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dBZ (meteorology)
From Wikipedia, the free encyclopedia
For other uses, see DBZ.
The scale of dBZ values can be seen along the bottom of the image.
dBZ stands for
decibels relative to Z. It is a
meteorological measure of equivalent
reflectivity (Z) of a
radar signal reflected off a remote object.[SUP]
[1][/SUP] The reference level for Z is 1 mm[SUP]6[/SUP]
m[SUP]−3[/SUP], which is equal to 1
μm[SUP]3[/SUP]. 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, graupel, 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:
[*=right]>65 Extreme
[*=right]46-65 heavy
[*=right]24-45 moderate
[*=right]8-23 light
[*=right]0-8 Barely anything
dBZ values can be converted to rainfall rates in millimetres per hour using this formula:
| dBZ | R (mm/h) | Rate (in/hr) | Intensity |
|---|
| 5 | 0.07 | < 0.01 | Hardly Noticeable |
| 10 | 0.15 | < 0.01 | Light Mist |
| 15 | 0.3 | 0.01 | Mist |
| 20 | 0.6 | 0.02 | Very Light |
| 25 | 1.3 | 0.05 | Light |
| 30 | 2.7 | 0.1 | Light to Moderate |
| 35 | 5.6 | 0.22 | Moderate Rain |
| 40 | 11.53 | 0.45 | Moderate Rain |
| 45 | 23.7 | 0.92 | Moderate to Heavy |
| 50 | 48.6 | 1.90 | Heavy |
| 55 | 100 | 4 | Very Heavy / Small Hail |
| 60 | 205 | 8 | Extreme / Moderate Hail |
| 65 | 401 | 15.6 | Extreme / Large Hail |
http://en.wikipedia.org/wiki/DBZ_(meteorology)