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  • 1
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    Analysis of the 16 May 2015 Tipton, Oklahoma, EF-3 Tornado at High Spatiotemporal Resolution Using the Atmospheric Imaging Radar (2018)
    American Meteorological Society
    Details
    Publication Date: 2018-07-01
    Description: In this study, data collected by the Atmospheric Imaging Radar (AIR) are analyzed in conjunction with WSR-88D data (KFDR) for a tornado near Tipton, Oklahoma, on 16 May 2015. The analysis presented herein utilizes PPIs from both radars, polarimetric data from KFDR, time–height plots from the AIR, and a ground-based velocity track display (GBVTD) analysis. This study is novel in that it uses high-resolution mobile radar data (update time of 6–7 s) in tandem with polarimetric data from KFDR in order to identify possible areas of debris, including a debris ring contained within the outer vortex circulation. Leveraging the high spatiotemporal resolution of the AIR with the polarimetric capability of KFDR leads to analysis of reflectivity distributions, debris lofting, kinematic changes, and oscillations in tornado intensity during a portion of the mature stage of the tornado, with a particular focus on the relationship between changes in the reflectivity field and dynamical changes around the tornado. Debris is lofted in a high-reflectivity concentric ring of increasing radius and height around the tornado over several minutes, within the outer weak-echo hole (WEH). Simultaneously, debris lofting and asymmetric reflectivity distribution around the WEH coincide with changes in vortex tilt on multiple occasions. In one instance, hydrometeor fallout appears to precede a possible descending reflectivity core. Using the GBVTD results, near-surface convergence intensifies at the same time and location as when the debris ring is lofted. Additionally, strengthening of the tornado via multiple modes of vertical evolution (i.e., bottom-up intensification over time vs simultaneous intensification throughout the lowest few hundred meters) is observed.
    Print ISSN: 0027-0644
    Electronic ISSN: 1520-0493
    Topics: Geography , Geosciences , Physics
    Published by American Meteorological Society
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  • 2
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    Polarimetric Observations of Chaff Using the WSR-88D Network (2018)
    American Meteorological Society
    Details
    Publication Date: 2018-04-30
    Description: Chaff is a radar countermeasure typically used by military branches in training exercises around the United States. Chaff within view of the S-band WSR-88D beam can appear prominently on radar users’ displays. Knowledge of chaff characteristics is useful for radar users to discriminate between chaff and weather echoes and for automated algorithms to do the same. The WSR-88D network provides dual-polarimetric capabilities across the United States, leading to the collection of a large database of chaff cases. This database is analyzed to determine the characteristics of chaff in terms of the reflectivity factor and polarimetric variables on large scales. Particular focus is given to the dynamics of differential reflectivity ZDR in chaff and its dependence on height. In contrast to radar observations of chaff for a single event, this study is able to reveal a repeatable and new pattern of radar chaff observations. A discussion about the observed characteristics is presented, and hypotheses for the observed ZDR dynamics are put forth.
    Print ISSN: 1558-8424
    Electronic ISSN: 1558-8432
    Topics: Geography , Physics
    Published by American Meteorological Society
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  • 3
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    Observations of Severe Local Storms and Tornadoes with the Atmospheric Imaging Radar (2017)
    American Meteorological Society
    Details
    Publication Date: 2017-05-01
    Description: Mobile radar platforms designed for observation of severe local storms have consistently pushed the boundaries of spatial and temporal resolution in order to allow for detailed analysis of storm structure and evolution. Digital beamforming, or radar imaging, is a technique that is similar in nature to a photograwphic camera, where data samples from different spaces at the same range are collected simultaneously. This allows for rapid volumetric update rates compared to radars that scan with a single narrow beam. The Atmospheric Imaging Radar (AIR) is a mobile X-band (3.14-cm wavelength) imaging weather radar that transmits a vertical, 20° fan beam and uses a 36-element receive array to form instantaneous range–height indicators (RHIs) with a native beamwidth of 1° × 1°. Rotation in azimuth allows for 20° × 90° volumetric updates in under 6 s, while advanced pulse compression techniques achieve 37.5-m range resolution. The AIR has been operational since 2012 and has collected data on tornadoes and supercells at ranges as close as 6 km, resulting in high spatial and temporal resolution observations of severe local storms. The use of atmospheric imaging is exploited to detail rapidly evolving phenomena that are difficult to observe with traditional scanning weather radars.
