EL-NINO, LA-NINA AND INDIAN MONSOON

Written By Avinash Sharan

26th October 2020

HOW EL-NINO, LA-NINA AND INDIAN MONSOON ARE RELATED?

EL-NINO AND INDIAN MONSOON

  EL-NINO: WARM OCEANIC CURRENT

El-Nino, La-Nina and Indian Monsoon are very closely related.

It is known to suppress or increase the monsoon rainfall in India.

El-Nino and Indian Monsoon can affect the agricultural production and GDP of India.

It is basically a warm oceanic current.

El-Nino and La-Nina, not only affect the Indian monsoon but also has a global impact on CLIMATE .

EL-Nino:

It’s a warm ocean current.

It blows from western part of South America (Peru) towards Indian Ocean.

El-Nino in Spanish means “THE LITTLE BOY” or Baby Christ.

This is because it happens in the month of December, the day Jesus was born.

This was first recognized by the fishermen of S. America in 1600.

EL-Nino takes place once in 2 to 7 years of time.

THE CONCEPT OF EL-NINO AND INDIAN MONSOON

https://www.youtube.com/watch?v=WPA-KpldDVc

To understand the concept of El Nino, you will have to know the position of earth on 23rd September.

On 23rd September, the direct rays of the sun falls on Equator.

Day and night are of equal duration on equator.

This is known as Equinox.

As the sun rays falls on equator, the air above the equator becomes hot.

When the air becomes hot, it becomes light and rises high.

As the air rises high, low pressure is created on equator.

When low pressure is created on equator, winds will blow from Tropic of Cancer and Tropic of Capricorn towards equator.

Winds from both the hemispheres will meet at equator due to ITCZ PRESSURE BELTS AND WIND SYSTEM  (Low pressure area).

WHAT WILL HAPPEN IN OCTOBER, NOVEMBER AND DECEMBER?

EARTH'S REVOLUTION AROUND THE SUN

                   EARTH’S POSITION IN DIFFERENT MONTHS

In the months of October, November and December, the position of earth will also change.

Sun’s rays will fall directly at around 7° S in October, 14° S in November and 23° S in December.

As the rays of sun shift from 0° to 23°30′ S, the low pressure will also shift.

Now, the low pressure (ITCZ) also shifts from equator to 20° S.

Due to this, the winds coming from Tropic of Cancer, will also cross the equator, and reach up to 20° S.

Now the winds will merge at 20° S.

Ocean water will also get heated after the shift of ITCZ at 20° S.

As the winds reaches 20° S, it turns west due to Ferrell’s law.

Due to the force of wind, the warm sea water will also shift from equator to 20° S.

COLD OCEAN CURRENT FROM SOUTH POLE:

The cold ocean  current, which comes from South pole to equator will meet the hot water current coming from equator at 20° S (Peru coast).

The meeting of cold and hot water currents at 20° S will make the ocean water warm.

This warm water on the west coast of Peru is called Counter Peru Current in December. CLASS IX GEOGRAPHY: TOP 25 MOST EXPECTED NTSE QUESTIONS (Frequently asked in competitive exams)

Merging of cold and hot water current will give rise to Plankton (vegetation in sea).

Due to the availability of food ( Plankton), fishes will also reach here.

Deep trenches in the Pacific make fishing difficult.

Cold ocean current which used to reach up to equator becomes warm at around 20° S.

The temperature of water increases by 14° F.

As this warming of ocean water takes place around 25th December, it is known as El-Nino.

It is also known as FEVER OF SEA. अंडमान और निकोबार द्वीप समूह  .

MOVEMENT OF EL-NINO CURRENT: (FROM DECEMBER TO MARCH)

AL-NINO IN THE MONTH OF DECEMBER

AL-NINO: SEASONAL REVERSAL OF WARM CURRENT

After December, the sun once again starts moving towards equator.

Cold air and warm air, when they will meet, tropical cyclone will be formed on Peru coast.

Due to the presence of Andes mountains, these cyclones cannot move towards east.

Therefore, starts moving toward the west.

With the shift of low pressure from Tropic of Capricorn to equator, the cyclone also moves towards West and reaches equator.

Now, in the month of March, once again there will be equinox.

Low pressure will be at equator and winds coming from both the sides will again merge at equator.

IMPACT OF EL-NINO ON INDIAN MONSOON

What happens from March to June?

It’s time for the increase of temperature in the Northern Hemisphere.

India will get intensely heated by June.

Low pressure area will shift from equator to Tropic of Cancer.

This will create a difference in temperature at equator and in India.

On equator, Indian ocean will be comparatively colder than India.

Cols Indian ocean means High pressure and hot in India means low pressure.

Therefore, the winds will reverse it’s direction and move from Indian ocean towards India.

This is how monsoon gets attracted towards  INDIA   .

But,

the warm cyclonic winds will try to make the Indian ocean water warm.

If it is successful in making the Indian ocean water warm, high pressure over Indian ocean will not be created.

This will make the monsoon weak.

When this happens, the rainfall in India decreases.

It can also create shortage of water, Drought and failure of crops in India.

This is how Al-Nino is responsible for low rainfall in India.

WHAT HAPPENS IN NORMAL CONDITION?

La-Nina Ocean Current:

Let’s first understand what is the meaning of normal condition.

Normal condition means in general how the wind and ocean currents move every year.

Every year when the sun is over the tropic of Capricorn, low pressure shifts from equator to 20° S.

The warm ocean currents from equator reaches up to the western parts of South America. (PERU)

The cold current coming from the polar regions meets the warm ocean current near Peru.

Now, the sea water at 20° S (ACCORDING TO FERREL’S LAW) will start moving to it’s west towards N.E. parts of Australia.

When it reaches the N.E. coast of Australia, a cold current from the south pole meets.

Warm air above the N.E. part of Australian rises, condenses and create a very heavy rainfall.

The current which  moves from Peru to Australia, is called La-Nina.

This is the normal condition.

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