The Doppler Effect and Its Effect On You
If you watch a weather report on television, you may have heard of the term “Doppler radar” during weather forecasts. What exactly is a Doppler radar? Also, fundamentally, what is the Doppler effect?
The Doppler effect is a phenomenon that can be observed with a moving object which is emitting waves. Many objects emit waves: cars and trains emit sound waves, and stars emit light waves, just to name a few examples. Imagine a time when you were standing outdoors and a vehicle (such as a fire truck with its sirens on) drove by you. The sound you hear from the moving vehicle becomes higher-pitched as the vehicle moves toward you, and the sound becomes lower-pitched after the vehicle passes by and drives away from you. Why does this happen?
This visual could help you picture the fire truck example.
We can imagine wave-emitting objects like a siren-emitting fire truck as “point sources” of waves. This means the object can be modeled as a single point that emits circular waves that drift outward from itself, sort of like what you see when you drop a pebble into a pond. Keeping this in mind, if the point source moves, then the circular waves become more densely-packed in the direction that the object is moving in, and the waves become more sparse in the direction behind the object’s motion. For example, if we have a fire truck traveling to the left emitting the sound of a siren, then to the left of the fire truck the sound waves are closely-packed together, and to the right they are farther apart from each other. See if you can picture this, because this is the key to understanding the Doppler effect. This is why if you’re standing in front of a moving vehicle, you hear a high-pitched sound (high frequency, sound waves closer together), and if you’re standing behind a moving vehicle, the sound is low-pitched (low frequency, sound waves farther apart).
So, how does the Doppler effect affect weather forecasting? Doppler radars are devices that emit waves, which get reflected from objects in the sky such as raindrops, snowflakes, or even dust. The reflected waves can be interpreted in several ways. The number of reflected waves can tell weather forecasters how intense a storm is, and the frequency of the reflected waves can reflect (no pun intended) which direction the storm is traveling in relative to the direction that the Doppler radar is pointing in. These things are all useful information for weather forecasters, which is why you sometimes hear the term “Doppler radar” during weather forecasts.
(Image from Wikipedia.)
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