Quality of Weather Radar Wind Profiles Iwan Holleman

Quality of Weather Radar Wind Profiles Iwan Holleman (KNMI) l l l Introduction of VAD technique in early 60 s Development of VVP technique in late 70 s 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 l l l VAD 1 -2: Fourier expansion of radial velocity as a function of azimuth : Vrad( ) = a 0/2 + b 1 sin + a 1 cos + b 2 sin 2 + a 2 cos 2 +. . . VVP 1 -3: Use all available volume scan data for a given height layer at once Assumption of linear wind model at radar site: Ø Ø Ø 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 l l l 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 std. dev. 2 m/s l l T. Andersson: RMS of 3 -4 m/s for VAD Profiles from 1 October 2001 till 1 July 2002 22610 profiles on 268 days

Availability of VVP 1 profiles 40% 28% std. dev. 2 m/s 19%

VVP 1 versus wind speed WMO: simultaneous and within 5 km l WMO require ments for upperair wind observ ations

VVP 1 versus radiosonde l l Verification of speed and direction Both radiosonde and Hirlam model data as reference

VVP 1 against Hirlam

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

Conclusions l l l 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 VP 2 module: algorithms, output, and quality control Acknowledgment: Hans Beekhuis, Herman Wessels and Sylvia Barlag

Profiles during Bird Migration 28 October 2001 Birds? l Doppler Radar and Hirlam analyses l Std. dev. = 2. 0 or 1. 8 m/s l