How do meteorologists use the Doppler effect to predict weather?

The Doppler effect is based on the principle of Doppler radar operation. When radio waves are reflected from a moving object, their frequency perceived by the motionless observer is dependent on the speed of movement.


Meteorological Doppler radars

Meteorological Doppler radars are used to detect cloud and air movement, providing data for observing and forecasting the weather. Thanks to such measurements, it is possible to warn people threatened by violent atmospheric phenomena, such as storms, weather fronts and tornadoes. Results of meteorological radars are widely available on the Internet.


What is the Doppler effect

The Doppler effect is a phenomenon observed for waves, consisting in the creation of a frequency difference sent by the source of the wave and recorded by an observer who moves with respect to the source of the wave. For waves propagating in the medium, such as, for example, sound waves, the effect depends on the speed of the observer and the source relative to the medium in which these waves diverge. In the case of propagating waves without the participation of a material medium, such as light in a vacuum (in general electromagnetic waves), only the difference between the speed of the source and the observer is significant.


Doppler frequency

When the source emits a wave all the time with the same frequency and does not move, the distance between consecutive wave crests is the same in all directions, whereas when the source moves, the distance between consecutive ridges depends on the direction of the wave propagation. For this reason, the immobile observer may receive a wave with a different frequency than the one transmitted, the change depending on the source speed and the angle between the observation direction and the source movement direction. The frequency difference between the transmitted and the received wave is called the Doppler frequency or the Doppler shift.

Frequency changes caused by the Doppler effect are described by slightly different relationships in the case of mechanical waves (eg sound waves) than in the case of electromagnetic waves (eg light, radio waves).