Middle elevation alpine snow cover

Eric Martin

Relevance and characteristics Col de Porte is quite representative of middle elevation sites in a temperate alpine climate. Many ski resorts and hydropower stations in the Alps are located within the same elevation range.

The climate is wet (2000 mm w.e. yr-1) because it is situated in the western part of the European Alps. The mean winter temperature (December-February) is -1 °C. Rainfall events are common in winter. During the first part of the winter, the snowpack structure is highly variable; all grain types can be encountered. Because of regular rainfall events, a layer of wet grains topped by a layer of rounded grains constitutes a typical winter snowpack. Depth hoar is encountered only in cases of shallow snow cover and cold conditions. Surface hoar growth occurs several times in winter.

Site

At Col de Porte, at an altitude of 1320 m a.s.l., the snow cover lasts an average of five months, from the end of November to the beginning of May. The mean maximum snow depth is 130 cm at the beginning of March. Snowmelt events may occur at any time but ablation usually takes place after mid-March. The maximum snow water equivalent varies generally between 200 and 500 mm w.e.

Screening of shortwave radiation is important in December and January because of trees. At large scales, albedo is dependent on the presence of snow on branches but it may sometimes also be affected by the deposition of fragments of needles. Wind is generally light.

Energy balance

The site is equipped with shortwave and longwave radiation sensors. Air temperature, humidity, and wind speed are also measured at hourly time steps. Energy balance investigations are made using the snow model CROCUS (Brun et al., 1989, 1992). Radiation terms are measured while the model calculates turbulent fluxes. Parameterization of the latter fluxes is discussed in Martin and Lejeune (1997).

Along with the daily means of air temperature, wind and albedo, the daily means of energy fluxes at the surface and mass balance at Col de Porte are presented in Figs. 3.6 and 3.7 for the winter seasons 93/94 and 94/95, respectively. Turbulent fluxes (sensible and latent heat) transfer heat from the atmosphere to the snow cover as the atmosphere is usually stable. March 1994 was very warm and snowmelt occurred throughout this month. On the contrary, the first part of April was cold and snowy before the final melting period. In 94/95, melting only occurred in April.

Figure 3.6. Daily means and, where appropriate, daily minima and maxima (shaded band) at Col de Porte during the winter 93/94. The snow cover was continuous from November 13, 1993 to May 5, 1994. Net surface flux is the sum of surface fluxes, which corresponds to the net negative change rate of the snowpack's internal energy per unit area (-dH/dt) neglecting advective and ground heat fluxes (cf. Equation 3.1). Total mass is the accumulated difference of precipitations (snow and rain) to runoff, neglecting sublimation and evaporation (cf. Equation 3.4).

Figure 3.6. Daily means and, where appropriate, daily minima and maxima (shaded band) at Col de Porte during the winter 93/94. The snow cover was continuous from November 13, 1993 to May 5, 1994. Net surface flux is the sum of surface fluxes, which corresponds to the net negative change rate of the snowpack's internal energy per unit area (-dH/dt) neglecting advective and ground heat fluxes (cf. Equation 3.1). Total mass is the accumulated difference of precipitations (snow and rain) to runoff, neglecting sublimation and evaporation (cf. Equation 3.4).

Figure 3.7. Daily means and, where appropriate, daily minima and maxima (shaded band) at Col de Porte during the winter 1994/95. The snow cover was continuous from December 31, 1994 to May 8, 1995. Net surface flux is the sum of surface fluxes, which corresponds to the net negative change rate of the snowpack's internal energy per unit area (-dH/dt) neglecting advective and ground heat fluxes (cf. Equation 3.1). Total mass is the accumulated difference of precipitations (snow and rain) to runoff, neglecting sublimation and evaporation (cf. Equation 3.4).

Figure 3.7. Daily means and, where appropriate, daily minima and maxima (shaded band) at Col de Porte during the winter 1994/95. The snow cover was continuous from December 31, 1994 to May 8, 1995. Net surface flux is the sum of surface fluxes, which corresponds to the net negative change rate of the snowpack's internal energy per unit area (-dH/dt) neglecting advective and ground heat fluxes (cf. Equation 3.1). Total mass is the accumulated difference of precipitations (snow and rain) to runoff, neglecting sublimation and evaporation (cf. Equation 3.4).

The magnitude of net shortwave radiation is large during the melting period (March 94 and April 95). The variations of the net longwave radiation are more complex.

