Thunderstorms and especially lightning pose a safety risk to people outdoors whether they are working or enjoying themselves with recreational activities.  It is imperative to bring people inside to safety whenever thunderstorms and lightning are nearby.

NCAR has been developing algorithms to better diagnose lightning threats and prediction of such threats into the near future enabling more consistent and proactive decisions for bringing people inside to safety.  The BoltAlert^® system processes radar, temperature, and lightning data to derive statistically calibrated lightning probability and lightning safety guidance for specifiable locations.

ONGOING RESEARCH

BoltAlert® lightning potential (high risk in magenta) and actual strikes.

NCAR is working toward a better characterization of the true lightning hazard that is needed as basis for improving the safety of outdoor personnel and minimizing avoidable operational inefficiencies.  Research is underway to combine multiple sources of relevant information (e.g., radar and lightning data from more than one source) for a robust diagnosis of lightning threats.  Moreover, a nowcasting component is developed that enables recognizing lightning threats prior to impact allowing for proactive actions.  Such a capability to alert of impending lightning impacts is of particular interest to airports, sites for handling or testing equipment, fuel, ammunition and missiles, outdoor venues (e.g., baseball parks, swimming pools) and special events (e.g., Olympics), construction and open-air mining sites, utilities (e.g., energy, electricity transmission), recreation (e.g., hiking, camping, boating), transportation, and many others more.

To order BoltAlert® contact: 

info@ral.ucar.edu
303.497.8422

Related Project:
Lightning Impacts on Aviation

Windshear and Turbulence Warning System - Hong Kong

An operational Windshear and Turbulence Warning System (WTWS) was developed for Hong Kong's NewAirport at Chek Lap Kok. The WTWS provides alerts for terrain–and convective–induced windshear and turbulence. The system has been utilized by air traffic controllers and pilots since opening day, 6 July 1998. In addition to providing real–time windshear and turbulence alerts to controllers and pilots, the system provides up to 12–hour forecasts of terminal area turbulence to aviation meteorologists.

Project History

Hong Kong's New Airport at Chek Lap Kok (CLK) is located on partly reclaimed land adjacent to Lantau Island, whose rugged terrain has a maximum elevation of nearly 1,000 meters. Consequently, aircraft operating at the new airport may be affected by significant terrain-induced windshear and turbulence under certain meteorological conditions. In order to enhance safety and operational efficiency at the airport, Weather Information Technologies Inc. (WITI) developed a Windshear and Turbulence Warning System (WTWS) which was installed, tested and has been operational since the airport's opening day, 6 July 1998. Since 1998, the Hong Kong Observatory (HKO) has performed routine evaluations of the system and has made improvements to various sensing systems and wind shear and turbulence detection algorithms.

Hong Kong International Airport

The 44–month project was under the sponsorship of the Hong Kong Observatory. The WTWS development team included WITI, the National Center for Atmospheric Research (NCAR), Hong Kong University of Science and Technology (HKUST), and the University of Wyoming.

Topographical map of the region near Hong Kong's new airport. The highest elevations are above 800 meters.

Components include basic and applied research on wind flow over Hong Kong's terrain, a scientific field study, warning system concept and feasibility studies, system design, development, testing, implementation and training. The WTWS provides real–time hazardous weather information to air traffic controllers and pilots to enhance safety in the terminal area and improve predictions of hazardous weather to support strategic decision making by air traffic managers.

The WTWS is the first system worldwide to provide real–time alerts of terrain–induced turbulence and alerts for both convective and terrain–induced windshear, the WTWS also provides predictions of turbulence caused by terrain and airport surface wind as well as numerical weather prediction guidance. For detection of convective windshear, the WTWS relies partly on the output from a Terminal Doppler Weather Radar (TDWR) at Tai Lam Chung, about 12 kilometers from CLK. The windshear warning system ingests TDWR products including gust front, precipitation intensity, and storm motion, providing an integrated alert system. It generates graphics and text designed for easy interpretation by pilots, controllers, traffic managers and aviation forecasters. It also interfaces with other airport systems, reaching a broader user community including airport authority staff and airline offices.

Prior to the development of the windshear warning system, several studies were conducted in Hong Kong to gain insight into the meteorological conditions near the location of the new airport. These studies included analysis of routine weather observations, special observing programs and meteorological modeling of the differences between the existing Kai Tak Airport and the new airport. Variables that were analyzed included wind direction and speed, temperature, clouds, visibility, rainfall, thunderstorms and fog. Methods used to conduct these studies included investigative flights by light aircraft and water tank and wind tunnel experiments.

The probability of significant turbulence and windshear at Chek Lap Kok during specific meteorological conditions prompted the Hong Kong government to create the WTWS program. It was designed to investigate the detailed wind flow environment near the airport site and based on the scientific results, build and implement an operational windshear and turbulence warning and forecasting system. Following a competition, the project was awarded to Weather Information Technologies Inc. in October 1993.

Note: The WTWS was previously known as the OWWS – the Operational Windshear Warning System.

WTWS Products

The Hong Kong graphical display.

Example of animated replay of recent product history.

The primary WTWS product suite includes detection of terrain-induced turbulence, terrain-induced windshear, convective microburst and windshear, gust fronts, precipitation intensity and storm motion. It also predicts terrain-induced turbulence and airport surface wind and guides mesoscale numerical weather prediction guidance. The graphical and text formats are easily interpreted by pilots, controllers, air traffic managers and aviation forecasters. The alerts use commonly accepted aeronautical navigation terminology.

