Differential Reflectivity

  • Raindrops are not always spherical when they fall - especially the larger drops
  • They tend to become more oblate -->>
  • So, the reflectivity would be larger if the wave were horizontally polarized, or Zh > Zv
  • Define ZDR = differential reflectivity = 10 log (Zh/Zv)
  • ZDR is great for discriminating large drops from hail - hail tumbles randomly, looks like a spherical particle.
  • Here are typical ZDR values for different sized rain drops
  • So, ZDR for hail is about 0.
  • ZDR for ice is about 0 as well.

ZDR example for a summertime thunderstorm:

 Combining ZDR and other multi-parameter variables with dBZe can tell us much about the internal microphysical structure of storms


4. Dual-Pol Radar Products at:


image from NSSL