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Vincent T. Wood

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Vincent T. Wood

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A ground-based Doppler radar technique is developed for detecting a tropical cyclone center position. Accurate determination of the cyclone center position, based on Doppler velocity measurements, will become essential for the issuance of hurricane advisories, forecasts, and warnings once a network of WSR-88D Doppler radars is deployed on the United States coastlines, islands, and military bases during the 1990s. This will allow high-resolution detection and tracking of hurricanes nearing land for the first time.

Simulated Doppler velocity data, which were reconstructed from wind field data collected by reconnaissance aircraft during Hurricanes Alicia (1983) and Gloria (1985), were used to test the concept of using ground-based Doppler radar data to estimate cyclone center location. The center range and azimuth estimates of a hurricane signature were calculated from the simulated coastal Doppler radar velocity data. Preliminary results indicate that the technique performed well for estimating center locations from the radar measurements compared with storm center positions determined from in situ aircraft measurements.

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Rodger A. Brown and Vincent T. Wood

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A tornadic vortex signature (TVS) is a degraded Doppler velocity signature of a tornado that occurs when the core region of a tornado is smaller than the half-power beamwidth of the sampling Doppler radar. Soon after the TVS was discovered in the mid-1970s, simulations were conducted to verify that the signature did indeed represent a tornado. The simulations, which used a uniform reflectivity distribution across a Rankine vortex model, indicated that the extreme positive and negative Doppler velocity values of the signature should be separated by about one half-power beamwidth regardless of tornado size or strength. For a Weather Surveillance Radar-1988 Doppler (WSR-88D) with an effective half-power beamwidth of approximately 1.4° and data collected at 1.0° azimuthal intervals, the two extreme Doppler velocity values should be separated by 1.0°. However, with the recent advent of 0.5° azimuthal sampling (“superresolution”) by WSR-88Ds at lower elevation angles, some of the extreme Doppler velocity values unexpectedly were found to be separated by 0.5° instead of 1.0° azimuthal intervals. To understand this dilemma, the choice of vortex model and reflectivity profile is investigated. It is found that the choice of vortex model does not have a significant effect on the simulation results. However, using a reflectivity profile with a minimum at the vortex center does make a difference. The revised simulations indicate that it is possible for the distance between the peak Doppler velocity values of a TVS to be separated by 0.5° with superresolution data collection.

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Rodger A. Brown and Vincent T. Wood

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Simulations were conducted to investigate the detection of the Doppler velocity tornado signature (TS) and tornadic vortex signature (TVS) when a tornado is located at the center of the parent mesocyclone. Whether the signature is a TS or TVS depends on whether the tornado’s core diameter is greater than or less than the radar’s effective beamwidth, respectively. The investigation included three radar effective beamwidths, two mesocyclones, and six different-sized tornadoes, each of which had 10 different maximum tangential velocities assigned to it to represent a variety of strengths. The concentric tornadoes and mesocyclones were positioned 10–150 km from the radar. The results indicate that 1) azimuthal shear at the center of the mesocyclone increases as the associated tornado gains strength before a TS or TVS appears, 2) smaller tornadoes need to be much stronger than larger tornadoes at a given range for a signature to appear within the mesocyclone, and 3) when the tornado diameter is wider than about one-quarter of the mesocyclone diameter, the TS or TVS associated with a given mesocyclone appears when the tornado has attained about the same strength regardless of range.

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Vincent T. Wood and Rodger A. Brown

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When a thunderstorm mesocyclone changes range relative to a Doppler radar, the deduced core diameter and mean rotational velocity of the Doppler velocity mesocyclone signature oscillate back and forth, even though the radar beam’s physical width changes uniformly with range. The authors investigated the oscillations using a model mesocyclone and a simulated Doppler radar that collected data with an azimuthal sampling interval of 1°. They found that the oscillations are a consequence of changing data point separation with range relative to the Doppler velocity peaks of the mesocyclone signature.

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Rodger A. Brown and Vincent T. Wood

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The National Weather Radar Testbed was established in Norman, Oklahoma, in 2002 to evaluate, in part, the feasibility of eventually replacing mechanically scanned parabolic antennas with electronically scanned phased-array antennas on weather surveillance radars. If a phased-array antenna system is to replace the current antenna, among the important decisions that must be made are the design (flat faces, cylinder, etc.) that will be needed to cover 360° in azimuth and the choice of an acceptable beamwidth. Investigating the flat-face option, four faces seem to be a reasonable choice for providing adequate coverage. To help with the beamwidth decision-making process, the influence of beamwidth on the resolution of various-sized simulated vortices is investigated. It is found that the half-power beamwidth across the antenna should be no more than 1.0° (equating to a broadside beamwidth of 0.75°) in order to provide National Weather Service forecasters with at least the same quality of data resolution that is currently available for making tornado and severe storm warnings.