The WTWS graphic display (above) delivers hazardous weather warning information and other meteorological products. It shows the horizontal profile of various hazardous weather areas, vertical wind profiles near the approach and departure corridors, and textual warning messages. The meteorological situation is displayed in several user-selectable ranges and levels of detail. Critical products and important situation changes are highlighted visually on the display and/or announced by audible signals.

User needs were established over a two-year period culminating in a prototype demonstration in October 1995. As a result of comments by users, the system was designed to provide high performance, distinguish between the phenomena of windshear and turbulence, use existing aeronautical terminology and provide spatial extent of the phenomena as well as 12-hour forecasts of windshear and turbulence at a 30-minute resolution.

Example of an Alphanumeric Alarm Display (AAD) for Hong Kong.

Alerts had to be reserved for significant events and assigned a priority. They also had to be concise but informative and provided within three nautical miles of runways. Products had to support both tactical and strategic decision making and be updated fast enough to cover operations that occur every two minutes.

The alphanumeric alarm display (above) is designed to alert controllers to time-critical weather hazards and to provide textual warnings for communication to pilots. Alerts are given as microburst, windshear or turbulence, with associated intensity and location. For windshear and microburst alerts, intensity is given as headwind "loss" or "gain" in knots; for turbulence, intensity is specified as "moderate" or "severe". The intensity is the maximum expected along the alert corridor and the alert location is where the event is first expected to be encountered. Event locations for windshear alerts are given as one, two or three nautical miles on approach or departure - or on the runway. Event locations for turbulence alerts are identified as departure or approach.

WTWS Status

The Hong Kong Windshear and Turbulence Warning System (WTWS) research and development program, previously known as the Operational Windshear Warning System (OWWS) program, successfully concluded in January 1998. The Hong Kong Government accepted the WTWS system on schedule in July 1997.

Hong Kong International Airport opened its new international airport at Chek Lap Kok (CLK) in July 1998. The WTWS system has been operating since the airport opened. The WTWS is providing windshear and turbulence alerts to pilots arriving or departing the airport when conditions warrant. Input from pilots and controllers is being used to evaluate and tune the system.

Meteorological Reviews

One of the first program tasks was to perform a meteorological review and analysis of historical Hong Kong data. An initial report included a review of scientific theory on airflow around complex terrain, analysis and identification of the conditions which could cause terrain–induced windshear and turbulence near Chek lap Kok, numerical experiments aimed at gaining additional insight into conditions that produce windshear caused by terrain, and an estimate of the timing and location of significant windshear at the new airport.

That review indicated that the primary parameters for determining the nature of the airflow include wind direction and speed, stability, and the presence of critical levels. These parameters were further studied by performing small–scale modeling simulations using the Clark model of a wide range of atmospheric phenomena such as downslope winds, gravity waves and wave amplification, which are often associated with terrain–induced wind flow perturbations. Preliminary results indicated that both mechanical and gravity–wave processes contribute to windshear and turbulence and confirmed that the intensity and location of the turbulence are sensitive, among other things, to wind direction, speed and stability.

A study of test flight results indicated that terrain–induced windshear and turbulence was not related to a single weather phenomenon and should be expected at any time of year. The atmosphere during the turbulence events was variable, although wind speed appeared to have a dominant role in determining intensity. Using 10 years of data, it was found that significant episodes of terrain–induced windshear and turbulence could last from a period of several hours up to a number of days since they were governed by long–term atmospheric motions. Principal phenomena likely to affect aircraft operations at Chek Lap Kok include crosswinds, longitudinal windshear, large wind changes, turbulence, updrafts and downdrafts. It was unclear which condition, if any, would dominate.

Using the knowledge gained from preparing the first meteorological report and from other sources, WITI designed a field experiment to understand fine–scale wind flow in the vicinity of Chek Lap Kok. The basic objectives of the experiment, which was conducted between March 1994 and September 1995, were to quantify the frequency and severity of turbulence and windshear; define more clearly the meteorological conditions under which significant terrain–induced windshear and turbulence occur; validate airflow predictions made by the small–scale model; determine the elements necessary to develop the windshear warning system; and collect verification data.

The major observational platforms used in the field experiment included a King Air research aircraft operated by the U.S. National Center for Atmospheric Research, a scanning Doppler light detection and ranging (lidar) device, integrated sounding system, wind profiler and a network of surface weather stations. Digital flight data from Cathay Pacific B–747–400s operating at Hong Kong also were collected.

Principal findings of the second meteorological report generally supported the conclusions of previous studies. It indicated that moderate to severe terrain–induced turbulence occurs in the vicinity of Chek Lap Kok and that it is more frequent than terrain–induced windshear. Turbulence is found almost exclusively in a well–defined region in the wake of the surrounding terrain. Ambient wind speed determines the magnitude of this turbulence, whereas ambient wind direction governs location. Other factors, such as stability, affect the wind flow response but are secondary.

Both mechanical and gravity–wave processes appear to be important in the dynamics and the net response of both processes appears to be quasi–linear and similar. There is no indication of resonance or unusual responses. Significant terrain–induced windshear and turbulence will occur in episodes that are typically several days in duration and separated by several weeks.

The wealth of scientific information provided by the field study was used in the design of the WTWS system. Coupled with feedback from controllers, pilots and aviation meteorologists, this information was used to develop an operational concept for the new alerting system.

