What makes the snow melt?
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Factors Influencing Snow Melt
Snow melt is a complex process influenced by various environmental and meteorological factors. Understanding these factors is crucial for accurate predictions in hydrology, climate modeling, and water resource management. This article synthesizes key insights from recent research on the primary drivers of snow melt.
Wind-Driven Snow Melt
Turbulent Heat Fluxes and Advection
Wind plays a significant role in snow melt, particularly in areas with patchy snow cover. The advection of turbulent heat from snow-free areas to snow patches can enhance melt rates at the leading edges of snow patches. This process is driven by differences in net radiation, which create horizontal temperature gradients and heat fluxes. Studies have shown that turbulent heat fluxes, including latent heat flux, can account for 60-80% of the melt at the upwind edges of snow patches1. This phenomenon is independent of the size of the snow patches, indicating a consistent pattern of heat transfer and melt reduction over distance from the leading edge1.
Influence of Forest and Topography
Elevation, Aspect, and Forest Cover
Topography and vegetation significantly influence snow accumulation and melt at the watershed scale. Elevation has the greatest impact on snow water equivalent (SWE), with higher elevations typically accumulating more snow. Aspect and forest cover also play crucial roles, with forests generally accumulating less snow than clearcuts due to shading and wind blocking effects. However, in warmer winters, forests can accelerate snow melt by increasing longwave radiation, reducing snow duration by 1-2 weeks compared to open areas2 4. The combined effects of elevation, aspect, and forest cover can explain 80-90% of the variability in snow accumulation2.
Warm Air Advection
Sensible Heat and Moisture Transfer
When warm, moist air moves over a snow surface, it transfers sensible heat and moisture, which are used to melt the snow. This process is influenced by horizontal wind speeds and vertical wind shear, which determine the depth of the cooled layer. Turbulent mixing is the primary mechanism for this air mass modification, leading to significant snow melt3.
Snow Surface Energy Exchange
Radiation and Turbulent Exchange
The energy exchange at the snow surface is a critical factor in snow melt. Radiation transfer (both shortwave and longwave) and turbulent exchange processes (sensible and latent heat transfer) are the two most important mechanisms. Radiation is often the dominant process, especially in open areas and during clear days. However, the presence of forest cover or cloudy skies can complicate the modeling of radiation exchange. Turbulent heat transfer, influenced by air mass conditions, altitude, and terrain features, also plays a significant role in snow melt5.
Micro-Meteorological Conditions
Atmospheric Variables and Boundary Layer Stability
The energy budget of a snow surface is determined by atmospheric variables such as solar and atmospheric longwave radiation, air temperature, and humidity. The stability of the atmospheric boundary layer, influenced by vertical profiles of wind speed and temperature, affects the transfer of energy to the snow surface. Snow can melt at air temperatures as low as -10°C and remain frozen at +10°C, depending on these micro-meteorological conditions6.
Mesoscale Circulations
Melting-Induced Circulations
The melting of snow extracts latent heat from the environment, leading to mesoscale circulations. These circulations consist of forced downdrafts and gravity waves, which can induce horizontal wind perturbations and vertical motions. These dynamic effects can influence the environment far from the precipitation region, highlighting the complex interactions between snow melt and atmospheric conditions7.
High Rates of Snow Melting
Convection and Condensation
High rates of snow melting are primarily driven by the heat contributed through convection and condensation of moisture via turbulent diffusion of warm, moist air. Factors such as air temperature, humidity, and wind velocity are critical in determining the rate of snow melt8.
Conclusion
Snow melt is influenced by a combination of factors, including wind-driven heat fluxes, topography, forest cover, warm air advection, radiation and turbulent exchange processes, micro-meteorological conditions, and mesoscale circulations. Understanding these factors is essential for improving snow melt modeling and managing water resources effectively.
Sources and full results
Most relevant research papers on this topic
Understanding wind-driven melt of patchy snow cover
Wind-driven melt of patchy snow cover is mainly driven by turbulent heat fluxes, with latent heat fluxes playing a significant role in upwind melt, and net radiation contributing to downwind melt.
The influence of forest and topography on snow accumulation and melt at the watershed-scale
Elevation, aspect, and forest cover significantly influence snow accumulation and melt in snow-dominated watersheds, with elevation having the greatest impact on snowmelt.
Highly CitedA case study of warm air advection over a melting snow surface
Warm, moist air over a snow surface extracts heat and moisture, melting the snow, with turbulent mixing playing a key role in air mass modification.
Lower forest density enhances snow retention in regions with warmer winters: A global framework developed from plot‐scale observations and modeling
Lower forest density reduces snow duration by 1–2 weeks in regions with warmer winters, affecting snow retention and forest management strategies.
Meta-AnalysisHighly CitedSnow surface energy exchange
Snow surface energy exchange, influenced by radiation transfer and turbulent exchange, significantly impacts snowmelt rates and water management.
Literature ReviewHighly CitedMicro-Meteorological Conditions for Snow Melt
Snow may melt at air temperatures as low as -10°C and stay frozen at +10°C, depending on atmospheric variables and surface conditions.
Mesoscale Circulations Forced by Melting Snow. Part I: Basic Simulations and Dynamics.
Melting snow can induce mesoscale circulations, causing horizontal wind perturbations and vertical motions, with significant effects on the environment remote from the precipitation region.
Analysis of high rates of snow‐melting
High snow-melt rates are primarily driven by convection and condensation of moisture through turbulent diffusion of warm, moist air, with air temperature, humidity, and wind velocity playing a significant role in snow-melt rates.
A Thermodynamic Nonequilibrium Model for Preferential Infiltration and Refreezing of Melt in Snow
Preferential melt infiltration and refreezing of melt in snow significantly impact snow porosity and thermal and mass transport in nonlinear ways not captured by simpler models.
Anatomy of a late spring snowfall on sea ice
Late spring snowfalls can halt melt initiation and delay sustained melt by 11 days, affecting surface energy balance by mid-August.
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