Later, the term was scientifically used to refer to
the abnormal warming of sea surface temperatures in
the eastern Pacific Ocean, thousands of kilometers
from Peru and Ecuador. When this happens, the temperature
of large areas of seawater is three to six degrees
higher than it is all year round. The rise in the
water temperature of the vast waters in Pacific Ocean
have changed traditional equatorial currents and
southeast trade winds, causing global abnormal climate.
As the meteorological science is highly developed
nowadays, it has been known to all that the central
part of the Pacific Ocean is the main source of the
change of summer climate in the northern hemisphere.
In most cases, there is a cold current from Peru going
northwards along the west side of South America in the
Pacific Ocean, part of which turns into equatorial
currents moving westwards. At this point, the monsoon
blowing westwards along the equatorial waters leads the
warm currents to stimulate in the western part of the
Pacific Ocean, while the lower cold water upwells in
the east warming the western part of Pacific Ocean,
south of the Philippines, and north of New Guinea.
This sea area is called "the equatorial warm pool”,
the temperature of the east section of the same
latitude s relatively low.
There is also a temperature difference in the atmosphere
over the two seas. The temperature is lower in the east
and the pressure is higher. While in the west the
temperature is higher and the pressure is lower.
In this way, in the middle of the Pacific, there is
a sea level where cold air flows to the west, and
higher hot air flows to the east, which forms the
southeast trade wind near it. But sometimes the
pressure difference is lower than the average for
previous years and sometimes it can be higher. This
phenomenon of atmospheric varieties is known as the
In the 1960s, meteorologists found that El Nino
was closely related to the southern oscillation,
which was the trigger of El Nino when the pressure
After the appearance of El Nino, the monsoon of Pacific
Ocean from east to west is weakened greatly by the warm
currents with higher temperature, making significant
changes in the atmospheric circulation with great influence
on the climates of different countries along the Pacific
coast. Droughts appear in humid areas whilre floods strike
dry areas. When the pressure difference increases, the
temperature of sea drops abnormally and here comes a phenomenon
known as La Nina.