Modeling aspects

Turbulent fluxes are probably the most difficult factor to take into account at this site because of the complex topography. All types of snowpack can be encountered at this site: cold or completely wet even in winter, which induces difficulties in modeling the structure and layer texture of the snowpack.

3.5.3 Snow-covered sea ice on a high arctic ice flow

Rachel E. Jordan Relevance and characteristics

Between 1937 and 1991, Russian scientists embarked on 31 "North Pole" field experiments within the Arctic Ocean. With the recent relaxing of East-West relations, the extensive set of meteorological, oceanographic and ice flow data from these expeditions has been made available to Western scientists on a CD-ROM (National Snow and Ice Data Center, 1996). There is now a general consensus that energy exchange over the polar ice caps is of critical importance to long-term climatological change. A comparison of historical data with that from the recent SHEBA expedition (Persson et al., 2002; Uttal et al., 2002) may reveal emerging trends in the surface energy balance of the Arctic Ocean.

Site

The Russian drifting station North Pole 4 (NP-4) was within 5° latitude of the North Pole from April 1956 until April 1957. Instrumentation at the NP-4 site is described by Kucherov and Sternzat (1959), Marshunova and Mishin (1994), and Jordan etal. (1999). The NP-4 site was characterized by high winds, fine-grained, dense snow, and a relatively shallow snowpack. Spring, summer, and winter seasons had distinct characteristics. Much of the snow was lost through melting during the summer and melt ponds formed in the sea ice, causing extreme variability in albedo. Cloud cover was heavy over the melting snow and the air temperature remained near 0 °C. In contrast, the amplitude of temperature swings associated with the passing of synoptic systems was up to 40 °C in winter (see Fig. 3.8).

Energy balance

Energy balance studies over arctic ice flows include works by Nazintsev (1963, 1964), Maykut (1982), Ebert and Curry (1993), Radionov et al. (1996), Lindsay (1998), and Uttal et al. (2002). Jordan et al. (1999) describe in detail the NP-4 data presented here in Fig. 3.8.

Figure 3.8. Daily means and, where appropriate, daily minima and maxima (shaded band) on snow-covered sea ice on a high arctic ice flow from April 30, 1956 to April 3, 1957. Net surface flux is the sum of surface fluxes, which corresponds to the net negative change rate of the snowpack's internal energy per unit area (-dH/dt) neglecting advective fluxes and heat flux from the sea ice (cf. Equation 3.1). Total mass is the accumulated difference of precipitations (snow and rain) to runoff, neglecting sublimation and evaporation (cf. Equation 3.4).

Figure 3.8. Daily means and, where appropriate, daily minima and maxima (shaded band) on snow-covered sea ice on a high arctic ice flow from April 30, 1956 to April 3, 1957. Net surface flux is the sum of surface fluxes, which corresponds to the net negative change rate of the snowpack's internal energy per unit area (-dH/dt) neglecting advective fluxes and heat flux from the sea ice (cf. Equation 3.1). Total mass is the accumulated difference of precipitations (snow and rain) to runoff, neglecting sublimation and evaporation (cf. Equation 3.4).

Net shortwave radiation was the dominant energy flux to the snowpack during the late spring and summer. During these seasons at NP-4, the turbulent fluxes were close in magnitude and predominantly upwards, thus cooling the surface. Figure 3.8 shows a positive radiation balance after mid-September and simultaneously the appearance of downward spikes in the sensible heat flux, which increase in magnitude over the winter. The largest longwave radiation losses occurred under cloudless skies and were primarily compensated by sensible heat exchange. Latent heat fluxes were predominantly upward or evaporative. The magnitude of latent heat was small during the winter because saturation vapor pressure decreases exponentially with temperature.

Figure 3.8 shows a high snow albedo between 0.8-0.9 for new snow and a low albedo of 0.65 for older snow, near the value for bare ice. Snow cover persisted throughout the summer at this location, with depths ranging between 3 and 8 cm. About one-half of summer precipitation fell as snow and the increases in albedo reflect this in Fig. 3.8. The 1997-1998 SHEBA expedition, by contrast, reported loss of snow cover by early August. The remaining surface mix of bare ice and melt ponds had a much lower albedo than snow. Such dramatic alterations in albedo lead to an ice albedo feedback (Perovich et al., 2002), which plays a key role in the energy budget of the high Arctic.

