Quality of Weather Radar Wind Profiles Iwan Holleman KNMI

1
Quality of Weather Radar Wind Profiles Iwan
Holleman (KNMI)

• Introduction of VAD technique in early 60s
• Development of VVP technique in late 70s
• Strong effort in retrieval of divergence and
  other non-linear parameters
• Hardly any comparison or verification studies
  focused on horizontal wind field
• This study Focus on high quality and high
  availability of horizontal wind vectors

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Velocity Azimuth Display (VAD)
ff20.4 m/s dd217 deg
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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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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

5
Verification against radiosonde
std.dev. 2 m/s

• Profiles from1 October 2001 till1 July 2002
• 22610 profiles on 268 days

T. Andersson RMS of 3-4 m/s for VAD
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Availability of VVP1 profiles
40
std.dev. 2 m/s
28
19
7
VVP1 versus wind speed
WMO simultaneous and within 5 km

• WMO requirements for upper-air wind observations

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VVP1 versus radiosonde

• Verification of speed and direction
• Both radiosonde and Hirlam model data as
  reference

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VVP1 against Hirlam
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Example of Wind Profiles

• 6 October 2003
• Doppler Radar and Hirlam analyses

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Conclusions

• VVP wind profile retrieval algorithms perform
  better than VAD algorithms
• Most simple VVP algorithm provides highest
  quality and availability horizontal wind data
• Availability is reasonable in boundary layer
  (?40)
• Retrieved wind vectors meet the WMO quality
  requirements
• Improvements for Rainbow VP2 module algorithms,
  output, and quality control

Acknowledgment Hans Beekhuis, Herman Wessels and
Sylvia Barlag
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Profiles during Bird Migration

• 28 October 2001
• Doppler Radar and Hirlam analyses
• Std.dev. 2.0 or 1.8 m/s

Birds?