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An improved gust front detection algorithm for the TDWR
June 24, 1991
Conference Paper
Published in:
25th Int. Conf. on Radar Meteorology, Paris, France, 24-28 June 1991, pp. J37-J42.
Summary
Gust fronts are associated with potentially hazardous wind shears and cause sustained wind shifts after passage. Terminal Air Traffic Control (ATC) is concerned about the safety hazard associated with shear regions and prediction of the wind shift for runway reconfiguration. The Terminal Doppler Weather Radar (TDWR) system has a gust front detection algorithm which has provided an operationally useful capability for both safety and planning. However, this algorithm's performance is sensitive to the orientation of the gust front with respect to the radar radial. Due to this sensitivity, the algorithm is unable to detect about 50% of gust fronts that cross the airport. This paper describes a new algorithm which provides improved performance by using additional radar signatures of gust fronts. The performance of the current TDWR gust front algorithm for the various operational demonstrations has been documented in Klingle-Wilson et al. (1989) and Evans (1990). These analyses highlighted deficiencies in the current algorithm, which is designed to detect radial convergent shears only. When gust fronts or portions of gust fronts become aligned nearly parallel to a radial, the radial component of the shear is not as readily evident. In addition, gust fronts that are near or over the radar exhibit little radial convergence along their lengths and ground clutter can obscure the gust front near the radar. Thus, special handling is needed for fronts that approach the radar. Figure 1 illustrates the various components of a gust front as viewed by Doppler radar. The portion of the gust front in the figure labelled radial convergence is detectable with the current algorithm. Fronts, or portions of fronts, that are aligned along the radar radial and those that pass over the radar are examples of events which can exhibit little or no radial shear signature. These events are often detectable by variations in the radial velocities from azimuth to azimuth (i.e., azimuthal shear)., and/or by radar reflectivity thins lines. The new algorithm improves the detection and prediction of gust fronts by merging radial convergence features with azimuthal shear features, thin line features, and the predicted locations of gust fronts which are passing over the radar. The next four sections of this paper describe the individual components of the improved algorithm. Section 6 describes the rule base used to combine detections from the four components into single gust front detections and Section 7 discusses the output of the algorithm.
Summary
Gust fronts are associated with potentially hazardous wind shears and cause sustained wind shifts after passage. Terminal Air Traffic Control (ATC) is concerned about the safety hazard associated with shear regions and prediction of the wind shift for runway reconfiguration. The Terminal Doppler Weather Radar (TDWR) system has a gust...
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Status of the Terminal Doppler Weather Radar - one year before deployment
June 24, 1991
Conference Paper
Published in:
25th Int. Conf. on Radar Meteorology, Paris, France, 24-28 June 1991, pp. J1-J6.
Summary
The Federal Aviation Administration (FAA) initiated the Terminal Doppler Weather Radar (TDWR) program in the mid-1980s in response to the need for improved real time hazardous weather (especially low altitude wind shear) detection in the terminal area. The program is designed to develop a reliable automated Doppler radar based system to detect terminal weather hazards and provide warnings that will help pilots successfully avoid these hazards. Following the successful operational evaluation of the TDWR concept which was described at the last conference, a production contract was awarded to the Raytheon Company, with the first deliveries scheduled for fall of 1992. This paper will describe the current status and deployment strategy for the operational systems and present recent results from the extensive testing of the radar system concept and weather information dissemination approach.
Summary
The Federal Aviation Administration (FAA) initiated the Terminal Doppler Weather Radar (TDWR) program in the mid-1980s in response to the need for improved real time hazardous weather (especially low altitude wind shear) detection in the terminal area. The program is designed to develop a reliable automated Doppler radar based system...
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Characteristics of thunderstorm-generated low altitude wind shear: a survey based on nationwide Terminal Doppler Weather Radar testbed measurements
December 1, 1990
Conference Paper
Published in:
Proc. 29th IEEE Conf. on Decision and Control, 5-7 December 1990, Vol. 2, pp. 682-688.
Summary
The characteristics of microbursts and gust fronts, two forms of aviation-hazardous low altitude wind shear, are presented. Data were collected with a prototype terminal Doppler weather radar and a network of surface weather stations in Memphis, Huntsville, Denver, Kansas City, and Orlando. Regional differences and features that could be exploited in detection systems such as the associated reflectivity, surface wind shear, and temperature change are emphasized.
