Clear Air Turbulence is on the rise, according to a recent study

What does the study say?

Well, here it is if you want to purr-use it yourself. The study was carried out at the University of Reading (go Reading! My home town!), and published in June 2023.

Here is a summary of what they discov-furred:

• CAT has increased, particularly in Europe, the US and over the North Atlantic
• Over the North Atlantic, the total annual duration of severe turbulence increased by 55%. In other words, there were 17.7 hours in 1979 and in 2020 there were 27.4 hours
• Overall, moderate turbulence increased by 37% from 70.0 to 96.1 hours, and light turbulence increased by 17% from 466.5 to 546.8 hours
• Windshear in jetstreams has increased by 15% since 1979. A further increase of around 17 to 29% is projected by 2100
• In the US alone it is costing around $200million a year in fixing damage and hospital bills!

Some Sciencey Stuff

OK, so CAT is defined as aircraft turbulence that occurs at altitudes of around 23,000 to 39,000′. It is the result of air masses moving about at different speeds and directions and meeting up. It is usually the worst near jet streams and where the high troposphere meets the tropopause.

Do we think it is increasing just because more aircraft are flying and reporting it though?

No. The studies actually looked at the levels of wind shear inside jet streams. – which they can monitor using satellites.

“Wait? What! How come we can’t have that in the airplane?“

I don’t really know. I know the satellites utilise infrared technology so can see the water vapour swilling about, but remote systems cannot easily detect it along specific aircraft tracks. Another challenge is that current Numerical Weather Prediction (NWP) models have grid sizes that are many times larger than the turbulent eddies which impact airplanes.

In other words, they can look at the big stuff, but spotting little areas which impact aircraft is much harder.

Of course, we do get to ‘use’ some of what they see because we get nice pictures of it in our briefing packs, and if you have digital planning tools like FD Pro then you can select the turbulence function on there as well.

So what can we do?

Here are some recommendations:

• Check those charts
  Forecasting CAT areas is not an exact science, but they do get it fairly accurate. SIGMETs are the best thing to review, but check the shear rates along your route and the height of the tropopause as well – these are good indicators.
• Brief your crew
  Let them know approximate timings of when turbulence is predicted so they can prepare the cabin and service in advance.
• Know the regions
  Some areas are more known for it, and AIPs may even contain info on local turbulence areas.
• Listen out for PIREPS
  And don’t forget to make your own ones. ‘Ride reports’ help ATC manage flight levels for aircraft and give other crew a headsup.
• Try other levels
  If it is too bumpy, request other levels to try and avoid it.
• Look after your people
  Get the belts on. Do a PA, and seat your crew if you need to.
• Look after your airplane
  Consider putting engine ignition on. Slow down to your turbulence penetration speed. Monitor for possible overspeeds (but caution pulling your speed brake out – going below your safe clean speed is a harder situation to recover from) and if severe turbulence is encountered, have it checked for damage on the ground.

References

The NTSB are talking about it. This is a good resource with links to others.

Here is the original article I stole the info from.

Here is the paper (helpfully pre-downloaded for you).

National Weather Service page on turbulence. It has the levels described if you need them.

National Weather Service Aviation weather page for all your SIGMET needs.