls. Soil temperature during snowmelt was 3°C greater on average and soil moisture was 4% lower on average in heated plots compared to controls. In NM, snow accumulation was 23% lower, snow melted 23 days earlier, soil temperature was 0.6°C greater, and soil moisture was 13% lower on average relative to CO controls. In order to estimate differences in energy and mass balance fluxes at the snow–atmosphere interface in control versus warmer plots, the 1-D, physically based snowmelt model, SNOWPACK, was used. Model results indicated that heaters alter radiative, turbulent and mass fluxes by amounts comparable to the differences between CO and NM fluxes. The proportion of the energy flux associated with latent heat exchange during snowmelt was 9–27% of the total energy flux in heated models and 19–22% of NM models compared to 3–7% in control models. Thus, sublimation loss to the atmosphere was greater in both experimentally and naturally warmer cases relative to the control case. We conclude that IR heaters can provide alterations to the timing and magnitude of snow accumulation and snowmelt consistent with conditions observed at a warmer analog site and with climate and hydrology model projections. Impacts of IR heating on energy partitioning and sublimation should be considered when designing manipulations of the snowpack, as reductions in snowmelt water may alter biological or ecological processes.

Development and Application of Improved Double Layer Snow-Melting Model in Changing Environment

Climate change is a hot issue on the current time and snow melting process in alpine areas has be affected on the background of climate change, so it is necessary to study snow melting process especially the snowmelt model. In view of the shortcomings of the degree-day model (DDM), the double layer snow-melt model (DSMM) is improved and developed based on the original theory. Then the simulation of the snowmelt process of the upper reaches of Lancang-Mekong River is performed by the improved double layer snow-melt model (IDSMM) and DDM respectively, the simulation results are analyzed in view of model theory, snowmelt critical control conditions, the effects of the simulation and working conditions in the changing environment. The results show that IDSMM based on the energy and mass balance is superior to DDM in the snowmelt physics mechanism, and it not only can simulate the snow melting process, but also can simulate many physical processes, such as the canopy interception of snowfall, vaporization and sublimation loss in evaporation, the second precipitation from canopy surface, the process of snowmelt water freezing again and so on. The simulation results of snowmelt process is more tally with the actual situation and it can provide a reference to the research of snow and ice hydrology and the whole water cycle in a changing environment.

THE LUNAR THERMAL ICE PUMP

It has long been suggested that water ice can exist in extremely cold regions near the lunar poles, where sublimation loss is negligible. The geographic distribution of H-bearing regolith shows only a partial or ambiguous correlation with permanently shadowed areas, thus suggesting that another mechanism may contribute to locally enhancing water concentrations. We show that under suitable conditions, water molecules can be pumped down into the regolith by day-night temperature cycles, leading to an enrichment of H2O in excess of the surface concentration. Ideal conditions for pumping are estimated and found to occur where the mean surface temperature is below 105 K and the peak surface temperature is above 120 K. These conditions complement those of the classical cold traps that are roughly defined by peak temperatures lower than 120 K. On the present-day Moon, an estimated 0.8% of the global surface area experiences such temperature variations. Typically, pumping occurs on pole-facing slopes in small areas, but within a few degrees of each pole the equator-facing slopes are preferred. Although pumping of water molecules is expected over cumulatively large areas, the absolute yield of this pump is low; at best, a few percent of the H2O delivered to the surface could have accumulated in the near-surface layer in this way. The amount of ice increases with vapor diffusivity and is thus higher in the regolith with large pore spaces.

Simulating cold regions hydrological processes using a modular model in the west of China

