Upper Air Wind Measurements by Weather Radar Iwan Holleman, Henk Benschop, and Jitze vd Meulen

1
Upper Air Wind Measurements by Weather Radar
Iwan Holleman, Henk Benschop, and Jitze vd Meulen

• Contents
• Introduction to Doppler Radar
• Velocity Azimuth Display (VAD)
• Volume Velocity Processing (VVP)
• Implementation and quality control
• Verification against radiosonde and Hirlam
• Conclusions

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KNMI Weather Radar

• Only in presence of scatterers
• Measures radial velocity as function of range,
  azimuth, and elevation
• Unambiguous velocity is limited ? outliers due to
  dealiasing technique (dual-PRF)
• Assumption wind speed observed velocity

3
Weather Radar Wind Profiles

• Volume scan of radial velocity
• Algorithm for analysis
• Wind profile above radar site

4
Velocity Azimuth Display (VAD)
ff20.4 m/s dd217 deg
5
Doppler Radar Volume Scan

• 10 Elevations between 0.5 and 25 degrees
• Multiple VADs per height layer

Height layer
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Retrieval Techniques

• VAD1-2 Fourier expansion of radial velocity as a
  function of azimuth
• Vrad(?) a0/2 b1?sin? a1?cos?
• b2?sin2? a2?cos2? ...
• VVP1-3 Use all available volume scan data for a
  given height layer at once
• Assumption of linear wind model at radar site
• U(x,y,z) u0 x ?u/?x y ?u/?y (z-z0) ?u/?z
• V(x,y,z) v0 x ?v/?x y ?v/?y (z-z0) ?v/?z
• W(x,y,z) w0 (z-z0) ?w/?z

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Weather Radar Wind Profiles

• 8 January 2005
• Doppler Radar and Hirlam analyses

8
Implementation and Quality Control

• Volume scan data are input to retrieval
  techniques
• Application of minimum and maximum range
• Removal of radial velocities close to zero
• Binning of scan data in 8 azimuth sectors
  neighboring empty sectors are not allowed
• Linear fit using Singular Value Decomposition
  (SVD)
• VAD parameters per height layer are determined
  using weighted average
• Removal of radial velocity outliers and re-run of
  wind model fit

9
Verification of Wind Profiles

• Verification of Weather Radar Wind Profiles
  against radiosonde and Hirlam
• 9 Months of volume scan data, radiosonde and
  Hirlam profiles
• Comparison of different wind profile retrieval
  algorithms
• Availability
• Quality
• Impact of quality control procedures

10
Availability of VVP profiles
40
std.dev. 2 m/s
28
19
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VAD and VVP against radiosonde
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VVP and radiosonde against Hirlam
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Conclusions

• Weather radar provides wind profiles
• VVP algorithm performs better than VAD
• Availability of wind profiles is reasonable
• Weather radar winds are at least as good as
  radiosonde winds

More info I. Holleman, JAOT 2005, in press