Publications

The Convective Weather Product Development Team (PDT) was formed in 1996 as part of the reorganization of the FAA Aviation Weather Research Program, to provide an effective way to conduct critical applied research in a collaborative and rational fashion. Detecting and predicting convective weather is extremely important to aviation, since approximately half of the national airspace delay in the warm season is caused by thunderstorms. Reliable 0--6 hr storm predictions are essential for aviation users to achieve safe and efficient use of the airspace, as well as for future air traffic control automation systems. Our goal on this PDT is to direct our research and development activities toward operationally useful convective weather detection and forecast products, and delivery of those products, so that users can receive benefits on an immediate and continual basis. Given that we have many more initiatives than funding, we have chosen to prioritize our activities according to near-term achievable benefits to users. Our hope is that the success of initial planned demonstrations will help the FAA identify a consistent level of long-term R&D funding, so that we can make real progress towards achieving our full set of goals. In this paper, we present our statement of the FAA Convective Weather Forecasting problem, evidence of the need for forecasts in the National Airspace System (NAS), and an illustration of the air traffic delay caused by convective weather. We then discuss our research plan and rationale, and outline our main initiatives for the upcoming year.

Accurate, short-term forecasts of where thunderstorms will develop, move and decay allow for strategic traffic management in and around the aviation terminal and enroute airspace. Pre-planning to avoid adverse weather conditions provides safe, smooth and continuous air traffic flow and savings in both fuel cost and time. Wolfson, et. al ( 1997) describe the problem of convective weather forecasting for FAA applications. In 1995, National Center for Atmospheric Research (NCAR), MIT Lincoln Laboratory (MIT-LL) and National Severe Storms Laboratory (NSSL) scientists and engineers agreed to collaborate on the development of a convective weather forecasting algorithm for use in airport terminal areas. Each laboratory brings special strengths to the project. NCAR has been developing techniques for precise, short-term (0-60 minutes) forecasts of thunderstorm initiation, movement and dissipation for the FAA over the past ten years and has developed the Auto-Nowcaster software. MIT-LL has been developing real-time algorithms for the Integrated Terminal Weather System (ITWS), including techniques for storm tracking, gust front detection, and calculating storm growth and decay (as part of predicting microbursts) . NSSL has been working on the NEXRAD Storm Cell Identification and Tracking (SCIT) algorithm, and on understanding the predictive value of the storm cell information. Thus by using the latest research results and best techniques available at each laboratory, the collaborative effort will hopefully result in a superior convective weather forecasting algorithm. Our goal in the immediate future is to develop a joint algorithm that can be demonstrated to users of terminal weather information, so that the benefits of convective weather forecast information can be realized, and the remaining needs can be assessed. As a first effort in the collaboration, the laboratories fielded their individual algorithms at the Memphis ITWS site. This paper gives an overview of our collaborative experiment in Memphis, the system each laboratory operated, some preliminary analysis of our performance on one case, and our plans for the near future.

The Federal Aviation Administration's Terminal Doppler Weather Radar (TDWR) system was primarily designed to address the operational needs of pilots in the avoidance of low-altitude wind shears upon takeoff and landing at airports. One of the primary methods of wind-shear detection for the TDWR system is the gust-front detection algorithm. The algorithm is designed to detect gust fronts that produce a wind-shear hazard and/or sustained wind shifts. It serves the hazard warning function by providing an estimate of the wind-speed gain for aircraft penetrating the gust front. The gust-front detection and wind-shift algorithms together serve a planning function by providing forecasted gust-front locations and estimates of the horizontal wind vector behind the front, respectively. This information is used by air traffic managers to determine arrival and departure runway configurations and aircraft movements to minimize the impact of wind shifts on airport capacity. This paper describes the gust-front detection and wind-shift algorithms to be fielded in the initial TDWR systems. Results of a quantitative performance evaluation using Doppler radar data collected during TDWR operational demonstrations at the Denver, Kansas City, and Orlando airports are presented. The algorithms were found to be operationally useful by the FAA airport controllers and supervisors.

The Terminal Doppler Weather Radar (TDWR) system which has been developed by Raytheon Co. for the Federal Aviation Administration (FAA), provides automatic detection of microbursts and low-altitude wind shear. Microburst- and gust front-induced wind shear can result in a sudden, large change in airspeed which can have disastrous effect on aircraft performance. during take off or landing. The second major function of TDWR is to improve air traffic management through forecasts of wind shifts, precipitation and other weather hazards. The TDWR system generates Doppler velocity, reflectivity, and spectrum width data. The base data are automatically dealiased and clutter is removed through filtering and mapping. Precipitation and windshear products, such as microbursts and gust fronts, are displayed as graphic products on the Geographic Situation Display which is intended for use by Air Traffic Control supervisors. Alphanumeric messages indicating the various windshear alerts and derived airspeed losses and gains are sent to a flat panel ribbon display which is used by the controllers in the control tower. The TDWR proof-of-concept and operational feasibility have been demonstrated in a number of FAA-sponsored tests and evaluations conducted by Massachusetts Institute of Technology's Lincoln Laboratory (MIT/LL) in Memphis, TN (1985); Huntsville, AL (1986); Denver, CO (1987, 1988); Kansas City, MO (1989, and Orlando, FL (1990-1992). In order to verify that the TDWR meets FAA operational suitability and effectiveness requirements, an Operational Test & Evaluations (OT&E) was conducted at the Oklahoma City site during the period from 24 August to 30 October 1992. The testing addressed National Airspace System (NAS)-SS-1000 requirements, weather detection performance, safety, operational system performance, maintenance, instruction books, Remote Maintenance Monitoring System (RMMS), system adaptable parameters, bullgear wear, and limited Air Traffic (AT) suitability. The TDWR OT&E Integration and Operational testing was conducted using a variety of methods dependent on the area being tested. This paper discusses primarily the weather detection performance testing. A rough analysis was performed on the algorithm output and the base data to determine the performance of the TDWR in detecting wind shear phenomena. Final results will be available after additional testing, which is scheduled for Spring of 1993, and post analysis in conducted.

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.

During the summer of 1988, the Terminal Doppler Weather Radar (TDWR) Operational Test and Evaluation (OT&E) was conducted near Denver, CO. One of the objectives of this test was to assess the performance of the Gust Front Detection and Wind Shift Algorithms (Gust Front Algorithm) to be used in the TDWR system. This paper presents an overview of the Gust Front Algorithm system from data collection to products displays and discusses the performance of the algorithm during the 1988 OT&E. Data editing, product generation, ground truth and scoring issues are addressed. Scoring results for the various products are presented and problems identified during the OT&E are discussed. The design of the Gust Front Algorithm is discussed in the companion paper (Part 1 Current Status) numbered 1.6 in this preprint volume. The Gust Front Algorithm serves two functions: warning and planning. Warnings are provided in alphanumeric messages on a "Ribbon Display Terminal", Wind shear warnings are issued when a gust front impacts the runways or within 3 miles of the ends of the runways. The planning function consists of alerting an Air Traffic Control Supervisor when a change in wind speed and/or direction due to a gust front at the airport will occur within 20 minutes. This planning information is displayed on a Geographic Situation Usplay (GSD).

The gust front detection and wind shift algorithm is one of the two main algorithms developed for the Terminal Doppler Weather Radar (TDWR) program. This two-part paper documents some recent enhancements to, and the current status of, the algorithm (Part 1) and presents some results from recent testing of the algorithm during the TDWR Operational Test and Evaluation (OT&E) (Part 2: Klingle-Wilson et al., 1989).