Summary
The characteristics of microbursts and gust fronts, two forms of aviation-hazardous low altitude wind shear, are presented. Data were collected with a prototype terminal Doppler weather radar and a network of surface weather stations in Memphis, Huntsville, Denver, Kansas City, and Orlando. Regional differences and features that could be exploited...
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A case study of the Claycomo, Missouri microburst on July 30, 1989
October 22, 1990
Conference Paper
Published in:
16th Conf. on Severe Local Storms/Conf. on Atmospheric Electricity, 22-26 October 1990, pp. 388-392.
Summary
The Terminal Doppler Weather Radar (TDWR) testbed collected thunderstorm measurements in the Kansas City area from March 27 through October 6, 1989. Of the 393 microbursts detected by the radar, 21 were classified as severe, with a differential velocity > 24 m/s. None of the severe events impacted terminal operations at Kansas City International Airport (KCI). Nevertheless, there were 42 microbursts within 3 nautical miles of the airport.
Summary
The Terminal Doppler Weather Radar (TDWR) testbed collected thunderstorm measurements in the Kansas City area from March 27 through October 6, 1989. Of the 393 microbursts detected by the radar, 21 were classified as severe, with a differential velocity > 24 m/s. None of the severe events impacted terminal operations...
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Aspect angle dependence of outflow strength in Denver microbursts: spatial and temporal variations
October 22, 1990
Conference Paper
Published in:
16th Conf. on Severe Local Storms/Conf. on Atmospheric Electricity, 22-26 October 1990, pp. 397-402.
Summary
MIT Lincoln Laboratory is being sponsored by the Federal Aviation Administration (FAA) to develop and test the Terminal Doppler Weather Radar (TDWR) wind shear surveillance system. As part of this program Lincoln has developed algorithms for automatically detecting microbursts, or thunderstorm outflows using the radial velocity data gathered from a single TDWR. Output from the detection algorithms will be used to warn aircraft of microburst hazards. While the success in automatically detecting microbursts using the Lincoln Laboratory microburst detection algorithm has been encouraging, one issue which continues to cause concern is microburst asymmetry. Asymmetry, or aspect angle dependence, in microbursts refers to outflows that have a divergent surface outflow strength or extent what varies depending on the aspect (or viewing) angle of the radar. The TDWR detection algorithms utilize input from a single Doppler radar; therefore, an asymmetric microburst may be underestimated or go undetected if the radar is viewing the event from an aspect angle where the strength of the outflow is weak. Additionally, the size and location of the event may be distorted when the outflow extent is significantly asymmetric. Most of the present outflow modeling and detection methods are based on the assumption of axial symmetry both in the strength and extent of outflows. Asymmetry in microbursts, therefore, is a major concern for TDWR microburst detection performance. Past work by Wilson et al. and Eilts has indicated that some microbursts are highly asymmetric, for at least a portion of their lifetime. However, this previous work has been limited in scope to single "snap-shots" of the microbursts, generally at their peak outflow strength. Strength asymmetries from these previous studies indicated asymmetry ratios (maximum over minimum strength) ranging from 1.3:1 to as high as 6:1. None of the studies dealt with shape (or extent) asymmetries. This paper describes the results from a detailed study of 96 individual observations from 27 microburst events. Measurements were taken to determine both the strength and extent of each microburst at multiple aspect angles. The data clearly show that microbursts, on average, have maximum strengths and extents which are 1.9:1 and 1.5:1 asymmetric, respectively.
Summary
MIT Lincoln Laboratory is being sponsored by the Federal Aviation Administration (FAA) to develop and test the Terminal Doppler Weather Radar (TDWR) wind shear surveillance system. As part of this program Lincoln has developed algorithms for automatically detecting microbursts, or thunderstorm outflows using the radial velocity data gathered from a...
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Observed differences between Denver and Kansas City gust fronts and their impact upon the performance of the gust front detection algorithm
October 22, 1990
Conference Paper
Published in:
16th Conf. on Severe Local Storms/Conf. on Atmospheric Electricity, 22-26 October 1990, pp. 236-239.
Summary
The Terminal Doppler Weather Radar (TDWR) testbed radar (known as FL-2) collected data near Denver's Stapleton Airport during 1988 and near the Kansas City International Airport (MCI) during 1989. One objective of the TDWR Program is to detect gust fronts and their associated wind shifts. This information can be used by an Air Traffic Control (ATC) supervisor to plan runway changes and for warnings of potentially-hazardous gust front-related wind shears to arriving and departing pilots. This function is performed by the gust front detection algorithm. An ongoing assessment of the performance of the current TDWR gust front algorithm is necessary to ensure that the algorithm performs consistently in different environments. Such assessments were performed after the 1988 TDWR Operational Test and Evaluation in Denver and after the 1989 operational season in Kansas City. This paper presents a comparison of gust front characteristics such as length, duration, strength, and propagation speed and direction that occurred in Denver and Kansas City and a comparison of algorithm performance at each location. In the following, the term gust front refers to the leading edge of the thunderstorm outflow throughout its life cycle. A gust front event is a single observation of a gust front (on a radar volume scan) by the National Severe Storms Laboratory (NSSL) ground-truth analyst.
