Weather Radar



Radar bounces radio waves off raindrops in clouds
Click on image for full size (19K JPEG)
Radar is an important part of forecasting because it can tell where rain is. It bounces radio waves off raindrops in clouds. A computer measures how long it takes for the waves to reflect back. It then figures out how far away the rain is by how long it takes for the waves to travel back. The computer also measures how much energy is reflected back. The more energy reflected, the more rain is in the clouds.

A new kind of radar called Doppler radar can do a lot more. It can not only figure out how far away a raindrop is, it can also tell where it's moving towards us or away from us. Scientists know that if the rain is moving, the wind must be pushing it. That's how they know where the wind blows in clouds.


Current U.S. Radar

Weather Radar



Radar bounces radio waves off water particles in clouds
Click on image for full size (19K JPEG)
Radar is important to weather forecastors because it tells where rain and hail are. It bounces radio waves off water particles in clouds. A computer measures how long it takes for the waves to reflect back and then uses the time to calculate how far the particle is away from the radar. It also measures how much energy is backscattered (reflected back to the radar) and can tell how much precipitation is in the clouds.

A new kind of radar called Doppler radar can do a lot more. It not only can figure out how far away a raindrop is, it can also calculate if it's moving toward or away from the radar. Meteorologists know that if the rain is moving, then the wind must be pusing it. That's how they can tell where the wind is blowing in clouds.


Current U.S. Radar

Weather Radar



Radar bounces radio waves off water particles in clouds
Click on image for full size (19K JPEG)
Radar is important to weather forecastors because it can detect rain and hail in clouds. The radar emits radio waves in all directions. When a wave hits water or ice particles, some of the energy is backscattered to the radar. A receiver pickes up the returning energy and calculates how many particles there are (by how much energy is returned) and how far away the particles are (by how long it took for the energy to return).

The next generation of weather radar, NEXRAD, uses Doppler technology. It is also called WSR--88D, which is short for Weather Surveillance Radar--1988 Doppler. 1988 was the year they were developed to replace the previous radar, WSR-57 (which still used vacuum tube technology). The new radars can detect a doppler-shift in the returning radio waves and uses this shift to measure the speed of the particles toward or away from the radar. Meterologists know that the wind must be pushing the particles. Using the doppler radar they can measure the wind speed and direction in a cloud.


Current U.S. Radar


Last modified July 31, 2008 by Vanessa Pearce.
The source of this material is Windows to the Universe, at http://www.windows.ucar.edu/ at the University Corporation for Atmospheric Research (UCAR). © The Regents of the University of Michigan. Windows to the Universe® is a registered trademark of UCAR. All Rights Reserved. Site policies and disclaimer