Characterizing The Severe Turbulence Environments Associated With Commercial Aviation Accidents

A 44 case study analysis of the large-scale atmospheric structure associated with development of accident-producing aircraft turbulence is described. Categorization is a function of the accident location, altitude, time of year, time of day, and the turbulence category, which classifies disturbances. National Centers for Environmental Prediction Reanalyses data sets and satellite imagery are employed to dang- nose synoptic scale predictor fields associated with the large-scale environment preceding severe turbulence. These analyses indicate a predominance of severe accident-producing turbulence within the entrance region of ajet stream at the synoptic scale. Typically, a flow curvature region is just upstream within the jet entrance region, convection is within 100 krn of the accident, vertical motion is upward, absolute vorticity is low, vertical wind shear is increasing, and horizontal cold advection is substantial.

A 44 case study analysis of the large-scale atmospheric structure associated with development of accident-producing aircraft turbulence is described. Categorization is a function of the accident location, altitude, time of year, time of day, and the turbulence category, which classifies disturbances. National Centers for Environmental Prediction Reanalyses data sets and satellite imagery are employed to diagnose synoptic scale predictor fields associated with the large-scale environment preceding severe turbulence. These analyses indicate a predominance of severe accident-producing turbulence within the entrance region of a jet stream at the synoptic scale. Typically, a flow curvature region is just upstream within the jet entrance region, convection is within 100 km of the accident, vertical motion is upward, absolute vorticity is low, vertical wind shear is increasing, and horizontal cold advection is substantial. The most consistent predictor is upstream flow curvature and nearby convection is the second most frequent predictor.Kaplan, Michael L. and Huffman, Allan W. and Lux, Kevin M. and Charney, Joseph J. and Riordan, Allan J. and Lin, Yuh-Lang and Proctor, Fred H. (Technical Monitor)Langley Research CenterTURBULENCE EFFECTS; AIRCRAFT ACCIDENTS; AIRCRAFT STABILITY; CURVATURE; VORTICITY; ADVECTION; AIRLINE OPERATIONS; COMMERCIAL AIRCRAFT; CONVECTION; POSITION (LOCATION); SATELLITE IMAGERY; UPSTREAM; VERTICAL MOTION; WIND SHEAR

Simulation experiments reveal key processes that organize a hydrostatic environment conducive to severe turbulence. The paradigm requires juxtaposition of the entrance region of a curved jet stream, which is highly subgeostrophic, with the entrance region of a straight jet stream, which is highly supergeostrophic. The wind and mass fields become misphased as the entrance regions converge resulting in the significant spatial variation of inertial forcing, centripetal forcing, and along- and cross-stream pressure gradient forcing over a mesobeta scale region. This results in frontogenesis and the along-stream divergence of cyclonic and convergence of cyclonic ageostrophic vertical vorticity. The centripetally forced mesoscale front becomes the locus of large gradients of ageostrophic vertical vorticity along an overturning isentrope. This region becomes favorable for streamwise vorticity gradient formation enhancing the environment for organization of horizontal vortex tubes in the presence of buoyant forcing.Kaplan, Michael L. and Huffman, Allan W. and Lux, Kevin M. and Cetola, Jeffrey D. and Charney, Joseph J. and Riordan, Allen J. and Lin, Yuh-Lang and Waight, Kenneth T., III and Proctor, Fred (Technical Monitor)Langley Research CenterSIMULATION; HYDROSTATICS; TURBULENCE; GEOSTROPHIC WIND; CIVIL AVIATION; COMMERCIAL AIRCRAFT; AIRCRAFT ACCIDENTS; JET STREAMS (METEOROLOGY); CENTRIPETAL FORCE; PRESSURE GRADIENTS; VORTICITY; FRONTS (METEOROLOGY)

