Wind speed

Wind speed, or wind flow velocity, is a fundamental atmospheric rate. Wind speed is caused by air moving from high pressure to low pressure, usually due to changes in temperature.

Wind speed affects weather forecasting, aircraft and maritime operations, construction projects, growth and metabolism rate of many plant species, and countless other implications.

Wind speed is now commonly measured with an anemometer but can also be classified using the older Beaufort scale which is based on people's observation of specifically defined wind effects.

Factors affecting wind speed

Wind speed is affected by a number of factors and situations, operating on varying scales (from micro to macro scales). These include the pressure gradient, Rossby waves and jet streams, and local weather conditions. There are also links to be found between wind speed and wind direction, notably with the pressure gradient and surfaces over which the air is found.

Pressure gradient is a term to describe the difference in air pressure between two points in the atmosphere or on the surface of the Earth. It is vital to wind speed, because the greater the difference in pressure, the faster the wind flows (from the high to low pressure) to balance out the variation. The pressure gradient, when combined with the Coriolis effect and friction, also influences wind direction.

Cyclone Phailin

Extremely Severe Cyclonic Storm Phailin (Thai: ไพลิน meaning "sapphire") was the most intense tropical cyclone to make landfall in India since the 1999 Odisha cyclone. The system was first noted as a tropical depression on October 4, 2013 within the Gulf of Thailand, to the west of Phnom Penh in Cambodia. Over the next few days, it moved westwards within an area of low to moderate vertical wind shear, before as it passed over the Malay Peninsula, it moved out of the Western Pacific Basin on October 6. It emerged into the Andaman Sea during the next day and moved west-northwest into an improving environment for further development before the system was named Phailin on October 9, after it had developed into a cyclonic storm and passed over the Andaman and Nicobar Islands into the Bay of Bengal.

During the next day Phailin intensified rapidly and became a very severe cyclonic storm on October 10, equivalent to a category 1 hurricane on the Saffir-Simpson hurricane wind scale (SSHWS). On October 11, the system became equivalent to a category 5 hurricane on the SSHWS before it started to weaken during the next day as it approached the Indian state of Odisha. It made landfall later that day, near Gopalpur in Odisha coast at around 2130 IST (1600 UTC). It subsequently weakened over land as a result of frictional forces, before it was last noted on October 14, as it degenerated into a well marked area of low pressure.