What are the causes of origin of south west monsoon?

  1. Northward shifting of ITCZ : This shift in June causes low pressure at Tibetan plateau. Tropical Easterly Jets move towards the Mascarene High and moist monsoon winds from Mascarene High move towards Tibetan plateau.
  2. Appearance of Somali Jet Stream in Summer : Somali Jet Streams appear in summer and intensify the Somali Ocean current. This pushes monsoon winds towards India
  3. Absence of STWJ in winter : In winters, Sub Tropical Westerly Jet (STWJ) gets bifurcated and its one strand causes high pressure in India. In summers, entire STWJ shift beyond Himalayas and hence low pressure is maintained over India.
  4. Indian Ocean Dipole and Walker Cell : The Indian Ocean Dipole between Western Pacific Pool and Mascarene High pushes monsoon winds towards India. In an El Nino year, this push is weak whereas in La Nina year it is strong.


The cumulative effect of these factors is that a low pressure is created over the Indian subcontinent while a high pressure is formed in the Indian Ocean. This pushes the moist, rain bearing monsoon winds from the Arabian sea towards the subcontinent. The blockage of these winds by Western Ghats causes rains in the southern region while that by Himalayas leads to downpours over North India.



Write a note on the important factors that determine the climate of India. Also examine how the monsoon regime emphasises the unity and diversity of India in its pattern. (200 Words)


Factors affecting climate of India

  1. The Monsoon winds : The South west monsoon and the North east monsoon are crucial for bringing rainfall in India and directly affect the Indian economy, esp. agriculture.
  2. Location of Himalayas, western and eastern Ghats:  Himalayas force the monsoon winds to give most of its rainfall in India before crossing. They also prevent the cold winds from central asia from entering India. The western and eastern ghats force monsoon winds to give most of the rainfall in the coastal regions, esp. western slopes of Western ghats.
  3. Altitude: The variation in altitude also causes changes in climate .
  4. Distance from sea: The presence of sea moderates the climate in coastal regions whereas the landlocked regions experience extremes of climate.
  5. Latitudinal location: The tropic of cancer divides India into the subtropical and colder region of the north, and topical and warmer region of the south.


The monsoon is a defining feature of the climate in India. India stands united to

accept the rain bearing winds and agriculture in almost all of India is patterned on the monsoon. A bad monsoon year hampers crops across India.


The diversity of India can be seen in floods in one place and droughts in another.

The difference in rainfall caused by the monsoon is extreme, with the coastal and

eastern regions receiving most rainfall, and north western and central regions

receiving least. Also, Tamil Nadu receives most rainfall from the North east




What do you understand by the Indian Ocean Dipole (IOD)? Examine its relevance to India‘s monsoon rains. (200 Words)




The Indian Ocean dipole refers to a Low Pressure – High Pressure mechanism that develops in the Indian Ocean region and facilitates the onset of monsoons to the Indian subcontinent. There is difference between the Sea Surface Temperatures (SSTs) of Western and Eastern parts of the Indian Ocean. The High Pressure region develops at Mascarene high and a weak pressure region develops in eastern Indian ocean. This is the di-pole

  1. Due to the northward shifting of the ITCZ in summers, the Tibetan plateau gets heated up and develops into a low pressure zone.
  2. A high pressure zone develops at Mascarene High near Madagascar in the Indian Ocean. It is aided by the Walker cell that develops between the Western Pacific Pool near Australia and Peruvian coast.


IOD can be of two types – positive and negative.

A positive IOD results in a strong monsoon and vice versa. Positive Indian dipole-it occurs when sea temperature of Arabian Sea is more than that of Bay of Bengal. Negative Indian dipole-it occurs when sea temperature of Bay of Bengal is more than that of Arabian Sea.
During positive IOD, there is enhanced cloud formation and rainfall in western part of equatorial ocean near African coast while such activity is suppressed near Sumatra therefore this condition becomes positive for India. e.g. in El-Nino years 1983, 1994,1997 India got surplus or normal rainfall.

Negative IOD Under this condition Sumatran and Indonesian coast get more rainfall that retards the rains over India. When negative IOD and El-Nino come together it becomes the reason of deficit rainfall in India and other countries depending upon monsoon e.g. in 1992 this condition gave rise to deficient rainfall. Therefore IOD has a special impact on India’s monsoon as rainfall does not only depend upon the El-Nino effect but also get sufficient or deficient rainfall due to combination of these two phenomenon.



Write a note on the objectives and achievements of India’s Monsoon Mission. (200 Words)


India’s monsoon system is one of the most complex weather systems in the world, which makes its scale largely unpredictable, as still all the factors affecting it have not been discovered.


Hence, to improve the assimilation and forecasting system especially for the monsoon region, the Ministry of Earth Sciences (MoES) has formulated a focused mission mode programme ‘Monsoon Mission’ on the national scale under the leadership of IITM.


Its objectives are:

  1. To build a working partnership between the Academic R&D Organizations and the Operational Agency to improve the monsoon forecast skill.
  2. To set up a state of the art dynamical modelling frame work for improving prediction skill of Seasonal and Extended range prediction system, Short and Medium range prediction system
  3. To set up the infrastructure and manpower required to improve the prediction skill at all the time scales.


Achievements include delivering quantifiable improvement in forecasting extreme events, such as El Nino, flood and drought years, active and dry spells of monsoon, flash floods, and monsoon depressions. It will also predict sea surface temperature.


The project uses high resolution coupled ocean atmospheric model, which gives information on both atmosphere and ocean.


The ultimate goal of the mission is to develop an Indian Model which will have the capability to better simulate and predict the monsoon rainfall.