The Southern Oscillation is a periodic variation in winds and sea surface temperatures over the tropical eastern Pacific Ocean that affects global climate. It involves alternating phases known as El Niño and La Niña. During El Niño, trade winds weaken and warmer waters shift eastward, while during La Niña trade winds strengthen and cooler waters shift westward. This cycle, known as the El Niño-Southern Oscillation (ENSO), typically occurs every 2-7 years and influences weather patterns and ocean temperatures around the world.

1. Southern osscilation:
Southern Oscillation is an irregularly periodic variation in winds and sea
surface,temperatures over the tropical eastern Pacific Ocean, affecting the
climate of much of the tropics and subtropics.
Characteristics:
 Two endpoints of oscillation, La Nina and El Nino
 Cycles between endpoints every 2-7 years, a temporal scale
 larger than seasons
 Palerecord indicates it has been occurring for 50 million
 years ago
 Global warming does not cause the Southern Oscillation, but
 they are likely to be influencing each other
 Also referred to as ENSO (El Nino – Southern Oscillation)
 Has global teleconnections: strong El Nino and La Nina
events shape weather around the globe
WHAT CAUSES SOUTHERN
OSCILLATION:
Although the exact initiating causes of an ENSO warm or cool event are not
fully understood,
The two components of ENSO – sea surface temperature and atmospheric
pressure are strongly related.
During an El Niño event, the easterly trade winds converging across the
equatorial Pacific weaken.
El Niño and La Niña are opposite phases of what is known as the El
Niño-Southern Oscillation (ENSO) cycle.

2. The ENSO cycle is a scientific term that describes “the fluctuations in
temperature between the ocean and atmosphere in the east-central Equatorial
Pacific” (approximately between the International Date Line and 120
degrees West).
La Niña is sometimes referred to as the cold phase of ENSO and El Niño as
the warm phase of ENSO.
These deviations from normal surface temperatures can
have large-scale impacts not only on ocean processes, but also on global
weather and climate.
El Niño and La Niña episodes typically last nine to 12 months, but some
prolonged events may last for years. While their frequency can be quite
irregular,
El Niño and La Niña events occur on average every two to seven years.
Typically, El Niño occurs more frequently than La Niña.
WHAT DO YOU MEAN BY ENSO?
El Niño Southern Oscillation (ENSO) is a coupled ocean–atmosphere
phenomenon in the Pacific Ocean that has widespread meteorological and
ecological impacts on the Earth's surface.
Enso (formally spelled ensō) is a sacred symbol in Zen Buddhism meaning
circle,or sometimes, circle of togetherness.
It is traditionally drawn using only one
Brushstroke as a meditative practice in letting go of the mind and allowing
the body to create, as the singular brushstroke allows for no modifications.
WHAT HAPPENS DURING AN ENSO EVENT?
During an El Niño, the trade winds weaken in the central and western
Pacific.
Surface water temperatures off South America warm up, because there is
less upwelling of the cold water from below to cool the surface. The clouds
and rainstorms associated with warm ocean waters also shift toward the east.
PHASES OF ENSO
THERE ARE THREE PHASES

3.  NEUTRAL PHASE
 EL NINO
 LA NINA
NEUTRAL PHASE
In the neutral state (neither El Niño nor La Niña) trade winds blow east to
west across the surface of the tropical Pacific Ocean, bringing warm moist
air and warmer surface waters towards the western Pacific and keeping the
central Pacific Ocean relatively cool.
The thermo cline is deeper in the west than the east.
Warm sea surface temperatures in the western Pacific pump heat and
moisture into the atmosphere above. In a process known as atmospheric
convection, this warm air raises high into the atmosphere and, if the air is
moist enough, causes towering cumulonimbus clouds and rain.
EL NINO PHASE
During an El Niño event, trade winds weaken or may even reverse, allowing
the area of warmer than normal water to move into the central and eastern
tropical Pacific Ocean.
These warmer than normal ocean temperatures are associated with a
deepening of the thermocline in the central to eastern Pacific.
A weaker upwelling of cooler ocean waters from below also contributes to
warmer sea surface temperatures.
Sea surface temperatures around northern Australia are cooler than normal
and the focus of convection migrates away from Australia eastward towards
the central tropical Pacific Ocean.
This results in increased rainfall for nations such as Kiribati and Peru, but
less rainfall over Australia.

4. Impacts
The greatest impacts are usually felt over inland eastern Australia, while
effects for regions such as southwest Western Australia and coastal New
South Wales can vary from event to event, and in western Tasmania the
effects are generally weak.
LA NINA PHASE
During a La Niña event, the Walker Circulation intensifies with greater
convection over the western Pacific and stronger trade winds.
As the trade winds strengthen, the pool of warmer water is confined to the
far western tropical Pacific, resulting in warmer than usual sea surface
temperatures in the region north of Australia.
Sea surface temperatures across the central and eastern tropical Pacific
Ocean become cooler than usual and the thermocline moves closer to the
surface – cool waters from the deep ocean are drawn to the surface as
upwelling strengthens.
HOW LONG DOES ENSO LAST?
El Ni o typically lasts 9-12 months, and La Ni a typically lasts 1-3 years.
They both tend to develop during March-June, reach peak intensity during
December-April, and then weaken during May-July. However, prolonged El
Nio episodes have lasted2 years and even as long as 3-4 years.
HOW IS SOUTHERN OSCILLATION
CALCULATED?
Climate Glossary. The Southern Oscillation Index, or SOI, gives an
indication of the development and intensity of El Niño or La Niña events in
the Pacific Ocean.
The SOI is calculated using the pressure differences between Tahiti and
Darwin.
El Nino and La Nina impact hurricane numbers

5. Fewer hurricanes in Atlantic/Caribbean with El Nino Reversal of tradewinds
and strong more southerly subtropical jet weaken hurricanes through
increased wind shear
More hurricanes in Atlantic/Caribbean with La Nina Tradewinds blowing
from east to west favor hurricane development.
Subtropical jet stream further north El Nino and La Nina can cause coral
Bleaching events,Caused by prolonged high sea surface temperatures.
At high temps:
Mutualistic photosynthetic algae in coral decrease production of
photosynthetic for coral animal.
These changes result in the expulsion of algae from
coral polyps
Corals deprived of food (and source of their color), which can result in
decline and death

6. Fewer hurricanes in Atlantic/Caribbean with El Nino Reversal of tradewinds
and strong more southerly subtropical jet weaken hurricanes through
increased wind shear
More hurricanes in Atlantic/Caribbean with La Nina Tradewinds blowing
from east to west favor hurricane development.
Subtropical jet stream further north El Nino and La Nina can cause coral
Bleaching events,Caused by prolonged high sea surface temperatures.
At high temps:
Mutualistic photosynthetic algae in coral decrease production of
photosynthetic for coral animal.
These changes result in the expulsion of algae from
coral polyps
Corals deprived of food (and source of their color), which can result in
decline and death