Water hydrometeors have a larger ZDR than ice hydrometeors when they are what?

The relationship between water hydrometeors and ice hydrometeors in terms of differential reflectivity (ZDR) is fundamentally linked to their shape and composition. Water hydrometeors, such as raindrops, typically take on a more spherical shape when they are in a liquid state. This spherical shape allows for better scattering of radar waves, resulting in a higher ZDR value.

In contrast, ice hydrometeors, which can take various forms such as snowflakes or ice crystals, have more irregular shapes and can include a wide variety of geometric complexities. These more varied shapes lead to less effective scattering of radar waves compared to the more uniform shape of liquid water droplets. Consequently, when comparing water and ice hydrometeors under the same conditions of size and physical shape, water hydrometeors will generally exhibit a larger ZDR.

The remaining options—different temperatures, varying altitudes, and mixing with wind—do not specifically address the crucial factor of shape affecting ZDR. While temperature and altitude may influence the phase and size of precipitation particles, they do not inherently account for the fundamental difference in shape and resulting ZDR values between water and ice hydrometeors. Thus, the most pertinent factor in the observed differences