Short Notes on Mechanism of Monsoons
Mechanism of Monsoon:
Today the Mechanism of Monsoon is a widely-studied subject globally.
The following facts are important to understand the mechanism of Indian monsoon:
Differential Heating and Cooling of Land and Water
a. Due to this lower pressure is found on the landmass.
b. High pressure is found on the water bodies/seas and oceans around India.
Shift in the position of Inter Tropical Convergence Zone (ITCZ)
a. Inter Tropical Convergence Zone is the equatorial trough (lower pressure area). It is normally positioned at 5° north of equator.
b. During summer it shifts its position to the Ganga plain, and is also known as monsoon trough, during the monsoon season.
Presence of High Pressure Area, East of Madagascar
a. High pressure area is found east of Madagascar approximately at 20° S over the Indian Ocean.
b. The intensity and position of this high pressure area affects the Indian monsoon.
Intensely Heated Tibetan Plateau
a. Tibetan plateau gets intensely heated during summer.
b. It results in the strong vertical currents.
c. At 9 km over the plateau from mean sea level high pressure is formed.
Westerly Jet Stream and Tropical Easterly Jet Stream
a. Westerly Jet stream moves to the north of the Himalayas.
b. At this time (during summer) tropical easterly jet stream is present over the Indian Peninsula.
a. Changes in the pressure conditions over the southern oceans also affect monsoons. Normally when the tropical Eastern south Pacific Ocean experiences high pressure, the tropical Eastern south Indian Ocean experiences low pressure.
b. But in certain years, the usually prevailing pressure conditions are reversed. It results in the low pressure on the Eastern Pacific Ocean, in comparison to the eastern Indian Ocean. Winds oscillate between Eastern south Pacific Ocean and Eastern Indian Ocean.
c. This periodic change in pressure conditions and wind is known as the Southern Oscillation or so.
A feature connected with the SO is the EI Nino.
a. It is a warm ocean current that flows past the Peruvian coast, in place of the cold Peruvian current every 2 to 5 years.
b. The changes in pressure conditions are connected to the EI Nino. Hence, the phenomenon is referred to as ENSO (EI Nino Southern Oscillations).
Warm waters along the Pacific coast in the South Pacific Ocean cause heavy rainfall on the Peruvian coast. Rainfall may fail in south East Asia due to the shift of warm water from eastern south Indian Ocean. This is called Elnino effect.