Aircraft Turbulence Clouds

Yesterday, I took a very bumpy flight from Seattle to Dallas/Fort Worth--turbulence that was associated with a strong jet stream.  Intriguingly, one look look at the satellite imagery should have told me that the seat belt sign would be on much of the flight.  In this blog, I will talk about clear air turbulence, the impact of vertical wind shear, and something called transverse cloud banding.  Throw phrases like that around at a party and your friends will either be impressed or walk away.

First, here is the path for my flight that started about 7 AM (1500 UTC Sunday Feb 14).  The turbulence began once we reached initial cruising altitude (around 30,000 ft) over northern Oregon.

My aircraft was not the only one experiencing turbulence, as shown by the graphic below from the Aviation Weather Center-- there were lots of other reports (these are pireps...pilot reports of turbulence for 6 AM to 7:30 AM)

I knew that this was going to be in interesting flight with a strong jet stream along my route.  Here are the wind at 30,000 feet at 7 AM, with the shading giving the wind speed and the barbs parallel to the winds (at least 125 knots in the core of strongest winds).

Where the winds increase rapidly with height one has large wind shear and often turbulence.  One sign of that turbulence are transverse cloud bands....bands of clouds oriented roughly perpendicular to the wind direction.  And we had a lot of such clouds along my flight path.   Here are some examples in infrared, water vapor, and visible imagery at nearly the same time (around 8 AM)

The pilot tried several altitudes, as shown by this graphic of altitude and wind speed (from the web site:  flight advisor).  First, at 30,000 ft the flight was rough, then 36,000 ft (still rough), and later 39,000 ft...much better.

We were not in clouds during the turbulence....thus, it is called clear air turbulence.  The radiosonde sounding at Boise, Idaho at 4 AM PST, show why things were better at 39,000 ft.  If you can read the wind barbs, you can see a lot of wind shear (winds changing with height) below 10420 meters (34,000 ft).  Energy for turbulence.  At 11820 meters (38700 ft) there was much less vertical wind shear and we were entering the stable stratosphere.  That is the fascinating thing about clear air turbulence...a little change in elevation can make a huge difference.

One good thing about the bumpy flight---riding the jet stream provided a lot of tail winds and we arrived a half-hour early.

Finally,a nother, more colorful, example of the banding structure is shown below.