What is differential reflectivity (ZDR)?

Differential reflectivity (ZDR) is specifically defined as the difference between the horizontal reflectivity (Z_hh) and the vertical reflectivity (Z_vv). It provides valuable information about the shape, size, and type of hydrometeors in a radar volume. ZDR is particularly useful for distinguishing between different types of precipitation, such as rain, snow, or hail, because varying shapes of particles will have different reflectivity values in horizontal versus vertical orientations.

By measuring this difference, meteorologists gain insight into the characteristics of precipitation, which can help in enhancing weather analysis and forecasts. Other options do not define ZDR accurately; for example, simply taking the average of horizontal and vertical reflectivity does not capture the essential concept behind ZDR, nor do the definitions related to signal power or precipitation intensity.