El Nino- A Natural Phenomenon
‘El
Nino’ is a Spanish word that literally means little boy in
English. El Nino is an oceanic atmospheric phenomenon where the equatorial pacific waters warm up
abnormally because of the weakening of the trade winds. El-Nino leads
to the warming of the sea surface temperatures, in turn affecting wind patterns
and acts as a trigger to issues such as floods and droughts. These events can
be characterized by extreme and erratic weather conditions in the world. El
Nino as a phenomenon also benefits a few places across the globe. It is
essentially a weather system that which re-emerges after a gap of 2 to
5 years in the Pacific Ocean and its effect lasts for a span of 12
months on an average scale.
El Nino occurs
when the threshold value of 0.5 degree Celsius of Oceanic Nino Index (ONI) is
met or crossed for a minimum of 5 consecutive overlapping seasons of three
months each.
During the
period of El Nino phenomenon, the Pacific warm pool expands to cover the tropical
regions. The other extreme of
this situation, happens during the La – Nina phenomenon. La-Nina
can be stated as an oceanic atmospheric phenomenon where
the temperatures of the equatorial Pacific Waters become cooler than normal.
La-Nina conditions occur on an average every 3 to 5 years and can persist for
as long as two years. La-Nina conditions are followed by a buildup of a cooler
ocean waters rather than normal subsurface waters of the tropical Pacific
Waters. La-Nina a phenomenon when
the easterly trade winds strengthen and the cold rushes along the Equator and
the West Coast of South America intensifies. The sea- surface temperatures
along the equator could fall by 13.88
Degree Celsius.
The atmospheric
and oceanic waves travelling eastwards help in bringing the cold
water to the surface through a complex series of events.
The easterly trade winds strengthen along with the cold upwelling off
Peru and Ecuador intensifies. Ultimately, the sea -surface temperatures [SST]
drop below normal levels. Records suggest that during the 1988-89
La Nina episodes, the SST‘s fell 4 degree Celsius below
normal.
El Nino and
La
Nina conditions are stemmed out from the interaction between the surfaces
of the ocean and the atmosphere of the tropical
Pacific .Changes in the ocean have an impact on atmosphere and climatic
conditions of the world, similarly changes in the atmosphere take a toll on the
ocean temperature and currents. This is a recurring phenomenon, oscillating
between warm and cold ie; El-Nino and La Nina conditions.
El
-Nino and La –Nina : Both are extreme phases
of a naturally occurring climatic cycle. These two terms refer to changes on a
large scale in the sea surface temperature across the eastern tropical Pacific.
Normally, the sea surface temperatures off south America ‘s west coast range
from 15 to 20 degree Celsius. On the
other hand, they exceed 26 degree Celsius in the ‘Warm Pool’ located in the central and western Pacific.
El Nino- Impact on Indian Monsoon
T his phenomenon
affects rainfall and these Trade winds normally blow westward from South
America towards Asia during the monsoon months in India. The Warming of the
Pacific results in the weakening of
these winds. Moisture and heat content, thereby gets limited and results in
reduction and uneven distribution of rainfall across the Indian Sub continent.
The most
prominent droughts in India since 1871 have been the El Nino triggered
droughts that includes the recent 2002 and 2009 droughts respectively. During
an El
Nino, Monsoon never witnesses excess rainfall baring a few exceptions
for example the year 1997 -98 was a strong El Nino year but that did not cause
drought in India.
Aishwarya Barathi
II B.A English.,
Kg Cas.,
Coimbatore.
