Severe turbulence has been in the news lately… This is always a good time to bring up an example or two of how and why this occurs. This type of event can be associated with thunderstorms, but they are not required to cause severe turbulence. In the cases were thunderstorms are not involved, the jet stream is normally a significant player in describing why this happens. Terrain can cause turbulence issues as well, especially when strong wind patterns flow perpendicular to a ridge or mountain chain.
The images above display (1) forecast model-derived winds, (2) pilot reports, (3) a description of a report, and (4) a sigmet displaying areas to avoid. All images above were obtained on 1 February 2012 to be used as an example. These images display the life-cycle of a severe turbulence event to a weather forecaster and/or pilot: forecast phase, observation, reporting, warnings/forecasts.
- The first image displaying the winds at a level of 30,000 ft above mean sea level describe the wind speed and direction. The wind barbs do this with the long stick and the notches or flags on the end. The wind is flowing from the end of the barb with the flag or notches to the end without. The speed is indicated by how many flags (50 kt) or notches (10 kt for full). Severe turbulence is often found where there are significant changes in wind direction over a short distance (directional shear). Significant changes in speed over a short distance can cause turbulence as well (speed shear). Where the circle is drawn indicates an area where the jet is flowing from the north to the south and takes an abrupt turn eastward. This area has significant directional and speed shear and is indicative of significant turbulence.
- The second image displays reports made by pilots during flight when they encountered and reported significant turbulence. The area where most reports are located is consistent with the abrupt changes in the jet stream over southern California.
- The third image describes the pilot report noting moderate to severe turbulence was encountered at a flight level of 33,000 feet. The aircraft type was a Boeing 738 (relatively large passenger jet).
- The fourth image displays a sigmet or a warning for the area of severe turbulence. This is an observed warning with a forecast for severe turbulence to continue for at least the next few hours over the boxed region over southern California.
A few notes of when this was most recently reported in the news are below.
Early January 7 passengers were injured when a huge Airbus aircraft (A380) encountered severe turbulence enroute from London to Sydney (Source).
Last week on the 23rd of January a flight from Brazil to Miami encountered severe turbulence, and three flight attendants were injured (Source). The image below is from NASA found at the linked source displaying where the flight encountered the area of turbulence.
An interesting article describing how transportation providers have been sued in the past (and potentially will be in the future) for inducing fear in customers during services can be found here: http://www.forbes.com/sites/deborahljacobs/2012/02/01/costa-shipwreck-survivors-can-sue-for-being-scared-to-death/