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

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  1. Contents: Introduction to Doppler Radar Velocity Azimuth Display (VAD) Volume Velocity Processing (VVP) Implementation and quality control Verification against radiosonde and Hirlam Conclusions Upper Air Wind Measurements by Weather RadarIwan Holleman, Henk Benschop, and Jitze vd Meulen

  2. 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) ff=20.4 m/s dd=217 deg

  5. Doppler Radar Volume Scan • 10 Elevations between 0.5 and 25 degrees • Multiple VADs per height layer Height layer

  6. 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

  7. Weather Radar Wind Profiles • 8 January 2005 • Doppler Radarand 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%

  11. VAD and VVP against radiosonde

  12. VVP and radiosonde against Hirlam

  13. 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

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