Engineering Design

WTWS graphical display

Designers developed the WTWS products to enhance the safety, capacity and efficiency of operations at Chek Lap Kok by automatically providing pilots with concise windshear and turbulence alerts. The system also was designed to provide air traffic managers and supervisors with information to aid effective decision–making and to present high–resolution, real–time meteorological data and forecast guidance to forecasters.

The WTWS integrates data from various sensors and sources, including anemometers, Doppler weather radar, Doppler wind profilers, numerical weather prediction models and an array of global weather observations. Indirectly, it receives data from the ICAO world area forecast system (WAFS) and the World Meteorological Organization (WMO) global telecommunications system.

To enhance flexibility, the system was designed to run on commercially available Unix platforms. Modular system software, written in the C and Fortran programming languages, was designed to conform to international standards, allowing WTWS to run on vendor–neutral platforms. To heighten reliability, a redundant array of independent computers environment was employed. This ensures that all critical system processes are running somewhere on a network of WTWS computers. The capability to refine or tune system algorithms after, as well as before, installation is an important feature because optimization can be achieved only after it is used in an operational environment. The system also includes provisions for accommodation of new types of data, such as real–time aircraft and lidar data, after initial deployment.

An advanced version of the mesoscale model (MM5) developed by Penn State University and NCAR is used to predict atmospheric conditions around the new airport. The MM5 modelling system was adapted to provide real–time, short–range prediction of the mesoscale atmospheric conditions conducive to terrain–induced windshear and turbulence.

Although the MM5 produces weather guidance for the entire Hong Kong region, airport–specific forecasts are generated with a post-processing algorithm. Similar to model output statistics (MOS) techniques commonly used at major forecast centers, this algorithm provides 12–hour forecasts with 30–minute resolution of wind and turbulence at Chek Lap Kok.

The WTWS algorithms, many of which utilize an analysis technique known as 'fuzzy logic', produce turbulence and windshear products based on sensor data. This technique makes use of disparate data types and keeps important information throughout the decision process, maximizing algorithm performance. Sensor inputs include automatic weather stations, TDWR, and an aerodrome meteorological observing system – and each is used by specific windshear and turbulence detection algorithms. The weather product algorithms are used to produce gridded information, which is integrated using decision algorithms. By employing such a scheme, a new turbulence or wind shear algorithm can be added to the system by tailoring its output to a standardized format.

Radar-based Wind Shear Alert System

Wind shear experts in RAL provide consultancy services to public and private organizations and governments around the world to help them understand wind shear and various wind shear detection system solutions. The consultancy services include identifying the exposure to wind shear, providing technical information on wind shear detection system solutions, siting systems, training aviation personnel on the impacts of wind shear on aviation, preparing technical specifications for wind shear systems, supporting the tendering process, and assisting with the implementation of wind shear detection solutions.

The Research Applications Laboratory (RAL) of NCAR has over twenty years of experience in system development and technology transfer. NCAR/RAL has successfully developed and transferred to operations weather decision support technologies to the aviation community (e.g., airlines, Federal Aviation Administration (FAA), National Weather Service (NWS), international governments (Taiwan, Hong Kong, Korea, Australia, United Arab Emirates, Singapore, and others), private sector companies, Army, Air Force, Defense Threat Reduction Agency (DTRA), Pentagon Force Protection, National Ground Intelligence Center (NGIC), Department of Homeland Security (DHS), Department of Transportation (DOT), National Aeronautics and Space Administration (NASA), and many other clients. As a national center, NCAR is able to utilize advancements developed not only at NCAR, but at research centers, universities, and national laboratories worldwide.

NCAR/RAL has extensive experience in aviation weather. This experience in aviation weather has emphasized

1. Expert knowledge in aviation weather science
2. The development of aviation weather decision support systems that make weather information easy to use in operational environments
3. The development of detection and forecast algorithms, methods, and techniques which generate aviation specific information
4. the use of specialized models and data systems to improve the accuracy of detections and forecasts.

Significant aviation-weather research and development experience includes the following:

