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An Investigation of a Commercial Aircraft Encounter with Severe Clear-Air Turbulence over Western Greenland

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  • 1 National Center for Atmospheric Research,* Boulder, Colorado
  • | 2 Naval Research Laboratory, Monterey, California
  • | 3 National Center for Atmospheric Research,* Boulder, Colorado, and Geophysical Institute, University of Bergen, Bergen, Norway
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Abstract

This study presents digital flight data recorder (DFDR) analyses and high-resolution numerical simulations relevant to a severe clear-air turbulence (CAT) encounter over western Greenland by a Boeing 777 aircraft at 10-km elevation at 1305 UTC 25 May 2010. The environmental flow was dominated by an extratropical cyclone to the southeast of the Greenland tip, resulting in easterly flow at all levels. The results of the analyses indicate that the CAT encounter was related to mountain-wave breaking on the western lee (downslope) of the Greenland plateau. The simulations were not of especially high resolution (5-km horizontal grid spacing) by today’s standards, yet the simulation results do produce large-amplitude lee waves and overturning in good agreement with the encounter location as indicated by the DFDR. The success of this and other simulations in reproducing mountain-wave turbulence (MWT) events suggests that operational implementation of high-resolution nonhydrostatic simulation models, possibly an ensemble of models, over MWT-prone areas could produce more reliable forecasts of MWT than are currently available using gravity-wave-drag or MWT-postprocessing algorithms derived from global weather prediction models of relatively coarse scale.

The National Center for Atmospheric Research is sponsored by the National Science Foundation.

Corresponding author address: Dr. Robert D. Sharman, National Center for Atmospheric Research, P.O. Box 3000, Boulder, CO 80307-3000. E-mail: sharman@ucar.edu

Abstract

This study presents digital flight data recorder (DFDR) analyses and high-resolution numerical simulations relevant to a severe clear-air turbulence (CAT) encounter over western Greenland by a Boeing 777 aircraft at 10-km elevation at 1305 UTC 25 May 2010. The environmental flow was dominated by an extratropical cyclone to the southeast of the Greenland tip, resulting in easterly flow at all levels. The results of the analyses indicate that the CAT encounter was related to mountain-wave breaking on the western lee (downslope) of the Greenland plateau. The simulations were not of especially high resolution (5-km horizontal grid spacing) by today’s standards, yet the simulation results do produce large-amplitude lee waves and overturning in good agreement with the encounter location as indicated by the DFDR. The success of this and other simulations in reproducing mountain-wave turbulence (MWT) events suggests that operational implementation of high-resolution nonhydrostatic simulation models, possibly an ensemble of models, over MWT-prone areas could produce more reliable forecasts of MWT than are currently available using gravity-wave-drag or MWT-postprocessing algorithms derived from global weather prediction models of relatively coarse scale.

The National Center for Atmospheric Research is sponsored by the National Science Foundation.

Corresponding author address: Dr. Robert D. Sharman, National Center for Atmospheric Research, P.O. Box 3000, Boulder, CO 80307-3000. E-mail: sharman@ucar.edu
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