ANS: Turbulence remains one of the most unpredictable and challenging weather phenomena for pilots, characterized by irregular air motion from eddies and vertical currents. This can range from minor bumps to severe turbulence that momentarily disrupts airplane control or causes structural damage, often linked to weather fronts, wind shear, and thunderstorms.
Turbulence, categorized as light, moderate, severe, or extreme, depends on the initiating factors and the air’s stability.
Light turbulence causes slight altitude or attitude changes, with occupants feeling minor strain against seat belts.
Moderate turbulence is more intense but does not cause loss of control, resulting in a definite strain against seat belts and dislodging unsecured objects.
Severe turbulence induces large, abrupt changes in altitude and attitude, with significant variations in airspeed, momentarily putting the airplane out of control and violently straining seat belts.
Extreme turbulence, the most dangerous, violently tosses the airplane, making it uncontrollable and potentially causing structural damage.
Causes of Turbulence
Mechanical Turbulence: This occurs from friction between the air and the ground, especially over irregular terrain or man-made obstacles, generating eddies. The intensity depends on wind speed, surface nature, and air stability. Strong winds, typically above 20 knots, over rough terrain or unstable air increase turbulence. Even hangars and large buildings can cause eddies in strong winds, which are usually gusty, leading to severe turbulence.
Thermal (Convective) Turbulence: Common on warm days when the sun unevenly heats the earth’s surface, causing isolated convective currents. These currents create bumpy conditions as planes fly through warm rising and cool descending air. Turbulence extends from the convection layer’s base to its top, intensifying with convective updrafts. Pilots often prefer flying in the early morning or evening to avoid severe thermal turbulence. Convective currents can also produce thunderstorms with severe turbulence, especially in cold air masses over warm surfaces, creating unstable conditions, gusty winds, and bumpy flights.
Frontal Turbulence: Caused by the lifting of warm air by sloping frontal surfaces and friction between opposing air masses, this turbulence is most severe when the warm air is moist and unstable, potentially leading to thunderstorms. Cold fronts typically exhibit more turbulence than warm fronts.
Wind Shear: This is the change in wind direction and/or speed over a specific distance, occurring in areas with temperature inversions, troughs, lows, and around jet streams. Pronounced wind shear can result in severe turbulence, particularly clear air turbulence at high altitudes (above 15,000 feet). Temperature inversions, due to radiational cooling, create zones of vertical wind shear and associated turbulence. Lows and troughs experience horizontal directional and speed shear turbulence at various altitudes. Jet streams, with strong horizontal winds, generate turbulence along strong isotach gradient zones, especially on the poleward side of cyclonic jet streams or the equatorward side of anticyclonic jet streams. Turbulence intensifies around amplified jet streams.
Understanding these causes helps pilots anticipate and manage turbulence, ensuring passenger safety and aircraft integrity.