Monday
Monday: Which Way Is the Wind?
A gust rattles the rain gauge at Station Rooftop, and Rocket grabs it before it tips. "Wind!" he says. "We need to measure it."
Raven watches the lab flag snap on its pole. "What do you notice? The flag points one way, but the leaves blow the same way."
"So where is the wind coming from?" Rocket asks. He turns in a circle until his hair blows into his eyes.
Nova hovers beside the flag, holding steady against the gust. "A flag points away from the wind," she says. "Think about which side the wind must be pushing on."
Rocket faces into the wind, and the flag streams out behind him. "The wind is coming from the west," he says. "A west wind."
Raven writes it in the log. "First wind entry," she says. "Now we need to know why it blows at all."
Wind is air in motion
Wind is simply air in motion. When weather reports talk about wind, they mean the air moving sideways across the ground.
We cannot see air move, but we can measure its push on objects. A wind vane shows the wind's direction, and an anemometer measures its speed.
Even without instruments, you can tell the direction. A flag points away from the wind, and blown leaves travel away from where the wind comes from.
Airplanes take off and land facing into the wind.
Named for where it comes from
A wind is named for the direction it blows FROM. A report of a west wind at 15 miles per hour means air is moving from the west, toward the east.
Wind direction is also given in degrees, measured clockwise around a compass. North is 360 degrees, east is 90, south is 180 and west is 270.
This one rule trips up almost everyone at first. Say it to yourself: a north wind comes from the north.
- Read the question.
- Tap your answer.
| Statement | True or false? |
|---|---|
| Wind is air in motion. | ? |
| A west wind blows toward the west. | ? |
| A flag points away from the wind. | ? |
| Airplanes take off facing into the wind. | ? |
| Wind direction in degrees is measured clockwise from north. | ? |
Why air moves at all
Air moves because of pressure differences. High pressure pushes air toward low pressure, the way air rushes out of a squeezed balloon.
Meteorologists call the difference in pressure between a high and a low the pressure gradient.
The bigger the pressure difference, the faster the wind blows. Weather maps draw lines of equal pressure called isobars, and when they crowd together, the wind is strong.
If nothing else acted on the air, it would flow straight from high to low pressure. Later this week you will see why it curves.
Note what is in front of you, such as a tree, a fence or a street. If you know that compass direction, note it too.
Write the wind direction in your station log. If the air is still, write "calm".
The station stays on the ground, a railing or a windowsill. Nobody goes on a roof or a ladder.
Wind facts this week come from the National Weather Service's JetStream school, which you can read at weather.gov.
Good start. Tomorrow you will find out what gets the air moving in the first place: heat from the Sun.