66 Mountain Winds-Mid

Mountain Winds FOCUS Question How do mountains help create wind?

Air on the Move Whoosh! Hold on to your hat! Wind can seem as if it comes out of nowhere. But it doesn't just happen Wind is moving air. You can't see it, but you can feel it. Air begins to move when sunlight warms Earth's surface. The air above the warming surface heats up and rises into the atmosphere. That's because warm air. is lighter than cold air High in the sky, the air cools down and begins to sink. The sinking cold air is replaced by more warm air rising up from the ground. This up-and-down motion of warm and cool air creates a cycle of moving air that we experience as wind.

Mountain Wind Landforms on Earth's surface, such as mountains, also play a role in how wind forms. For example, strong winds can move up a mountain slope and blast down the other side. One reason that mountains create wind is because of their height. The air at the top of a tall mountain is cooler than the air near the base. These differences in air temperature on a mountain help get wind moving. Do You Know? For every 305 meters (1,000 ft.) of elevation a person climbs up a mountain, the temperature drops by 3°C (5.5°F).

Up the Mountain Air that moves up the side of a mountain is called upslope wind. This type of wind happens during the day when sunlight warms a mountain slope. The air just above the slope gets warmer and lighter than the air farther up the mountainside. The warm air moves up the slope toward the cool summit. This upslope air motion is also called anabatic (an-uh-BA-tik) wind. If you have hiked up a mountain, you may have felt anabatic wind "pushing" you up the trail.

Down the Mountain Air moving down the side of a mountain is called a downslope wind. When the air on a mountain slope is colder than the air near the base of the mountain, it sinks. Downslope wind often happens at night as mountain slopes cool down. The colder the air, the faster it sinks and the stronger the wind. Katabatic (kat-uh-BA-tik) wind is a type of downslope wind common in Antarctica and Greenland. Icy mountain slopes chill the air just above them. The cold heavier air quickly sinks down the mountain, resulting in strong, cold wind Brrr!

Downslope Damage Sometimes downslope winds cause a lot of damage to towns that are near mountains. Gravity helps pull the heavy, cold air down the mountain. Downslope winds can develop into strong windstorms. Boulder is a town in Colorado near the Rocky Mountains. This town has had downslope winds blow at 160 kilometers (99 mi.) per hour. Winds that strong can rip roofs from buildings and shatter windows. They can topple trees and even flip parked motor homes.