Drifting Snow Sublimation Research Articles

A Drifting and Blowing Snow Scheme in the Weather Research and Forecasting Model

AbstractWind‐driven redistribution of surface snow is one of the key factors leading to heterogeneous accumulation of snow at small scales. Understanding the processes that lead to this heterogeneous accumulation is, therefore, of great importance to many glaciological and hydrological questions. High‐quality information on the wind field is necessary to realistically represent drifting snow. Here, we introduce a novel, intermediate‐complexity drifting and blowing snow module for the Weather Research and Forecasting (WRF) model that integrates seamlessly into the standard WRF infrastructure. The module also accounts for snow particle sublimation and considers the thermodynamic feedback on the atmospheric fields. In an idealized model environment the module was tested for physical consistency. Sensitivity experiments showed that drifting snow sublimation has on the one hand local effects on the erosion and deposition patterns and on the other hand non‐local effects on the larger‐scale atmosphere. The simple and computationally efficient implementation allows this module to be used for small‐scale and large‐scale simulations in polar and glaciated regions.

Sensitivity of the surface energy budget to drifting snow as simulated by MAR in coastal Adelie Land, Antarctica

Abstract. In order to understand the evolution of the climate of Antarctica, dominant processes that control surface and low-atmosphere meteorology need to be accurately captured in climate models. We used the regional climate model MAR (v3.11) at 10 km horizontal resolution, forced by ERA5 reanalysis over a 9-year period (2010–2018) to study the impact of drifting snow (designating here the wind-driven transport of snow particles below and above 2 m) on the near-surface atmosphere and surface in Adelie Land, East Antarctica. Two model runs were performed, one with and one without drifting snow, and compared to half-hourly in situ observations at D17, a coastal and windy location of Adelie Land. We show that sublimation of drifting-snow particles in the atmosphere drives the difference between model runs and is responsible for significant impacts on the near-surface atmosphere. By cooling the low atmosphere and increasing its relative humidity, drifting snow also reduces sensible and latent heat exchanges at the surface (−5.7 W m−2 on average). Moreover, large and dense drifting-snow layers act as near-surface cloud by interacting with incoming radiative fluxes, enhancing incoming longwave radiation and reducing incoming shortwave radiation in summer (net radiative forcing: 5.7 W m−2). Even if drifting snow modifies these processes involved in surface–atmosphere interactions, the total surface energy budget is only slightly modified by introducing drifting snow because of compensating effects in surface energy fluxes. The drifting-snow driven effects are not prominent near the surface but peak higher in the boundary layer (fourth vertical level, 12 m) where drifting-snow sublimation is the most pronounced. Accounting for drifting snow in MAR generally improves the comparison at D17, especially for the representation of relative humidity (mean bias reduced from −14.0 % to −0.7 %) and incoming longwave radiation (mean bias reduced from −20.4 W m−2 to −14.9 W m−2). Consequently, our results suggest that a detailed representation of drifting-snow processes is required in climate models to better capture the near-surface meteorology and surface–atmosphere interactions in coastal Adelie Land.

The Surface Energy Balance at Panda 1 Station, Princess Elizabeth Land: A Typical Katabatic Wind Region in East Antarctica

AbstractUsing automatic weather station and reanalysis data (ERA5) from 2011 at Panda‐1 Station, situated in the katabatic region of Princess Elizabeth Land, East Antarctica, the surface energy balance was calculated using a surface temperature iteration method, and the characteristics of each energy component were analyzed. Downward shortwave and longwave radiation were the two primary energy sources during summer days with seasonal means of 346 and 142 W m−2. The turbulent fluxes of sensible and latent heat flux represent smaller heat sources. In the annual mean, reflected shortwave radiation exceeds the upward longwave radiation with a seasonal average values of −287 W m−2. During winter, the shortwave radiation is small, and the main energy input and output terms of the surface energy balance are downward and upward longwave radiation, with seasonal average values of 149 and −159 W m−2, respectively. The combination of high wind speed and a large near‐surface humidity gradient during summer resulted in significant frost depositional events. The total surface frost deposition for the whole year was 24 kg m−2, which accounted for 61% of the total accumulation (averaged over 10 years). When a high‐pressure ridge blocks cyclones and deflects fronts of low‐pressure systems to inland East Antarctica during winter, this has a significant impact on the surface energy balance at Panda 1 automatic weather station, with daily sensible and latent heat fluxes increasing by as much as 25 and 12 W m−2, respectively. These results still contain uncertainties as we only address a single year, when interannual variability may be considerable, and we do not consider drifting snow sublimation.

