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Peter S. Ray
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Peter S. Ray

Abstract

Tornadic storms passed between the two NSSL Doppler radars on 20 April and 8 June, 1974. Both radars simultaneously collected Dopplar data throughout these storms. From the derived velocity fields, vorticity and divergence calculations were made. Strongest convergence is noted in the weak echo region and between opposing vorticity centers.

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Peter S. Ray

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No abstract available.

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Peter S. Ray
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Peter S. Ray
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Terence Given and Peter S. Ray

Abstract

The wind field resulting from a two-dimensional dual-Doppler synthesis algorithms is spectrally modified from the true wind field. The effects of spatial filtering on wind fields from the processes of interpolation, the averaging of pulses, and the effect of the finite radar pulse dimension were assessed. The effect resulting from the use of different interpolation techniques was also evaluated. Of those techniques tested, the best are the Cressman distance-weighted averaging and linear distance-weighted averaging, with the closest neighbor and uniform weighting having more undesirable characteristics.

The optimum influence radius is defined as the influence radius at which the ratio of the rms difference between the Fourier and least-squares responses (a measure of the aliasing) and the variance of the filtered wind field is minimized. This seeks to minimize the effect of energy aliased into scales other than the input wavelength. For the Cressman interpolation technique, the optimum influence radius is between 1.85 and 2.25 times the maximum data spacing. The range of acceptable influence radii includes consideration of the filtering by the radar of the data as it is collected, as well as the resolution of the final dataset. The optimum influence radius is dependent upon the largest data separation in the analysis domain. The absolute optimum influence radius is not significantly affected by inclusion of the radar-beam filtering effects.

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Peter S. Ray and Conrad Ziegler

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A technique to remove the ambiguity in Doppler mean velocity estimates is described. The technique assumes that along a radial, or portion of a radial, the velocity estimates are quasi-uniformly distributed about the mean. If the data do not meet this criterion, the velocities are adjusted such that they are distributed about the mean.

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Peter S. Ray and Mary Stephenson

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On 20 April 1984, the NOAA WP-3D aircraft, equipped with a Doppler radar in its tail, flew around a growing thunderstorm new Norman, Oklahoma. Doppler wind data was collected as the airplane flew six legs around the storm. During this time, the National Severe Storms laboratory (NSSL) dual-Doppler network collected data on the same storm. Different combinations of synthesis techniques were examined employing direct and pseudo-dual-Doppler observations from aircraft alone, and combinations of aircraft and ground-based Doppler radar. The effect of temporal resolution errors was assessed and related to uncertainties caused by geometric configuration. For this system, it was found that although the aircraft did provide useful data by extending the analysis to the region between the ground-based radars, the contribution was limited by the rapid evolution of the storm. Greater utility may generally be found for storms that evolve less rapidly.

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Paul Bieringer and Peter S. Ray

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The installation of the network of NEXRAD (Next Generation Weather Radar) WSR-88D (Weather Surveillance Radar—1988 Doppler) radars has been an ongoing process for more than three years. An assessment is made on how these radars and related changes at National Weather Service Offices have impacted the warning of tornadoes. Tornado warning statistics were employed to evaluate the improvements in warning lead times and detection after the installation of the WSR-88D. In an effort to remove a bias from the warning dataset, the statistics based on the first tornado event of each day were also considered. This early evaluation of the warning capability of these radars indicates an improvement at selected sites over the previous five years.

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Gene B. Walker and Peter S. Ray

Abstract

A vertically looking, multiple-wavelength Doppler radar technique to estimate vertical velocity, drop size distribution and turbulence is presented. The ratio of the Doppler spectra, corresponding to the drop fall velocities at two different wavelengths, is uniquely related to the ratio of the radar scattering cross sections at the appropriate temperature. These ratios are used to estimate drop fall velocities and therefore drop size distributions and vertical wind. Turbulence, which broadens the velocity power spectrum, can be estimated by deconvolution and the drop size distribution subsequently derived.

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