1. Joint Airport Weather Studies (JAWS) Project – This was an NCAR–directed research project in the 1980s in which physical processes associated with thunderstorm–initiated downbursts and wind shear were investigated. The knowledge gained served as the basis for future development of airport wind shear detection systems.
2. Low–Level Windshear Alert System (LLWAS) – NCAR developed this first airport wind shear alert system for detecting microbursts. Over 110 systems have been installed in the US to assist in providing warnings of microburst and gust–front–related low–level wind shear. This technology has also been implemented at airports worldwide. NCAR holds the patent for LLWAS wind shear detection algorithms.
3. Terminal Doppler Weather Radar (TDWR) – Convective weather research and prototype development at NCAR in the 1980s and 1990s strongly influenced the design, scanning strategies and end–user products generated by this aviation–weather radar system that was installed at 50 major airports in the US. NCAR also holds the patent for algorithms integrating TDWR and LLWAS data. NCAR's prototype TDWR system was successfully used to protect Denver's Stapleton Airport from wind shear for six years until the operational TDWR took its place at Denver International Airport.
4. Terminal–Area Surveillance System (TASS) – The TASS was a next–generation (electronic scanning) airport radar surveillance system prototype that was designed to track aircraft as well as weather and weather hazards. NCAR developed prototype weather hazard detection algorithms for this system, including those that detect microbursts and other wind–shear–related phenomena.
5. Aviation Weather Research Program (AWRP) – The AWRP is a 20 year research and development program supported by the US Federal Aviation Administration (FAA) in which NCAR is a major participant. The objective of the AWRP is to develop improved detection and forecasting techniques for all weather factors that influence aviation safety and efficiency, including turbulence, icing, snowfall, convective weather, cloud ceiling, and visibility.
6. Convectively Initiated Precipitation Research – Automated nowcasting techniques have been developed at NCAR for the very short range (0 to 2 hour) prediction of convective precipitation and related hazards near airports.
7. Wind Shear Detection and Warning System (WTWS) – NCAR designed, developed, tested, and installed an operational wind shear and turbulence detection and forecast system for Hong Kong International Airport, which was constructed in a location that experiences terrain–induced windshear that is potentially hazardous to aircraft. In order to enhance the safety of aircraft operations at the new airport, the WTWS was developed to detect, forecast, quantify, display and provide warnings for significant terrain–induced and convective windshear and turbulence. Components of this system include automated surface sensing systems, a Terminal Doppler Weather Radar, and wind profilers. Doppler lidar systems were recently added to the WTWS by the Hong Kong Observatory as a system enhancement.
8. Advanced Operational Aviation Weather System (AOAWS) – NCAR developed an advanced aviation weather system for the Taiwan Civil Aeronautics Administration to cover the Taipei Flight Information Region (FIR). The AOAWS includes advanced aviation weather prediction capabilities, turbulence and icing algorithms, and flight planning tools. The AOAWS also includes wind shear detection systems at Songshun Airport and TTY International Airport.
9. Aeronautical Meteorology System Technical Assistance Unidad Administrativa Especial de Aeronautica Civil (UAEAC), Colombia, South America – NCAR teamed with Earth Satellite Corporation in 2005 to perform a detailed assessment of the current state of the Colombian Aeronautical Meteorology System. NCAR performed airport site visits, assessed the current aviation weather infrastructure, and developed a phased development plan for modernizing the Colombian aeronautical Meteorology system. This consultancy included an assessment of windshear and turbulence technologies as well as other aviation hazards.
10. Juneau Airport Wind System – NCAR developed a sophisticated wind information system for Juneau Airport that provides terrain–induced windshear and turbulence alerts for specific aircraft arrival and departure corridors. This FAA funded system incorporates data from anemometers near the runways and on nearby mountaintops, and data from wind profilers.
11. Assessment of Meteorological Services – Kingdom of Saudi Arabia – At the request of the Presidency of Meteorology and Environment (PME), NCAR conducted a study to assess the current status of PME meteorological services including aeronautical meteorology, forecasting operations, radar systems, and their air quality program. NCAR provided recommendations regarding how the PME could modernize its capabilities over five–year and ten–year periods.
12. Sydney Airport Wind Shear Consultancy – Between 2009 and 2010, NCAR wind shear system experts performed a detailed study of wind shear detection system technologies that are appropriate for Sydney International Airport and other sites across Australia. This study provided as assessment of several technologies including Doppler weather radar, Doppler lidar, Low-Level Wind Shear Alert System (LLWAS), sodar, wind profiler, and combinations of these technologies. This study was performed for a team of aviation stakeholders including the Bureau of Meteorology, airlines, Airway Services of Australia, and the Sydney Airport Authority.

NCAR has demonstrated its ability and willingness to share its research results with aviation weather stakeholders. This enables results to be quickly communicated and implemented into operations to support decision makers. NCAR's commitment to the development and long–term support of a suite of open–source sophisticated technologies (e.g., weather models, algorithms, decision support systems, etc.) has transformed the scientific and engineering fields and has contributed to technical advancements throughout the nation and world.

The Research Applications Laboratory is addressing oceanic weather needs for aviation through the development of an intelligent system that generates 0-2 hour nowcasts.

Remote, oceanic regions have severely limited data availability and therefore, have few, if any, high resolution weather products that indicate current locations of convection. Convective hazards impact the safety, efficiency and economic viability of oceanic aircraft operations by producing turbulence, icing and lightning and by necessitating aircraft rerouting while in-flight, leading to higher fuel costs and delays. The Research Applications Laboratory is addressing oceanic weather needs for aviation through the development of convection diagnostic products. These products are the Cloud Top Height (CTH) and the Convection Diagnosis Oceanic (CDO). Both use geostationary satellite data as a primary input with the CDO also utilizing lightning data. These two products focus on the needs of pilots, dispatchers, air traffic managers and forecasters within the oceanic aviation community.

CLOUD TOP HEIGHT (CTH)

The Cloud Top Height (CTH) product combines geostationary satellite Infrared data and numerical weather prediction output to create a detailed diagnosis of the estimated heights of convective cloud tops over the open ocean. Provided that clouds are of sufficient optical thickness such that transmission from the lower atmosphere may be safely neglected (such as occurs within deep convection), the emitting temperature of the cloud across the ~11.0 micron window channel is assumed to be representative of the ambient environment. Soundings generated by the National Center for Environmental Prediction (NCEP) Global Forecasting System (GFS) numerical model are employed to convert the satellite brightness temperatures to flight-level altitudes (expressed in Kilo-feet). Specifically, the CTH makes a conversion from satellite brightness temperature to the equivalent GFS pressure surface. This pressure level is then used to interpolate to a standard atmosphere height. Similarly, aircraft altimeters also convert a pressure measurement to an equivalent altitude using the standard atmosphere.