    Print ISSN: 0003-0007
    Electronic ISSN: 1520-0477
    Topics: Geography , Physics
    Published by American Meteorological Society
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  • 4
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    Weather Radar Network Benefit Model for Nontornadic Thunderstorm Wind Casualty Cost Reduction (2020)
    American Meteorological Society
    Details
    Publication Date: 2020-09-28
    Description: An econometric geospatial benefit model for nontornadic thunderstorm wind casualty reduction is developed for meteorological radar network planning. Regression analyses on 22 years (1998–2019) of storm event and warning data show, likely for the first time, a clear dependence of nontornadic severe thunderstorm warning performance on radar coverage. Furthermore, nontornadic thunderstorm wind casualty rates are observed to be negatively correlated with better warning performance. In combination, these statistical relationships form the basis of a cost model that can be differenced between radar network configurations to generate geospatial benefit density maps. This model, applied to the current contiguous U.S. weather radar network, yields a benefit estimate of $207 million (M) yr−1 relative to no radar coverage at all. The remaining benefit pool with respect to enhanced radar coverage and scan update rate is about $36M yr−1. Aggregating these nontornadic thunderstorm wind results with estimates from earlier tornado and flash flood cost reduction models yields a total benefit of $1.12 billion yr−1 for the present-day radars and a remaining radar-based benefit pool of $778M yr−1.
    Print ISSN: 1948-8327
    Electronic ISSN: 1948-8335
    Topics: Geosciences , Physics
    Published by American Meteorological Society
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  • 5
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    Geospatial QPE Accuracy Dependence on Weather Radar Network Configurations (2020)
    American Meteorological Society
    Details
    Publication Date: 2020-10-27
    Description: The relatively low density of weather radar networks can lead to low-altitude coverage gaps. As existing networks are evaluated for gap fillers and new networks are designed, the benefits of low-altitude coverage must be assessed quantitatively. This study takes a regression approach to modeling quantitative precipitation estimation (QPE) differences based on network density, antenna aperture, and polarimetric bias. Thousands of cases from the warm-season months of May–August 2015–17 are processed using both the specific attenuation [R(A)] and reflectivity–differential reflectivity [R(Z, ZDR)] QPE methods and are compared with Automated Surface Observing System (ASOS) rain gauge data. QPE errors are quantified on the basis of beam height, cross-radial resolution, added polarimetric bias, and observed rainfall rate. The collected data are used to construct a support vector machine regression model that is applied to the current WSR-88D network for holistic error quantification. An analysis of the effects of polarimetric bias on flash-flood rainfall rates is presented. Rainfall rates that are based on 2-yr/1-h return rates are used for a contiguous-U.S.-wide analysis of QPE errors in extreme rainfall situations. These errors are then requantified using previously proposed network design scenarios with additional radars that provide enhanced estimate capabilities. Last, a gap-filling scenario utilizing the QPE error model, flash-flood rainfall rates, population density, and potential additional WSR-88D sites is presented, exposing the highest-benefit coverage holes in augmenting the WSR-88D network (or a future network) relative to QPE performance.
    Print ISSN: 1558-8424
    Electronic ISSN: 1558-8432
    Topics: Geography , Physics
    Published by American Meteorological Society
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  • 6
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    High-Temporal Resolution Observations of the 27 May 2015 Canadian, Texas, Tornado Using the Atmospheric Imaging Radar (2019)
    American Meteorological Society
    Details
    Publication Date: 2019-02-26
    Description: On 27 May 2015, the Atmospheric Imaging Radar (AIR) collected high-temporal resolution radar observations of an EF-2 tornado near Canadian, Texas. The AIR is a mobile, X-band, imaging radar that uses digital beamforming to collect simultaneous RHI scans while steering mechanically in azimuth to obtain rapid-update weather data. During this deployment, 20°-by-80° (elevation × azimuth) sector volumes were collected every 5.5 s at ranges as close as 6 km. The AIR captured the late-mature and decaying stages of the tornado. Early in the deployment, the tornado had a radius of maximum winds (RMW) of 500 m and exhibited maximum Doppler velocities near 65 m s−1. This study documents the rapid changes associated with the dissipation stages of the tornado. A 10-s resolution time–height investigation of vortex tilt and differential velocity is presented and illustrates an instance of upward vortex intensification as well as downward tornado decay. Changes in tornado intensity over periods of less than 30 s coincided with rapid changes in tornado diameter. At least two small-scale vortices were observed being shed from the tornado during a brief weakening period. A persistent layer of vortex tilt was observed near the level of free convection, which separated two layers with contrasting modes of tornado decay. Finally, the vertical cross correlation of vortex intensity reveals that apart from the brief instances of upward vortex intensification and downward decay, tornado intensity was highly correlated throughout the observation period.