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Rodger A. Brown and Vincent T. Wood

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Although the flow field within a severe thunderstorm is complex, it is possible to simulate the basic features using simple analytical flow models (such as uniform flow, axisymmetric rotation, axisymmetric divergence). Combinations of such flow models are used to produce simulated Doppler velocity patterns that can be used as “signatures” for identifying quasi-horizontal flow features within severe thunderstorms. Some of these flow features are: convergence in the lower portions of a storm and divergence in the upper portions associated with a strong updraft, surface divergence associated with a wet or dry downdraft, mesocyclone (rotating updraft), flow around an updraft obstacle, and tornado. Recognition of the associated Doppler velocity patterns can aid in the interpretation of single-Doppler radar measurements that include only the radial component of flow in the radar viewing direction.

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A Hole in the Weather Warning System

Improving Access to Hazardous Weather Information for Deaf and Hard of Hearing People

Vincent T. Wood and Robert A. Weisman

In this article, the problems deaf and hard of hearing people experience when attempting to access the weather warning systems in Oklahoma and Minnesota are documented. Deaf and hard of hearing people cannot hear Civil Defense sirens, cannot listen to local radio stations that are broadcasting emergency information through the Emergency Alert System, cannot access weather warnings through conventional National Oceanic and Atmospheric Administration (NOAA) Weather Radio, and often have problems obtaining weather information from local television stations due to the lack of text information. These problems had forced deaf and hard of hearing people to rely on looking at the sky or having hearing people alert them as their primary methods of receiving emergency information. These problems are documented through the use of a survey of277 deaf and hard of hearing people in Minnesota and Oklahoma as well as specific examples.

During the last two years, some progress has been made to “close this hole” in the weather warning system. The Federal Communications Commission has approved new rules, requiring that all audio emergency information provided by television stations, satellite, and cable operators must also be provided visually. In addition, the use of new technology such as pager systems, weather radios adapted for use by those with special needs, the Internet, and satellite warning systems have allowed deaf and hard of hearing people to have more access to emergency information.

In this article, these improvements are documented but continuing problems and possible solutions are also listed.

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Vincent T. Wood and Rodger A. Brown

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A variety of single Doppler velocity patterns that simulate those observed in a nondivergent environment is presented. Measurements in optically clear air and/or widespread precipitation are simulated, using horizontally uniform wind fields that vary with height. Vertical profiles of wind speed and direction indicated by the simulated Doppler velocity fields agree well with Doppler radar measurements. Horizontally uniform winds veering with height produce a striking S-shaped pattern, indicative of warm air advection; winds backing with height produce a backward S, indicative of cold air advection. A maximum in the vertical profile of wind speed is indicated by a pair of concentric contours, one upwind and one downwind of the radar. The presence of a frontal discontinuity is indicated by rapid variation of wind direction within the frontal zone. The wind speed profile controls the overall pattern including the spacing between contours, whereas the vertical profile of wind direction controls contour curvature.

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Vincent T. Wood and Luther W. White

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A parametric tangential wind profile model is presented for depicting representative pressure deficit profiles corresponding to varying tangential wind profiles of a cyclostrophic, axisymmetric vortex. The model employs five key parameters per wind profile: tangential velocity maximum, radius of the maximum, and three shape parameters that control different portions of the profile. The model coupled with the cyclostrophic balance assumption offers a diagnostic tool for estimating and examining a radial profile of pressure deficit deduced from a theoretical superimposing tangential wind profile in the vortex. Analytical results show that the shape parameters for a given tangential wind maximum of a non-Rankine vortex have an important modulating influence on the behavior of realistic tangential wind and corresponding pressure deficit profiles. The first parameter designed for changing the wind profile from sharply to broadly peaked produces the corresponding central pressure fall. An increase in the second (third) parameter yields the pressure rise by lowering the inner (outer) wind profile inside (outside) the radius of the maximum. Compared to the Rankine vortex, the parametrically constructed non-Rankine vortices have a larger central pressure deficit. It is suggested that the parametric model of non-Rankine vortex tangential winds has good potential for diagnosing the pressure features arising in dust devils, waterspouts, tornadoes, tornado cyclones, and mesocyclones. Finally, presented are two examples in which the parametric model is fitted to a tangential velocity profile, one derived from an idealized numerical simulation and the other derived from high-resolution Doppler radar data collected in a real tornado.

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