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Gravity waves can occur above and in the outflow region of convection, including also Kelvin Helmholts instability.

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 Fig8.1.14-4: IFS forecast CAT chart (top) and satellite visible imagery (bottom) illustrating violent turbulence encountered by an inter-continental flight 21 May 2024. The aircraft suffered strong descents and ascents over a short period of time necessitating an emergency diversion. The aircraft might have encountered strong convective draughts, but there are numerous studies and literature about gravity waves above and in the outflow region of convection, including also Kelvin Helmholts instability.  The CAT forecast indicated local strong to severe turbulence (>0.3m2/3 s-1) but it is unclear which effects were the stronger factors.  Kelvin Helmholts instability above deep active convection is considered more likely.


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Fig8.1.14-5: IFS forecast vertical profile within the red circle shown in Fig8.1.14-4, DT 00UTC 21 May 2024, VT 06UTC 21 May 2024.  This supports CAT above and around the outflow associated with deep convection.  There is weak stability in the upper troposphere and a wind maximum in the vertical which supports breaking strong gravity waves.  IFS CAT accounts for this which is an important contribution in the tropics.

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