Kim Pratt, age 11, of Union Grove, Ala., for her question:
WHAT IS A CHINOOK WIND?
Wind is air that moves across the surface of the earth. Sometimes it blows gently and other times it can be so hard and fast that it topples trees and knocks down buildings. Winds are named according to the direction from which they blow. An east wind blows from the east to the west while a north wind moves air from the north to the south.
Wind is caused by an uneven heating of the atmosphere by energy from the sun. The atmosphere is the air around the earth.
Air is heated by the sun unevenly. Air above hot areas expands and rises. Air from cooler areas then flows in to take the place of the heated air in a process called circulation. This circulation of air causes winds.
A Chinook wind is a warm, dry wind that blows down the slopes of the Rocky Mountains in early spring and winter. You'll find it in the northwestern United States and in southwestern Canada. A Chinook will usually blow from the west.
Chinook winds were named by early settlers who thought the winds came from the country of the Chinook Indians along the Columbia River.
As the winds move down a mountain slope, a Chinook gets warmer. Its temperature increases by about one degree Fahrenheit for every 180 feet of descent. A Chinook that moves 5,500 feet down a mountain slope is about 30 degrees warmer when it reaches the foot than it was at the top.
A warm Chinook wind takes up moisture by evaporation. It often melts snow as it spreads out at the base of the mountain, exposing grass so that cattle in the area are able to graze.
A wet Chinook is the name used by people who live along the Pacific Coast in Oregon and Washington. This type of wind is warm, moist air that moves in from the southwest.
Winds similar to the Chinook found in other parts of the world are often called foehns. The warm, dry wind from a foehn frequently blows down the side of the Alps in Europe. A foehn can affect the climate. Often the weather where the dry wind blows regularly is much warmer than at neighboring places.
Wind is measured with an instrument called an anemometer. The most common kind has three or four cups attached to the spokes on a rotating shaft. The spokes turn the shaft as the wind blows. The wind speed is then indicated by the speed of the spinning shaft.
In the United States, wind speeds are reported in miles per hour or in knots, which are nautical miles per hour. In other countries they are stated in kilometers per hour.