Conditions

Skiing, like all sports in the world, need some type of playing field to operate on. The playing field effects the way you can perform on skis, like a pitcher has a hard time pitching on a bad mound. The playing field for skiing is the snow bank of some mountain, small or large, in a resort or the outback. On resorts slopes are maintained every but the undeveloped areas is completely natural expect the few skiers that have gone through them and usually are thick powder. The formations of snow in the atmosphere The first step in the formation of snow is the water evaporating usually from an ocean or large body of water. But fog droplets or ice crystals could not even begin to happen without foreign nucleation sites. Gaseous molecules of vapor (evaporated water) condense with these foreign nucleation sites. Sea-salt particles serve as the foreign nucleation sites usually for fog droplets because fog is created by and/or over water. But on land where there is not a lot of slat particles, dust or mineral particles work to make the cloud instead. The water vapor that was been evaporated is supersaturated like an ice crystal but not like supercooled water droplets. The degree of the supersaturation is the ratio of the atmospheric water vapor pressure relative to the water vapor pressure over a surface at the give temperature. In cold areas the vapor condenses in the air right onto ice crystals instead of becoming water droplets. This vapor goes directly form a vapor state to a solid state bypassing the liquid step. And unlike water that grows in the air and then when it gets heavy enough falls, a snowflake grows as it falls while vapor freezes and attaches to it. Precipitation of Snow As snow crystals are falling to the earth they looking nothing like we think of them.

When snow falls to the ground and gathers together into a snow pack, in a mater of hours or even minutes it no longer has atmospheric conformation. These flakes barely look their original atmospheric forms. The falling rate of the snow actually depends on the temp are supersaturation from where the snow comes from. We think that snow is snow but actually 10 different types of snow have been catalogued within 10 general classifications. Still there are other outside forces that effect snowfall. For one there is air circulation. In the North Hemisphere the wind flows east to west in equatorial regions, west to east in the mid-latitudes, and east to West in the polar latitudes. The Southern Hemisphere it is mirrored in the same way. The heaviest precipitation and snowfall happens along the North Pacific Coast in areas like America, Norway, and the Northern Alps in Europe. But in the Southern Hemisphere the southern West Coast gets most of the snow. Depending on where it is air circulates around low-pressure storm cells in a counter-clockwise motion, clockwise in a high-pressure cell. The atmospheric snowfall determines most of the locations of major ski resorts. Most prosperous ski resorts are in Mountains where there is good flow of maritime, vapor-laden air, and usually on the windward side (Where the air is moist, incoming, rising, and cooling; and the depth of the snow there is the greatest). These mountains that get maritime airflow have large snow deposition rates with temperatures close to freezing, as well as a high humidity level. This condition makes a heavy, dense snow-pack that may even have some liquid water in it (some may think that liquid water in snow is a bad thing but actually it helps make snow compact and bond, which is very good for snowballs). In the continental interior mountains get snow that forms when temperature is lower and wither lower humidity. So the snow is lighter and colder as well and has less water, little settlement, and less internal bonding of the ice grains. Here the snow grows in the atmosphere from water vapor that first condenses directly into ice, first on nucleation particles, and into large amounts on the nucleated ice crystals. Then flakes get big enough to fall to the ground as snow. Artificial snow To make artificial snow ski resorts take big high pressure guns and eject liquid 20 to 20 feet into the air above a ski run that makes an artificial fog of small water droplets. To freeze the fog they add a nucleating agent (usually a harmless bacterial protein) with the water that is in the air. But all natural water has some type of foreign particles in it that can be a nucleating agent. When water contains only natural nucleating agents and it is used to make artificial snow, the temperature must be lower for it to freeze (usually Ð8û C or 19û F). Because they add a bacterial nucleating agent to the snow mix the temperature doesn't have to so cold (it only needs to be Ð2.9û C or 26.9û F) This way is really effective because it initiates the conversion of the water directly into in ice crystals from the interior of the water droplets. This can even happen at as warm a temperatures as Ð2û C (30û f). This way makes artificial snow have a superior base for heavily used ski runs; it is much denser than natural snow. Each water droplets has to have a diameter between 100-700 microns (100 hundred microns is about 0.004 of an inch) to become snow. These are shot 20-30 into the air from the guns into the cold air that is still needs to be very cold, so freezing is usually done in the morning. But these water droplets have to freeze before they hit the ground (which would be 15 seconds in the air), if they don't, when they hit the ground in a liquid from they instantly become ice instead of snow. With a bacterial nucleating agent the water can freeze faster and have a better chance of becoming snow. The bacterium strain Pseudomonas syringae is widely distributed in the environment and makes a good ice-nucleating agent. But what is interesting is that this bacterium was originally isolated in a corn plant. These bacteria are collected and then freeze-dried so that there are no live cells left in the protein mass. The cell membrane of this bacterium is the active nucleating agent and isn't always made exactly the same. Picture of p. 20 This protein is composed of amino acid chains of 8 units that couple to form 16-member chains which group to from 48-uinit structure. Each of these 48-unit structures is made up of 8 of the 8-unit building blocks of protein, which coil to form a hexagonal array that repeats with increasing fidelity toward one end. The liquid water content in artificial snow is extremely small, the density is from 400-440 gm m-3, but newly fallen snow is not usually above 100kg m-3. All of these grains have high density and are rounded from their beginning but natural snow takes a very long time to become rounded. So this makes artificial snow stronger than natural snow. Inside every snowflake there is a piece of solid ice that is actually very close to the melting point or you as it is also called, the triple point (wher4e ice, water, and vapor meet). Once the snow hits the ground the convex points and edges of the flake evaporate, so the snow loses its sharp corners and edges they had and become rounded and all the same size.