dBZ????????????

Question

What does a negative dBZ on the doppler radar mean?

Answer 1

Somebody will probably give a better answer than this, but I know this much:

If you view a radar presentation with the scale beginning in negative dBZ's, the radar is in "clear air mode" ("CAM"). The local meteorologists ("mets") use CAM when there is no, or very little, precipitation.

In CAM, the radar's sensitivity is enhanced, which allows the mets to observe very subtle disturbances in the air. Even with a perfectly cloudless, blue sky, CAM can often detect old outflow boundaries from the previous night's thunderstorm activity, or differences in pressure or temperature from other boundaries. On a day when thunderstorms are forecast, these boundaries are often where new thunderstorms initiate, so seeing them can help the mets get a handle on what may soon transpire.

As soon as convection gets underway and there is some significant precipitation, the mets switch the radar over to precipitation mode (and then the scale starts at 0dBZ).

I have been told that "negative dBZ's" is not a false scale or whatever, but that they are, in fact.......negative dBZ's, if you know what I mean. I didn't get any further details.

That's not really "doppler", or velocity, radar, though. That's reflectivities...just how "loud' the echo is to the radar.

Answer 2

Based on the source provided:

In short, a negative dBZ describes a small reflectivity.

Basically, it is just a measurement of the reflectivity, Z, in decibels which describes the refelectivity or the amount of backscattered signal of different objects. The detectable range of reflectivities for different objects from a given radar systems can be large and may range from 0.0001 to 1,000,000,000 (for instance).

This is a vast range of numbers and therefore interpretation at a glance is not easy. We can choose to rescale this range of numbers using logarithms, we call this new scale dBZ:

dBZ=10 log(Z)

As a result of the logarithm the negative values appear for dBZ. For example,

10 log (0.0001) ,

where, 0.0001, is the smallest aforementioned reflectivity produces a dBZ value of:

-40

Answer 3

i think its the thing to find the dragons bawls

Answer 4

say what!?!?