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WEATHER: What forces affect our weather?

The Official Punxsutawney Phil Groundhog Site
Meet the groundhog in Groundhog Day—Pennsylvania's Punxsutawney Phil—and get the scoop on his "predictions."

StormFax Winter Weatherlore and Folklore Forecasts
"For every fog in August, there will be a snowfall in Winter," and other folklore about the weather.

A Meteorologist's Toolbox: Gathering Weather Data

Meteorologists use a variety of tools to help them gather information about weather and climate. Some more familiar ones are thermometers which measure air temperature, anemometers which gauge wind speeds, and barometers which provide information on air pressure. These instruments allow meteorologists to gather data about what is happening near Earth's surface. Collecting data from other sources—and other parts of the atmosphere—helps to create a more descriptive picture of weather.

Weather satellites

For viewing large weather systems on a worldwide scale, weather satellites are invaluable. Satellites show cloud formations, large weather events such as hurricanes, and other global weather systems. With satellites, forecasters can see weather across the whole globe: the oceans, continents, and poles. Recent satellite data is very detailed, even to the point of showing states and counties.

On each satellite there are two types of sensors. One is a visible light sensor called the "imager," which works like a camera in space and helps gather information on cloud movements and patterns. This sensor can only be used during daylight hours, since it works by capturing reflected light to create images. Since different surface features reflect light in distinctive ways, they can be distinguished from each other in the images. Water reflects very little light, making it appear black on the satellite image. Land masses tend to appear as shades of gray, depending on their temperature and moisture.

The second sensor is called the "sounder." It's an infrared sensor that reads temperatures. The higher the temperature of the object, the more energy it emits. This sensor allows satellites to measure the amount of energy radiated by Earth's surface, clouds, oceans, air, and so on. Infrared sensors can be used at night—a helpful feature for forecasters, considering that the imager can only pick up data during daylight hours.

Doppler radar

Doppler radar is another essential meteorological tool. Radar works a little differently from satellite sensors. Instead of reading reflected light or energy, radar measures reflected sound waves.

When sound waves are broadcast from a radar antennae, they may come into contact with objects in their path, such as dust particles or ice crystals. If they come into contact with an object that is moving away from the radar, the sound waves will be reflected back at a decreased frequency (that is, fewer sound waves will be reflected back within a certain time period). If the object they come in contact with is moving toward the radar, the sound waves will be reflected back at an increased frequency. This effect was discovered in 1842 by Christian Doppler. Later, scientists applied Doppler's principle to weather radar. Using Doppler radar, meteorologists can get a picture of precipitation that allows them to track a storm's progress over time.

[Back to "Forecasting"] [Next Topic: "Our Changing Climate"]

 "Weather" is inspired by programs from Planet Earth.

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