The product performs for both day- and night-time hours and gives valid results for clouds with tops at and above 15,000 feet.

The Naval Research Laboratory in Monterey, CA (NRL-MRY) originally developed the CTH algorithm. The following reference applies:

Donovan, M.F., E.R. Williams, C. Kessinger, G. Blackburn, P.H. Herzegh, R.L. Bankert, S. Miller, and F.R. Mosher, 2006: The identification and verification of hazardous convective cells over oceans using visible and infrared satellite observations, Preprints-CD, 12th Conference on Aviation, Range and Aerospace Meteorology, AMS, Atlanta, GA, 30 January-2 February 2006.

REFERENCES

Bedka et al., 2010: Objective satellite-based detection of overshooting tops using infrared window channel brightness temperature gradients, J. Appl. Meteor. Clim., 49, 181-202.

Donovan et al., 2008: The identification and verification of hazardous convective cells over oceans using visible and infrared satellite observations, J. Appl. Meteor. Clim., 47, 164-184.

Donovan et al., 2009: An evaluation of a Convection Diagnosis Algorithm over the Gulf of Mexico using NASA TRMM Observations. 16th Conf. Satellite Meteor. Ocean., Amer. Meteor. Soc., Phoenix, AZ, 12-15 Jan 2009.

Frazier, E., C. Kessinger, T. Lindholm, J. Olivo, B. Barron, G. Blackburn, B. Watts, R. Stone, D. Keany, D. Tyler and T. J. Horsager, 2017: The Remote Oceanic Meteorology Information Operational (ROMIO) Demonstration. World Meteorological Organization, Proceedings of the 2017 WMO Aeronautical Meteorology Scientific Conference, Toulouse, France, 6-10 November 2017, pages P2-94:P2-102.

Kessinger, C., et al., 2015: Demonstration of a Convective Weather Product into the Flight Deck. 17th Conf. Aviation, Range and Aerospace Meteorology, Amer. Meteor. Soc., 4-8 January 2015, paper 13.4.

Kessinger, C., et al., 2017: The global weather hazards project. 18th Conf. Aviation, Range and Aerospace Meteorology, Amer. Meteor. Soc., 23-26 January 2017, paper 9.3.

Kessinger, C., D. Megenhardt, G. Blackburn, J. Olivo, L. Lin, V. Hoang, M. Nayote, K. Sievers, A. Ritter, D. Wolf, O. Matz, R. Scheinhartz and J. Cahall, 2017: Displaying convective weather products on an electronic flight bag, The Journal of Air Traffic Control, 59 (3), 52-61.

Kessinger, C., 2017: An update on the Convection Diagnosis Oceanic Algorithm, 18th Conf. on Aviation, Range, and Aerospace Meteorology, American Meteorological Society, Seattle, WA, 22-26 Jan. 2017, poster 211.

Kessinger, C., E. Frazier, T. Lindholm, B. Barron, J. Olivo, B. Watts, R. Stone, S. Abelman, A. Trani, M. DeRis and C. Gill, 2019: “The Remote Oceanic Meteorology Information Operational (ROMIO) Demonstration”, 19th AMS ARAM Conference, 7-10 Jan 2019, Phoenix, AZ.

Kessinger, C., E. Frazier, A. Izadi, A. Trani, T. Lindholm, J. Olivo, B. Watts, R. Stone, B. Norris, S. Abelman,  E. Senen, and K. Bharathan, 2020: “Remote Oceanic Meteorology Information Operational (ROMIO) Demonstration”, 20th AMS ARAM Conference, 12-16 Jan 2020, Boston, MA, paper 12.1.

Miller, S., et al., 2005: Technical Description of the Cloud Top Height (CTOP) Product, the first component of the Convective Diagnosis Oceanic (CDO) Product. Submitted to FAA AWRP, 11 March 2005, 30 pp.

Mosher, 2002: Detection of deep convection around the globe. Preprints, 10th Conf. Aviation, Range, Aerospace Meteor., Amer. Meteor. Soc., Portland, OR, 289-292.

Funding

Federal Aviation Administration (FAA)

NCAR's demonstration system merges NTDA output from multiple radars to form a 3–D turbulence map, revealing regions of moderate and severe turbulence within clouds and thunderstorms.

166 FAA, NWS and DoD NEXRADs are currently in operation, providing Doppler wind and wind variability measurements as well as the more familiar reflectivity. The NTDA is a software upgrade that uses these data to detect in–cloud turbulence before aircraft encounter it.

Making use of the wind variability data provided by Doppler weather radars, RAL scientists have developed and tested the NCAR Turbulence Detection Algorithm (NTDA), designed for use on the nation's network of NEXRAD radars. The NTDA utilizes NEXRAD Level II data – the reflectivity, radial velocity, and spectrum width – to perform data quality control and produce atmospheric turbulence intensity (eddy dissipation rate, EDR) measurements of "in–cloud" turbulence. The expert system combines multiple modules for quality control and turbulence estimation using a "fuzzy logic" methodology to produce a final EDR and associated quality control index, or confidence. By providing direct detection of turbulence, NTDA provides an important addition to radar reflectivity as an indication of in–cloud aviation hazards. NTDA development has been funded by the FAA's Aviation Weather Research Program.

Example of text–based graphic used in uplink demonstration.

