Presented byDEEPCHAND VDept. Of GeologyUniversity of Keraladeepchandgeology@gmail.com

Introduction

Monsoon rainfall is the life-blood of more than half the world’s population.

Most developing countries, live under the influence of monsoon-dominated climates.

Term “Monsoon” derived from an Arabic word “Mausim” means Season

“ monsoon is a seasonal change in the direction of the prevailing, or strongest, winds of a region”

Monsoons are controlled by Winds and most prominent through tropical atmosphere

wet and dry seasons

North American monsoon (NAM) North African monsoon (NAF), Indian monsoon (IND), East Asian monsoon (EAS), Western North Pacific monsoon (WNP), South American monsoon (SAM), South African monsoon (SAF), and the Australian monsoon (AUS).

Monsoon is the reversal of wind direction in every six month.Caused by the differential heating of land and ocean.

High pressure and low pressure area

Winter to Summer and Summer to Winter.

Heated air in equator release energy to atmosphere

Raised air from equatorial atmosphere moved towards subtropical low pressure region.

This cause increase pressure in subtropics and decrease in near equator.

Air from subtropics flows into equator to fill the space.

Thus forming a loop called Hadley Circulation.

Origin of Monsoon

Origin of Monsoon ITCZ -This is the low pressure area near equator with converging and then rising

winds.

Temperature Increases water vapor rise cools Condense clouds Rains near ITCZ

Hadley circulation is not same through out the year It changes with seasons This seasonal change in Hadley circulation cause World Monsoons

Wind flows towards equator turns Right in NH and turns Left in SH.

This turn is due to the Rotation of Earth Coriolis Effect

(Monsoons, Ocean Currents, Hurricane)

It was the spin of earth that caused the winds to turn as they blew towards the equator

Origin of Monsoon

Wind change through year

December SH Heats more than NH

So ITCZ lies below equator

Wind flows from NH to ITCZ in SH

June NH Heats more than SH

So ITCZ lies above equator

Wind flows from SH to ITCZ in NH

As the ITCZ changes location through the year winds, Rains, Location of Monsoon also change

Factors effecting Monsoon

Latitude

AltitudeWind direction

Physiography

Indian Monsoon

INDIAN MONSOON

largest and most powerful monsoon circulation

Also known as South Asian Monsoon.

Most prominent of the world’s monsoon systems

North-East Monsoon and South-West Monsoon

Reversal of wind from Indian ocean to Indian subcontinent

South West Monsoon

• June to September• 1 June coast of Kerala• At Indian subcontinent divide in to two

Arabian branch and bay of Bengal branch• Arabian branch western coast• Bay of Bengal branch eastern Ghats and

north eastern part• Meet at indo Gangatic plane • The ITCZ shifts northwards • Insolation over Northern India increases,

causing air to rise and creating low pressure• The humid unstable air results in rainfall.

Amounts are increased as air is forced aloft over the Himalayas and Western Ghats.

North East Monsoon

• Retreating

• September to December

• Start retreating June itself

• Winter air reach cost of Tamil nadu in middle of December

• Low temperatures over central Asia create areas of high pressure

• at the same time, the sub-tropical jet and ITCZ shift south.

• Air moving out from the area of high pressure is very dry and becomes drier as it crosses over the Himalayas

Theories of formation of Indian Monsoon• Thermal theory- Halley

• Flohn’s Theory migration of Thermally produced zones of pressure belts and planetary winds.

• Modern Theory

Role of Himalaya

Role of Tibet Platuo

Role of High pressure zone of East Madagascar

Role of El Niño

Southern Oscillation

East Asian Monsoon

East Asian Monsoon

carries moist air from the Indian Ocean and Pacific Ocean to East Asia.

It affects approximately one-third of the global population

driven by temperature differences between the Asian continent and the Pacific Ocean.

Warm and Wet Summer Monsoon

Dry and Cold Winter Monsoon(Loess plateau)

winds being southeasterly in late June, bringing significant rainfall to the KoreanPeninsula and Japan

In the winter, the winds are northeasterly and the monsoonal precipitation bands move back to the south, and intense precipitation occurs over southern China and Taiwan.

American Monsoon

North American Monsoon Monsoons are less pronounced over America than in other parts of the world.

Formed by a regional-scale circulation.

July through September

NAM is characterized by intense rainfall & thunderstorms in Mexico and South west USA.

The mechanism of formation of NAM is similar to that of Indian Monsoon

Summer daytime heating over the Sonoran Desert and Arizona forms large low-pressure cell over the region.

moist tropical air from the high pressure regions of Gulfs of California and Mexico move towards the land surface to fill the space

Also known as South West Monsoon, Arizona Monsoon and New Mexican Monsoon

South American Monsoon

The South American monsoon (SAM) receives moisture from the tropical Atlantic and Amazon River basin

In South America, the monsoon starts in the spring

Rainfall accumulations reach their maximum over eastern and southeastern region during the mature summer monsoon and then decrease during the monsoon retreat in autumn.

Large seasonal changes result in an increase of precipitation over the Amazon basin

plays an important role in distribution and duration of the rainy season manually over the South Western Amazonia, and the central west and southeast Brazil region

Australian Monsoon

Australian MonsoonAlso known as East Asian Winter Monsoon.

Alternates between two seasons linked to wind direction

In winter easterly winds bring dry condition

In summer westerly winds bring sustained rainy conditions.

In summer the sun heats the Australian land faster than the surrounding ocean

difference in heating produces a difference in pressure

Pressure lower over the land than the ocean

warm, moist air from the tropical ocean is drawn towards the lower pressure over the hot and dry north of Australia

increasing humidity development of deep clouds and storms sustained rains

simple monsoonal patterns size and compact shape

The north shore is subject to a clear-cut wind reversal between summer (November–April, northwesterly flow) and winter (May–September, southeasterly flow)

AFRICAN MONSOON

African Monsoon

West African Monsoon and East African Monsoon

WAM Northern Hemisphere Summer (June through September)

EAM rains during spring and autumn

Combined effect of Indo-pacific and Atlantic ocean

West African Monsoon• ITCZ Lies above equator • low level southwesterly flow from the Atlantic Ocean• Monsoon rainfall over West Africa( June-September)• primary northeast trade wind, which blows from the Sahara and the Sahel as a

deep stream of dry, often dusty air

African Monsoon

East African Monsoon • ITCZ Moved towards southern hemisphere• long rains prevail during spring and the short rains during

autumn• Thus the transition (equinox) seasons bring most rainfall to

East Africa • Abrupt decline in the long rains have resulted in droughts

over this region.

Advantages of Monsoon

Brings rain for cropsAllow rise to ripen and harvestRelief from heatVegetation Comes to lifePower productionEconomy

Disadvantages of Monsoon

FloodingDrought (If rain comes late)Durst storm Insects and reptilesDestruction