The Cold Regions Hydrological Model platform (CRHM), a flexible object-oriented modeling system, was devised to simulate cold regions hydrological processes and predict streamflow by its capability to compile cold regions process modules into purpose-built models. In this study, the cold regions hydrological processes of two basins in western China were evaluated using CRHM models: Binggou basin, a high alpine basin where runoff is mainly caused by snowmelt, and Zuomaokong basin, a steppe basin where the runoff is strongly affected by soil freezing/thawing. The flexibility and modular structure of CRHM permitted model structural intercomparison and process falsification within the same model framework to evaluate the importance of snow energy balance, blowing snow and frozen soil infiltration processes to successful modeling in the cold regions of western China. Snow accumulation and ablation processes were evaluated at Binggou basin by testing and comparing similar models that contained different levels of complexity of snow redistribution and ablation modules. The comparison of simulated snow water equivalent with observations shows that the snow accumulation/ablation processes were simulated much better using an uncalibrated, physically based energy balance snowmelt model rather than with a calibrated temperature index snowmelt model. Simulated seasonal snow sublimation loss was 138 mm water equivalent in the alpine region of Binggou basin, which accounts for 47 % of 291 mm water equivalent of snowfall, and half of this sublimation loss is attributed to 70 mm water equivalent of sublimation from blowing snow particles. Further comparison of simulated results through falsification of different snow processes reveals that estimating blowing snow transport processes and sublimation loss is vital for accurate snowmelt runoff calculations in this region. The model structure with the energy balance snowmelt and blowing snow components performed well in reproducing the measured streamflow using minimal calibration, with R2 of 0.83 and NSE of 0.76. The influence of frozen soil and its thaw on runoff generation was investigated at Zuomaokong basin by comparing streamflow simulated by similar CRHM models with and without an infiltration to frozen soil algorithm. The comparison of simulated streamflow with observation shows that the model which included an algorithm describing frozen soil infiltration simulated the main runoff events for the spring thawing period better than that which used an unfrozen infiltration routine, with R2 of 0.87 and NSE of 0.79. Overall, the test results for the two basins show that hydrological models that use appropriate cold regions algorithms and a flexible spatial structure can predict cold regions hydrological processes and streamflow with minimal calibration and can even perform better than more heavily calibrated models in this region. Given that CRHM and most of its algorithms were developed in western Canada, this is encouraging for predicting hydrology in ungauged cold region basins around the world.

Estimation of Snowmelt Infiltration into Frozen Ground and Snowmelt Runoff in the Mogot Experimental Watershed in East Siberia

Understanding how spring runoff is generated in East Siberia during the spring thaw is important to predicting river flows. To evaluate the snowmelt runoff generated, a simple runoff model was developed. The model involves processes of water and energy balance within the snowpack and energy balance within soil, snowmelt infiltration into the frozen ground, and surface runoff. The model reproduced inter-seasonal and seasonal variations of snow depth, active layer depth within soil, and snowmelt runoff. Snowmelt infiltration into frozen ground within the upper 20 cm of soil was also reproduced by the model. Thus, we believe the model can simulate snowmelt infiltration and surface runoff in the Mogot experiment watershed. The model suggested that the inter-annual variation in infiltration determined the amount of spring runoff. The amount of infiltration during thaws exceeded the discharge; the range was from 20 to 60 mm and the percentage of infiltration to melt water was 44% to 60%. Therefore, infiltration into the frozen ground strongly determined snowmelt runoff. In addition, ongoing climatic change can increase snowmelt runoff, because of less sublimation loss and snowmelt infiltration into the frozen ground.

Sensitivity of snowmelt hydrology in Marmot Creek, Alberta, to forest cover disturbance

AbstractA model including slope effects on snow redistribution, interception and energetics was developed using the Cold Regions Hydrological Model platform, parameterized with minimal calibration and manipulated to simulate the impacts of forest disturbance on mountain hydrology. A total of 40 forest disturbance scenarios were compared with the current land cover for four simulation years. Disturbance scenarios ranged from the impact of pine beetle kill of lodgepole pine to clear‐cutting of north‐ or south‐facing slopes, forest fire and salvage logging. Pine beetle impacts were small in all cases with increases in snowmelt volume of less than 10% and streamflow volume of less than 2%. This small impact is attributed to the low and relatively dry elevations of lodgepole pine forests in the basin. Forest disturbances due to fire and clear‐cutting affected much larger areas and higher elevations of the basin and were generally more than twice as effective as pine beetle in increasing snowmelt or streamflow. For complete forest cover removal by burning and salvage logging, a 45% increase in snowmelt volume was simulated; however, this only translated into a 5% increase in spring and summer streamflow volume. Forest burning with the retention of standing burned trunks was the most effective forest cover treatment for increasing streamflow (up to 8%) because of its minimizing of winter snow sublimation losses from interception and blowing snow. However, increases in streamflow volumes were almost entirely due to reductions in intercepted snow sublimation with decreasing canopy coverage. Peak daily streamflow discharges responded more strongly to forest cover disturbance than did seasonal streamflow volumes, with increases of almost 25% in peak streamflow from the removal of forest canopy by fire and the retention of standing burned trunks. Peak flow was most effectively increased by forest removal on south‐facing slopes and level sites. Copyright © 2012 John Wiley & Sons, Ltd.

