In a Nutshell - El Nino

The west coast of Peru has been a prosperous place for fishermen. The northward moving cool Peruvian Current fosters upwelling, bringing phosphates and nitrates from the deep sea to the surface. These minerals help the tiny phytoplankton to flourish. This phytoplankton bloom supports the marine food chain and invites diverse marine organisms to feed on.

However, Peruvian fishermen experience a recurring natural phenomenon during Christmas emphasized by paucity in fishing and high precipitation. They called this El Nino, Spanish for The Christ Child or an infant boy.

They also experience an entire reversal of events with a glut in fishing and drought inland. They termed this phenomenon La Nina, an infant girl.

Global Impact

El Nino and La Nina are phenomenon that occurs in the tropical Pacific, but with the energy content of a million atomic bombs, it has a cataclysmic effect on the global weather pattern.

Our planet does not receive a uniform solar insolation - tropics receiving the most heat and the poles receiving the least. Earth has developed an intricate mechanism to deal with this differential heating. There is a complex coordination between our oceans and the atmosphere to make our planet a sustainable place to live on.

Extreme weather events – drought in India and China, ice storm in the northern US can be linked to a strong El Nino whereas strengthening tropical storm in the Atlantic could be due to a knock-on effect of La Nina.

The impact this natural phenomenon in a remote part of the globe has on our entire planet is profound. The loss in lives and economic havoc created by El Nino has made it important for us to better understand its excruciating presage and take proactive measures to minimize its impact on our society.

ENSO

Southern Oscillation is the atmospheric phenomenon of the see-saw pattern of reversing surface air pressure, temperature and precipitation between the eastern and western tropical Pacific.

El Nino is the oceanic phenomenon of the flip-flop of location and depth of warm pools of water in the tropical Pacific.

The atmospheric and oceanic phenomenon is collectively called El Nino Southern Oscillation (ENSO).

When and How Often?

Based on a study, from the period of 1950 to 1997, El Nino conditions were present for 31%, La Nina for 23% and La Nada (Spanish: nothing) for 46% of the time. Although, there is no concrete number, El Nino is believed to occur every 2-7 years and each occurrence lasting 1-2 years.

La Nada

In normal scenario, Trade Winds blow from the east to the west in the tropics. These winds induce surface currents resulting in the sea surface to be 50cm higher in Indonesia than Ecuador. Sea temperature is usually 8°C higher in Indonesia as compared to Peru in the East Pacific. The high temperature in the waters of the West Pacific induces moisture laden wind to precipitate and result in higher rainfall. The East Pacific is relatively dry.

El Nino and La Nina

	El Nino	La Nina
Cause	Weakening of the Trade Winds. A surge of hot moisture laden wind blowing from the West Pacific to the East Pacific takes the charge.	Strengthening of the Trade Winds.
Trigger	If the temperature of the West Tropical Pacific is 0.5°C above long term average, it is officially declared as El Nino	If the temperature of the West Tropical Pacific is 0.5°C below the long term average, it is officially declared as La Nina
Mechanism	High Atmospheric Pressure in the West Low Atmospheric Pressure in the East The pool of warm water from the West Pacific moves towards Peru driven by the hot moisture laden wind. This wind brings thunderstorm and rainfall to the South American countries. Eastward moving warm pool of water stalls upwelling in Peru and leads to the decline in fisheries.	Low Atmospheric Pressure in the West High Atmospheric Pressure in the East The pool of cold water from the East Pacific (brought to the equator by the Peruvian Current) move towards Indonesia driven by the strong Trade Winds. It gets warm and saturated during its journey and brings high precipitation to the West Tropical Pacific. When this pool gets too large, it begins to slosh back eastward. Kelvin Waves which can be as long as 1000km, travels along the equator and carries warm west tropical water to the east. When it hits the South American coast, it generates long lived Rossby Waves.
Effects	Drought in usually wet Indonesia, Philippines, Australia and India. Heavy rainfall in Peru, Ecuador, Brazil, Argentina and Southern USA. Due to decrease in the sea level in Western Pacific, many corals in Indonesia and Australia die due to Coral Bleaching Decline in fisheries in Peru	Drought in South American countries. Heavy rainfall in Indonesia, Philippines, Australia and India. Devastating effects in the Atlantic Coast of USA bringing thunderstorms and hurricanes. Increased fisheries in Peru
Occurrence	Summer of Southern Hemisphere [Dec-Feb] May last 1-2 years	Summer of Southern Hemisphere [Dec-Feb] May last 1-2 years

2014: El Nino or La Nada?

