Why in News:
- A Boeing 737-800 aircraft of SpiceJet experienced severe turbulence
What is it?
- Turbulence is an irregular motion of the air resulting from eddies and vertical currents.
- Eddy is nothing but a fluid current which has a different flow direction from the general flow direction. When the flow is in the turbulent region it produces eddies.
- In an air mass moving, vertical movements occur when there is convergence and divergence at different levels of the atmosphere. There are two types of vertical currents: those that flow downward from near the surface toward the bottom and those that flow upward from the bottom toward the surface. The downward flow is called a downwelling and the upward flow an upwelling.
- Turbulence can 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.
- In terms of the categorisation of turbulence, there is : convective turbulence (or turbulence linked to cloud convection); mechanical turbulence (low-level turbulence); orographic turbulence (linked to elevated terrain such as mountains); clear air turbulence; low-level jet streams, and also wake turbulence caused by other aircraft.
- Aviation experts drew attention to a weather phenomenon (and an aviation hazard) called the Norwester over eastern and northeastern India which occurs in March, with its frequency increasing in May and early June as another cause for the accident.
- Norwesters are destructive squalls which take place in the afternoon/evening; and, cells of weakening down drafts regenerate themselves as new storm cells.
- Violent thunderstorms in the Gangetic plains of India are locally known as Kal Baisakhi or Nor’westers. These localised events are generally associated with thunderstorms accompanied by strong squally winds and torrential rainfall.
- An aircraft can experience a stall and loss of lift when flying near or through them. There is also an additional high risk of hail damage.
- In a typical Norwester, if flying in proximity of what is called its downwind wake area, an aircraft can get sucked into the centre of the storm cell and experience damage and severe turbulence.
- Experts also highlighted the importance of the factor of Total Air Temperature (TAT) in analysing turbulence
- The TAT is the temperature measured on the outer skin of an aircraft.
- Norwesters appear in West Bengal and neighbouring parts of Jharkhand, Odisha, and Assam.
- Squalls with speeds of 60 to 80 kilometres per hour are common. Hailstones, which may reach the size of a golf ball, often accompany showers.
- The rainfall brought by the norwesters is known as the spring storm showers.
- They wreak significant damage to standing crops, trees, houses, and livestock, as well as human life.
- They are, however, occasionally beneficial in the growth of tea, jute, and rice and are known as tea showers in Assam.
- These storms are called ‘Barodoli Chheerha’ in Assam. The month of Vaisakh (mid-March to mid-April) is when these storms are most common, and so they are known locally as Kalabaisakhis, meaning black storms or a mass of dark clouds.