Atmospheric turbulence refers to the irregular and chaotic motion of air masses, resulting in the “bumpy” sensations experienced during flight. This phenomenon is caused by variations in wind speed, pressure, and temperature at different altitudes, creating swirling motions called eddies. Whether a flight encounters more turbulence at night is a complex question, as the answer depends entirely on the type of turbulence and the specific location of the aircraft.
Daytime Turbulence Driven by Convection
During daylight hours, the primary source of atmospheric instability is solar radiation heating the Earth’s surface. As the sun warms the ground, the air directly above it heats up, becoming less dense and more buoyant. These pockets of warm air, known as thermals, rise rapidly, creating strong vertical air currents and convective or thermal turbulence.
This vertical mixing occurs within the atmospheric boundary layer, the lowest part of the atmosphere directly influenced by the surface. As daytime heating continues, this layer expands, sometimes reaching heights of 6,000 to 10,000 feet. The movement of these thermals creates the characteristic moderate, choppy air often felt on flights over land during the afternoon.
Thermal turbulence peaks when surface heating is strongest, typically mid-afternoon, and is most pronounced over surfaces that heat quickly, such as deserts. Because this mechanism relies directly on the sun’s energy, this specific type of vertical turbulence is suppressed once the sun sets.
How Nighttime Stability Creates Wind Shear
When the sun goes down, the nature of turbulence changes due to radiational cooling. The ground rapidly emits heat, cooling the air layer immediately above it via conduction. This forms a cold, stable layer near the surface known as the nocturnal boundary layer, which can be only a few hundred feet thick.
The stability of this cold layer suppresses the vertical air movement and convective turbulence that dominates the day. However, this stability sets the stage for a different type of turbulence: wind shear. Wind shear is a significant difference in wind speed or direction over a short vertical or horizontal distance.
Above the cold, stable air, the wind often remains fast because it is decoupled from ground friction. This difference in wind speed creates substantial vertical wind shear between the air above and within the nocturnal layer. Sometimes, a low-level jet forms—a narrow band of fast-moving air developing just a few thousand feet above the surface. The shear generated by these nocturnal jets can cause severe turbulence, particularly during takeoff or landing.
Turbulence Independent of Solar Cycles
Not all atmospheric disturbances are tied to the daily cycle of solar heating and cooling; many sources of turbulence persist regardless of the time of day. Strong weather systems, such as thunderstorms and cold fronts, generate intense turbulence through powerful updrafts, downdrafts, and localized wind shear. This kind of turbulence depends entirely on the storm’s life cycle, not the sun’s position.
Another major contributor is mechanical turbulence, which occurs when air flows over geographical features. When strong winds flow over mountains, they create atmospheric gravity waves that can extend hundreds of miles downwind and reach high altitudes. The disruption and eddies within these mountain waves can cause severe clear air turbulence (CAT).
High-altitude CAT is also frequently found near the jet stream, a core of fast-moving air located high in the troposphere. The intense wind shear along the edges of the jet stream, where wind speeds change drastically over a short distance, generates turbulence that is not visible.
These powerful, large-scale dynamics mean that while lower-level turbulence shifts from convective to shear-driven at night, high-altitude turbulence is a persistent factor and a constant threat to high-flying aircraft.