Why was Singapore flight turbulence severe?

Sub: Science and tech

Sec: Msc

Context:

On May 20-21, a Singapore Airlines flight, SQ321, with 211 passengers and 18 crew, from London’s Heathrow Airport to Singapore encountered severe turbulence while over the Andaman Sea/Bay of Bengal near the Irrawaddy Basin, Myanmar.

More on news:

The United States National Transportation Safety Board (NTSB) is to assist Singapore’s investigation as the aircraft is a Boeing jet.

What is Turbulence?

Turbulence occurs by the relative movement of disturbed air through which an aircraft is flying.
It could be thermal or mechanical and can happen either within or when it is clear of clouds.
Turbulence is one of the most unpredictable of all the weather phenomena that are of significance to pilots.
Turbulence is an irregular motion of the air resulting from eddies and vertical currents.
It may be as insignificant as a few annoying bumps or severe enough to momentarily throw an airplane out of control or to cause structural damage.
Turbulence is associated with fronts, wind shear, thunderstorms, etc.
Its severity depends on the rate at which the speed or the direction of airflow/or both changes
Turbulence is basically what happens when there is friction between airflow or wind flowing in different directions.
When it involves aviation, there are two main forms, which are Clear Air Turbulence (CAT), which happens around jet streams, and the other being inside or around cumulonimbus clouds.
The clouds have very strong upwards air currents in the middle and downwards air currents around the outside, which can result in quite serious turbulence.
The faster an aircraft is, the more severe the response to the turbulence.
Turbulence on flights can be caused by storms, mountains, and strong air currents called jet streams.
It is called clear air turbulence, and can be difficult to avoid because it does not show up on the weather radar in the flight deck.

TURBULENCE INTENSITY:

In reporting turbulence, it is usually classed as light, moderate, severe or extreme.
The degree is determined by the nature of the initiating agency and by the degree of stability of the air.
Light turbulence momentarily causes slight changes in altitude and/or attitude or a slight bumpiness.
- Occupants of the airplane may feel a slight strain against their seat belts.
Moderate turbulence is similar to light turbulence but somewhat more intense. There is, however, no loss of control of the airplane.
- Occupants will feel a definite strain against their seat belts and unsecured objects will be dislodged.
Severe turbulence causes large and abrupt changes in altitude and/or attitude and, usually, large variations in indicated airspeed.
- The airplane may momentarily be out of control. Occupants of the airplane will be forced violently against their seat belts.
In extreme turbulence, the airplane is tossed violently about and is impossible to control.
- It may cause structural damage.
Chop is a type of turbulence that causes rapid and somewhat rhythmic bumpiness.

Causes of Turbulence:

Mechanical Turbulence:

Friction between the air and the ground, especially irregular terrain and man-made obstacles, causes eddies and therefore turbulence in the lower levels.
The intensity of this eddy motion depends on the strength of the surface wind, the nature of the surface and the stability of the air.
The stronger the wind speed (generally, a surface wind of 20 knots or higher is required for significant turbulence), the rougher the terrain and the more unstable the air, the greater will be the turbulence.

Thermal (Convective) Turbulence:

Turbulence can also be expected on warm summer days when the sun heats the earth’s surface unevenly.
Certain surfaces, such as barren ground, rocky and sandy areas, are heated more rapidly than are grass covered fields and much more rapidly than is water.
Isolated convective currents are therefore set in motion with warm air rising and cooler air descending, which are responsible for bumpy conditions as an airplane flies in and out of them.
Turbulence extends from the base to the top of the convection layer, with smooth conditions found above.

Frontal Turbulence:

The lifting of the warm air by the sloping frontal surface and friction between the two opposing air masses produce turbulence in the frontal zone.
This turbulence is most marked when the warm air is moist and unstable and will be extremely severe if thunderstorms develop.
Turbulence is more commonly associated with cold fronts but can be present, to a lesser degree, in a warm front as well.

Wind Shear:

Wind shear is the change in wind direction and/or wind speed over a specific horizontal or vertical distance.
Atmospheric conditions where wind shear exists include: areas of temperature inversions, along troughs and lows, and around jet streams.
When the change in wind speed and direction is pronounced, quite severe turbulence can be expected. Clear air turbulence is associated at high altitudes (i.e, above 15,000 feet AGL) with the jet stream.

Turbulence and Climate Change:

There is strong evidence that turbulence is increasing because of climate change.
It was recently discovered that severe clear air turbulence in the North Atlantic has increased by 55% since 1979.

Work of Aviation attorneys:

Aviation attorneys work with aviation and weather experts to plot the aircraft’s route, obtain satellite images of the weather at the time and location of the encounter, and to quickly secure airline data to help prove the claim.
They even look at whether the crew knew there was bad weather ahead but decided not to deviate to save time, fuel, and airline money.