Summary
The Terminal Doppler Weather Radar (TDWR) testbed radar (known as FL-2) collected data near Denver's Stapleton Airport during 1988 and near the Kansas City International Airport (MCI) during 1989. One objective of the TDWR Program is to detect gust fronts and their associated wind shifts. This information can be used...
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Predicting summer microburst hazard from thunderstorm day statistics
October 22, 1990
Conference Paper
Published in:
16th Conf. on Severe Local Storms/Conf. on Atmospheric Electricity, 22-26 October 1990, pp. 383-387.
Summary
Low-altitude wind shear, specifically, the aviation-hazardous form of wind shear known as the microburst, has been cited as the cause of several aviation disasters over the past two decades. Microbursts are strong, small-scale convective storm downdrafts that impact the ground and cause a violent divergent outflow of wind. The Federal Aviation Administration (FAA) recently awarded a contract for the production of 47 Terminal Doppler Weather Radars (TDWRs) to detect microbursts. Since the TDWR systems are expensive, only a limited number will be available for use at major U.S. airports. In deciding which airports will receive the TDWRs or any other advanced detection equipment, such as the ASR-9 with wind shear detection capability or the Enhanced Low Level Wind Shear Alert System, a detailed cost-benefit study will be performed. One factor that would aid in determining the benefit of advanced wind shear detection equipment is a knowledge of the average relative microburst threat at each major airport. Using "thunderstorm day" statistics and the results of measurements by the FAA TDWR testbed systems, we propose a method for predicting this threat.
Summary
Low-altitude wind shear, specifically, the aviation-hazardous form of wind shear known as the microburst, has been cited as the cause of several aviation disasters over the past two decades. Microbursts are strong, small-scale convective storm downdrafts that impact the ground and cause a violent divergent outflow of wind. The Federal...
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Vertical reflectivity profiles: averaged storm structures and applications to fan-beam radar weather detection in the U.S.
October 22, 1990
Conference Paper
Published in:
16th Conf. on Severe Local Storms/Conf. on Atmospheric Electricity, 22-26 October 1990, pp. 213-218.
Summary
The FAA is deploying over 100 next generation airport surveillance radars (ASR-9) at selected major airports across the country. Like previous ASRs, the ASR-9 utilizes dual broad elevation fan beams Figure 1) along with a rapid scan rate (12.5 RPM to exercise its primary function of detecting aircraft over a 60 nmi radius. In addition, the ASR-9 has a separate dedicated weather reflectivity channel which allows air traffic controllers to display quantitative precipitation intensity reports corresponding to the NWS six-level intensity scale on their PPI display. The 30 second update rate of the weather channel coupled with the large sample volume swept by the ASR-9 fan-beam combine to provide timely and useful indications of precipitation intensity within the terminal airspace. The PPI display of precipitation intensity which is presented to the air traffic controller is essentially a 2-D representation of the 3-D reflectivity field sampled by the fan-shaped beam of the ASR-9. Since the antenna gain varies with elevation angle (Figure 1), the parameter reopned by the ASR-9 weather channel represents a beam-weighted, vertically averaged estimate of storm intensity. Previous research has shown that the vertically integrated reflectivity automatically reported by fan-beam radars such as the ASR-9 correlates well with estimates of vertically integrated liquid water content (VIL), a useful meteorological parameter which is a measure of overall storm intensity. Dobson found a linear relationship between W and fan-beam reflectivity from 30 to 60 dBZ assuming the beam is filled with precipitation (see discussion in Section 4). If the beam is non-uniformly or only partially filled with precipitation, then the inherent vertical integration introduced by the fan-beam may cause an underestimation of the storm intensity. This beam filling loss is most acute at long range, where the vertical extent of the beam intercepts more than 10 km of altitude. The magnitude of this error depends on the complex interaction between the vertical reflectivity structure of the storm and its interception by the fan-shaped beam. If the shape and altitude extent of the vertical reflectivity profile (such as could be provided by a pencil-beam radar) are known, then a suitable adjustment can be calculated and applied to the fan-beam reflectivity estimate in order to produce the desired reflectivity report. The six-level weather thresholds are stored in processor memory for each range sate as functions of receive beam (high or low). The thresholds can be adjusted to compensate for beam filling losses. The adjustments initially implemented in the ASR-9 were derived using a reflectivity profile model which assumes the maximum reflectivity of the storm is distributed constantly from the surface up to 4 km, and then falls off at 3 dBZ per km above 4 km. The success of the reflectivity correction depends on how well the model profile matches actual storm profiles. If regional variations in general storm morphology are significant, then different beam filling loss correction models may need to be developed for specific regions. Understanding the significance of these regional variations in storm vertical reflectivity structure and their impact on ASR-9 weather report accuracy provided the motivation for this study.
