University of Auckland X-Band Rain Radar Page

FAQ

• What is dBZ?
  The radar return from meteorological targets is called reflectivity, denoted by the letter Z. As the return can differ in strength by more than 10000 times between drizzle and heavy rainfall, a logarithmic scale is used giving the abbreviation dBZ (decibels of Z). dBZ is related to rainfall by what is known as a Z-R relationship. At the Mangakino site, we use the Marshall-Palmer relationship. Reflectivity less than around 22dBZ is considered drizzle, between 22-32dBZ light rain, moderate rain around 40dBZ getting to heavy rain over 45dBZ.
• Where can I find examples of radar observations?
  Some examples of observations made with Atmospheric Physics Group radars are listed below:
  
  • Storm over Tokoroa
  • Ash cloud at Mt Ruapehu
  • Waipapa Catchment
  • Beam Overshooting Example
  • More coming soon!
• Why does the rain sometimes appear only around the centre of the image?
  This occurs when either the rain is not intense enough for the radar to detect past a certain distance or the radar beam passes over the top of the rain at a certain distance.
• Why do some regions of the map always show high dBZ?
  This is due to ground clutter. When part of the radar beam intercepts the ground, a strong return can be received by the radar. These areas can be spotted in the PPI animation as the targets which do not move between images.
• Why are there sometimes concentric circles around the radar?
  Information from two elevation angles are used to construct the PPI image. This is so ground clutter near the radar can be minimized and the beam can be kept lower further from the radar. There is a cut-off distance where the image changes from the low elevation beam to the high elevation beam. At this point there may be substantially different rainfall rates at the two different beam heights. This can create circular artifacts.
• How can I get my own radar?
  The Atmospheric Physics Group does not manufacture radars for sale. We do however make our radars available for lease from time to time. If you are interested in incorporating one of our rain radars into a monitoring campaign enquires can be made with Prof. Geoff Austin.