Estimating surface sublimation losses from snowpacks in a mountain catchment using eddy covariance and turbulent transfer calculations

AbstractSublimation is a critical component of the snow cover mass balance. Although sublimation can be directly measured using eddy covariance (EC), such measurements are relatively uncommon in complex mountainous environments. The EC measurements of surface snowpack sublimation from three consecutive winter seasons (2004, 2005 and 2006) at a wind‐exposed and wind‐sheltered site were analysed to characterise sublimation in mountainous terrain. During the 2006 snow season, snow surface and near‐surface air temperature, humidity and wind were also measured, permitting the calculation of sublimation rates and a comparison with EC measurements. This comparison showed that measured and simulated sublimation was very similar at the exposed site but less so at the sheltered site. Wind speeds at the exposed site were nearly four times than that at the sheltered site, and the exposed site yielded measured sublimation that was two times the magnitude of that at the sheltered site. The time variation of measured sublimation showed diurnal increases in the early afternoon and increased rates overall as the snow season progressed. Measured mean daily sublimation rates were 0.39 and 0.15 mm day−1 at the exposed and sheltered sites, respectively. At the exposed site, measured sublimation accounted for 16% and 41% of the maximum snow accumulation in 2006 and 2005, respectively. At the sheltered site, measured seasonal sublimation was approximately 4% in 2004 and 2006 and 8% in 2005 of the maximum snow water equivalent. Simulated sublimation was only available for 2006 and suggested smaller but comparable percentages to the sublimation estimated from observations. At the exposed site, a total of 42 mm sublimated for the snow season, which constituted 12% of the maximum accumulation. At the sheltered site, 17 mm (2.2% of maximum accumulation) was sublimated over the snow season. Copyright © 2011 John Wiley & Sons, Ltd.

Effects of shelterbelts on snow distribution and sublimation

On the Canadian Prairies and the northern US Great Plains, snow is an important component of annual precipitation, sometimes constituting over 40% of the total, although there is much annual and regional variability. Much of this snow is transported by wind, causing substantial sublimation losses, which are reduced by obstacles and topographic features on the landscape that reduce snow transport and trap snow. Agroforestry configurations trap snow and reduce the amount and distance of snow movement and, because of this, reduce the amount of moisture lost to sublimation. The planning of agroforestry measures should therefore take into account their effects on snow hydrology. In this study, the effects of shelterbelts on snow quantity and distribution are shown over multiple years, including a number of locations in Manitoba and Saskatchewan. Results show that snow transport reached equilibrium in 400 m or less (i.e., that sublimation rates were at their maximum beyond 400 m leeward of a shelterbelt). Also, in a paired landscape inventory, the landscape with shelterbelts had 29% more snow water equivalent (SWE) than the unsheltered landscape. Site-specific meteorological data was used in the Prairie Blowing Snow Model, now a component of the Cold Regions Hydrological Model, to calculate the effects of agroforestry configurations on snow water conservation. Modeled snow distribution agreed well with measured snow at Conquest, Saskatchewan, in the winter of 2009/2010. Using actual weather data for the same location for the period 1996–2011, the model calculated the annual sublimation from 200 m wide fields protected by shelterbelts to be up to 12.5 mm less than similar unsheltered fields.

Drifting snow sublimation: A high-resolution 3-D model with temperature and moisture feedbacks

The snow transport model of Alpine3D is augmented with a drifting snow sublimation routine. Contrary to other three-dimensional high-resolution snow transport models, Alpine3D now accounts for feedback mechanisms on the air temperature, humidity, and snow mass concentration in three dimensions. Results show that the negative feedbacks of sublimation on the snow mass concentration, temperature, and humidity are, in general, small but relevant on the slope scale. We analyzed the deposition on a leeward slope for simulations including sublimation and compared these to a reference simulation of the model without sublimation. Including sublimation, but neglecting sublimation feedbacks, leads to a reduction in deposition of approximately 12% on this slope. In a simulation including sublimation and its feedbacks, the reduction in snow deposition on the same slope was 10%. The feedbacks thus reduced the loss of snow due to sublimation by 2%. The sublimation process is therefore quite important for a leeward slope influenced by drifting snow. However, we also show that the spatial variability is large and that drifting snow sublimation will mainly affect small regions within a catchment. Averaged over our model domain (2.4 km(2)) in the Swiss Alps, drifting snow sublimation causes a reduction in deposition of 2.3% during a 43 h test period, which is comparable to the sublimation loss from the snow cover during the same time.