Real-time prediction of environments predisposed to producing moderate-severe aviation turbulence is studied. We describe the numerical model and its postprocessing system designed for said prediction of environments predisposed to severe aviation turbulence as well as presenting numerous examples of its utility. The numerical model is MASS version 5.13, which is integrated over three different grid matrices in real time on a university work station in support of NASA Langley Research Center s B-757 turbulence research flight missions. The postprocessing system includes several turbulence-related products, including four turbulence forecasting indices, winds, streamlines, turbulence kinetic energy, and Richardson numbers. Additionally, there are convective products including precipitation, cloud height, cloud mass fluxes, lifted index, and K-index. Furthermore, soundings, sounding parameters, and Froude number plots are also provided. The horizontal cross-section plot products are provided from 16 000 to 46 000 ft in 2000-ft intervals. Products are available every 3 hours at the 60- and 30-km grid interval and every 1.5 hours at the 15-km grid interval. The model is initialized from the NWS ETA analyses and integrated two times a day.Kaplan, Michael L. and Lux, Kevin M. and Cetola, Jeffrey D. and Huffman, Allan W. and Riordan, Allen J. and Slusser, Sarah W. and Lin, Yuh-Lang and Charney, Joseph J. and Waight, Kenneth T.Langley Research CenterTURBULENCE MODELS; REAL TIME OPERATION; PREDICTION ANALYSIS TECHNIQUES; FORECASTING; MATHEMATICAL MODELS; KINETIC ENERGY; CLOUD HEIGHT INDICATORS; COMPUTATIONAL GRIDS

Anyone who has experienced turbulence in flight knows that it is usually not pleasant, and may wonder why this is so difficult to avoid. The book includes papers by various aviation turbulence researchers and provides background into the nature and causes of atmospheric turbulence that affect aircraft motion, and contains surveys of the latest techniques for remote and in situ sensing and forecasting of the turbulence phenomenon. It provides updates on the state-of-the-art research since earlier studies in the 1960s on clear-air turbulence, explains recent new understanding into turbulence generation by thunderstorms, and summarizes future challenges in turbulence prediction and avoidance.

The book is a concise guide dealing with the subject of air turbulence and its methods of detection with particular applications to aviation turbulence. It begins with a general description of turbulence and provides a background into the nature and causes of atmospheric turbulence that affect aircraft motion, giving updates on the state-of-the-art research on clear air turbulence (CAT). Important physical processes leading to the Kelvin-Helmholtz instability, a primary producer of CAT, are also explained. The several categories of CAT along with its impact on commercial aviation are also presented in a separate chapter, with particular emphasis on the structural damages to planes and injuries. The central theme of the book deals with both the earlier and the latest CAT detecting methods and techniques for remote and in situ sensing and forecasting. A concise presentation of new technologies for reducing aviation weather-related accidents is also offered. A chapter on the weather accident prevention project of the NASA aviation safety program is also included. Additionally, the book ends with a full description of the recent research activities on CAT and future challenges in turbulence detection, prediction and avoidance.

During the grant period, several tasks were performed in support of the NASA Turbulence Prediction and Warning Systems (TPAWS) program. The primary focus of the research was on characterizing the preturbulence environment by developing predictive tools and simulating atmospheric conditions that preceded severe turbulence. The goal of the research being to provide both dynamical understanding of conditions that preceded turbulence as well as providing predictive tools in support of operational NASA B-757 turbulence research flights. The advancements in characterizing the preturbulence environment will be applied by NASA to sensor development for predicting turbulence onboard commercial aircraft. Numerical simulations with atmospheric models as well as multi-scale observational analyses provided insights into the environment organizing turbulence in a total of forty-eight specific case studies of severe accident producing turbulence on commercial aircraft. These accidents exclusively affected commercial aircraft. A paradigm was developed which diagnosed specific atmospheric circulation systems from the synoptic scale down to the meso-y scale that preceded turbulence in both clear air and in proximity to convection. The emphasis was primarily on convective turbulence as that is what the TPAWS program is most focused on in terms of developing improved sensors for turbulence warning and avoidance. However, the dynamical paradigm also has applicability to clear air and mountain turbulence. This dynamical sequence of events was then employed to formulate and test new hazard prediction indices that were first tested in research simulation studies and then ultimately were further tested in support of the NASA B-757 turbulence research flights. The new hazard characterization algorithms were utilized in a Real Time Turbulence Model (RTTM) that was operationally employed to support the NASA B-757 turbulence research flights. Improvements in the RTTM were implemented in an effo