Sastrugi Sastrugi Sastrugi, or zastrugi, are sharp irregular grooves or ridges formed on a snow surface by wind erosion, saltation of snow particles, and deposition, and found in polar and open sites such as frozen lakes in cold temperate regions. The ridges are usually perpendicular to the prevailing winds; they are steep on the windward side and sloping to the leeward side. Smaller irregularities of this type are known as ripples (small, ~10 mm high) or wind ridges. Larger features are especially troublesome to skiers and snowboarders. Traveling on the irregular surface of sastrugi can be very tiring, and can risk
Surface-wave-sustained mode the generation of high density plasmas. Electromagnetic waves cannot propagate in over-dense plasmas. The wave is reflected at the plasma surface due to the skin effect and becomes an evanescent wave. Its penetration depth corresponds to the skin depth formula_1, which can be approximated by The non-vanishing penetration depth of an evanescent wave opens an alternative way of heating a plasma: Instead of "traversing" the plasma, the conductivity of the plasma enables the wave to propagate "along" the plasma surface. The wave energy is then transferred to the plasma by an evanescent wave which enters the plasma perpendicular to its