Severe North Atlantic Clear-Air Turbulence Rose 55%, Yet Weather Radar Cannot See It

Fifty-five percent is the increase in the annual duration of severe clear-air turbulence diagnosed over an average point in the North Atlantic between 1979 and 2020. In practical terms, the figure rose from 17.7 hours a year to 27.4 hours, according to a 2023 study in Geophysical Research Letters. That is 9.7 additional hours of severe conditions at a representative location in one of the world’s major long-haul corridors.

The same analysis found that moderate clear-air turbulence increased 37%, from 70.0 to 96.1 hours annually. Light turbulence increased 17%, from 466.5 to 546.8 hours. The results were derived from atmospheric reanalysis data and 21 turbulence diagnostics covering 1979 through 2020, rather than a continuous four-decade record of measurements taken aboard airliners.

The operational problem is that conventional onboard weather radar cannot directly reveal clear-air turbulence. Radar helps pilots identify precipitation and avoid thunderstorms, but clear-air turbulence forms in cloudless regions, typically around cruising altitude. A cockpit display can therefore show no storm return even when the surrounding wind field contains the shear needed to produce a rough encounter.

Why clear skies can still become violent

Clear-air turbulence is closely associated with jet streams and wind shear, meaning a rapid change in wind speed or direction. Under suitable atmospheric conditions, that shear can destabilize airflow and create turbulent motion without the visible cloud structure associated with a thunderstorm.

The North Atlantic is particularly important because its busy routes cross a major jet-stream corridor. The researchers associated the long-term increases with changing atmospheric temperatures and wind patterns that affect jet-stream behavior and vertical wind shear. Their analysis found some of the largest increases over the North Atlantic and the continental United States, although significant changes also appeared in other regions.

Because radar does not provide direct warning, crews build a picture from forecasts, reports submitted by aircraft ahead of them and updates from air traffic control. Airlines can use that information to alter flight level, suspend cabin service or direct passengers and crew to their seats. But turbulence is dynamic: conditions can change before the next aircraft reaches a location described in an earlier report, and reports are useful only when they arrive in time.

Data sharing is intended to narrow that gap. The International Air Transport Association’s Turbulence Aware platform distributes observations from participating aircraft to flight crews and airline operations teams. Compared with relying solely on subjective pilot reports, shared aircraft data can give operators a broader, more current view of where rough air has been encountered. It still describes and forecasts an evolving atmosphere rather than giving every aircraft a guaranteed view of turbulence directly ahead.

The aircraft and its occupants face different risks

Commercial aircraft are designed to withstand considerable aerodynamic forces, so the immediate safety concern inside the cabin is often unsecured people and objects. A sudden vertical movement can throw an unrestrained passenger or crew member into the ceiling or cabin fittings even when the airframe remains within its structural capability.

The consequences were stark in May 2024, when Singapore Airlines flight SQ321, a Boeing 777 flying from London to Singapore, encountered severe turbulence. One passenger died and numerous people were injured. The event illustrates why restraint and cabin procedures remain central protections against abrupt motion, regardless of how much structural load the aircraft can tolerate.

Keeping a seatbelt loosely fastened while seated provides protection during an encounter that arrives before the sign can be activated. Cabin crews face a more complicated exposure because their work requires movement through the aircraft. Forecasts and reports can allow service to be stopped and crew members seated before expected turbulence, but an unforecast encounter leaves little time to secure a cabin.

Forward detection remains a development problem

Researchers and manufacturers have explored airborne lidar, which uses laser pulses to sense atmospheric changes ahead of an aircraft. An RTCA feasibility assessment found that the technology still required further research, simulation, data collection and flight testing. Lidar is not a standard clear-air turbulence warning system across commercial fleets.

That leaves aviation managing a growing hazard through layered but imperfect defenses: atmospheric forecasting, reports from other aircraft, air traffic control information, airline data networks, cockpit decisions and cabin restraint. The 55% figure does not mean an airliner spends 55% more of every flight in severe turbulence; it measures the rise in diagnosed annual hours over an average North Atlantic point. What it does show is that the rarest and most consequential category increased the fastest across the study period, while the sensor fitted to find hazardous weather still cannot directly see it.

By David Whitaker — Associate editor for AMI’s aerospace and drone systems desk, translating flight systems, aircraft programs, spaceflight, and UAV developments into accessible technical stories.