The Effect of Turbulence on Drifting Snow Sublimation

AbstractSublimation of drifting snow, which is significant for the balances of mass and energy of the polar ice sheet, is a complex physical process with intercoupling between ice crystals, wind field, temperature, and moisture. Here a three‐dimensional drifting snow sublimation model in a turbulent boundary layer is proposed. In contrast to most previous models, it takes into account turbulent diffusion of moisture from lower to higher elevations, allowing the air humidity near the surface to be undersaturated and thus sublimation to occur. From simulations with this model, we find that snow sublimation in the saltation layer near the surface dominates overall snow sublimation, despite an only marginal departure from humidity saturation (<1%), because of a large particle concentration.

On the suitability of the Thorpe–Mason model for calculating sublimation of saltating snow

Abstract. The Thorpe and Mason (TM) model for calculating the mass lost from a sublimating snow grain is the basis of all existing small- and large-scale estimates of drifting snow sublimation and the associated snow mass balance of polar and alpine regions. We revisit this model to test its validity for calculating sublimation from saltating snow grains. It is shown that numerical solutions of the unsteady mass and heat balance equations of an individual snow grain reconcile well with the steady-state solution of the TM model, albeit after a transient regime. Using large-eddy simulations (LESs), it is found that the residence time of a typical saltating particle is shorter than the period of the transient regime, implying that using the steady-state solution might be erroneous. For scenarios with equal initial air and particle temperatures of 263.15 K, these errors range from 26 % for low-wind, low-saturation-rate conditions to 38 % for high-wind, high-saturation-rate conditions. With a small temperature difference of 1 K between the air and the snow particles, the errors due to the TM model are already as high as 100 % with errors increasing for larger temperature differences.

The significance of vertical moisture diffusion on drifting snow sublimation near snow surface

Abstract. Sublimation of blowing snow is an important parameter not only for the study of polar ice sheets and glaciers, but also for maintaining the ecology of arid and semi-arid lands. However, sublimation of near-surface blowing snow has often been ignored in previous studies. To study sublimation of near-surface blowing snow, we established a sublimation of blowing snow model containing both a vertical moisture diffusion equation and a heat balance equation. The results showed that although sublimation of near-surface blowing snow was strongly reduced by a negative feedback effect, due to vertical moisture diffusion, the relative humidity near the surface does not reach 100 %. Therefore, the sublimation of near-surface blowing snow does not stop. In addition, the sublimation rate near the surface is 3–4 orders of magnitude higher than that at 10 m above the surface and the mass of snow sublimation near the surface accounts for more than half of the total snow sublimation when the friction wind velocity is less than about 0.55 m s−1. Therefore, the sublimation of near-surface blowing snow should not be neglected.

Drifting snow and its sublimation in turbulent boundary layer

Drifting snow is a special process of mass-energy transport in hydrological cycle especially in alpine region. It can not only change the snow distribution, but also result in phase change of ice crystal into water vapour, which is so called drifting snow sublimation. Thus drifting snow is of glaciological and hydrological importance in cold regions. In this paper, recent research on drifting snow and its sublimation is reviewed, and some new progresses by our research team in Lanzhou University are also introduced.

The impacts of moisture transport on drifting snow sublimation in the saltation layer

Abstract. Drifting snow sublimation (DSS) is an important physical process related to moisture and heat transfer that happens in the atmospheric boundary layer, which is of glaciological and hydrological importance. It is also essential in order to understand the mass balance of the Antarctic ice sheets and the global climate system. Previous studies mainly focused on the DSS of suspended snow and ignored that in the saltation layer. Here, a drifting snow model combined with balance equations for heat and moisture is established to simulate the physical DSS process in the saltation layer. The simulated results show that DSS can strongly increase humidity and cooling effects, which in turn can significantly reduce DSS in the saltation layer. However, effective moisture transport can dramatically weaken the feedback effects. Due to moisture advection, DSS rate in the saltation layer can be several orders of magnitude greater than that of the suspended particles. Thus, DSS in the saltation layer has an important influence on the distribution and mass–energy balance of snow cover.

Cloud and precipitation properties from ground-based remote-sensing instruments in East Antarctica

