NEXRAD Detection of Hazardous Turbulence

Abstract

*† ‡ Historical data suggest that over 60% of turbulence-related aviation accidents are due to convectively-induced turbulence (CIT), a phenomenon that is particularly difficult to forecast accurately. In order to provide airline dispatchers, air traffic controllers, and pilots an improved tactical and strategic decision support tool for the avoidance or mitigation of CIT encounters, the FAA’s Aviation Weather Research Program has sponsored the development of the NCAR Turbulence Detection Algorithm (NTDA). The NTDA makes use of NEXRAD-measured reflectivity, radial velocity, and spectrum width to perform quality control and produce estimates of eddy dissipation rate (EDR), a commonly-used turbulence intensity metric. It is anticipated that NTDA EDR data will be used along with in situ aircraft, satellite, and numerical weather model data to produce a rapid-update “nowcast” enhancement to the current operational Graphical Turbulence Guidance (GTG) product, supplying a 4-D grid of turbulence intensity over the conterminous U.S. As a first step toward this goal, a real-time demonstration of the NTDA was performed in the summer of 2005 using data from sixteen NEXRADs in the upper Midwest. The resulting EDR estimates were mosaicked onto a 3-D grid and made displayed available via a web-accessible Javabased display, and customized 2-D turbulence hazard maps were generated and uplinked to a select number of United Airlines aircraft via the Aircraft Communications Addressing and Reporting System (ACARS). The NTDA’s performance was evaluated based on comparisons of the 3-D EDR grids with collocated in situ turbulence measurements produced by an automated EDR reporting system operating on a large number of United Airlines’ B-757 aircraft. A website allowed pilots to provide feedback on the uplinked text messages. In addition, messages were created for all United Boeing 757s entering the domain, and the subsequent in situ EDR reports used to perform a statistical evaluation.