Radar beam refraction modelling

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Radar beam refraction modelling
Nordic weather radar workshop Helsinki
3.10.-4.10.2002

Uta Gjertsen, met.no, FoU
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• For the quantitative use of weather radar data in
  Norway it is essential to correct for beam
  shielding. The degree of beam shielding is
  variable due to changes in atmospheric humidity
  and temperature profiles. In the near future we
  will implement a model deriving the degree of
  beam blockage from actual radiosonde profiles.
  The model will increase the accuracy of the
  shielding correction and identify regions where
  data is missing due to anaprop. The model gives
  also an indication on situations with beam
  splitting. Beam splitting can produce large
  errors and is difficult to identify from NWP
  model or radar data alone.

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Todays precipitation composite

• Spatial gauge adjustment with mean monthly
  gauge/radar factors
• Precipitation intensity
• Accumulated precipitation

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Accumulated precipitation
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Radar OsloMean daily precipitation for a winter
and spring season, beam blocking and topography
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BeamsplittingRadar beam height as a function
of distance modeled from radiosonde data
16.8.2002 (elevation 0.5 degrees, radar Oslo)
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Beam shielding west of radar Oslo 16.8.2002

• Lower edge height of radar beam

Blue line measurement volume Red line
meausrement volume after beam blockage Dashed red
line measurement volume from standard atmosphere
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Beam splitting east of radar Oslo 16.8.2002
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Examples for vertical humidity and temperature
profiles causing anaprop.
Condition dN/dh
Trapping lt -157
Superrefraction -157 to -79
Normal -79 to 0
Standard -39
Subrefraction gt 0