What North America Can Expect From El Nio

A major El Nio is currently underway now. It already has substantially influenced climate patterns around the globe, but could have even bigger impacts this wintertime. There have been only two super El Nios until now: in 1982 -8 3 and 1997 -9 8. We are now experiencing a third super El Nio.

Every El Nio cycle is different. The consequences from this years already include a record number of hurricanes/ cyclones in the Pacific and intense wildfires in Indonesia.

In the United States over the next several months, El Nio ought to be able to cause heavy rains across the South, with the potential for coastal flooding in California, along with relatively mild and dry weather in the northern nations. Global climate change, which, along with the El Nio, is stimulating 2015 the warmest year on record, is likely to amplify these impacts.

What is El Nio ?

El Nios are not uncommon. Every three to seven years or so, the surface waters of the tropical Pacific Ocean become extremely warm from the International Dateline to the west coast of South America. This process causes changes in the local and regional ecology, and is clearly linked with abnormal global climate patterns.

The Oceanic Nio Index( ONI) demonstrates warm( red) and cold( blue) the stages of abnormal sea surface temperatures in the tropical Pacific Ocean. NCAR, Author

Historically El Nio referred to the appearance of remarkably warm water off the coast of Peru near Christmastime( Nio is Spanish and refers to the son Christ child ). Today it describes broader changes that occur across the Pacific basin.

Oceanic and atmospheric conditions in the tropical Pacific fluctuate somewhat irregularly between warm El Nio phases and cold stages in which surface waters cool across the tropical Pacific. These cooling events are called La Nia( the girl in Spanish ). The most intense phase of each event typically lasts about a year.

El Nio is linked to major changes in the atmosphere known as the Southern Oscillation( SO ). Scientists call the whole phenomenon the El NioSouthern Oscillation( ENSO ). During El Nio, higher-than-normal surface air pressures develop over Australia, Indonesia, Southeast Asia and the Philippines, rendering drier conditions or even droughts. Dry conditions also prevail in Hawaii, parts of Africa, and northeastern Brazil and Colombia.

Lower pressures develop over the central and eastern Pacific, along the west coast of South America, parts of South America near Uruguay and southern parts of the United States in winter, often creating heavy rains and flooding. Regions that are typically dry during El Nio events tend to become excessively wet during La Nina events, and vice versa.

Flooding in Clear Lake, California, March 1 1998, during the course of its 1997 -1 998 super El Nio event. Dave Gatley/ FEMA

Why does El Nio happen ?

ENSO is a natural phenomenon arising from coupled interactions between the ambiance and the ocean in the tropical Pacific Ocean. Changing sea surface temperatures alter rainfall and surface breezes, which in turn alter ocean currents and sea surface temperatures. These interactions produce a positive feedback loop, in which each change tends to promote further changes. There is good evidence from core samples taken from coral reefs and glacial ice in the Andes that ENSO has been going on for millennia.

During El Nio, trade winds that typically blow from east to west across the Pacific weaken. Sea level falls in the western Pacific and rises in the east by as much as a foot as warm water surge eastwards along the equator. The resulting increase in ocean temperatures warms and moistens the overlying air. This triggers a process called convection: the warm, moist air rises into the atmosphere, altering normal rainfall patterns and related releases of heat.

Somewhat like a boulder sitting in a river of water, this unusual heating defines up teleconnections: continental-scale waves in the atmosphere that widen into the midlatitudes in winter. These waves alter gusts and change the jet creek and blizzard ways, generating persistent climate patterns. The changes in sea surface temperatures associated with El Nio reach their most extreme point during winter in the Northern Hemisphere, so we see the biggest consequences then.

The 2015 -1 6 El Nio event

Because Pacific surface waters are much warmer and atmospheric circulation patterns throughout the tropics are altered, fewer tropical storms and hurricanes than normal are available in the tropical Atlantic during El Nio. But there is much more activity than usual in the Pacific. Super Typhoon Pam, which ripped through Vanuatu in March 2015 causing enormous injury, was fueled by warm water from El Nio.

During the northern Pacific hurricane season in the summer and fall of 2015, 25 category 4 and 5 hurricanes/ typhoons developed, a record as compared to the previous record of 18. Changed weather patterns resulted in absence of rain and thus strong drought and wildfires in Indonesia that have degraded air quality over hundreds of miles.

El Nio has recently affected the Indian Ocean. The Bay of Bengal is already exceptionally warm, which has led to record-breaking rains and widespread flooding and desolation in Chennai, southeastern India, with 47 inches of rainfall in November and a further 11 inches of rain in the first week of December. This Indian Ocean activity may disrupt the expected development of El Nio patterns around the world. El Nio-related heavy rains have also recently( December 2015) occurred in the Americas: in Paraguay and surrounding areas, and in Missouri. The latter has led to considerable flooding of the Mississippi, reminiscent of the El Nio-related Mississippi flooding in 1993.

Sea surface temperature anomalies from El Nio tend to peak in December, and this year the changes may already have peaked in late November. However, the seasonal cycle further increases total sea surface temperatures, so the biggest impacts on the atmosphere often occur in the following February or March. This El Nio began in 2014, but stalled, and then regrouped in 2015. Every El Nio event is different, but according to NOAAs latest monthly outlook, El Nio conditions are expected to peak during the winter of 2015-16 before gradually weakening through springtime 2016 and discontinuing by late spring or early summertime 2016.

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Sea surface temperature anomalies through early December during the super El Nio in 1997 and the present El Nio .

During the coming months, climate scientists expect that El Nio will pull the east Pacific Northern Hemisphere plane stream and its related blizzard track southward. Normally these storms veer to the north toward the Gulf of Alaska or enter North America near British Columbia and Washington, where they often link up with cold Arctic and Canadian air mass and bring them down into the United States. Instead, with the plane creek following an altered track, the northern countries are likely to experience relatively mild and drier-than-normal climate. Storms tracking across the continent further to the south will likely create wet conditions in California and across the South as far east as Florida.

Each El Nio event has its own character. In the El Nio winters of 199293, 199495, 199798 and 2004 -0 5, southern California was battered by blizzards and experienced flooding and coastal erosion. However, in more modest El Nios, including the 198687 and 198788 winters, California was more at risk from droughts. Given the scale of this years El Nio, Californians should prepare for heavy rains, possible flooding and heavy coastal erosion, driven by the combined effects of higher sea levels( driving in climate change and El Nio impacts) and storm surges.

El Nio and global warming

All of the impacts of El Nio are exacerbated by global warming. Globally, temperatures for 2015 are the highest on record, in part because of the El Nio event. Global warming defines the background and El Nio decides regional climate patterns. When they work together in the same direction, they have the biggest impacts and records are broken.

Changes links with El Nio, including droughts, floods, heat waves and other changes, take a heavy toll in many parts of the world. They can severely disrupt agriculture, fisheries, the environment, health, energy demand and air quality, and increase health risks of wildfires. The risk of adverse effects and more frequent extremes or even records passing is heightened by global climate change from human activities.

By better understanding El Nio, predictions and alertings can allow us to be prepared for possible unusual impacts, but we can and should act to slow down climate change.

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