Z-R Relationship - a mathematical equation that converts radar-measured reflectivity to an estimated rainfall rate. The reflectivity factor (Z) is related to both the dropsize distribution and the 6th power of the drop diameters. However, the radar only measures reflectivity, not the dropsize distribution. Hence, the dropsize distribution must be assumed and can be wrong. Unfortunately, different dropsize distributions can produce the same reflectivity factor but have markedly different rainfall rates. For example, many small drops can produce the same reflectivity as one large drop; however, the rainfall rate from the small drops is very different from the one large drop.

Zulu Time (Z) - global time scale based on the local time observed on the Prime Meridian; also called Greenwich Mean Time (GMT) or Universal Coordinated Time (UTC)