Detection of Gust Fronts Using the Doppler Velocity Derived Divergence Product
Detection of Gust Fronts Using the Doppler Velocity Derived Divergence Product

Author: Russell J. Clemins

Publisher:

Published: 2018

Total Pages: 152

ISBN-13:

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Identifying gust fronts can be essential for situational awareness when developing nowcasts during convective events. In addition to bearing potentially damaging winds, gust fronts also act as forcing mechanisms; influencing storm initiation, development, and propagation. Using doppler radar, gust fronts are usually observed by the presence of a reflectivity thin line ahead of the parent storm. In the situation where a thin line is not visible on radar, there is a loss of situational awareness. This study aimed to determine if gust fronts can be observed through the doppler velocity derived divergence product by isolating contiguous areas of divergence (convergence) that form couplets or line features, relative to the leading edge or ahead of a storm. Radar data for the study was collected using the University of Missouri -- Columbia's MZZU X-Band radar, as well as the WSR-88D from the NWS Saint Louis CFO. Data processing was performed through the Warning Decision Support System Integrated Information (WDSS-II), and the data was analyzed using the MatLab software. Thresholds for minimum pixel area, as well as minimum and maximum divergence (convergence) were used to establish a range of interest. Data was then filtered through a process of dilation and erosion, to prune out noise and highlight larger features. Through multiple cases using MZZU and KLSX, suitable criteria were developed that allowed the identification of Div-Conv couplets and linear regions of convergence that suggest the presence of gust fronts. Eddy covariance towers near Columbia, MO were used for surface observations of vertical velocity (w) and Turbulence Kinetic Energy (TKE). Good agreement was found between increases in w and TKE when gust fronts were detected and propagating through the region.

Development and Testing of the Gust Front Algorithm
Development and Testing of the Gust Front Algorithm

Author: Arthur Witt

Publisher:

Published: 1987

Total Pages: 42

ISBN-13:

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Threshold changes, additions, and other refinements to the original version of the Gust Front Algorithm are documented. Threshold changes include a minimum velocity difference threshold, the maximum azimuthal separation between vectors, and maximum range separation. Additions include gust front tracking and forecasting in Cartesian coordinates, vertical continuity checks of gust front features to reduce the occurrence of false detections, and horizontal wind estimation both ahead and behind a detected gust front using single Doppler velocity data. Results of these additions and the effects of threshold changes on detection capability are presented for several case studies. Keywords: Wind shear; Doppler radar; Gust fronts.

Investigation of the Detectability and Lifetime of Gust Fronts and Other Weather Hazards to Aircraft
Investigation of the Detectability and Lifetime of Gust Fronts and Other Weather Hazards to Aircraft

Author: Dušan S. Zrnić

Publisher:

Published: 1983

Total Pages: 0

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Low-altitude wind shear associated with diverging outflows has been related to several aircraft accidents. We examine several gust fronts using Doppler radar data and measurements from surface stations and tall tower. We present radar-derived parameters such as reflectivity, height, maximum shear, peak velocity, distance of the front from the producing storm and the nearest 30 dBZ contour for several gust fronts within 60 km of the radar during 1980 to 1982. For all orientations of the front, even along the radial direction, the forntal discontinuity was evident in both mean velocity and spectrum width fields. Thus, while detection is practical with a single Doppler radar, accurate estimation of shear magnitudes is more difficult when the frontal discontinuity is aligned along the radial. Several downdrafts of different sizes are present simultaneously behind some of the fronts and the maximum measured shear of radial velocities produced by one downdraft was .02/s. A more typical value of 100/s was observed at several locations. Maximum azimuthal shear of 470/s occurred at the wave crest.

On the Potential Use of the Terminal Doppler Weather Radar Gust Front Detection Algorithm on the WSR-88D System. Part II: Detecting Non-gust Front Convergent Weather Phenomena
On the Potential Use of the Terminal Doppler Weather Radar Gust Front Detection Algorithm on the WSR-88D System. Part II: Detecting Non-gust Front Convergent Weather Phenomena

Author:

Publisher:

Published: 1991

Total Pages: 44

ISBN-13:

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This study examines the capability of the Gust Front Detection Algorithm (GFDA) developed for the Terminal Doppler Weather Radar (TDWR) system to detect other types of non-gust front weather phenomena which are associated with patterns of convergence in a Doppler-radar radial velocity field. The potential use of the GFDA as a nowcasting tool, a mesoscale forecasting tool, and as a tool to detect other kinds of aviation hazards besides gust fronts, needs investigation. The phenomena studied include synoptic fronts, sea-breeze fronts, gravity waves, terrain-induced convergence boundaries, old thunderstorm outflow boundaries, and the convergence bands within extratropical cyclones associated with enhanced precipitation. Comparisons of the convergent characteristics of these other phenomena to those of gust fronts are made. In addition, several case studies are presented to demonstrate the ability of the GFDA to detect the non-gust front phenomena.

A Gust Front Case Studies Handbook
A Gust Front Case Studies Handbook

Author: Diana Lynn Klingle

Publisher:

Published: 1985

Total Pages: 96

ISBN-13:

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Gust fronts produce low altitude wind shear that can be hazardous to aircraft operations, especially during takeoff and landing. Radar meteorologists have long been able to identify gust front signatures in Doppler radar data, but in order to use the radars efficiently, automatic detection of such hazards is essential. Eight gust front case studies are presented. The data include photographs of the Doppler weather radar displays, thermodynamic and wind measurements from a 440 m high tower, environmental soundings and tables of gust front characteristics. The tabulated characteristics are those though to be the most important in developing rules for automatic gust front detection such as length and height, maximum and minimum values of reflectivity, velocity and spectrum width, and estimates of radial shear. For the cases studied, outflows could be detected most reliably in the velocity field, but useful information also could be gleaned from the spectrum width and reflectivity fields. The signal-to-noise ratio threshold was found to be a major factor in the ability of an observer to discern the gust front signature in the Doppler radar displays. Detection within the spectrum width field required a higher SNR than did the radial velocity field. Keywords: Doppler Weather Radar; Gust fronts; Low altitude wind shear; and Aviation weather hazards.