Modeling aspects

High arctic sites are subject to blowing and drifting snow and exhibit considerable variability in snow depth. Thus, the wind transport of snow must be considered to build realistic snow covers. Precipitation measurements reported here are corrected for wind effects, evaporation, and wetting error (Yang, 1995; Jordan et al., 1999). Because arctic snow is fine-grained and packed by wind, polar snowpacks are much denser than their temperate counterparts. The density of newly fallen snow should therefore be around 150-300 kg m-3 and increase with wind speed.

Sturm et al. (2002) infer an effective thermal conductivity of 0.33 W m-1 K-1 from snow temperature profiles at SHEBA, which is higher than that for temperate snow and also higher than recent field measurements by Sturm et al. (1997, 2002). Sturm et al. (2002) conclude that mechanisms other than one-dimensional conduction may enhance the heat exchange within the polar snowpack. Jordan et al. (2003) suggest that high winds may induce wind ventilation in the upper 10-20 cm of the snowpack and thereby increase its effective thermal conductivity.

Persistent radiative losses in winter lead to periods when the standard stability correction for stable atmospheres can shut down sensible heat exchange. To avoid unrealistically low surface temperature predictions, Jordan et al. (1999) therefore replaced the usual log-linear stability function with one that maintains a minimal turbulent exchange.

3.5.4 Canadian prairies John W. Pomeroy and Donald M. Gray

Relevance and characteristics

"Prairie" snow seasonally covers northern continental grain-growing and grassland regions of North America, Europe, and Asia. These snow covers impact both the social and the economic aspects of the region because: a large proportion of the population lives in rural districts, grain and livestock exports are globally important food supplies, the region experiences long and severe winters and summer water deficits, and agriculture and industry rely on long distance transport by road and rail (Steppuhn, 1981).

Although snowfall only comprises about one-third to one-half of annual precipitation, snowmelt runoff often exceeds 90% of annual streamflow (Gray, 1970). Spring floods caused by prairie snowmelt water are the most economically destructive natural phenomena in the U.S.A. and Canada and defensive measures such as large "ring-dikes" are used to protect major cities such as Winnipeg, Manitoba.

On the prairies, blowing snow erosion and sublimation may result in increased water deficits, termed "northern desertification" in Russia (Dyunin et al., 1991), which may be enhanced by the suppression and removal of natural vegetation. In many areas, blowing snow storms result in winter restrictions on transportation and a specialized design of infrastructure to minimize snow removal costs and snow load damage (Tabler and Schmidt, 1986.)

Prairie snow covers persist from November to April. They are generally cold, dry, and wind-packed. Blowing snow causes redistribution several times during a winter season and results in dense (generally greater than 250 kg m-3), crusted and variable (coefficient of variation of SWE 0.3-0.58) snow covers (Pomeroy et al., 1998b). Snow accumulation is very sensitive to vegetation cover and topography, and the depths in sheltered sites can be five or six times that on exposed sites (Steppuhn and Dyck, 1974; Pomeroy et al., 1993). In early spring the energy for melting snow is largely derived from shortwave radiation and as melt progresses the magnitude of net radiative flux generally increases due to the increase in magnitude of incoming shortwave flux and the decrease in areal albedo due to the decreases in snow depth and in snow-covered area (O'Neill and Gray, 1973). Advection of sensible heat from bare ground to snow has been shown to play an important role in the melting of a patchy snow cover (Shook and Gray, 1997). As a result, areal melt rates are greatest when the snow-covered area is between 40% and 60% (Shook, 1995). Ground heat flux is negligible during melt because of the infiltration of meltwater into frozen soils, which leads to the release of latent heat upon freezing and very small temperature gradients near the soil surface (Zhao et al., 1997; Pomeroy et al., 1998b).

Plate 1.2. Mean seasonal variation in snow (gray) and sea-ice cover (white) between February (left) and August (right) as derived from satellite data. Data from NSIDC "Weekly Snow Cover and Sea Ice Extent," CD-ROM, NSIDC, 1996.

(b)

Plate 1.4. Comparison of mean March winter SWE (mm) simulated by the Canadian coupled global climate model (CGCM3) for the 1981-2000 "current climate" period (a) with simulated mean SWE for the 2081-2100 period (b) based on the SRES A2 emission scenario. Data courtesy of the Canadian centre for climate modeling and analysis.

