WX 101: How Radar Works

Weather 101: All
Doppler radar is the most powerful tool that meteorologists use when tracking weather, especially severe weather.  Radar stands for RAdio, Detection, And Ranging and has been used to track rain and thunderstorms since the 1940s.  During World War II, radar was used to track enemy planes, but every once in a while, the planes were just rain, leading radar technicians to realize radar’s potential as a weather forecasting tool. 
 

The Basic Data Collection

Though radar looks like Paul Bunyan’s golf ball sitting on a tee, there’s actually a spinning satellite inside of that ball.  As the radar spins, it emits small busts of energy then listens.  That small burst of energy sometimes interacts with objects (rain, bugs, ice) in the sky and a small part of the energy will be scattered back to the satellite.  The radar can then identify the location of that object by its rotational position (which way its facing) and how long it took to “hear” the returned energy (the longer it takes, the further away it is).  

Radar is also able to tell the intensity of the object it hits, depending on how strong the returned energy is.  This is how we can tell if the rain is light (usually a green color) or heavy (usually a red color).  Typically ice appears brighter because it is a larger object than rain drops.  

As the radar spins, it collects data for the entire 360 degrees and this is what we see as the radar image.  
 

Watching Objects Move

Doppler Radar doesn’t just tell us where an object is, but it has the ability to tell us which way those objects are moving too.  When the pulse of energy is scattered back, the radar reads the phase of the radio waves.  The phase is a mix of shape, position, and form.  By measuring how that phase changes, the radar can tell whether the object that its tracking is moving towards, or away from the radar and how fast it is doing so.  This allows for meteorologist to see the movement of the raindrops in the storm.  Because of this, rotation or strong areas of wind can be see, which improves the ability to track tornadoes, or damaging wind storms, which improves warnings. 
 

More Than One Level

Weather radars scan multiple levels of the atmosphere, which allows for the computer that puts the radar data together to create a 3-D model of the storm.  This aids in detecting hail.  By knowing the height of the storm as well as the amount of water (vertically integrated liquid) the radar meteorologist can predict the size of the hail in the storm. 
 

Counting Rain Drops

Radar has the potential to predict the amount of rainfall that falls from a storm.  This creates better flash flood warnings, as well as information to emergency officials of where the heaviest amounts have fallen.  This can help with evacuations or sandbagging.  However, this radar product can sometimes be skewed by hail in the storm, since the radar thinks the hail stone has more rain than it actually does. 

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