The first version of the algorithm, NTDA–1, was delivered to the NWS Radar Operations Center and deployed on all NEXRADs in 2008. The next version, NTDA–2, accommodates recent NEXRAD changes and is targeted for deployment in the 2012–2013 timeframe. A prototype version, running in real–time at NCAR, processes Level II data from 133 NEXRADs around the U.S. and produces a 3–D mosaic of in–cloud EDR updated every 5 min. In addition to possible direct use by pilots, airline dispatchers and air traffic control meteorologists, the NTDA data are being incorporated into a new Graphical Turbulence Guidance Nowcast (GTGN®) product. Given the highly transient and spatially variable nature of in–cloud turbulence, maximum benefit of the NTDA product can be achieved if pilots can receive this information in the cockpit in nearly real time. This capability has been demonstrated in collaboration with United Airlines: character graphics depictions of in–cloud turbulence 100 miles ahead and 40 miles to either side of the planned route were uplinked to selected United Airlines flights via ACARS. Pilots indicated that this information could be very useful for making tactical decisions near storms, suggesting that this product could improve airline safety while reducing delays due to unneeded deviations.

Coverage provided in a 24 hour period of in situ EDR measurements (colored code in units of m 2/3 s -1) from UAL mostly 757–200 aircraft (top panel), with one–minute routine reporting and DAL 737–800 aircraft (bottom panel) with event–based EDR reporting plus 15–minute routine reporting.

For both research and operational purposes, there are currently an insufficient number of reliable, accurate, and timely measurements of atmospheric turbulence locations and intensities. Turbulence "measurements" in the form of pilot reports (PIREPs), although useful, do not comprise a satisfactory turbulence detection system. NCAR, under FAA sponsorship, has developed in-situ algorithms for inferring and reporting turbulence encountered by commercial transport aircraft. The algorithms compute an eddy dissipation rate, or EDR (m 2/3 s –1), from available on–board flight parameters. EDR is truly a "state–of–the–atmosphere" turbulence metric; it is widely used in the research community as a measure of turbulence intensity, and has been adopted as the ICAO standard for aviation turbulence. About 100 757 aircraft from United Airlines are presently equipped with software which downlinks EDR reports recorded at one–minute intervals (in cruise) In order to reduce communication costs, an improved algorithm has been developed that downlinks turbulence encounter information immediately if the EDR is above a certain threshold, and still provides routine reporting but at less frequent intervals. This improved algorithm has been recently implemented on about 70 Delta Air Lines 737–800s. The algorithm will also soon be deployed on DAL’s 767 fleet.  As the airline industry becomes more aware of the benefits of this program, it is anticipated that some form of in situ EDR observation systems will ultimately operate on the majority of commercial aircraft flying both continental U.S. (CONUS) and international routes. Although EDR is the preferred prediction metric for forecasting purposes, some users may also require the aircraft acceleration loads associated with an atmospheric EDR measurement. This is easily provided by an aircraft/configuration dependent linear mapping factor.

Remote sensing

The NEXRAD Turbulence Detection Algorithm is described in the Radar section. The feasibility of using other remote sensing techniques to detect turbulence for tactical avoidance is also being studied. These include airborne forward–looking Doppler radar, lidar, GPS scintillation, and forward–looking infrared interferometer methods.

Over the last several years the FAA has funded NCAR and others to develop a turbulence nowcast and forecast system for application over the continental U.S. The forecast system, named GTG for "Graphical Turbulence Guidance," provides contours of turbulence potential based on NWP model forecasts out to 12 hours lead time. The GTG system is part of the NCEP operational suite. An example as it currently appears on ADDS is shown below.

The GTG procedure uses numerical weather prediction model forecasts to compute a number of turbulence diagnostics which are then weighted and combined. The relative weights for the combination are dynamically optimized for best agreement with the most recent available turbulence observations (in situ EDR data and pilot reports). This procedure allows the algorithm to minimize forecast errors due to uncertainties in individual diagnostic performance and thresholds. Rigorous statistical verification exercises have been performed in which probabilities of yes and no detections were determined by comparing turbulence forecasts to PIREPs and in situ EDR data. These statistics have made it possible to compare performance of the individual diagnostics, as well as test various diagnostic thresholding and weighting strategies. The overall forecast performance using the weighted diagnostics provides superior skill to the use of individual diagnostics.

The GTG is a constantly evolving product, with specific mountain wave turbulence, clear air turbulence and in the future also convectively–induced turbulence diagnostics (CIT) as well as probabilistic forecasts. Furthermore, a global GTG forecast product has been developed that has been shared with NCEP and the UKMet Office as part of the ICAO World Area Forecast System (WAFS) efforts to be operational in 2020.

Muñoz-Esparza, D. and R. Sharman, 2018: An Improved Algorithm for Low-Level Turbulence Forecasting. J. Appl. Meteor. Climatol., 57, 1249–1263, https://doi.org/10.1175/JAMC-D-17-0337.1

Sharman, R., and J. Pearson, 2017: Prediction of energy dissipation rates for aviation turbulence. Part I: Forecasting nonconvective turbulence. J. Appl. Meteor. Climatol., 56, 317–337, https://doi.org/10.1175/JAMC-D-16-0205.1.

Sharman, R., and T. Lane, 2016: Aviation Turbulence: Processes, Detection, Prediction. Springer, 523 pp.

Sharman, R., C. Tebaldi, G. Wiener, and J. Wolff, 2006: An integrated approach to mid- and upper-level turbulence forecasting. Wea. Forecasting, 21, 268–287, https://doi.org/10.1175/WAF924.1.