Date

Plate 4.1. Simulation of temporal evolution of snowpack layering at Col de Porte during winter 1998/99. Each color represents a snow type (see Brun et al., 1992).

--Measured snow depth

- - - Reference simulated snow depth

- - - CROCUS albedo without ageing effects --CROCUS albedo without grain effects

--Measured snow depth

- - - Reference simulated snow depth

- - - CROCUS albedo without ageing effects --CROCUS albedo without grain effects

Date

Plate 4.2. Sensibility to ageing and grain size in albedo calculation on snow depth simulations.

-Measured snow depth

--Constant albedo = 0.725

--Constant albedo = 0.6 (lower curve)

Date

Plate 4.3. Sensibility to albedo on snow depth simulations.

Effects of water retention

-Measured snow depth

- - No immobile retention — - Immobile retention = 5% of pore volume

-Measured snow depth

- - No immobile retention — - Immobile retention = 5% of pore volume

30/10/93 27/11/93 25/12/93 22/01/94 19/02/94 19/03/94 16/04/94 14/05/94 11/06/94

Date

30/10/93 27/11/93 25/12/93 22/01/94 19/02/94 19/03/94 16/04/94 14/05/94 11/06/94

Date

Plate 4.4. Sensibility to water retention on snow depth simulations.

-Measured snow depth

Effect of the stability - - - Full effect of stability of the boundary layer — Half effect of stability

-Measured snow depth

Effect of the stability - - - Full effect of stability of the boundary layer — Half effect of stability

Date

Plate 4.5. Sensibility to the stability of the boundary layer on snow depth simulations.

Date

Plate 4.6. Sensibility to snow length roughness on snow depth simulations.

Effect of snow-rain criterion

-Measured snow depth -Snow-rain criterion = 0 °C Snow-rain criterion = 0.5 °C -Snow-rain criterion = 1.0 °C Snow-rain criterion = 1.5 °C

-Measured snow depth -Snow-rain criterion = 0 °C Snow-rain criterion = 0.5 °C -Snow-rain criterion = 1.0 °C Snow-rain criterion = 1.5 °C

30/10/93 27/11/93 25/12/93 22/01/94 19/02/94 19/03/94 16/04/94 14/05/94 11/06/94

Date

30/10/93 27/11/93 25/12/93 22/01/94 19/02/94 19/03/94 16/04/94 14/05/94 11/06/94

Date

Plate 4.7. Sensibility to snow-rain criterion on snow depth simulations.

* * I ■ I I ■. ■ ■ ■ ■ i i ■ ■ I I . i ■ I ■

30 40 50 60 70 80 9C

Latitude

* * I ■ I I ■. ■ ■ ■ ■ i i ■ ■ I I . i ■ I ■

30 40 50 60 70 80 9C

Latitude

Plate 4.14. Surface air temperature change in 15 coupled GCMs that have doubled atmospheric CO2 concentrations. All models show "polar amplification" and enhanced warming in the Arctic compared to tropical latitudes. Taken from Holland and Bitz (2003).

Snow mass change (kg/m2)

90NP 1 1

Snow mass change (kg/m2)

90NP 1 1

180 90W 0 90E

180 90W 0 90E

Snowfall change (kg/m2/month)

Snowfall change (kg/m2/month)

-12 -8-4 0 4 8 12

Plate 4.19. Differences between 2030-2050 averages from the climate-change simulation and 130-year averages from the control of the Hadley GCM for (a) snow mass (b) temperature and (c) snowfall. Taken from Essery (1997).

Plate4.20. Annual time series (thin line), overlaid with nine-year running means (thick line), of ensemble-mean January North American snow cover extent, including both twentieth century and twenty-first century scenarios, for nine available coupled atmosphere-ocean GCMs. Taken from Frei and Gong (2005).

September October November December

Armstrong and Brodzik, NSDIC

September October November December

Armstrong and Brodzik, NSDIC

Plate 5.2. Monthly Northern Hemisphere snow cover (1966-2005) and sea ice extent (19782005) climatologies (Source: NSIDC Northern Hemisphere EASE-Grid Weekly Snow Cover and Sea Ice Extent Version 3, 2005).

Northern Hemisphere Snow-Covered Area

Northern Hemisphere Snow-Covered Area

Year

Plate 5.3. Northern Hemisphere monthly SCA, 1978-2005, from NOAA snow charts (orange) and microwave satellite (purple/green) data sets.