Abstract. A new comprehensive cloud–precipitation–meteorological observatory has been established at Princess Elisabeth base, located in the escarpment zone of Dronning Maud Land (DML), East Antarctica. The observatory consists of a set of ground-based remote-sensing instruments (ceilometer, infrared pyrometer and vertically profiling precipitation radar) combined with automatic weather station measurements of near-surface meteorology, radiative fluxes, and snow height. In this paper, the observatory is presented and the potential for studying the evolution of clouds and precipitating systems is illustrated by case studies. It is shown that the synergetic use of the set of instruments allows for distinguishing ice, liquid-containing clouds and precipitating clouds, including some information on their vertical extent. In addition, wind-driven blowing snow events can be distinguished from deeper precipitating systems. Cloud properties largely affect the surface radiative fluxes, with liquid-containing clouds dominating the radiative impact. A statistical analysis of all measurements (in total 14 months mainly during summer–beginning of winter) indicates that these liquid-containing clouds occur during as much as 20% of the cloudy periods. The cloud occurrence shows a strong bimodal distribution with clear-sky conditions 51% of the time and complete overcast conditions 35% of the time. Snowfall occurred during 17% of the cloudy periods with a predominance of light precipitation and only rare events with snowfall >1 mm h−1 water equivalent (w.e.). Three of such intense snowfall events occurred during 2011 contributing to anomalously large annual surface mass balance (SMB). Large accumulation events (>10 mm w.e. day−1) during the radar-measurement period of 26 months were always associated with snowfall, but at the same time other snowfall events did not always lead to accumulation. The multiyear deployment of a precipitation radar in Antarctica allows for assessing the contribution of the snowfall to the local SMB and comparing it to the other SMB components. During 2012, snowfall rate was 110 ± 20 mm w.e. yr−1, from which surface and drifting snow sublimation removed together 23%. Given the measured yearly SMB of 52 ± 3 mm w.e., the residual term of 33 ± 21 mm w.e. yr−1 was attributed to the wind-driven snow erosion. In general, this promising set of robust instrumentation allows for improved insight into cloud and precipitation processes in Antarctica and can be easily deployed at other Antarctic stations.

Numerical simulation of drifting snow sublimation in the saltation layer

Snow sublimation is an important hydrological process and one of the main causes of the temporal and spatial variation of snow distribution. Compared with surface sublimation, drifting snow sublimation is more effective due to the greater surface exposure area of snow particles in the air. Previous studies of drifting snow sublimation have focused on suspended snow, and few have considered saltating snow, which is the main form of drifting snow. In this study, a numerical model is established to simulate the process of drifting snow sublimation in the saltation layer. The simulated results show 1) the average sublimation rate of drifting snow particles increases linearly with the friction velocity; 2) the sublimation rate gradient with the friction velocity increases with increases in the environmental temperature and the undersaturation of air; 3) when the friction velocity is less than 0.525 m/s, the snowdrift sublimation of saltating particles is greater than that of suspended particles; and 4) the snowdrift sublimation in the saltation layer is less than that of the suspended particles only when the friction velocity is greater than 0.625 m/s. Therefore, the drifting snow sublimation in the saltation layer constitutes a significant portion of the total snow sublimation.

Snowdrift modelling for the Vestfonna ice cap, north-eastern Svalbard

Abstract. The redistribution of snow by drifting and blowing snow frequently leads to an inhomogeneous snow mass distribution on larger ice caps. Together with the thermodynamic impact of drifting snow sublimation on the lower atmospheric boundary layer, these processes affect the glacier surface mass balance. This study provides a first quantification of snowdrift and sublimation of blowing and drifting snow on the Vestfonna ice cap (Svalbard) by using the specifically designed snow2blow snowdrift model. The model is forced by atmospheric fields from the Polar Weather Research and Forecasting model and resolves processes on a spatial resolution of 250 m. The model is applied to the Vestfonna ice cap for the accumulation period 2008/2009. Comparison with radio-echo soundings and snow-pit measurements show that important local-scale processes are resolved by the model and the overall snow accumulation pattern is reproduced. The findings indicate that there is a significant redistribution of snow mass from the interior of the ice cap to the surrounding areas and ice slopes. Drifting snow sublimation of suspended snow is found to be stronger during spring. It is concluded that the redistribution process is strong enough to have a significant impact on glacier mass balance.

Seasonal simulation of drifting snow sublimation in Alpine terrain

Key Points Seasonal drifting snow sublimation in Alpine terrain is small

Drifting snow climate of the Greenland ice sheet: a study with a regional climate model

Abstract. This paper presents the drifting snow climate of the Greenland ice sheet, using output from a high-resolution (∼11 km) regional climate model. Because reliable direct observations of drifting snow do not exist, we evaluate the modeled near-surface climate instead, using automatic weather station (AWS) observations from the K-transect and find that RACMO2 realistically simulates near-surface wind speed and relative humidity, two variables that are important for drifting snow. Integrated over the ice sheet, drifting snow sublimation (SUds) equals 24 ± 3 Gt yr−1, and is significantly larger than surface sublimation (SUs, 16 ± 2 Gt yr−1). SUds strongly varies between seasons, and is only important in winter, when surface sublimation and runoff are small. A rapid transition exists between the winter season, when snowfall and SUds are important, and the summer season, when snowmelt is significant, which increases surface snow density and thereby limits drifting snow processes. Drifting snow erosion (ERds) is only important on a regional scale. In recent decades, following decreasing wind speed and rising near-surface temperatures, SUds exhibits a negative trend (0.1 ± 0.1 Gt yr−1), which is compensated by an increase in SUs of similar magnitude.

