dBZ

dBZ, or decibels of Z, is a logarithmic unit used in radar meteorology to express radar reflectivity. The reflectivity factor Z is a measure of the amount and intensity of hydrometeors in a volume of air and is derived from the radar return signal. By using a decibel scale, the wide range of Z values encountered in weather radar data can be represented compactly.

Z is proportional to the sixth power of particle size and the number of particles; more specifically, Z is the sum over all hydrometeors of D^6 times their concentration. In practice, dBZ is computed as 10 log10(Z) with Z in units of mm^6 m^-3. Higher dBZ values indicate stronger radar echoes and, on average, heavier precipitation, though exact rainfall rate cannot be read directly from dBZ alone.

Radar meteorologists relate Z to rainfall rate R through empirical Z-R relationships, such as Z = a R^b; typical rain values are a ≈ 200 and b ≈ 1.6, as in the Marshall-Palmer relation, though coefficients vary with drizzle, snow, and hail. Meteorologists also use dBZ mosaics and cross sections to identify storm structure, intensity, and movement.

Limitations include attenuation at higher frequencies, partial beam filling, and non-precipitation echoes. Mixed-phase or non-meteorological targets can distort dBZ. Despite caveats, dBZ remains a standard, intuitive measure for assessing precipitation with weather radar.