Plate 5.4. Comparison of mean monthly Northern Hemisphere snow extent derived from visible and passive microwave satellite data, 1978-2005 (50% or more of the weeks in the particular month over the total time period classified as snow covered).

Northern Hemisphere Snow-Covered Area Departures from Monthly Means

Northern Hemisphere Snow-Covered Area Departures from Monthly Means

80 85 90 95 00 05

Year

80 85 90 95 00 05

Year

Plate 5.5. Northern Hemisphere SCA departures from monthly means, 1978-2005, from NOAA snow charts (orange) and microwave satellite (purple/green) data sets. The NOAA time series for this period exhibits a significant decreasing trend of -2.0% per decade (solid orange line); the microwave snow-cover time series exhibits a decreasing trend of -0.7% per decade that is not significant at a 90% level (dashed green line).

Site

Kernen Farm (500 m a.s.l.) is east of the City of Saskatoon (52° N, 107° W) in the central southern half of the Province of Saskatchewan, Canada. The farm is situated on an open, flat, lacustrine plain, which is cropped to cereal grains and pulse crops under the practice of dryland farming (Shook and Gray, 1996). Trees are limited to farmyards, which are located several kilometers distant from the site. The climate is subhumid and typical of northern prairies with cold winters and continuous snow cover from late November to early April.

Experiments were conducted in December 1998 and March 1999 at level sites with continuous snow cover on fields of uniform short vegetation or fallow. Energy balance and related parameters were measured and recorded half-hourly using eddy correlation equipment (Gill Instruments "Solent" or Campbell Scientific "CSAT" sonic anemometers, Campbell Scientific "Krypton" hygrometers, fine wire thermocouple controlled by a datalogger for covariance calculation), Radiation and Energy Balance System "REBS" net radiometers and ground heat flux plates, "NRG40" cup anemometer, "Everest" infrared thermometer, "Vaisala" HMP35CF platinum resistance thermometers, Campbell Scientific "SR-50" ultrasonic snow depth gauge and University of Saskatchewan blowing snow particle counters (Brown and Pomeroy, 1989; Shook and Gray, 1997; Pomeroy et al., 1998b, 1999b). During the measurement periods, the sites were frequently manned, which provided a high confidence in the observations.

Energy balance

Two energy balances and related measurements are shown in Figs. 3.9 and 3.10. As stated previously, negative values indicate downward fluxes. Figure 3.9 shows fluxes during an early winter snow accumulation period with blowing snow, Fig. 3.10 shows fluxes during a snow warming and melt sequence in spring. The snow accumulation period (Fig. 3.9) shows a characteristic prairie weather pattern of highly variable meteorology associated with the passage of frontal systems.

On 17 December the air temperature warmed to slightly above freezing, then dropped dramatically with strong winds to below -20 °C in about 12 hours. During this cooling period snowfall and blowing snow were recorded and the lower surface boundary layer remained well mixed. Over the next two days the temperature dropped below -30 °C (by 20 December) with lower wind speeds and a stable lower surface boundary layer forming. During short periods around mid-day, the magnitude of net radiation was small but negative (peak -20 to -90 W m-2), however at other times it was positive, reaching 40 W m-2, while staying smaller than 10 W m-2 during cloudy nights. Turbulent fluxes are enhanced over that expected from smooth snow covers because of exposed vegetation (snow depth <10 cm,

— Net radiation

— Latent heat -e— Sensible heat -«— Ground heat

— Sublimation

— Net radiation

— Latent heat -e— Sensible heat -«— Ground heat

— Sublimation

(b)

-•-Surface temperature

-Wind r

Air temperature

- -Blowing snow particles 1

-e-Snow depth 1

17 Dec 1200

17 Dec 1800

18 Dec 0000

18 Dec 0600

18 Dec 1200

18 Dec 1800

19 Dec 0000

17 Dec 0000

17 Dec 0600

17 Dec 1200

17 Dec 1800

18 Dec 0000

18 Dec 0600

18 Dec 1200

18 Dec 1800

19 Dec 0000

Figure 3.9. Direct measurements made during a snow accumulation period with blowing snow in December, 1998, Kernen Farm, Saskatoon, Saskatchewan, Canada. (a) Fluxes of net radiation, latent heat, and sensible heat, measured 1 m (net radiation) and 2 m (turbulent fluxes) above the snow cover, as well as ground heat flux measured 5 cm into the soil and (b) snow surface temperature, air temperature, and wind speed measured 1.3 m above the snow surface as well as blowing snow particle flux (measured 0.2 m above the snow surface) and snow depth.

