The Cooling Effect of Wind
Highland (alpine) tundra begins at the timberline on mountains. The patchy forest of short, bent trees bordering the tundra is called krummholz (German for "crooked wood"). These trees, usually low, bent, wind-shaped spruce and fir trees, are not a special species, instead the same trees if grown at a lower elevation where there is less wind would be taller and straighter.
Wind is the movement of air from one place to another in a direction relatively parallel to Earth's surface. Winds are produced by differences in atmospheric pressure, which are primarily due to differences in temperature. Persistent winds are a feature of both the lowland and highland tundras. Winds in highland tundras are due primarily to differences in air temperature between high and low elevations. Since tundra temperatures vary, wind speeds will vary, but highland tundra generally have high winds. For example, winds of 45 to 65 miles (74 to 105 km) per hour are common on Mount McKinley in Alaska, with gusts up to 100 miles (160 km) per hour even in summer.
In a cold, very windy environment, organisms must produce more heat and have better insulation and other adaptations for conserving heat than organisms living in a warm, slightly windy environment. This is because the body heat at the surface of an animal's skin is carried away by wind. The faster the wind, the faster it carries heat away from surfaces it passes over.
Winds also dry surfaces they pass over by speeding up evaporation of water from the surfaces. Some plants in the tundra have a waxy coating, much like desert plants, which prevents water loss as well as helps to keep the plant warm.
Winds also pick up particles of dirt, ice, and snow that grind away surfaces they hit, much the way sandpaper grinds away surfaces it is rubbed against. Animals can hide behind rocks and live in underground dwellings to protect themselves from the abrasive winds. Rocks also protect plants from the wind, and at times snow covers and protects above-ground plant parts.
To demonstrate the cooling effect of wind.
- Hold the back of your hand close to, but not touching, your mouth.
- Open your mouth and blow as hard as possible. Observe how warm or cold your breath makes your hand feel.
- Repeat steps 1 and 2, pursing your lips.
Your hand feels warmer when you blow on it with an open mouth and cooler when you blow on it through pursed lips.
The temperature of your breath is the same whether your mouth is open or your lips are pursed. The difference in the perceived temperature is that with your mouth open your warm breath comes out slowly, gently pushing away the air layer above your hand and taking its place. Since your breath is warmer than the air layer, your skin feels warmer. But when you purse your lips, the air is forced through a smaller opening and comes out of your mouth more rapidly. The faster-moving air blows away the air layer above your hand, allowing cooler air from the room to move in. This makes your skin feel cooler.