Chapter 11 Section 9 How is wind measured? Objective: Explain how weather instruments are used to describe wind.

Key Terms wind vane: instrument that indicates wind direction anemometer: instrument that measure wind speed

Showing Wind Direction Both wind speed and wind direction are significant to weather watchers. A wind is named for the direction from which it comes. If a wind comes from the north it is a north wind. If it comes from the east it is an east wind.

Showing Wind Direction The direction of a wind is determined with a wind vane. A wind vane shows the direction a wind is coming from. Many wind vanes are shaped like arrows. When the wind blows, the arrow turns and points into the wind. Often the direction of the wind is shown on a dial connected to the wind vane. The dial may indicate wind direction by points on a compass (E, W, N, S) or by degrees on a scale.

NAME: What is a wind that blows from the northeast named?

Measuring Wind Speed An anemometer is an instrument used to measure wind speed. It is often made of cups turned on their sides. These cups are attached to rods. Wind blowing against the cups causes the anemometer to turn. The faster and stronger the wind, the faster the anemometer turns. Anemometers usually have a meter attached to them that measures how fast the wind is blowing. It does this by measuring how fast the cups turn.

2. DESCRIBE: How does an anemometer work?

Weather Balloons Scientists sometimes use weather balloons to determine wind speed and direction. A weather balloon is filled with the gas helium. Helium gas is lighter than air. As a result, balloons filled with helium gas rise into the air.

Weather Balloons Winds high in the troposphere move a weather balloon along. Scientists can measure the speed of the wind by measuring the speed at which the balloon moves along. The direction it moves shows wind direction.

3. IDENTIFY: What do weather balloons measure?

11-9 Classwork Winds are named based upon the ___ from which they come. Wind direction is shown with a ___. Wind speed is measured with an ___. Weather balloons are filled with ___. Helium gas is ___ than air. INFER: A weather vane points to the north. From which direction is the wind blowing? HYPOTHESIZE: If carbon dioxide is heavier than air, can it be used in a weather balloon? Explain.