Monsoon part 1

Compiled By – Dr. Bheekam Singh
Part 1

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
1. Differential heating
2. Shift in ITCZ
3. High pressure area in east of Madagascar
4. Tibetan Plateau Heating in Summer
5. Movement of Jet Stream
6. 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
i. As a physical barrier
ii. 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

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

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

Monsoon part 1

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