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- shear instabilities (Kelvin–Helmholtz instabilities).
- upper-level fronto-genesis.
- large-amplitude mountain waves.
- breaking convectively-generated gravity waves generated from convection.
Eddy dissipation rate (EDR) is the International Civil Aviation Organization (ICAO) standard for aircraft reporting of turbulence and hence is also the standard measure for clear-air turbulence (CAT). The units of EDR are m2/3 s-1.
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Clear air turbulence correspond approximately to the eddy diffusion rate
| CAT | EDR | ecChart colours (Fig8.1.14-1) |
|---|---|---|
| Weak | <0.05 m2/3 s-1 | Light blue |
| Moderate | 0.05 – 0.3 m2/3 s-1 | Blue, dark blue, green, yellow |
| Strong to severe | >0.3 m2/3 s-1 | Orange, dark orange, red, dark brown, purple |
| Severe (observed example) | >0.5 m2/3 s-1 | Light purple and clear |
Table1Table8.1.14-1: Relationship between CAT descriptions and eddy dissipation rate. Colours refer to ecChart presentation (Fig1)Further reading
ECMWF Newsletter 168
ECMWF Technical Memorandum No874
Fig1Fig8.1.14-1: ecChart of energy dissipation rate. DT 12UTC 2 March 2023, VT 03UTC 3 March 2023. Colours given in table 1Table81.14A.
Fig2Fig8.1.14-2: ecChart of 300 hPa contours (dam). 300hPa winds (kt) shown as arrows and isotachs (coloured). DT 12UTC 2 March 2023, VT 03UTC 3 March 2023. Severe CAT values of EDR to the east of the strongest jet and extend into the unshaded area enclosing winds below 50kt. Pin shows Dallas, Texas. Severe turbulence was encountered by an aeroplane in this system causing emergency diversion to an available airfield.
Additional Sources of Information
(Note: In older material there may be references to issues that have subsequently been addressed)
ECMWF Newsletter 168
ECMWF Technical Memorandum No874
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