Indian Monsoon Part 1 Compiled By – Dr. Bheekam Singh Associate Professor, Department of Geography, Mihir Bhoj P.G. College, Dadri Gautam Budh Nagar (U.P.) 203207

Introduction Complex meteorological phenomena Number of concepts about the origin of monsoon. Climate and economy of India are completely driven by the monsoon winds. Refers to a season in which wind system reverse completely

Name and Definitions Phenomena first observed by the sailors and traders, when their boats were flicked by these winds Arabs also came to India and observed this seasonal reversal of winds They named it Monsoon on Arabic word Mausim means Season. It can be said that these are seasonal winds in which there is a complete reversal of winds after every six months.

Name and Definitions By Chang-Chia-Cheng “Monsoon is a flow pattern of general atmospheric circulation over a wide geographical area, in which there are clearly dominated winds in one direction, in every part of the region concerned, but this direction of wind is reversed or almost reversed from summer to winter and winter to summer.”

Regions of Monsoon Mainly in Tropical area between 20 degree north to 20 degree south India is a typical Monsoon region Indian sub-continent and South east Asia including China, Japan and Korea. Seasonal changes are also seen in USA, Carrabin Islands, Madagascar, East Africa, Guinea Coast and Australia

Conditions affecting Monsoon Differential heating Shift in ITCZ High pressure area in east of Madagascar Tibetan Plateau Heating in Summer Movement of Jet Stream Changes in pressure of Indian and Pacific Ocean (Southern Oscillation)

Measuring the Intensity of Monsoon By computing the difference in Heating over Tahiti Island (Pacific) and Darwin (Australia) Negative pressure differences -Below average and late Monsoon Positive Pressure Differences - Good and On time Monsoon

1.Differential Heating or Thermal Concept By Halley 1686 Concept – Monsoon are the extended land and sea breeze on a large scale, produced by differential heating of continents and oceans. Two conditions Summer conditions Winter conditions

Differential heating during Day and Night time

Summer Conditions High temp. in Northern Hemisphere Low pressure area near Peshawar and Lake Baikal Northward Shift of ITCZ (concept) Low pressure area in Indian subcontinent and High pressure area in Arabian and Pacific Ocean Creation of Ocean to land pressure gradient

Change in the position of ITCZ

Wind Moves from High pressure to low pressure Warm and moist wind, strike with land obstructions, hence

Winter Conditions Position of Sun and ITCZ shift southward Hence, high pressure at Lake Baikal and Peshawar Relatively high temp and low pressure at Indian and Pacific ocean. Land to sea movement of winds but cold and dry

Criticism Low pressure area in Northern hemisphere is not stationary, it changes its positions and not only thermally induced. If thermally induced then there would be anti monsoon circulation in upper atmosphere, which is absent High temperature and low pressure starts in April, but no rain before June

Criticism Modern meteorology seems to have a idea that Indian monsoon is not an orographic rainfall There are not only two but four seasons India which are having different levels of rainfall and temperature Role of latent heat from oceans is missed

Role of Tibetan Plateau In 1973 – MONEX (Monsoon Expedition) By Soviet Union and India 4 Russian and 2 Indian well equipped ships were sent into Arabian sea and Indian Ocean Aim was to identify the phenomena of monsoon Soviet meteorologists find out that Tibet plateau has a great importance in occurrence of monsoon Already pointed out by P. Koteshwaram in 1958

Tibetan Plateau 600km wide in west and 1000 km wide in East Enormous block of high ground as a formidable barrier Receives 2-3 degree more isolation than surrounding area

Tibet Plateau most Important found by Indian but credit goes to Russian

Role of Tibet Plateau Effects in Two ways As a physical barrier As a relatively high source of heat

As a physical barrier By Maung Tun Yin ITCZ shift in north of Himalaya and Tibet in summer near 40 degree north Relationship between shifting of ITCZ and slowing down of westerly jet stream So opening of monsoon in June is a result of hydro dynamic effect of Himalayas not the thermally induced low pressure Become very cold in October and create jets in its south as easterly

As a high level heat source High heat and low pressure creates anticyclones These anticyclones slow down the sub tropical jet streams but intensifies the tropical jets in south These tropical jets extends westward from India to Arabian sea on Kolkata-Banglore axis Create high pressure cell in Arabian sea and also called sinks into Arabian sea Finally moves as South west monsoon

Hot Tibet with cool people

Role of Madagascar The intense high pressure formed at east of Madagascar near 20 degree south in Indian Ocean cause the wind to flow towards the low pressure in India Not continuous but temporary phenomena Whenever there will be low pressure zone here in extreme conditions, monsoon in India will be weak

Madagascar is it Important?

Monsoon and SO Normally there is high pressure in tropical east Pacific ocean and low pressure in Tropical Indian Ocean In certain years there is reversal in pressure conditions This periodic change in pressure condition is known as Southern Oscillation (SO) The SOI is computed from fluctuations in the surface air pressure difference between Tahiti (Over Pacific Ocean) and Darwin, (Indian Ocean near Australia). El Niño episodes are associated with negative values of the SOI, meaning that the pressure at Tahiti is relatively low compared to Darwin. This results in a decrease in the strength of the Pacific trade winds, and a reduction in rainfall over eastern and northern Australia.

Normal Condition Extreme condition

Monsoon and El Nino (ENSO)  In a typical ENSO, the strong easterly winds of the equatorial Pacific weaken, which allows warm eastward-flowing subsurface waters to rise, increasing surface temperatures 1-2°C  and sometimes  in the central and Eastern Pacific. Along the West coast of South America, El Niño's warm waters persist and deepen, and cold, upwelling, nutrient- rich waters fail to reach surface waters; the resulting warm, nutrient-poor waters devastate coastal fisheries. Heavy rain falls along the South American coast, and heavy rainfall also moves from the western to central Pacific, causing drier than normal conditions in Indonesia and nearby areas including India.

Monsoon and Somalian Current Somalian current change its flow direction at every six month Generally low pressure zone After every seven or eight years changes into high pressure area Creates weeker monsoon over India