Earth Science: Geology, the Environment, and the Universe

Chapter 13: The Nature of Storms

Problem of the Week

Doppler Radar: A Key to Tracking Severe Weather

The Perfect Storm

In the 2000 blockbuster movie, "The Perfect Storm," the captain of the swordfish ship, Andrea Gail, received regular weather reports via a type of onboard FAX system. The captain monitored weather factors, such as barometric pressure, temperature, wind speed, and radar images that showed the converging paths of three storm systems. In this true story, the three weather systems met head on, out in the North Atlantic, to produce one of the most intense storms in recorded history. Receiving meteorological reports allows ship captains to keep their ship and crew out of harms way, and in good fishing waters. You'll have to rent the movie to see how this captain used the information he had about the storm.

Severe or Clear?

Severe or Clear? When the weather is clear, we don't pay much attention to the weather reports given by the local meteorologists. But in the event of a severe weather system, such as a blizzard, thunderstorm, hurricane, or tornado we look to them to give us the most current, precise information possible. We expect them to predict the path of these storms, to tell us how fast the winds will blow, when to expect them in our area, and when the storms will be over. One of the most important tools used by the meteorologist to provide us with this information is Doppler radar. Doppler radar works by using the reflective nature of water in the atmosphere. Radar waves are sent out from a transmitter. These waves bounce off of, and are scattered by, raindrops, hail, and other things like large flocks of birds and buildings. As the scattered radar beam returns to the radar station, a receiver collects and measures the intensity of the beam. An image is produced from the returned radar beams giving information about a storm's intensity. The image is usually color enhanced by computers to clearly show the intensity of the weather activity within a storm system.

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Look at the Doppler radar image below. You can see that various colors are used to represent the different intensities of precipitation within a storm. Using the key beside the radar image, determine where the centers of heaviest precipitation are located. If you were a weather forecaster, how would you describe this storm that is affecting the state of Texas?

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NOAA

http://www.srh.noaa.gov/oun/wxdata/radarindex.html (image source page)

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Doppler radar is also used to detect the relative velocity of storm movement, that is, the motion of winds toward and away from the radar location. In a relative storm velocity image, blues and greens represent parts of the storm system where winds are moving toward the radar, and reds and yellows represent winds blowing away from the radar. A combination of these two colors extremely close to each other in a very small area of the radar image, is often the signature of a tornado. Take a look at the Doppler radar images below. Locate the tornado signatures.

Take a look at the Doppler radar images below. Can you find the tornado signatures?

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NOAA

  1. http://www.nssl.noaa.gov/noaastory/book.html

  2. http://www.spc.noaa.gov/coolimg/cape_may.htm

Websites to Visit:

  1. IMAX Film - Storm Chasers: Streaming Video of Tornado formation

  2. The Franklin Institute Online: Radar-ology

  3. Radar Meteorology: Online Remote Sensing Guide

  4. Severe Storms: Online Meteorology Guide

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