Modeling Snow–Canopy Processes on an Idealized Mountain

Abstract Snow interception in a coniferous forest canopy is an important hydrological feature, producing complex mass and energy exchanges with the surrounding atmosphere and the snowpack below. Subcanopy snowpack accumulation and ablation depends on the effects of canopy architecture on meteorological conditions and on interception storage by stems, branches, and needles. Mountain forests are primarily composed of evergreen conifer species that retain their needles throughout the year and hence intercept snow efficiently during winter. Canopy-intercepted snow can melt, fall to the ground, and/or sublimate into the air masses above and within the canopy. To improve the understanding of snow–canopy interception processes and the associated influences on the snowpack below, a series of model experiments using a detailed, physically based snow–canopy and snowpack evolution model [Alpine Multiscale Numerical Distributed Simulation Engine (AMUNDSEN)] driven with observed meteorological forcing was conducted. A cone-shaped idealized mountain covered with a geometrically regular pattern of coniferous forest stands and clearings was constructed. The model was applied for three winter seasons with different snowfall intensities and distributions. Results show the effects of snow–canopy processes and interactions on the pattern of ground snow cover, its duration, and the amount of meltwater release, in addition to showing under what conditions the protective effect of a forest canopy overbalances the reduced accumulation of snow on the ground. The simulations show considerable amounts of canopy-intercepted snowfall can sublimate, leading to reduced snow accumulation beneath the forest canopy. In addition, the canopy produces a shadowing effect beneath the trees that leads to reduced radiative energy reaching the ground, reduced below-canopy snowmelt rates, and increased snow-cover duration relative to nonforested areas. During snow-rich winters, the shadowing effect of the canopy dominates and snow lasts longer inside the forest than in the open, but during winters with little snow, snow sublimation losses dominate and snow lasts longer in the open areas than inside the forest. Because of the strong solar radiation influence on snowmelt rates, the details of these relationships vary for northern and southern radiation exposures and time of year. In early and high winter, the radiation protection effect of shadowing by the canopy is small. If little snow is available, an intermittent melt out of the snow cover inside the forest can occur. In late winter and spring, the shadowing effect becomes more efficient and snowmelt is delayed relative to nonforested areas.

Effects of orbital evolution on lunar ice stability

[1] Many regions near the lunar poles are currently cold enough that surface water ice would be stable against sublimation losses for billions of years. However, most of these environments are currently too cold to efficiently drive ice downward by thermal diffusion, leaving impact burial as the primary means of protection from surface loss processes. In this respect, most of the present near-surface thermal environments on the Moon may actually be quite poor traps for water ice. This was not always the case. Long-term orbital changes have dramatically altered the lunar polar thermal environment. We develop a simple model of the evolution of the lunar orbit and spin axis to examine the thermal environments available for volatile deposition and retention in the past. Our calculations show that some early lunar polar environments were in the right temperature regime to have collected subsurface ice if a supply were available. However, a high-obliquity period, which occurred when the Moon was at about half its present distance from the Earth, would either have driven this ice out into space or deep into the lunar subsurface. Since that time, as the lunar obliquity has slowly decreased to its present value, environments have undergone their own thermal evolution, and each of the current cold traps experienced a period when they were most efficient at thermally burying ice. We examine the thermal history of a lunar polar crater to provide a framework for examining other processes effecting volatiles in the Moon's near-surface cold traps.

Modeling of the Hydrological Cycle of a Forest River Basin and Hydrological Consequences of Forest Cutting

Physically based model of the hydrological cycle of a forest basin was developed. The model includes descrip- tion of processes of liquid water and snow interception by forest canopy, snow accumulation and melt, vertical soil mois- ture transfer and evapotranspiration, overland, subsurface and channel flow. The case-study has been carried out on the basis of experimental observations on the Valday water balance station, situated in the north-western part of Russia. The model has been calibrated and validated using 5-year hydrometeorological observations at the completely forested Tayoz- hny Creek experimental basin. Then the 17-years hydrometeorological observations were used to estimate the possible change of hydrological cycle of this basin after forest cutting. The numerical experiments have shown that the averaged snow water equivalent before snowmelt for the Tayozhny Creek basin can increase in case of forest cutting by 15%. The snow sublimation losses can decrease almost twice .The snowmelt rates after forest cutting turned out to be about 30% larger and the duration of snowmelt, on average, on 10 days longer. The simulated annual runoff from the Tayozhny Creek basin (mainly of snowmelt origin) averaged for 17 years appeared to be only about 10% higher than in case of for- est cutting. However, its seasonal distribution and water balance components changed essentially. The spring flood peak discharge from the forested basin appeared to be, on average, 50% lower, the spring floods started 5-7 days later and the flood recession turned out to be much longer. About 80% of the total runoff from the Tayozhny Creek basin is now sub- surface flow, while in case of deforestation overland flow may become dominant. The numerical experiments were carried out to estimate the sensitivity of the hydrological cycle to changes of leaf area index as a forest age characteristic. The es- timates obtained by simulation are quite consistent with the estimates obtained on the basis of experimental research.

