El Nino-ENSO

relationship between hurricanes and el nino pt 3

El Nino Events tend to decrease the number of tropical storms/typhoons in the West Pacific because the normally high SST's in the West Pacific Warm Pool have migrated to the East Pacific.

ENSO

El Nino Southern Oscillation

West Pacific Warm Pool

A region in the western equatorial Pacific Ocean with unusually high sea surface temperature (as high as 31oC or ~88oF).

11. What Indices are used to determine whether the Equatorial Pacific is experiencing an El Nino Event or a La Nina Event?

A variety of indices are used to characterize ENSO because it affects so many elements of the atmosphere-ocean climate system. Probably the two principal indices are the Southern Oscillation Index (SOI), which is given by the difference in sea-level pressure between Tahiti and Darwin, Australia, and the Nino 3 and 3.4 Indices, which refers to the anomalous SST within the region bounded by 5N-5S and 150W-90W.

6. Why do El Nino and La Nina events occur?

During an El Nino unusually high atmospheric sea level pressures develop in the western Pacific and Indian Ocean regions and unusually low sea level atmospheric pressures develop in the southeastern tropical Pacific due to deterioration or shut down of the Southeast Trade Winds, which allows the warm, low pressure, moist air mass system of the West Pacific to move across or oscillate to the East Pacific, temporarily bringing higher sea levels and warmer surface waters (>80o F) to the East Pacific region.

What is the periodicity of El Nino events, and how long do they typically last?

El Nino events occur on average about every 3 to 5 years but historically have occurred at wider intervals from 2-7 years.

El Nino = El Nino is a disruption of the ocean-atmospheric system, which is characterized

El Nino is a disruption of the ocean-atmospheric system, which is characterized by a large scale weakening of the trade winds and warming of the surface layers in the eastern and central equatorial Pacific Ocean.

relationship between hurricanes and el nino pt 2

El Niño Events tend to increase the numbers of tropical storms in the East Pacific Ocean because of the intrusion of high SST's.

9. What is the relationship between hurricanes and El Nino? (Be specific about El Nino effects on hurricanes in the Atlantic and Caribbean versus hurricanes in the Northeast Pacific and typhoons in the West Pacific)

El Niño conditions suppress the development of tropical storms and hurricanes in the tropical Atlantic and Caribbean due to the increased strength of the high level winds blowing from west to east in tropical latitudes; La Niña (cold conditions in the equatorial Pacific) favor hurricane formation in the tropical Atlantic and Caribbean because they decrease the strength of the west to east blowing high level winds in tropical latitudes.

7. Where did the name El Nino come from, and when was it discovered?

El Niños were originally recognized by fisherman off the coast of South America as the appearance of unusually warm water in the Pacific ocean, occurring near the beginning of the year. El Niño means The Little One or Christ Child in Spanish. This name was used for the tendency of the phenomenon to arrive around Christmas.

What are the primary meteorological, oceanographic, geologic, and biologic impacts that an El Nino brings to the West Pacific Region (Australia, SE Asia and South Asia) and Africa?

For the western Pacific region (Australia, Southeast and South Asia) and Africa El Nino events bring cooler, drier air, cooler sea surface temperatures, and higher atmospheric pressure conditions. These conditions bring drought conditions to parts of Australia and the Sub-Sahara region of Africa. It also diminishes the intensity of the South and Southeast Asian monsoon rains and thus can cause some agricultural dislocations, failures, and famine. Recently, due to the 1997-1998 El Nino, which may be the strongest one in the 20th century, the forest fires in Borneo and Sumatra and other parts of Southeast Asia burned longer and stronger than they possibly would have.

What is the periodicity of La Nina events, and how long do they typically last?

La Nina Events typically last 1-3 years. Both El Nino and La Nina Events tend to develop during March-June, reach peak intensity during December-April, and then weaken during May-July.

Nino 3 Index

Refers to the anomalous SST's in the Equatorial Pacific within the region bounded by 5N-5S and 150W-90W.

SST

Sea Surface Temperature

10. Why was El Nino such a big deal in 1997-1998?

The 1997-98 El Niño was the strongest on record, and it developed more rapidly than any El Niño of the past 40 years. As a result, we started to see it impacts on weather, marine ecosystems and fisheries very quickly, and these impacts were spectacular. Early effects in August-October 1997 included record flooding in Chile, Marlin caught off the coast of Washington, the extensive smog cloud over Indonesia, and a quiet Atlantic hurricane season. The press is geared towards reporting sensational stories, and this El Niño provided high drama through natural disasters and other unusual events.

What does SOI stand for, and how is it defined?

The Southern Oscillation Index, (SOI), is defined as the normalized difference in surface pressure between Tahiti in French Polynesia (East Pacific) and Darwin, Australia (West Pacific), is a measure of the strength of the trade winds, which have a component of flow from regions of high to low pressure.

La Nina

The normal climatic pattern in the East Equatorial Pacific is cool, high atmospheric pressure, dry conditions, and relatively strong NE Trade Winds. When it is at a maximum intensity, the Southern Oscillation (SO) produces unusually low pressures west of the International Date Line and high pressures east of the Date Line have, which have been linked to periods of anomalously cold equatorial Pacific sea surface temperatures (SST's) in the East Pacific.

What are the primary meteorological, oceanographic, geologic, and biologic impacts that an El Nino brings to the west coasts of North and South America?

The swing from the "normal" or La Nina conditions of the East Pacific to El Nino conditions suppresses upwelling of cool, nutrient-rich bottom waters along the east coast of South America and brings warm, moist air to the East Pacific region. The suppression of the upwelling causes severe disruptions in the fishing and anchovy catch for countries along the west coast of South America, especially Peru. The shut down/severe weakening of the NE Trade winds allows warm, moist air to move into the East Pacific, which brings heavy and more frequent rainfall to the west coasts of North and South America, thus sometimes causing severe flooding and landsliding in these regions. The warm moist air and the warmer surface temperatures in the East Pacific during an El Nino are in part also responsible for the increased intensity of East Pacific hurricanes.