Question

What information does Doppler radar give that conventional radar cannot? air pressure relative humidity wind speed and direction vertical development Rayleigh scattering

Answer 1

1> Conventional radar detects the presence of dense objects (such as precipitation) in the field, while the Doppler system detects a phase shift between the outgoing and incoming signals.

2>

Doppler radar weather equipment

The electronics in the Doppler radar weather observing unit can track and find the correct way to interpret the shift. Then we can tell if the object is moving towards the radar station or away from it, and how fast.

Bear in mind, though, it cannot detect any lateral movement, any motion towards to the left and right when viewed from the radar. It cannot tell the difference between a lateral wind and no wind at all. You need a person to look at the animated figures for that.

It is this capability that enables Doppler radar users to identify rotating areas and twisters. As well as mesocyclone signatures giving the possibility of vortex tornadoes.

3> Rayleigh scattering :

When the size of the particle is much less than the wavelength of the radar, a nearly linear relationship (called the "Rayleigh scattering regime") exists for the amount of scattering produced. This applies to most precipitation, as average raindrops range in size from about 1 mm to 4 mm and snowflakes are typically a bit larger. When the size of a particle is about the same as, or larger than, the radar wavelength, the scattering produced by particles becomes more complicated and falls under the "Mie scattering regime."

Because the radar equations are based on Rayleigh scattering approximations, any large targets (for example, hailstones, birds, some insects) will result in errors in scattering calculations and therefore reflectivity values. Furthermore, scattering calculations assume that the targets are spheres while birds, insects, and many hailstones are not. Therefore, reflectivity values from large targets should not be taken to be representative of their size.