DCIT EDR output at FL370 for 00 UTC 5/14/09; (Bottom) blowup image of the upper Midwest showing overlaid 1–hr in situ EDR tracks validating the DCIT diagnosis. (Note that there are temporal offsets between the DCIT analysis time and some of the EDR measurements, so the correlation is not exact.)

While GTG forecasts turbulence based on NWP model data, limitations of the model accuracy, resolution and timeliness limit GTG's ability to adequately diagnose convectively–induced turbulence (CIT). The NEXRAD Turbulence Detection Algorithm (NTDA; see Radar section) partially addresses this deficiency by measuring in–cloud turbulence. However, there may often be regions of CIT above or adjacent to storms that are in clear air or otherwise not detectable by Doppler weather radar. To address this gap, the Diagnose CIT (DCIT) algorithm is being developed. Since DCIT is primarily concerned with resolving areas of turbulence close to but not in convective clouds, traditional PIREPs cannot be used as "truth" in evaluation and tuning because of their inherent location and timing uncertainty. Therefore in situ EDR data are required to tune and verify the DCIT algorithm.

DCIT is being developed using statistical learning and analysis techniques that provide estimates of the importance of candidate predictor variables and produces an empirical predictive model. An initial version of DCIT based on the RAP model, NEXRAD, and geostationary satellite data has been developed and is running operationally at NCAR.

Map of Taiwan

Advancements in science and technology, particularly computer and networking capacity, have allowed many civil aeronautics authorities to expand and modernize their aeronautical weather capabilities and services with the intention of providing their end users with more timely, accurate, and ready to use weather information. The primary objective of developing and implementing an advanced capability is to provide high-resolution four-dimensional (space and time) aviation weather products to meteorologists, pilots, air traffic controllers, and airline dispatchers and station operators in order to enhance flight safety and aviation system capacity.

Since 1998, the National Center for Atmospheric Research (NCAR) has been partnered with the Taiwan Civil Aeronautics Administration (CAA) to develop an advanced aviation weather system called the Advanced Operational Aviation Weather System (AOAWS) for Taiwan aviation system users. NCAR's local Taiwan partner on the project includes the Institute for Information Industry (III) (1998- 2008) and InfoExplorer Ltd. (2009 to 2010), and International Integrated Systems, Inc. (2011 to present). The main objective of the AOAWS is to enhance operational safety, capacity and efficiency in the terminal and Taipei Flight Information Region (FIR). The AOAWS product suite is designed to aid both tactical and strategic decision making for the direct users of the system, specifically pilots, controllers, traffic managers, and forecasters at the Taipei Aeronautical Meteorological Center (TAMC) supporting the formulation of aviation weather products.

Illustration of the major components of the AOAWS. The WMDS is the Web-based Multi-dimensional Display System, an integrated display including all relevant aeronautical weather information. A high-resolution numerical weather model is at the heart of the system.

The AOAWS system includes Low-Level Windshear Alert Systems (LLWAS) at Taiwan Taoyuan International Airport (TTY) and Sungshan Airport, advanced aviation weather display systems at the Taipei Aeronautical Meteorological Center (TAMC), Taipei Flight Information Service (FIS), Sungshan Weather Station, TTY Weather Station and FIS, Kaohsiung Weather Station and FIS, and the Taipei Area Control Center (TACC). The AOAWS also includes a World Wide Web system that allows airlines, pilots and other aviation system users to have remote access to AOAWS products.

The AOAWS operational concept has been developed by coupling user requirements with current scientific and engineering capabilities. Extensive experience gained by NCAR during development, deployment and operation of the Terminal Doppler Weather Radar (TDWR), Low-Level Windshear Alert System (LLWAS) and other advanced aviation weather systems for theFederal Aviation Administration (FAA) in the U.S. and the Windshear and Turbulence Warning System (WTWS) for Hong Kong provides a solid framework for an AOAWS operational concept.

AOAWS System Overview

Advanced aeronautical weather systems, such as the AOAWS, typically include a high-resolution weather model, model data post-processing system for calculating aviation impact variables such as icing and turbulence, display systems that allow users to interactively view weather products both in plan view and along flight routes, and servers to disseminate the information to end users in remote locations. A conceptual illustration of the AOAWS is shown below.

User Needs

The best starting point for developing an operational concept is to review the issues and needs raised by the future users of the AOAWS. User needs were developed during meetings held in Taipei in 1996, 1997 and 1999. Organizations represented in the meetings included the Taiwan Civil Aeronautics Administration (CAA), Far Eastern Transport (FAT), China Airlines, EVA Air, Air Force Meteorological Center, Central Weather Bureau (CWB), TransAsia, Hwa Hsin Airlines, Formosa Airlines and U-Land Airlines.

Chun-Ming Jou (So-So), visiting engineer from the CAA in Taipei,  is working on the MDS display at the AOAWS lab in Boulder.

Major issues considered in the development of AOAWS concepts:

1. Convective windshear (including microburst) detection in the terminal areas has higher priority than other advanced aviation weather products.
2. Terrain-induced windshear and turbulence in the terminal area has the second highest priority.
3. Thunderstorm hazards in the terminal area are important followed by thunderstorm hazards in the domestic enroute region and lastly in the FIR region. Thunderstorm hazards include windshear, turbulence, lightning, and to a lesser extent, icing.
4. Knowledge of airport surface winds and ceiling and visibility are necessary for safe operations. Better forecasts of those conditions are highly desired.
5. For flight planning, accurate information (current and forecast) of winds and temperature aloft are required.
6. The users agreed that better weather detection and forecasts accuracy for all aviation weather information is desired.

