El Nino is a climate cycle in the Pacific Ocean with a global impact on weather patterns. The cycle begins when warm water in the western tropical Pacific Ocean shifts eastward along the equator toward the coast of South America. Normally, this warm water pools near Indonesia and the Philippines. During an El Nino, the Pacific’s warmest surface waters sit offshore of northwestern South America.
El Nino was originally named El Nino de Navidad by Peruvian fishermen in the 1600s. This name was used for the tendency of the phenomenon to arrive around Christmas. Climate records of El Nino go back millions of years, with evidence of the cycle found in ice cores, deep sea muds, coral, caves and tree rings.
How it will be identified?
- Forecasters declare an official El Nino when they see both ocean temperatures and rainfall from storms veer to the east.
- Experts also look for prevailing trade winds to weaken and even reverse direction during the El Nino climate phenomenon.
- These changes set up a feedback loop between the atmosphere and the ocean that boosts El Nino conditions.
- The El Nino forecast for 2015 is expected to be one of the strongest on record, according to Mike Halpert, the deputy director of the Climate Prediction Center, part of the National Oceanic and Atmospheric Administration.
Where it arises?
The location of tropical storms shifts eastward during an El Nino because atmospheric moisture is fuel for thunderstorms, and the greatest amount of evaporation takes place above the ocean’s warmest water. There is also an opposite of an El Nino, called La Niña.
“This refers to times when waters of the tropical eastern Pacific are colder than normal and trade winds blow more strongly than usual. Collectively, El Nino and La Niña are parts of an oscillation in the ocean-atmosphere system called the El Nino-Southern Oscillation, or ENSO cycle, which also has a neutral phase.”
What causes an El Nino?
- Scientists do not yet understand in detail what triggers an El Nino cycle. Not all El Ninos are the same, nor do the atmosphere and ocean always follow the same patterns from one El Nino to another.
- To forecast an El Nino, scientists monitor temperatures in the upper 656 feet (200 meters) of the ocean. They are watching for the telltale temperature shift from the western Pacific to the eastern Pacific.
For example, in spring 2014, a very strong warm water swell called a “Kelvin wave” crossed the Pacific, leading some forecasters to predict a powerful El Nino for winter 2014. However, their forecast fizzled by fall because storms and trade winds never followed suit, and the feedbacks between atmosphere and ocean failed to develop.
How often do El Ninos occur?
El Ninos occur every three to five years but may come as frequently as every two years or as rarely as every seven years. Typically, El Ninos occur more frequently than La Ninas. Each event usually lasts nine to 12 months.
They often begin to form in spring, reach peak strength between December and January, and then decay by May of the following year. Their strength can vary considerably between cycles. One of the strongest in recent decades was the El Nino that developed the winter of 1997-98.
What happens when El Nino is not present?
In normal, non-El Nino conditions, trade winds blow toward the west across the tropical Pacific, away from South America. These winds pile up warm surface water in the west Pacific, so that the sea surface is about 1 to 2 feet (0.3 m to 0.6 m) higher offshore Indonesia than across the Pacific, offshore Ecuador.
The sea-surface temperature is also about 14 degrees Fahrenheit (8 degrees Celsius) warmer in the west. Cooler ocean temperatures dominate offshore northwest South America, due to an upwelling of cold water from deeper levels. This nutrient-rich cold water supports diverse marine ecosystems and major fisheries.
When an El Nino kicks in?
- During an El Nino, 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. The warm waters release so much energy into the atmosphere that weather changes all over the planet.
Known effects of El Nino?
The warmer waters in the central and eastern tropical Pacific Ocean have important effects on the world’s weather. The 1982-83 El Nino is estimated to have caused more than $10 billion in weather-related damage worldwide.
- An El Nino creates stronger wind-shear and more-stable air over the Atlantic, which makes it harder for hurricanes to form.
- However, the warmer-than-average ocean temperatures boost eastern Pacific hurricanes, contributing to more-active tropical storm seasons.
- Strong El Ninos are also associated with above-average precipitation in the southern tier of the United States from California to the Atlantic coast.
Record rainfall often strikes Peru, Chile and Ecuador during an El Nino year. Fish catches offshore South America are typically lower than normal because the marine life migrates north and south, following colder water.
El Nino also affects precipitation in other areas, including Indonesia and northeastern South America, which tend toward drier-than-normal conditions. Temperatures in Australia and Southeast Asia run hotter than average. El Nino-caused drought can be widespread, affecting southern Africa, India, Southeast Asia, Australia, the Pacific Islands and the Canadian prairies.
How it affects normal man?
- El Nino – a warming of sea-surface temperatures in the Pacific – affects wind patterns and can trigger both floods and drought in different parts of the world, leading to reduced harvests.
- The phenomenon is expected to peak between October and January and could turn into one of the strongest El Ninos on record, according to the World Meteorological Organization.