Modeling drifting snow in Antarctica with a regional climate model: 2. Results

This paper presents a model study of the impact of drifting snow on the lower atmosphere, surface snow characteristics, and surface mass balance of Antarctica. We use the regional atmospheric climate model RACMO2.1/ANT with a high horizontal resolution (27 km), equipped with a drifting snow routine and forced by ERA‐Interim (1989–2009) at its lateral and ocean boundaries. Drifting snow sublimation (SUds) is significant in Antarctica, especially in the coastal regions (>150 mm water equivalent yr−1). Integrated over the ice sheet, SUds removes ∼6% of the annually precipitated snow. Drifting snow interacts with the atmosphere, as it increases the lower atmospheric moisture content and reduces surface sublimation (SUs), and leads to increased snowfall in regions where the atmosphere usually is close to saturation. Drifting snow sublimation (SUds) is smallest in summer, when katabatic wind speeds are lower and melting and surface sublimation consolidate the snow surface. Compared to a simulation without drifting snow, total sublimation (SUds + SUs) doubles on the grounded ice sheet if drifting snow is considered. Drifting snow erosion is locally significant, but can be neglected on a continent‐wide scale.

A new, high‐resolution surface mass balance map of Antarctica (1979–2010) based on regional atmospheric climate modeling

A new, high resolution (27 km) surface mass balance (SMB) map of the Antarctic ice sheet is presented, based on output of a regional atmospheric climate model that includes snowdrift physics and is forced by the most recent reanalysis data from the European Centre for Medium‐Range Weather Forecasts (ECMWF), ERA‐Interim (1979–2010). The SMB map confirms high accumulation zones in the western Antarctic Peninsula (>1500 mm y−1) and coastal West Antarctica (>1000 mm y−1), and shows low SMB values in large parts of the interior ice sheet (<25 mm y−1). The location and extent of ablation areas are modeled realistically. The modeled SMB is in good agreement with ±750 in‐situ SMB measurements (R = 0.88), without a need for post‐calibration. The average ice sheet‐integrated SMB (including ice shelves) is estimated at 2418 ± 181 Gt y−1. Snowfall shows modest interannual variability (σ = 114 Gt y−1), but a pronounced seasonal cycle (σ = 30 Gt mo−1), with a winter maximum. The main ablation process is drifting snow sublimation, which also peaks in winter but with little interannual variability (σ = 9 Gt y−1).

Impact of model resolution on simulated wind, drifting snow and surface mass balance in Terre Adélie, East Antarctica

AbstractThis paper presents the impact of model resolution on the simulated wind speed, drifting snow climate and surface mass balance (SMB) of Terre Adélie and its surroundings, East Antarctica. We compare regional climate model simulations at 27 and 5.5 km resolution for the year 2009. The wind speed maxima in Terre Adélie and the narrow glacial valleys of Victoria Land are better represented at 5.5 km resolution, because the topography is better resolved. Drifting snow sublimation is >100 mm a-1 in regions with high wind speeds. Our results indicate a strong feedback between topography, wind gradients and drifting snow erosion. As a result, SMB shows much more local spatial variability at 5.5 km resolution that is controlled by drifting snow erosion, whereas the large-scale SMB gradient is largely determined by precipitation. Drifting snow processes lead to ablation in the narrow glacial valleys of Victoria Land. The integrated SMB equals 86 Gt. Although wind climate, drifting snow processes and SMB variability are better represented at 5.5 km, the area-integrated SMB is not significantly different between the simulations at 27 and 5.5 km. A horizontal resolution of 27 km is sufficient to realistically simulate ice-sheet wide SMB.

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.

Verification of moisture budgets during drifting snow conditions in a cold wind tunnel

Experiments in a cold wind tunnel were used to verify drifting snow sublimation models. A layer of drifting snow particles was formed over a sintered snow surface. Sublimation and drifting snow flux were estimated from two vertically resolved profile measurements separated along the flow path and were compared to a simple, one‐dimensional diffusion model of drift and drifting snow sublimation. The experiments show an increase in water vapor content of the air from drifting snow sublimation. The measured drifting snow sublimation appeared to be consistent with albeit somewhat larger than theoretical values found in the model study. Under wind tunnel conditions, particle number density appears to be the most important controlling factor on the sublimation rate. For experiments with external solar radiative forcing, the increase of the sublimation rate was also larger than theoretical predictions. The experiments suggest that irregular snow crystals and solar radiation might increase sublimation rates more than described by many drifting snow models.