A phenomenon in which the shape of sunspots flattens as they approach the Sun's limb due to the solar rotation. More specifically, when a sunspot approaches the solar limbs the width of the penumbra,
relative to the umbra, on the side facing the center of the Sun seems to become narrower than on the side facing the limb. This phenomenon arises from a projection effect, and is due to a geometrical depression (the Wilson depression) in the layers of constant optical depth in sunspots.
Snow lost to wind ablation on one part of the glacier surface is often re-deposited in more sheltered parts of the glacier surface, making no contribution to glacier-wide ablation.
Blowing snow or drifting snow. Windborne snow may be redistributed from one part of the glacier to another. It contributes to the glacier-wide mass balance only when it is carried across a lateral bou
ndary of the glacier, either inward or outward, or when it suffers sublimation instead of being redeposited.
Any device designed to obstruct wind flow and intended for protection against any ill effects of wind. Installations of this type include agricultural shelterbelts, snow fences, and rain-gauge wind sh
ields.
The portion of the cooling of a human body caused by air motion. Air motion accelerates the rate of heat transfer from a human body to the surrounding atmosphere, especially when temperatures are belo
w about 7C (45F).
A means of quantifying the threat of rapid cooling during breezy or windy conditions that may result in hypothermia in cold conditions. The index is used to remind the public to minimize exposure when
outdoors and to take precautionary actions. In the late 1940s, Antarctic explorers Siple and Passel experimented with measuring the time it took to freeze 250 grams of water in different temperature and wind conditions. They developed empirical formulas relating these data to the rate of heat loss from exposed human skin. They developed the following formula which was used to determine the wind-chill index. At wind speeds of 4 mph or less, the wind chill temperature is the same as the actual air temperature: T_WC = 0.0817(3.71V^0.5 + 5.81 - 0.25V)(T-91.4)+91.4 where V is wind speed in mph and T is temperature in F.
A type of snow crust formed by the packing action of wind on previously deposited snow. Wind crust may break locally, but, unlike wind slab, does not constitute an avalanche hazard.