Turbulence

National Center for Atmospheric Research

Far Reaching SupportOver the past several years, the National Center for Atmospheric Research (NCAR) has been involved in a number of research and development activities aimed at fielding better turbulence detection and forecasting products to support a variety of aviation users. These activities include in situ measurement and reporting of turbulence from commercial aircraft; improved turbulence forecasting products; remote sensing of turbulence using ground-based radars; and characterizing turbulence based on field measurement campaigns and high-resolution numerical simulations. This research is currently sponsored mainly by the Federal Aviation Administration’s (FAA) Aviation Weather Research Program.

Encounters of commercial and GA aircraft with turbulence pose significant safety, efficiency and workload issues. The cost to US airlines is substantial, with estimates in the $150–$500 million/year range.

In situ turbulenceUnder FAA sponsorship, work began in the early 1990’s by NCAR scientists and engineers to develop and deploy an in situ turbulence measurement and reporting system for commercial aircraft. The concept was to use existing sensors, avionics, and communication networks to produce and disseminate a state-of-the-atmosphere turbulence metric – the eddy dissipation rate (EDR). These data would be used for operational turbulence awareness and scientific purposes. Operational users include pilots, airline dispatch,

and meteorology personnel, aviation forecasters, and air-traffic personnel. The research and development community would use these data for building and improving turbulence detection, nowcast, and forecast products.

In 1997, the implementation of the first-generation EDR algorithm was begun on United Airlines aircraft. In 2005, a second-generation algorithm was installed on aircraft from Delta Air Lines and Southwest Airlines. Currently there are approximately 85 Delta 737, 85 Delta 767, 160 Southwest 737, and 30 United 757 aircraft implemented with the EDR algorithm and that report values in near real-time. Installation on other airline/aircraft types is planned in the

near future.

Ground-based Detectionvia Doppler RadarsNCAR scientists have developed and tested an algorithm to detect in-cloud turbulence - the NEXRAD Turbulence Detection Algorithm (NTDA) - designed for use with the nation’s NEXRAD and Terminal Doppler Weather Radar (TDWR) radars. The NTDA utilizes NEXRAD Level II data - the reflectivity, radial velocity, and spectrum width - to perform data quality Turbulence reports along the tracks of in situ EDR-equipped commercial aircraft superposed on

(a) 0240 UTC 5 August 2005 and (b) 0732 UTC 17 June 2005 GOES-12 infrared satellite images.continued on reverse side

Encounters of commercial and GA aircraft with turbulence pose significant safety, efficiency and workload issues.

number of turbulence diagnostics, which are then weighted and combined. The relative weights for the combination are statistically determined to provide best agreement to available turbulence observations (pilot reports – PIREPs and in situ EDR data). The overall forecast performance using the weighted diagnostic ensemble provides superior skill compared to the individual diagnostics.

GTG is a constantly evolving product, and regular upgrades are expected over the next few years. Future upgrades will include probabilistic forecasts and convectively induced turbulence nowcasts (based in part on in situ EDR and NTDA EDR analyses).

Turbulence characterizationFundamental research aimed at characterizing different sources of turbulence continues to be a focus of NCAR scientists in collaboration with international researchers. The research strategy uses high-resolution numerical simulations of cases involving actual airplane encounters with turbulence induced by shear, mountain waves, and convection. One area of concentration has been near-cloud turbulence (NCT). Recent progress has been made in this area through a combination of the use of accurate in situ EDR measurements to precisely identify regions of NCT while high-resolution computer simulations of idealized scenarios and well-observed cases have helped elucidate NCT processes. Incidents above cloud and adjacent to cloud have both been studied. Ultimately this improved understanding will lead to better thunderstorm avoidance guidelines.

control and derive turbulence intensity (EDR). The EDRs produced by the NTDA provide an important supplement to radar reflectivity as an indication of in-cloud aviation hazards, including convectively-induced turbulence (CIT). In addition to direct use by airline dispatchers and air traffic control meteorologists, it is anticipated that the NTDA EDRs will be incorporated into nowcast products for the aviation community.

Turbulence ForecastingOver the last several years NCAR has developed a turbulence diagnosis and forecast system covering the continental U.S. and, more recently, the globe. The forecast system, GTG (Graphical Turbulence Guidance), provides contours of forecasted EDR based on WRP RAP model forecasts (U.S.) and GFS model forecasts (global). The system, which since March 2003 has been part of the NCEP ADDS operational suite (www.aviationweather.gov/adds/), produces 0-18 hour forecasts of non-convective turbulence from the surface to 45,000 feet MSL. The procedure uses numerical weather prediction model forecasts to compute a

For More Information, Contact:Robert SharmanNational Center for Atmospheric ResearchResearch Applications LaboratoryPO Box 3000 Boulder CO 80307-3000303-497-8457303-497-8401 faxsharman@ucar.eduwww.ral.ucar.edu

High resolution cloud simulations of NCT above cloud top for two different atmospheric environments (left, high shear near cloud top;

right, low stability). Blue denotes cloud concentrations. Yellow, orange, and red denote regions of simulated turbulence of

increasing intensities.

Web-based Java display of in-cloud turbulence contours (EDR) detected by the NTDA with overlaid aircraft tracks indicating

measured in situ EDR.

GTG provides forecasts of EDR.