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R. J. Doviak and D. Sirmans

Abstract

In this note we propose a technique to uncouple the tie between unambiguous Doppler velocity and range. Transmission of orthogonally polarized waves in pairs of pulses increases a weather Doppler radar's capability to unambiguously resolve velocity spectrum mean and variance at simultaneous range locations sampled in real time.

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D. Sirmans and R. J. Doviak

Abstract

First results derived from an NSSL effort to develop a real-time Plan Position Indicator (PPI) display of Doppler isotachs are described. The mean Doppler velocity is estimated for multiple range locations by measuring the phase change of the complex echo envelope over time intervals equal to the pulse repetition period. This technique, phase change per pulse pair, provides velocity estimates directly from samples of the Doppler time record to circumvent spectrum computation.

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R. J. Doviak and Dusan Zrnić

Abstract

Probert-Jones' radar equation assumes receiver bandwidth large compared to the reciprocal of the transmitted pulse width τ. The advent of coherent radars with precise transmitter frequencies allows consideration of receiver bandwidth “matched” to and sometimes smaller than τ−1 in order to enhance measurement signal-to-noise ratio.

An extension to the radar equation has been made to show explicitly the dependence of echo power on the product of transmitter pulse width and receiver bandwidth. When receiver bandwidth is less than twice τ−1, there is significant loss in echo power. This should be accounted for when estimating reflectivities.

Considerable improvement in Doppler velocity estimation can often be obtained by matching range resolution to the angular one and this has implications of practical importance when moderately sensitive dual-Doppler radars are used to map the mesoscale wind in clear air.

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D. S. Zrnić and R. J. Doviak

Abstract

A perturbation method is applied to spheroidal oscillating drops to determine the effect of fundamental axisymmetric oscillations on the power spectra and polarimetric measurements. It is shown that vibration magnitudes that produce less than 10% change in equilibrium axial ratios are insufficient to produce measurable changes in the differential reflectivity or differential phase constant, yet they can lead to a detectable increase in sidebands of the power spectra. Larger oscillations do produce measurable effects on the polarimetric variables.

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Albert J. Koscielny, R. J. Doviak, and R. Rabin

Abstract

Methods of statistical regression have been applied to single-radar radial velocity fields to map certain mesoscale (20–100 km) kinematic properties (e.g., divergence) of the convective boundary layer (CBL). Several methods, previously proposed, were found to produce estimates that were biased or whose variances were too large. When wind fields are linear on the meso- or larger scale, then single-Doppler velocity accuracies allow the estimation of horizontal divergence with an accuracy of about 4 × 10−5 s−1 and a resolution of ∼30 km, which may be sufficient to sense pre-thunderstorm convergence

A case study for 19 June 1980 suggests that single-Doppler weather radars of modest sensitivity can map the mesoscale divergence patterns within the cloud-free CBL. For this day, convergence zones to the northeast seem to precede cloud development by 1–2 h, and to the west precede thunderstorms by 3–4 h.

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R. F. Reinking, R. J. Doviak, and R. O. Gilmer

Abstract

A case-study comparison is made of simultaneous airborne gust probe and dual-Doppler radar measurements of motions associated with roll vortices in the optically clear planetary boundary layer. Inter-comparison of the cross-roll component of motion is emphasized. Some similarities and some differences in the data obtained with the two systems are discussed. Considering the differences in measurement techniques, agreement is good between the independent depictions of the roll structure and quantitative determinations of the intensities and predominant scales of eddy motion. The observed roll vortices fit descriptions and cause-effect relationships from certain models and other observations.

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R. M. Rabin, R. J. Doviak, and A. Sundara-Rajan

Abstract

Dual Doppler-radars are used to obtain momentum flux and turbulence intensities in the cloudless convective boundary-layer (CBL) containing roll vortices. Momentum flux from small scales unresolved by the radar is determined from the difference between the measured flux and the flux implied by the velocity defect profile. While the small-scale flux indicates a reasonable eddy diffusivity profile, the measured flux is of the opposite sign expected from K theory. Two terms in the turbulent kinetic energy budget, viz, the shear production and the divergence of the energy flux, are calculated for measurable scales. It is proposed that the tilting of convective roll circulations by cross-shear produces the observed flux in the upper part of the CBL.

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Y. Y. Lu, R. J. Doviak, and C. Crisp

Abstract

Velocity-azimuth display (VAD) products (i.e., wind, divergence, deformations, etc.) and a Lagrangian advective scheme applied to the reflectivity factor field are jointly used to estimate vertical profiles of vorticity. The reflectivity field is assumed to be conserved over the time period between radar observations. The vorticity selected gives the best least squares fit between observed and predicted reflectivity fields. These results suggest that vorticity is retrieved with a precision better than about 1×10−1 s−1 for scales on the order of 100 km and larger. The vorticity profiles are consistent with U.S. National Weather Service's analysis. The surface value of vorticity, extrapolated from the estimated profiles, is also compared with the vorticity calculated from Oklahoma mesonet data. The agreement is within the estimated standard error.

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Pravas R. Mahapatra, Richard J. Doviak, and Dusan S. Zrnić

A detailed and unique multisensor observation of an undular bore is presented. The data include those from rawinsonde, satellite, two Doppler radars, and a tall instrumented tower. Noteworthy are Doppler radar images that resolve the wave's characteristics and capture a good part of its spatial extent. The basic parameters of the wave train are established from the observations.

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C. Frush, R. J. Doviak, M. Sachidananda, and D. S. Zrnić

Abstract

It has been demonstrated through simulations that the SZ phase code method of mitigating range ambiguities has a performance that exceeds any other known phase-coding scheme. This paper describes an implementation of this code on a weather radar and compares its performance with that derived from simulations. Spectral data obtained from NCAR's S-Pol radar, which had its transmitted phases coded with the SZ(8/64) switching code, are presented to illustrate the steps in this method. It is shown that fully coherent transmitters, such as that used in the U.S.'s WSR-88D weather radars of the National Weather Service, have a system phase stability that takes full advantage of the unique properties of the SZ-coding method. The performance of this coding technique is evaluated by implementing it on a research WSR-88D weather radar. Results verify the dramatic increase in the area of reliable velocities compared to that provided by techniques presently employed in the operations. The performance of the SZ algorithm to retrieve weak signals overlaid by stronger signals is evaluated in the spectral domain by comparing a subjective analysis of the data field where the two overlaid echo spectra can be visually separated and mean Doppler velocities calculated.

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