Clear Air Turbulence

What is Clear Air Turbulence?

Clear air turbulence is a type of atmospheric disturbance that affects aircraft flying in regions without visible clouds. It is most often encountered at cruising altitudes, typically between 20,000 and 40,000 feet, and is strongly linked to jet streams, high-level troughs, and other disturbed upper-level air flows. CAT is not associated with convective activity or surface features, but rather with wind shear—sudden changes in wind speed and direction over short distances.

Where is CAT Found?

• Jet Streams: The most common location for CAT is near the core of jet streams, especially on the cold side just below or near the tropopause.
• High-Level Troughs and Ridges: CAT can also occur in areas of strong upper-level wind gradients, such as troughs and ridges.
• Other High-Level Flows: Any region with significant wind shear at altitude, even away from jet streams, can produce CAT.

How Does CAT Form?

CAT develops where there is strong horizontal or vertical wind shear, particularly at the boundaries between different air masses or within rapidly changing wind fields. The sharp contrast in wind velocity creates eddies and turbulent air, which can jolt an aircraft unexpectedly.

Detection and Reporting

Traditional weather radar cannot detect CAT because it lacks moisture or particulates to reflect radar waves. Advanced systems like LIDAR are under development but not widely available. Therefore, pilot reports (PIREPs) are crucial for identifying and warning others about CAT. Forecasting is limited and often relies on model data and previous reports.

Avoidance Strategies

• Pre-Flight: Review weather briefings, SIGMETs, and pilot reports for CAT risk areas. Plan routes and altitudes to avoid known jet stream cores or regions with recent CAT reports.
• In-Flight: If CAT is encountered, changing altitude by 2,000–4,000 feet (preferably to the opposite side of the jet core) can often reduce or eliminate turbulence. Always secure passengers and crew when turbulence is expected.

Severity Levels

CAT is classified as light, moderate, or severe based on its impact on aircraft control and occupant comfort. Severe CAT can cause structural damage and serious injuries if precautions are not taken.