2014 is predicted to be an El Nino year. The governments in several countries are taking measures to prepare themselves for its consequences. Indian government had taken proactive measures to tackle food inflation which would have resulted due to weak monsoon and failed agriculture.

The first signs of an El Nino came in January 2014, when the Trade Winds suddenly weakened, and a burst of winds from the west triggered a slow surge of warm water into the eastern equatorial Pacific. But, the atmosphere did not coordinate with the ocean to substantiate the heat content of the ocean. The El Nino eventually stalled by the end of July.

NOAA still believes that there is a 65% chance of a weak to moderate El Nino to form by the end of this year.

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Notes

1. A flourishing coral has a symbiotic relation with algae it lives with. Algae give oxygen and organic compounds to the coral. Coral, in turn, gives shelter to the algae. But, when the temperature of the ocean exceeds 28°C, coral expels the algae that thrive within, leading to a loss of pigmentation and its eventual death. This is called Coral Bleaching.

Bibliography

1. The Oryx Resource Guide to El Niño and La Niña
2. NOAA
3. NEA Singapore
4. The Guardian
5. Nature

In a Nutshell - Cyclones

A cyclone is a huge system of rotating wind around a large scale low pressure area called "eye".

The rotation of wind is anti-clockwise in the Northern Hemisphere and clockwise in the South. This is due to Coriolis force which acts on a moving body (Wind) in a rotating reference frame (Earth).

Tropical Cyclones are known by different names in different areas:

• Hurricanes in the North Atlantic & Eastern Pacific
• Typhoons in Western Pacific

Tropical Cyclones arise over ocean in the tropical latitudes (5°N - 15°N) where Coriolis force is substantial enough to stabilize its low pressure eye.

There are two factors that fuel its growth:

1. Evaporation - When the temperature of the ocean surface (up to the depth of 50 m) exceeds 28°C, it intensifies evaporation. The warm and moist air above the ocean rises to create low pressure region. The cooler air swirls around to take its place.
2. Condensation - As the warm air rises, the water vapour condenses to form clouds and droplets of rain. This releases latent heat. This heat combined with heat from the ocean triggers more evaporation which in turn leads to greater condensation (chain of events)!

If Tropospheric Vertical Shear (change of wind velocity with height) is low, the storm builds into a cyclone within two to three days. Otherwise, frequently changing speed and direction of wind in upper atmosphere would halt the progress of storm in the upward direction.

When formed, a cyclone is roughly 600 km across and 15 km high. The winds in it can speed over 100 kmph. The eye of a cyclone is the region of lowest pressure and highest temperature (as compared to surrounding region). It experiences relatively calm wind and fair weather. It is usually about 50km across.

After the cyclone is formed, it is steered by the Trade Winds (global winds that blow predominantly from east to west in the Northern Hemisphere) which is responsible for Hurricane Landfalls in North America.

After reaching the land, the break in chain of evaporation and condensation diminishes the energy of the cyclone. Hence, it dies within few days after landfall.

The fancy names of Tropical Cyclones are used basically to facilitate easy communication. A list of 21 names is prepared for each year. The first tropical storm in that year is given the name with A; the second storm is given the name with B and so on(excluding the ones starting with Q, U, X, Y and Z).



Bibliography

• NOAA
• NASA
• Windows2Universe
• Oracle ThinkQuest
• Open Educational Resource Library

In a Nutshell - Atmospheric Circulation

Our atmosphere is incredibly powerful and is responsible for regulating our planet's temperature.

Due to uneven heating of the Earth’s surface, there is a heat surplus in the tropics and a heat deficit at the poles. The interaction between our atmosphere and the oceans to fill up this gap in the heat content makes our planet a sustainable place to live in.