' Net radiation Ground heat Latent heat Sensible heat

Air temperature ■ Snow temperature -Wind

Air temperature ■ Snow temperature -Wind

18 Mar 0000

18 Mar 0600

18 Mar 1200

18 Mar 1800

19 Mar 0000

19 Mar 0600

19 Mar 1200

19 Mar 1800

20 Mar 0000

Figure 3.10. Direct measurements made during a snowmelt period in March, 1999, Kernen Farm, Saskatoon, Saskatchewan, Canada. (a) Fluxes of net radiation, latent heat, and sensible heat, measured 1 m (net radiation) and 2 m (turbulent fluxes) above the snow cover, as well as ground heat flux measured 5 cm into the soil, (b) net change rate of the snowpack's internal energy per unit area (dH/dt). Positive values correspond to either warming or melting (cf. Equation 3.2), and (c) snow temperature at mid-pack depth as well as air temperature and wind speed measured 1.3 m above the snow surface.

patchy grass height approximately 25 cm) and are strongly affected by the occurrence of blowing snow. During the blowing snow event from 17 to 18 December, latent heat fluxes peak at 60 W m-2 and become small or negligible after that.

Sensible heat flux peaks at up to 50 W m-2 during cold, relatively calm, negative radiation periods (18-20 December). During cold, relatively calm, positive radiation periods, sensible heat is generally slightly negative, with peak values at - 30Wm-2 but most often not lower than -20 W m-2. A notable flux in this early winter period is the consistently positive ground heat flux into the snowpack, which becomes prominent (30-40 W m-2) as cooling of snow and air proceeds (18-20 December). The blowing snow event did not result in a large increase in snow depth but density increased from near 100 to 140 kg m-3 due to the impact of saltating snow particles and subsequent sintering.

An exemplary snowmelt period (Fig. 3.10) occurred in March 1999 over a smooth, continuous snow cover (average depth = 14.5 cm, density = 330 kg m-3). Internal temperatures show that the snowpack warmed from -5 °C on 18 March to isothermal conditions as temperatures reached nearly 0 °C on 19 March. The magnitude of daytime net radiation was large but negative, peaking at -182 W m-2 on 18 March (cloudy) and -360 W m-2 on 19 March (mostly clear). The preceding melt was a small blowing snow event (wind speed peak 7 m s-1) early on 18 March. The largest latent heat fluxes of the period (50 W m-2) occurred during this event. The magnitude (<6 W m-2) of the ground heat flux was quite small on both days, becoming slightly negative and thus directed to the soil as the snowpack warmed. Despite wind speeds of up to 5.5 m s-1, turbulent fluxes during the melt were small and similar in size (peak 40 W m-2), much smaller than the magnitude of net radiation. The net energy change rate shows a large positive input to the snowpack on both days (see Equation 3.1). On 18 March warming snow temperatures suggest that this positive input increased the internal energy of the snowpack while constant internal temperatures on 19 March imply that most went into snowmelt (see Equation 3.2). This melt period was ephemeral and the snowpack returned to subfreezing conditions at the end of 19 March.

Modeling aspects

Relatively uniform, level prairie snow covers should be one of the most successful types of snow for physical models; however, the complexity of prairie snow phenomena have resulted in several modeling challenges towards which long-term process research has been directed (Male and Gray, 1975, 1981; Pomeroy et al., 1998b). Shook and Gray (1994) described the variation of depth and density and the influence of covariance between these properties in determining areal snow mass. Granger and Male (1978) measured the turbulent exchange over melting prairie snow and derived stability corrections for eddy diffusivities for water vapor and heat with respect to momentum transfer; these corrections dampened the turbulent exchange from the normal log-linear formulations (e.g. Webb, 1970). Shook (1993,

1995) studied the depletion of the snow-covered area during melt and showed that changes in areal albedo can be adequately explained by the decrease in the snow-covered area and the assumption that albedo does not change significantly during melt. Shook (1995) found that the advection of sensible heat could contribute substantial melt energy when snow cover was incomplete. Pomeroy et al. (1998b) examined the performance of certain land surface schemes for prairie snowmelt and found that turbulent fluxes and ground heat flux were generally overestimated.

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