activities. Warming of ocean water in the Eastern Pacific causes a huge loss for the
fishing industries warm water kills all the microorganisms, making it difficult for the
smaller fishes to survive, so the fish start moving towards cold ocean water. In olden
days, predictions were based on these phenomena to find out whether it is a El Nino
or La Nina year.
La Nina
With cooling of the ocean surface below the average SST in the central and eastern
tropical Pacific Ocean (or Nino 3.4 region) in La Nina, these trade winds start to
blow more strongly from east to west, thus shifting the warm pool of ocean water
towards the west. A shift in atmospheric pressure is caused by the Southern
Oscillation. La Nina is an intensified form of neutral phase wherein floods exist
along Australia and the regions lying around the Western Pacific and severe drought
conditions prevail on western coast of South America. With the return of cold ocean
water in the Eastern Pacific, fish tend to return to the coast, which is favourable for
the fishing industries. Because El Nino and La Nina are opposite events, the
countries lying along the tropical Eastern Pacific experience El Nino conditions,
then the western part experiences the La Nina conditions, and vice versa. Atlantic
hurricanes are formed during La Nina conditions. In much simpler words, if floods
exist in South America, then it is the El Nino phase. Or, if floods occur in Australia
and in other Western Pacific regions, then it is the La Nina phase.
Indian Ocean Dipole
The dipole is the difference in SST between the eastern part (Bay of Bengal) and the
western part (Arabian Sea) of the tropical Indian Ocean. The Indian Ocean dipole is
classified into two types: positive and negative. When the SST of the Arabian Sea is
greater than that of the Bay of Bengal, it signifies a positive Indian dipole. When the
SST of the Arabian Sea is less than that of the Bay of Bengal, a negative Indian
Ocean dipole (IOD) forms (Fig. 10.2). The positive phase of IOD is more likely to
correspond with the El Nino conditions whereas the negative phase corresponds with
La Nina conditions. IOD occur during the months of May to December, lasting up to
2 to 7 months (Bureau of Meteorology). In the positive phase of IOD, SST is higher
west of the Indian ocean compared to the east. Similarly, in the negative phase the
eastern part of the Indian Ocean remains warmer than the west. The correlation
between the IOD and Indian summer monsoon rainfall (ISMR) is not clear (Saji et al.
1999).
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fishing industries warm water kills all the microorganisms, making it difficult for the
smaller fishes to survive, so the fish start moving towards cold ocean water. In olden
days, predictions were based on these phenomena to find out whether it is a El Nino
or La Nina year.
La Nina
With cooling of the ocean surface below the average SST in the central and eastern
tropical Pacific Ocean (or Nino 3.4 region) in La Nina, these trade winds start to
blow more strongly from east to west, thus shifting the warm pool of ocean water
towards the west. A shift in atmospheric pressure is caused by the Southern
Oscillation. La Nina is an intensified form of neutral phase wherein floods exist
along Australia and the regions lying around the Western Pacific and severe drought
conditions prevail on western coast of South America. With the return of cold ocean
water in the Eastern Pacific, fish tend to return to the coast, which is favourable for
the fishing industries. Because El Nino and La Nina are opposite events, the
countries lying along the tropical Eastern Pacific experience El Nino conditions,
then the western part experiences the La Nina conditions, and vice versa. Atlantic
hurricanes are formed during La Nina conditions. In much simpler words, if floods
exist in South America, then it is the El Nino phase. Or, if floods occur in Australia
and in other Western Pacific regions, then it is the La Nina phase.
Indian Ocean Dipole
The dipole is the difference in SST between the eastern part (Bay of Bengal) and the
western part (Arabian Sea) of the tropical Indian Ocean. The Indian Ocean dipole is
classified into two types: positive and negative. When the SST of the Arabian Sea is
greater than that of the Bay of Bengal, it signifies a positive Indian dipole. When the
SST of the Arabian Sea is less than that of the Bay of Bengal, a negative Indian
Ocean dipole (IOD) forms (Fig. 10.2). The positive phase of IOD is more likely to
correspond with the El Nino conditions whereas the negative phase corresponds with
La Nina conditions. IOD occur during the months of May to December, lasting up to
2 to 7 months (Bureau of Meteorology). In the positive phase of IOD, SST is higher
west of the Indian ocean compared to the east. Similarly, in the negative phase the
eastern part of the Indian Ocean remains warmer than the west. The correlation
between the IOD and Indian summer monsoon rainfall (ISMR) is not clear (Saji et al.
1999).
232
A. Stanley Raj and B. Chendhoor