Summary
The FAA is deploying over 100 next generation airport surveillance radars (ASR-9) at selected major airports across the country. Like previous ASRs, the ASR-9 utilizes dual broad elevation fan beams Figure 1) along with a rapid scan rate (12.5 RPM to exercise its primary function of detecting aircraft over a...
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Understanding and predicting microbursts
October 22, 1990
Conference Paper
Published in:
16th Conf. on Severe Local Storms/Conf. on Atmospheric Electricity, 22-26 October 1990, pp. 340-351.
Summary
Wind shear is a major cause of aircarrier accidents in the United States, and most of these accidents have been caused by one particular form of wind shear called a microburst (Zorpette, 1986). Microbursts have been defined as small scale, low-altitude, intense downdrafts which impact the surface and cause strong divergent outflows of wind. We know they are associated with thunderstorms and are usually but not always accompanied by heavy rainfall at the ground. However, a number of meteorologically distinct phenomena associated with thunderstorms can give rise to strong downdrafts and high surface winds. Most microburst research has focused on the main precipitation driven downdraft of thunderstorms, both with and without significant surface rainfall. But other downdraft types such as the dynamically driven downdrafts at low altitude associated with "vortices" at the leading edge of expanding thunderstorm outflows and with "roll clouds" have also been associated with the microburst problem. In this paper, I discuss these two primary forms of low altitude downdraft phenomena in thunderstorms. This differentiation is essential to discovering exactly what atmospheric conditions lead to the development of the most hazardous microbursts. A physically based predictive model for thunderstorm downdraft strength is presented which shows that the radar reflectivity of a storm alone cannot be used as a hazard index; information about the static stability of the atmosphere is also essential. I then show that the downdrafts associated with the gust front around a cold outflow from a small isolated thunderstorm, a microburst, are inherently stronger at low altitudes than those found in more straight-line gust fronts. Finally, I reexamine the most recent fatal U.S. microburst accident, the crash of Delta 191 at Dallas/Ft. Worth in 1985, and show that both types of low altitude downdrafts were encountered as part of the "microburst", although the downdrafts came from different storms.
Summary
Wind shear is a major cause of aircarrier accidents in the United States, and most of these accidents have been caused by one particular form of wind shear called a microburst (Zorpette, 1986). Microbursts have been defined as small scale, low-altitude, intense downdrafts which impact the surface and cause strong...
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Summer 1988 TDWR microburst analysis
July 1, 1990
Conference Paper
Published in:
Proc. Airborne Wind Shear Detection and Warning Systems, Second Combined Manufacturers' and Technologists' Conf., Pt. II, 18-20 October 1988, pp. 741-751.
Summary
The Terminal Doppler Weather Radar (TDWR) testbed system was operated during the months of July-August 1988 in a live operational demonstration providing microburst (and related weather hazard) protection to the Stapleton International Airport in Deilver, CO. During this time period, the performance of the detection system was carefully monitored in an effort to determine the reliability of the system. Initial performance analysis indicates that the microburst detection component of TDWR satisfies the basic performance goals of 90% probability of detection md 10% probability of false alarm. An in-depth study of the system performance, based on analysis of both dual-Doppler radar observations and surface mesonet measurements, is in progress to provide a detailed understanding of the observability of microbursts by the radar, the ability of the algorithms to detect microbursts observed by the radar, and the timeliness and accuracy of the microburst alarms provided to operational users.
Summary
The Terminal Doppler Weather Radar (TDWR) testbed system was operated during the months of July-August 1988 in a live operational demonstration providing microburst (and related weather hazard) protection to the Stapleton International Airport in Deilver, CO. During this time period, the performance of the detection system was carefully monitored in...
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