The way our atmosphere performs this temperature regulation is by building up several giant convection cells. These convection cells are driven by:

• Temperature Gradient
• Pressure Gradient
• Coriolis Force (deflects the wind to the right in the Northern Hemisphere and vice versa)

The atmospheric cell has two arms:

1. Low Altitude Arm - It blows at the surface of the earth. It is also called the Prevailing Winds as it remains constant on an average throughout the year.
2. High Altitude Arm – It constitutes the winds that blow in the high altitude troposphere.

There are three convection cells in each hemisphere of the Earth:

1. Hadley Cell (10° - 30°)
   When the warm moist air in the tropic rises and moves northwards (towards the pole) it is deflected to the east (in the Northern Hemisphere) due to the Coriolis Effect. At 30° latitude, the air cools down and sinks. It then moves southwest towards the equator to complete the cell. The low altitude arm of the Hadley Cell or the Prevailing Wind blows from the Northeast to the Southwest (in the Northern Hemisphere). They are called the Easterlies or the Trade Winds.
    
2. Farrel Cell (30° – 60°)
   Unlike other cells, Farrel Cell is induced by the effect of other cells and behaves like an atmospheric ball bearing. The Prevailing Winds blow from the Southwest to the Northeast and are called the Westerlies.
    
3. Polar Cell (60° – 90°)
   When the cold dry air at the pole descends and moves southwards it is deflected to the west. This wind, near to the surface of the earth, is called the Polar Easterlies.
    

Between these regions of strong prevailing winds, there are regions of calm air:

1. Doldrums (or Intertropical Convergence Zone)
   The equatorial humid region where warm moist air rises and shreds off its moisture as it cools.
    
2. Horse Latitude
   The high pressure boundary between the Hadley and the Farrel Cell at 30° latitude. This is the region where cool dry air descends. The major deserts on our planet lie at this latitude.
    

Images

• OSS Foundation
• Eastern Illinois University

Bibliography

• Oceanography Exploring Earth's Final Wilderness - Prof. Harold J. Tobin

In A Nutshell - Rare Earth Theory

Alien life forms have always been a human fascination. The unfathomable vastness and complexity of our universe incline us to believe that life in one form or another must exist outside our pale blue dot.

The evolution of life on earth is a consequence of extraordinary sequence of events. The probability of the same chronology of events occurring in nature is believed to be too low. The Rare Earth Theory suggests that the inception of simple organisms would be possible elsewhere in the universe but the evolution to an intelligent and complex life form would be very rare.

Size Matters

Our planet has just the right size to provide us the sustainable condition for life. If it would have been slightly smaller, the gravity would not be sufficient to hold our atmosphere. If it would have been slightly larger, it would attract too many asteroids causing frequent catastrophic events.

The Moon

The size of our Moon with respect to Earth is very large as compared to other planets. The perfect distance and its size with respect to Earth help our planet to maintain its tilt and prevent it from wobbling in space. This helps in having smooth transition between seasons which is extremely important for the species to adapt to the environment.

The Sun

Being in the habitable zone of the Sun, the temperature on Earth has been an optimum for life forms to evolve. We are lucky enough to have Sun of perfect mass. If it would have been larger, its life would be too short to allow evolution on Earth. If it would have been smaller, our planet would have to be closer to the Sun to be in the habitable zone. At such a short distance, Earth would go into a tidal lock, with one face of the Earth permanently facing the Sun while other in constant darkness.

Big Brother

Jupiter is the big brother of our neighbourhood. It attracts the asteroids which would otherwise hit our planet and make catastrophic events more common on Earth.

Active Molten Core

The core is responsible for Earth's Magnetic field. It deflects the harmful solar winds from Sun. In addition, it is also responsible for regulating our planet’s temperature and driving the plate tectonics.

Atmosphere and Ocean

Apart from providing necessary Oxygen to live, atmosphere and ocean drive our climate and help maintain an optimum temperature. They collaboratively transfer heat from warm places to the cold.

Although the theory suggests the rarity of existence of complex life, it doesn’t deny its subsistence. It is the exploring nature and the quest to comprehend the universe that has led to the profusion of ideas and innovations that we see around us. We should never stop looking!



Bibliography

1. BBC: Power of the Planet - Rare Earth