DUST STORM

Subject: Geography

Context : Beijing witnesses biggest dust storm in decade.

Concept :

Sand and dust storms are common meteorological hazards in arid and semi-arid regions. They are usually caused by thunderstorms – or strong pressure gradients associated with cyclones – which increase wind speed over a wide area.
Sand and dust particles are distinguished by their grain size. Storms carrying bigger particles are known as Sand Storm whereas those carrying smaller are called dust Storms.
Marginal dry lands are increasingly a source of major dust storms. These areas have fragile, delicately balanced ecosystems. Their degradation, called desertification, makes the soil less resilient to wind during prolonged drought.

Formation of Dust Storms

Sand and dust storms usually occur when strong winds lift large amounts of sand and dust from bare, dry soils into the atmosphere.
Once released from the surface, dust particles are raised to higher levels of the troposphere by turbulent mixing and convective updrafts.
They are transported by winds for lengths of time, depending on their size and meteorological conditions, before being pulled back down to the surface again.
As larger particles sediment more quickly than smaller ones, there is a shift toward smaller particle sizes during transport.
Areas which have higher moisture witness thunderstorm and areas relatively devoid of moisture suffer from dust storms.