With this in mind, a number of considerations for AOAWS development were reviewed and accepted. AOAWS design considerations include:

1. The windshear systems – Low–Level Windshear Alert Systems (LLWAS) and the Windshear Processor (WSP) – should have a high Probability of Detection (POD) and low False Alarm Rate (FAR).
2. If more than one sensing system is used for hazards detection, the resulting alert information should be based on an integrated approach.
3. Terminal alert information should be concise to keep the controller workload low.
4. The AOAWS should use standard terminology for describing weather phenomena. For example, products such as flight categories should use standard definitions for IFR, VFR, etc., and standard terms should be used for turbulence and windshear. Event intensities should also be given using standard terminology.
5. Alert conditions should be reserved for operationally significant (safety critical) events.
6. Crosswind shear may be an operational problem at some airports, particularly at CKS and Kaohsiung.
7. Vertical windshear is thought to be a common occurrence at CKS. More research is needed to understand this phenomenon and determine whether it is an aviation hazard.

The windshear alert generation strategy should be consistent with FAA and other established systems. For example:

1. Alerts should be provided, where possible, out to 3 nm on approach and departure.
2. Alert update rate should be approximately 60 seconds or faster.
3. The alert corridor around the runways should be 1/2 nautical mile wide on either side of the centerline to account for windshear event movement.
4. Windshear alerts should be provided as gains or losses in wind speed (knots).
5. The minimum windshear alert threshold should be 15 knots.
6. The minimum microburst threshold should be 30 knots (windspeed loss).

Ching-Huei Hsu (Jeff ), a visiting engineer from the CAA in Taipei,  working on the AOAWS MDS display at the Boulder lab.

Terminal Windshear Systems

From an operational perspective, the AOAWS windshear detection component provides two major functions:

1. To improve safety by providing tactical decision making information to pilots for windshear events.
2. To provide strategic meteorologists at the weather stations for use in decision-making for optimizing terminal efficiency and capacity.

Because airspace is limited, especially during bad weather, it will be important to utilize all available AOAWS information in order to optimize operations.

Maximizing the utility of the AOAWS windshear components is a function of how the system is ultimately used in an operational environment and this is governed by its capabilities and performance.

Convective Windshear and Microburst Products

Microbursts are well recognized as an aviation hazard. Until the U.S. TDWR and Enhanced LLWAS systems were developed and implemented, no explicit microburst alerts were available. Onboard reactive windshear devices now provide windshear alerts to help pilots recognize that they have entered a windshear event, but they are reactive and do not provide an alert that can help pilots avoid windshear before they enter the event. Forward-looking systems are now just coming into operation and these will provide alerts of a minute or two ahead of entering windshear events. The ground-based systems (TDWR and LLWAS), which define microbursts as windshears with peak-to-peak windspeed differences of > 30 kts over distances < 2.5 nm, have microburst probabilities of detection (PODS) > 90% and false alarm rates (FARs) < 10%. Due to the high performance, the U.S. airlines have developed the policy that aircraft operations (approaches or departures) must cease if a "microburst alert" is given by these systems. When the TDWR or LLWAS systems generate a "windshear-with-loss alert", which is defined as a peak-to-peak windspeed difference of 15-29 kts over a distance of < 2.5 nm, it is up to the pilot to determine whether to continue operating.

Convective windshear events and microbursts typically last about ten minutes. This short duration is due to a combination of the true life cycle of the events coupled with the fact that they are usually moving with the precipitation cells. At times when the precipitation cells are moving more slowly (< 20 kts), the windshear events may impact the airport operations for a longer period. The avoidance of the hazard is an obvious safety benefit; however, every delayed departure and missed approach will disrupt the traffic flow and hence, impact capacity (if airspace is limited). The geographical information provided to the air traffic supervisors and managers on the GSD provides an opportunity to see the "bigger picture" and minimize disruptions.

An example of an AOAWS web system homepage

Web System Format And Style

The AOAWS Web System will be styled after a Web system that was developed by NCAR and NOAA for the NWS Aviation Weather Center (AWC) in Kansas City, Missouri. The complete AWC Web System can be viewed here: www.aviationweather.gov

The web system developed for AWC was first implemented in 1996. Since that time it has evolved from a gridded data server to an excellent resource for accessing world wide aviation weather information. The AWC system was designed for non-meteorologists (pilots, airline dispatchers, etc.) and its interface is simple and intuitive.

The AOAWS Web system will follow the general style of the AWC system for the following reasons:

1. The AWC system has been developed with extensive user input
2. The AWC system is very successful
3. The aviation community will have continuity between the AWC system and the AOAWS system lessening the time necessary to become comfortable with its use
4. NCAR has experience in developing the AWC system and can incorporate many of the features and functions of the AWC system into the AOAWS Web system

After the completion of the AOAWS Web system, a Chinese language interface will be created in the appropriate places. The Help function will also be converted to Chinese to make it easier for Chinese speaking users to interpret the products.

Partners

• The Institute for Information Industry (III)
• Civil Aeronautics Administration (CAA)
• National Center for Atmospheric Research (NCAR)
• InfoExplorer Ltd.