The word turbulence has multiple meanings and can be applied to many situations. However, when we discuss atmospheric turbulence it is used in the context of fluid dynamics and meteorology. Atmospheric turbulence is any irregular motion of air masses within the atmosphere due to non-linearity and instabilities in the flow. This phenomenon can cause sudden changes in wind speed or direction at different altitudes and on large scales, as well as increased mixing of fluids such as gases with higher levels of entropy.
The atmosphere can be modeled as a set of five interconnected fluid domains: the troposphere, the stratosphere, two belts around the middle latitudes (the polar front), and finally between 60° N/S latitude. Each of these fluid domains has its own scale and affects the motion of air masses within it. Atmospheric turbulence is dependent on three main factors: the aircraft’s velocity vector, the aircraft’s altitude, and local time/season. Atmospheric turbulence can have a variety of effects on aircraft performance including aircraft movement, aircraft component damage, and aircraft power plant issues. Aircraft movement effects include aircraft drift, aircraft roll, aircraft yaw, and aircraft slip, as well as aircraft turning performance such as rate of turn and others.
Atmospheric turbulence is a problem for aircraft. Why?
Turbulence in the atmosphere can lead to unstable flight conditions, which could potentially result in accidents. Even though pilots try to avoid turbulent regions, it is inevitable that they will encounter some level of turbulence at some point during their flight. Aircraft need stable airflow to fly and encounters with turbulence can be very dangerous as evidenced by events such as the 1989 United Airlines Flight 232 crash. Prediction of atmospheric turbulence would allow pilots to choose more optimal routes.
How can we predict turbulence?
Atmospheric turbulence is caused by the sun’s radiation input into the atmosphere. The earth’s surface current transfers this energy by absorbing, re-emitting, and scattering incoming solar radiation. This causes an irregular distribution of heat in the atmosphere which in turn displaces air within the atmosphere. On a larger scale, this is known as Rossby waves which stretch around the globe. When these Rossby waves reach the mid-latitudes, they break up into planetary wave trains which then travel east and west around the earth. When these waves reach the polar front they amalgamate into a single wave train and end up traveling southward.
Along with atmospheric turbulence being caused by solar radiation input, there are other factors such as vertical wind shear (or change of velocity) in the atmosphere which can be caused by local time and season. This vertical wind shear is another reason for aircraft movements such as aircraft drift and aircraft roll, especially during landing and takeoff
Predicting atmospheric turbulence has been a major issue for meteorologists and aircraft pilots for decades. Aircraft currently use weather radar to detect large areas of upflow or downflow which aids in aircraft avoidance of dangerous regions. However, aircraft still often get caught in dangerous turbulence even when it is detected according to the NOAA. Turbulence can be predicted through aircraft observations and measurements of temperature and moisture profiles along with knowledge of the atmospheric stability which determines how much vertical motion there will be.
What are the benefits of predicting atmospheric turbulence?
The benefits of predicting aircraft turbulence are numerous. Pilots would be able to avoid dangerous regions of turbulence, aircraft could be designed with the knowledge that there is turbulence present in certain regions, and aircraft structures could be tested for their ability to handle disturbance weather conditions. By providing pilots with information about where turbulence exists aircraft will be safer during flight operations and aircraft could be designed specifically for turbulence in order to ensure safe aircraft operations.
How can we reduce aircraft accidents caused by atmospheric turbulence?
Currently, aircraft are designed to handle specific wind conditions. For example, aircraft that fly through mountainous regions must be able to resist high winds, or aircraft traveling across oceans must be capable of withstanding strong headwinds. However, aircraft do not currently take into account the effects of turbulence on aircraft motion and stability which can often lead to aircraft accidents due to aircraft design limitations.
Predicting atmospheric turbulence has many benefits for the aviation industry as well as future discoveries that could be made. New aircraft designs are always being tested for efficiency and safety, which would benefit from the prediction of atmospheric turbulence.