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Aviators should be prepared for an increased amount of clear air turbulence (CAT) in the future, according to new research into the possible effects of climate change.
The findings, published last fall by a group of researchers working out of the University of Reading in England, came from a study in which climate model simulations were run on a super computer for a 30-year period from 2050 to 2080. The group analyzed eight geographic regions, five turbulence strength categories, and all four seasons.
The results indicated an increase in CAT throughout all geographic regions, but most significantly in midlatitudes. “The increases occur in multiple aviation‐relevant turbulence strength categories, at multiple flight levels, and in all seasons,” the authors concluded. They said that some regions would experience “several hundred percent” more turbulence. Over North America, the North Atlantic and Pacific, and Europe, severe CAT occurrences could double.
A major source of CAT is wind shear. Winds that vary in strength and direction can generate waves that can then break down into turbulence, just like breaking ocean waves along a beach. The strongest winds are found within the jet stream.
The Reading study — and previous research — indicates that the jet stream will likely strengthen in the future. Tropospheric global warming, especially in polar regions, will enhance temperature contrasts near the troposphere/stratosphere interface, known as the tropopause. This will fuel the core of the jet stream typically located here. Farther below, the warming will induce more extreme weather events.
While the core of the jet stream is generally located around 30,000 feet — and many of the major CAT incidents on commercial jet aircraft have occurred around this height — the midlatitude or polar jet stream is in fact quite variable.
The core can drop down to 25,000 feet and lower. The jet stream also has considerable depth, so even if the core of strongest winds (up to 200 knots) is at or above 30,000 feet, a significant wind maximum (up to 100 knots) can extend downward to 15,000 feet or below. Under the right atmospheric conditions, strong winds can mix all the way down to the surface. In addition, the predicted increase in extreme weather events such as strong storms will also generate strong local winds and associated turbulence.