What is ZDR typically for prolate hydrometeors?

For prolate hydrometeors, which are elongated in shape (like raindrops or hailstones), the value of ZDR, or differential reflectivity, is typically less than 0 dB. Differential reflectivity is a measure of the difference in the reflectivity of the horizontal and vertical polarization of radar waves.

Prolate hydrometeors tend to reflect more radar energy in the horizontal polarization compared to vertical polarization because of their elongated shape. Thus, when measuring these hydrometeors, the horizontal component of reflectivity is greater than the vertical component, leading to a negative ZDR value.

In contrast, values such as approximately 0 dB or greater than 0 refer to other shapes of hydrometeors or specific conditions not associated with prolate shapes. For example, spherical hydrometeors, such as small raindrops, would typically yield ZDR values close to zero, while larger, more irregularly shaped particles might scatter radar waves in a way that does not significantly favor one polarization over another. The option referring to Z_hh, which represents the horizontal reflectivity, does not apply to prolate hydrometeors given that ZDR is specifically focused on the comparison between horizontal and vertical reflectivity