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The Assessment of VAD Wind Retrievable Method of Doppler Radar

Author: PeiLiSi
Tutor: YuXiaoDing；QiuChongJian
School: Lanzhou University
Course: Meteorology
Keywords: Doppler Radar VAD Wind profile Radiosonde Statistics Correlation
CLC: P412.25
Type: Master's thesis
Year: 2009
Downloads: 55
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Abstract


This article inter-compares the wind profiles retrieved from the Velocity Azimuth Display (VAD) technique against those observed at an adjacent radiosonde station(adjusted by NCEP data) for the period from 2004 through 2007 in Wenzhou, Zhejiang province, China. Extensive verification of Dpppler Radar VAD wind profiles were made at different heights and under different precipitation systems(widespread precipitation, convectional showery precipitation and tropical cyclone precipitation).A preliminary study of the influences caused by aerodynamic quantities has been carried out together with error analysis.The NCEP reanalysis data(1°×1°) were used to calculate the horizontal wind differences between the most adjacent radiosonde station and Radar site in order to correct the radiosonde data observed at this station. We therefore removed the obstacle that there is no radiosonde observations above the radar site. Results show that the correlation between the VAD wind profiles and radiosonde data were enhanced by this correction.There is a high correlation between the VAD wind profiles(both wind speed and wind direction) and the radiosonde data, with related coefficient of wind direction up to 0. 89 and 0. 81 for wind speed among all samples. The accuracy of retrieved wind direction data proves to be better than those of wind speed while the retrievability descends with height. The related coefficient of wind direction at 26 layers averaged to be 0. 86 with an averaged absolute deviation amounts to 20. 3 degree, for wind speed it is 0.78 and 3.81m/s respectively. The stability of VAD technique proves to be stable in 26 layers while slowly descends with height.The VAD technique provides the best wind profiles during widespread continuous precipitation whereas generates a reasonable estimate of wind speed and direction under tropic cyclones. It estimates wind speed and direction with significant errors during the convectional showery rain and is highly disabled by the aliased radial velocity data in tropical cyclones. Results show that there are significant underestimations of wind speed in both showery rain and tropical cyclones.Randomicity and uncertainty exist in the degree of correlation which has only been identified as related coefficients. As in this case,it depends much on the distribution of datas from different precipitation types. The fluctuation of related coefficient is caused rather by the distribution around the linear fitting line than the different precipitation system itself for it occurs relatively consistent with season in a settled site.We find that all of the vertical velocity, divergence and vorticity do not directly influence the accuracy of wind profile retrieved by using VAD method. These results prove that the VAD method is highly reliable. The vertical velocity, divergence and vorticity in zero order and second order harmonic waves seem not to directly influence the wind speed and direction which are obtained from the first harmonic wave.

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CLC: > Astronomy,Earth Sciences > Atmospheric science (meteorology ) > Atmospheric sounding ( meteorological observations ) > Detection techniques and methods > High-altitude meteorological service, the upper atmosphere > Radar
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