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

Velocity Azimuth Display (VAD) ff=20.4 m/s dd=217 deg

Retrieval Techniques VAD1-2: Fourier expansion of radial velocity as a function of azimuth : V rad (  ) = 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) = u 0 + x  u/  x + y  u/  y + (z-z 0 )  u/  z  V(x,y,z) = v 0 + x  v/  x + y  v/  y + (z-z 0 )  v/  z  W(x,y,z) = w 0 + (z-z 0 )  w/  z

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

Verification against radiosonde T. Andersson: RMS of 3-4 m/s for VAD std.dev. 2 m/s Profiles from1 Octobe r 2001 till1 July profiles on 268 days

Availability of VVP1 profiles 40% 28% 19% std.dev. 2 m/s

VVP1 versus wind speed WMO: simultaneous and within 5 km WMO require ments for upper- air wind observ ations

VVP1 versus radiosonde Verification of speed and direction Both radiosonde and Hirlam model data as reference

VVP1 against Hirlam

Example of Wind Profiles 6 October 2003 Doppler Radar and Hirlam analyses

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

28 October 2001 Doppler Radar and Hirlam analyses Std.dev.= 2.0 or 1.8 m/s Profiles during Bird Migration Birds?