dBZ (meteorology)

For other uses, see DBZ (disambiguation).

The scale of dBZ values can be seen along the bottom of the image.

dBZ stands for decibels of Z. It is a meteorological measure of equivalent reflectivity (Z) of a radar signal reflected off a remote object.^[1] The reference level for Z is 1 mm⁶ m⁻³, which is equal to 1 μm³. It is related to the number of drops per unit volume and the sixth power of drop diameter.

Reflectivity of a cloud is dependent on the number and type of hydrometeors, which includes rain, snow, and hail, and the hydrometeors' size. A large number of small hydrometeors will reflect the same as one large hydrometeor. The signal returned to the radar will be equivalent in both situations, so a group of small hydrometeors is virtually indistinguishable from one large hydrometeor on the resulting radar image.

A meteorologist can determine the difference between one large hydrometeor and a group of small hydrometeors as well as the type of hydrometeor through knowledge of local weather condition contexts.

One dBZ-scale of rain:

• >65 Extreme
• 46-65 heavy
• 24-45 moderate
• 8-23 light
• 0-8 Barely anything

dBZ values can be converted to rainfall rates in millimetres per hour using this formula:

• $\frac{\mathrm{mm}}{\mathrm{hr}} = \left ( \frac{10^{(dBZ/10)}}{200} \right )^{5 \over 8}$^[2]

References

1. ^ NWS JetStream - Weather Glossary: D's
2. ^ "NWS NEXRAD". http://www.desktopdoppler.com/help/nws-nexrad.htm#rainfall%20rates. Retrieved November 7, 2010.