The Weather Notebook: Doppler Radar

Doppler Radar
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Dave Thurlow, Host

Hi, I'm Dave Thurlow with The Weather Notebook and today, we're going to take a look at Doppler radar, something that sniffs out even the tiniest raindrops and snowflakes for all of us to see.

NSSL's first Doppler Weather Radar located in Norman, Oklahoma. 1970's research using this radar led to the NWS NEXRAD WSR-88D radar network. NOAA Photo Library

To understand how Doppler works, you should know a bit about conventional radar. In the late 19th century, a guy named Heinrich Hertz demonstrated that metal objects reflect radio waves. By the middle of the 20th century, meteorologists had discovered that precipitation - raindrops, snowflakes, and hailstones - do the same thing. Now this knowledge allowed them to gather information about approaching storms.

Now, Doppler radar -- named after Johann Doppler, who, in 1842 was the first to come up with the idea of sound waves changing frequency if either the source or the observer was moving -- takes storm detection to another level. First of all, it transmits three or four times the number of microwaves per second that conventional radar does. It then compares the incoming waves with the outgoing waves, looking for a shift in the wavelength. If the storm is approaching the radar, the wavelength will be shortened; if it's moving away, the wave will be lengthened. This effect is appropriately called "The Doppler Effect."

By using multiple radar units, a 3-dimensional picture of the storm can be taken. The other amazing thing about Doppler is its sensitivity. It is so sensitive that it sees not only precipitation, but it can also see the air; it can see the wind.

Doppler radar can even see into the future. By looking at wind profiles, Doppler can detect conditions that are perfect for creating tornadoes and severe weather. By being able to see this pre-storm environment, forecasters can issue warnings up to twenty minutes in advance of severe weather-something unheard of with conventional radar.

For more about Doppler, please visit our website at www.weathernotebook.org. Our show was written today by Jeanne Twehous, produced by Bryan Sejvar, and engineered by Sean Doucette. The Weather Notebook is underwritten by Subaru with major support provided by the National Science Foundation.