Severe turbulence cases NOMEK 2009

Aviation requirements ICAO Annex 3 – “The objective of meteorological service for international air navigation shall be to contribute towards the safety, regularity and efficiency of international air navigation.”

Some facts FAA: – “Two-thirds of turbulence-related accidents occur at or above feet” – “Among non-fatal accidents, in-flight turbulence is the leading cause of injuries” IATA: – “Globally each year, around passengers and crew are injured in turbulence related incidents.”

Definitions Turbulence – Severe whenever the peak value of the cube root of EDR exceeds 0.7; – Moderate whenever the peak value of the cube root of EDR is above 0.4 and below or equal to 0.7. Mountain waves – Severe whenever an accompanying downdraft of 3.0 m/s (600 ft/min) or more and/or severe turbulence is observed or forecast; and – Moderate whenever an accompanying downdraft of 1.75– 3.0 m/s (350–600 ft/min) and/or moderate turbulence is observed or forecast.

Turbulence definitions Light/LGT TURB – small changes in aircraft altitude – 0.05 to 0.2g Moderate/MOD TURB – moderate changes in aircraft attitude and/or height and small airspeed variations – 0.2 to 0.5g Severe/SEV TURB – Abrupt changes in aircraft attitude and/or height and large airspeed variations – 0.5 to 1.5g Extreme – Dramatic changes in aircraft attitude and/or height and large airspeed variations – >1.5g

Impacts of turbulence LGT – Fasten seatbelts signs turned on – “Business as usual” MOD – Occupants feel strain against seat belts; difficulty in walking; loose objects move about – Aircraft remains in control at all times SEV – Occupants forced violently against seat belts; loose objects are tossed about – Aircraft handling becomes difficult; aircraft may be out of control for short periods Extreme – Aircraft out of control – Structural damage to aircraft likely.

Common turbulence tools Prognostic: – WAFC SIGWX, – Windcharts (WAFS W&T, NMS NWP) – Others? Diagnostic: – Profiling (radiosondes, AMDAR ) – PIREPS/AIREPS/EDR in-situ – Satellite images

SIGWX MODERATESEVERE Horizontal wind shear 20 KT per degree of latitude 30 KT per degree of latitude Vertical wind shear 6 KT per 1000 ft9 KT per 1000 ft Dutton Index= (5(HWS)+(VWS) 2 +42)/4 CAT probable when DI>4 Used by UK WAFC in SIGWX diagnosis 80 knots lower limit for depiction of jet in SIGWX

MTW Reykjavik CTA >FL200 RVK FIR SFC-? En-route TURB CAT

ICE-653 SEV TURB REP FL /-500 FT

Remember NWP resolution!!!

SIGWX charts are not handy as MTW forecasts

ICE-653 Flight data recorder

Crew observations Visual of peculiar wavepattern in cirrus clouds – Seatbelt sign on – minor decrease of speed In ~10 secs the rapid descent stops and the autopilot brings the plane up again

Similar but fatal case X

Breaking gravity waves Dutton and Panofsky stated already in 1970 that the major cause of CAT can be traced to Kelvin-Helmholtz instability – strong vertical shear and low local Richardson number (strong inversions)

WAFS forecast

DMI HIRLAM-T

Vertical cross-section

Main findings in assessment Modern aviation forecasts are not even close to dealing with local scale turbulence features – WAFS forecasts to coarse to deal with small scale gravity waves, global smoothing in coarse grid – DMI HIRLAM (LAM, 15 km) showed stronger windshear and was closer to observations (air reports, radiosonde from Faroe Island) – MM5 show some sign of windshear induced turbulence outbreak, but not so clearcut answer – Fine resolution (less than 10 km, much likely less than 5 km) needed, but the aviation community would need those forecasts on global scale.

Tuesday

Tool assessment Satellite images Vertical profiles NWP Human turbulence observations

Thank you!! Questions?