    Print ISSN: 0027-0644
    Electronic ISSN: 1520-0493
    Topics: Geography , Geosciences , Physics
    Published by American Meteorological Society
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  • 7
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    Weather Radar Network Benefit Model for Tornadoes (2019)
    American Meteorological Society
    Details
    Publication Date: 2019-04-22
    Description: A monetized tornado benefit model is developed for arbitrary weather radar network configurations. Geospatial regression analyses indicate that improvement of two key radar parameters—fraction of vertical space observed and cross-range horizontal resolution—leads to better tornado warning performance as characterized by tornado detection probability and false-alarm ratio. Previous experimental results showing faster volume scan rates yielding greater warning performance are also incorporated into the model. Enhanced tornado warning performance, in turn, reduces casualty rates. In addition, lower false-alarm ratios save costs by cutting down on work and personal time lost while taking shelter. The model is run on the existing contiguous U.S. weather radar network as well as hypothetical future configurations. Results show that the current radars provide a tornado-based benefit of ~$490 million (M) yr−1. The remaining benefit pool is about $260M yr−1, split roughly evenly between coverage- and rapid-scanning-related gaps.
    Print ISSN: 1558-8424
    Electronic ISSN: 1558-8432
    Topics: Geography , Physics
    Published by American Meteorological Society
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  • 8
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    A Pulse Compression Waveform for Improved-Sensitivity Weather Radar Observations (2014)
    American Meteorological Society
    Details
    Publication Date: 2014-12-01
    Description: The progression of phased array weather observations, research, and planning over the past decade has led to significant advances in development efforts for future weather radar technologies. However, numerous challenges still remain for large-scale deployment. The eventual goal for phased array weather radar technology includes the use of active arrays, where each element would have its own transmit/receive module. This would lead to significant advantages; however, such a design must be capable of utilizing low-power, solid-state transmitters at each element in order to keep costs down. To provide acceptable sensitivity, as well as the range resolution needed for weather observations, pulse compression strategies are required. Pulse compression has been used for decades in military applications, but it has yet to be applied on a broad scale to weather radar, partly because of concerns regarding sensitivity loss caused by pulse windowing. A robust optimization technique for pulse compression waveforms with minimalistic windowing using a genetic algorithm is presented. A continuous nonlinear frequency-modulated waveform that takes into account transmitter distortion is shown, both in theory and in practical use scenarios. Measured pulses and weather observations from the Advanced Radar Research Center’s dual-polarized PX-1000 transportable radar, which utilizes dual 100-W solid-state transmitters, are presented. Both stratiform and convective scenarios, as well as dual-polarization observations, are shown, demonstrating significant improvement in sensitivity over previous pulse compression methods.
    Print ISSN: 0739-0572
    Electronic ISSN: 1520-0426
    Topics: Geography , Geosciences , Physics
    Published by American Meteorological Society
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  • 9
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    Objective Optimization of Weather Radar Networks for Low-Level Coverage Using a Genetic Algorithm (2012)
    American Meteorological Society
    Details
    Publication Date: 2012-06-01
    Print ISSN: 0739-0572
    Electronic ISSN: 1520-0426
    Topics: Geography , Geosciences , Physics
    Published by American Meteorological Society
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  • 10
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    High-Temporal Resolution Polarimetric X-Band Doppler Radar Observations of the 20 May 2013 Moore, Oklahoma, Tornado (2015)
    American Meteorological Society
    Details
    Publication Date: 2015-07-01
    Description: On 20 May 2013, the cities of Newcastle, Oklahoma City, and Moore, Oklahoma, were impacted by a long-track violent tornado that was rated as an EF5 on the enhanced Fujita scale by the National Weather Service. Despite a relatively sustained long track, damage surveys revealed a number of small-scale damage indicators that hinted at storm-scale processes that occurred over short time periods. The University of Oklahoma (OU) Advanced Radar Research Center’s PX-1000 transportable, polarimetric, X-band weather radar was operating in a single-elevation PPI scanning strategy at the OU Westheimer airport throughout the duration of the tornado, collecting high spatial and temporal resolution polarimetric data every 20 s at ranges as close as 10 km and heights below 500 m AGL. This dataset contains the only known polarimetric radar observations of the Moore tornado at such high temporal resolution, providing the opportunity to analyze and study finescale phenomena occurring on rapid time scales. Analysis is presented of a series of debris ejections and rear-flank gust front surges that both preceded and followed a loop of the tornado as it weakened over the Moore Medical Center before rapidly accelerating and restrengthening to the east. The gust front structure, debris characteristics, and differential reflectivity arc breakdown are explored as evidence for a “failed occlusion” hypothesis. Observations are supported by rigorous hand analysis of critical storm attributes, including tornado track relative to the damage survey, sudden track shifts, and a directional debris ejection analysis. A conceptual description and illustration of the suspected failed occlusion process is provided, and its implications are discussed.
    Print ISSN: 0027-0644
    Electronic ISSN: 1520-0493
    Topics: Geography , Geosciences , Physics
    Published by American Meteorological Society
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