On the importance of sublimation to an alpine snow mass balance in the Canadian Rocky Mountains

Abstract. A modelling study was undertaken to evaluate the contribution of sublimation to an alpine snow mass balance in the Canadian Rocky Mountains. Snow redistribution and sublimation by wind, snowpack sublimation and snowmelt were simulated for two winters over an alpine ridge transect located in the Canada Rocky Mountains. The resulting snowcover regimes were compared to those from manual snow surveys. Simulations were performed using physically based blowing snow (PBSM) and snowpack ablation (SNOBAL) models. A hydrological response unit (HRU)-based spatial discretization was used rather than a more computationally expensive fully-distributed one. The HRUs were set up to follow an aerodynamic sequence, whereby eroded snow was transported from windswept, upwind HRUs to drift accumulating, downwind HRUs. That snow redistribution by wind can be adequately simulated in computationally efficient HRUs over this ridge has important implications for representing snow transport in large-scale hydrology models and land surface schemes. Alpine snow sublimation losses, in particular blowing snow sublimation losses, were significant. Snow mass losses to sublimation as a percentage of cumulative snowfall were estimated to be 20–32% with the blowing snow sublimation loss amounting to 17–19% of cumulative snowfall. This estimate is considered to be a conservative estimate of the blowing snow sublimation loss in the Canadian Rocky Mountains because the study transect is located in the low alpine zone where the topography is more moderate than the high alpine zone and windflow separation was not observed. An examination of the suitability of PBSM's sublimation estimates in this environment and of the importance of estimating blowing snow sublimation on the simulated snow accumulation regime was conducted by omitting sublimation calculations. Snow accumulation in HRUs was overestimated by 30% when neglecting blowing snow sublimation calculations.

Simulation of snow accumulation and melt in needleleaf forest environments

Abstract. Drawing upon numerous field studies and modelling exercises of snow processes, the Cold Regions Hydrological Model (CRHM) was developed to simulate the four season hydrological cycle in cold regions. CRHM includes modules describing radiative, turbulent and conductive energy exchanges to snow in open and forest environments, as well as account for losses from canopy snow sublimation and rain evaporation. Due to the physical-basis and rigorous testing of each module, there is a minimal need for model calibration. To evaluate CRHM, simulations of snow accumulation and melt were compared to observations collected at paired forest and clearing sites of varying latitude, elevation, forest cover density, and climate. Overall, results show that CRHM is capable of characterising the variation in snow accumulation between forest and clearing sites, achieving a model efficiency of 0.51 for simulations at individual sites. Simulations of canopy sublimation losses slightly overestimated observed losses from a weighed cut tree, having a model efficiency of 0.41 for daily losses. Good model performance was demonstrated in simulating energy fluxes to snow at the clearings, but results were degraded from this under forest cover due to errors in simulating sub-canopy net longwave radiation. However, expressed as cumulative energy to snow over the winter, simulated values were 96% and 98% of that observed at the forest and clearing sites, respectively. Overall, the good representation of the substantial variations in mass and energy between forest and clearing sites suggests that CRHM may be useful as an analytical or predictive tool for snow processes in needleleaf forest environments.

Seasonal H2O and CO2 ice cycles at the Mars Phoenix landing site: 1. Prelanding CRISM and HiRISE observations

The condensation, evolution, and sublimation of seasonal water and carbon dioxide ices were characterized at the Mars Phoenix landing site from Martian northern midsummer to midspring (Ls ∼ 142° – Ls ∼ 60°) for the year prior to the Phoenix landing on 25 May 2008. Ice relative abundances and grain sizes were estimated using data from the Compact Reconnaissance Imaging Spectrometer for Mars and High Resolution Imaging Science Experiment aboard Mars Reconnaissance Orbiter and a nonlinear mixing model. Water ice first appeared at the Phoenix landing site during the afternoon in late summer (Ls ∼ 167°) as an optically thin layer on top of soil. CO2 ice appeared after the fall equinox. By late winter (Ls ∼ 344°), the site was covered by relatively pure CO2 ice (∼30 cm thick), with a small amount of ∼100 μm diameter water ice and soil. As spring progressed, CO2 ice grain sizes gradually decreased, a change interpreted to result from granulation during sublimation losses. The combined effect of CO2 sublimation and decreasing H2O ice grain sizes allowed H2O ice to dominate spectra during the spring and significantly brightened the surface. CO2 ice disappeared by early spring (Ls ∼ 34°) and H2O ice by midspring (Ls ∼ 59°). Spring defrosting was not uniform and occurred more rapidly over the centers of polygons and geomorphic units with relatively higher thermal inertia values.