Snow science

Scientists improve storm forecasting, study global snow cover and its effect on climate, glaciers, and water supplies around the world.

Johannes Kepler attempted to explain why snow crystals are hexagonal in his 1611 book, Strena seu De Nive Sexangula.

A list of the main categories (quoted together with their codes) comprises:[15] The classification of frozen particulates extends the prior classifications of Nakaya and his successors and are quoted in the following table:[15] at −8 °C and below–30 °C at super-saturation at −3 to −5 °C below −60 °C at 0 to −3 °C and −8 to −70 °C at supersaturation at 0 to −3 °C and at −12 to −16 °C environmental conditions hexagonal or irregular in shape accretion of supercooled water droplets or milky glazed surface supercooled water, size: >5 mm mostly small spheroids Graupel or snow pellets encased in thin ice layer (small hail).

Size: both 5 mm needles pointing into the wind Thin breakable crust forms on snow surface if process continues long enough.

Thus, at any one time, the type and state of the snow forming a layer have to be defined because its physical and mechanical properties depend on them.

One challenge to this assessment is where snow cover is patchy, for example during periods of accumulation or ablation and also in forested areas.

Passive microwaves sensors are especially valuable for temporal and spatial continuity because they can map the surface beneath clouds and in darkness.

Some important aspects of snow cover include its albedo (reflectivity of light) and insulating qualities, which slow the rate of seasonal melting of sea ice.

As of 2011, the melt phase of GCM snow models were thought to perform poorly in regions with complex factors that regulate snowmelt, such as vegetation cover and terrain.

These models compute snow water equivalent (SWE) in some manner, such as:[21] SWE = [ –ln( 1 – fc )] / D where: Given the importance of snowmelt to agriculture, hydrological runoff models that include snow in their predictions address the phases of accumulating snowpack, melting processes, and distribution of the meltwater through stream networks and into the groundwater.

Key to describing the melting processes are solar heat flux, ambient temperature, wind, and precipitation.

Initial snowmelt models used a degree-day approach that emphasized the temperature difference between the air and the snowpack to compute snow water equivalent (SWE) as:[21] SWE = M (Ta – Tm) when Ta ≥ Tm where: More recent models use an energy balance approach that take into account the following factors to compute the energy available for melt (Qm) as:[21] Qm = Q* +Qh + Qe + Qg + Qr – QΘ where: Calculation of the various heat flow quantities (Q ) requires measurement of a much greater range of snow and environmental factors than just temperatures.