El Nino and La Nina- imp Topic

**sunilware** · 09-18-2006

El Niño and La Niña

El Niño and La Niña Effects on Global Temperature

El Niño(Spanish for the little boy or the Christ Child) is a disruption of the ocean atmosphere system in the tropical Pacific. El Nino, an abnormal warming of surface ocean waters in the eastern tropical Pacific, is one part of what's called the Southern Oscillation. The Southern Oscillation is the see-saw pattern of reversing surface air pressure between the eastern and western tropical Pacific; when the surface pressure is high in the eastern tropical Pacific it is low in the western tropical Pacific, and vice-versa. Because the ocean warming and pressure reversals are, for the most part, simultaneous, scientists call this phenomenon the El Nino/Southern Oscillation or ENSO for short. Normally trade winds move westward carrying warm water to Australia. Cooler water can upwell along the South American coast. This cool water carries nutrients that support large fish populations in the region. Every three to seven years, these trade winds die and the warm water that was once pushed westward is allowed to shift back towards South America. South American fisherman have given this phenomenon the name El Niño, which is Spanish for "The Christ Child," because it comes about the time of the celebration of the birth of the Christ Child-Christmas.
El Niñodisrupts the ocean-atmosphere system in the tropical Pacific having important consequences for weather around the globe. Among these consequences are increased rainfall across the southern tier of the US and in Peru, which has caused destructive flooding, and drought in the West Pacific, sometimes associated with devastating brush fires in Australia.

El Nino conditions

La Niña(Spanish for the little girl) is essentially the opposite of El Nino The ocean becomes much cooler than normal. Although, La Niñais not as well understood as El Niño, it is thought to occur due to an increase in the strength of the trade winds This increases the amount of cooler water that flows toward the west coast of South American and reduces water temperatures. Global climate La Niñaimpacts tend to be opposite those of El Niñoimpacts. In the tropics, ocean temperature variations in La Niñatend to be opposite those of El Niño.

La Nina conditions
Environment Canada graphics

Normal Ocean conditions

The images show sea surface topography from NASA's TOPEX satellite, sea surface temperature's from NOAA's AVHRR satellite sensor and sea temperature below the surface as measured by NOAA's network of TAO moored buoys. The three dimensional relief map shows a sea level rise along the Equator in the eastern Pacific Ocean of up to 34 centimeters with the red colors indicating an associated change in sea surface temperature of up to 5.4 degrees Celsius.
El Nino conditions

The sea temperature below the surface illustrates how the thermocline (the boundary between warm and cold sea water at 20 degrees Celcius) is flattened out by El Niño. These images are beneath Sea Views of sea surface height (represented by the bumps) and sea temperature (represented by the color). Red is 30 degrees C and blue is 8 degrees C. The thermocline is the border between the dark blue at the bottom and the cyan. The thermocline exists at 20 degrees C. Data from 1/1/97 to 3/10/98.
La Nina conditions

El Niño, La Niña Rearrange South Pole Sea Ice

Goddard Space Flight Center Press Release

During the El Nino year of 1992, the Pacific Ocean from the Drake Passage to the Ross Sea (about 70W to 180W) had less sea ice than in a normal year. Meanwhile, the sea ice in the Weddell Sea (20E to 60W) extended further north.
In contrast, sea ice in the Pacific Ocean had a larger northward extension in 1999, a La Nina year, particularly east of the Ross Sea. Meanwhile, sea ice in the Weddell Sea had a less than normal northern extent.
COLOR KEY: The light blue areas indicate open ocean water. All other areas show the presence of sea ice.

Scientists have been mystified by observations that when sea ice on one side of the South Pole recedes, it advances farther out on the other side. New findings from NASA's Office of Polar Programs suggests for the first time that this is the result of El Niños and La Niñas driving changes in the subtropical jet stream, which then alter the path of storms that move sea ice around the South Pole.
The results have important implications for understanding global climate change better because sea ice contributes to the Earth's energy balance. The presence of sea ice, which is generated around each pole when the water gets cold enough to freeze, reflects solar energy back out to space, cooling the planet. When there is less sea ice, the ocean absorbs the sun's heat and that amplifies climate warming.
By looking at the relationship between temperature changes in the ocean, atmospheric winds, storms, and sea ice, the new study pinpoints causes for retreating and advancing ice in the Atlantic and Pacific ocean basins on either side of the South Pole, called the "Antarctic dipole."
"El Niños and La Niñas appear to be the originating agents for helping generate the sea ice dipole observed in the ocean basins around the Antarctic," said David Rind, lead author of the study and a senior climate researcher at the NASA Goddard Institute for Space Studies. The study appears in the September 17 issue of Journal of Geophysical Research.

This map shows the difference in sea ice cover between 1992 and 1999 around Antarctica. The red color indicates areas where there was a higher concentration of sea ice in 1992 than in 1999, as a result of a 1992 El Nino event. The blue color indicates places where ice concentrations were higher in 1999 than 1992, as a result of a 1999 La Nina event.

During El Niño years, when the waters of the Eastern Pacific heat up, warm air rises. As the air rises it starts to move toward the South Pole, but the earth's rotation turns the winds eastward. The Earth's rotation is just strong enough to cause this rising air to strengthen the subtropical jet stream, a band of atmospheric wind near the equator that also blows eastward.
When the subtropical jet stream gets stronger over the Pacific basin, it diverts storms away from the Pacific side of the South Pole. Since there are fewer storms near the Pacific-Antarctic region during El Niño years, there are less winds to blow sea ice farther out into the ocean, and ice stays close to shore.
At the same time, the air in the tropical Atlantic basin sinks instead of rising. That sinking air weakens the subtropical jet stream over the Atlantic, guiding storms towards the South Pole. The storms, which intensify as they meet the cooler Antarctic air, then blow sea ice away from the pole farther into the Atlantic.
During La Niña years, when the Eastern and central Pacific waters cool, there is an opposite effect, where sea ice subsides on the Atlantic side, and advances on the Pacific side.
The study is important because the amount of sea ice that extends out into the ocean plays a key role in amplifying or decreasing the warming effects of the sun on our climate. Also, the study explains causes of the Antarctic sea ice dipole for the first time,
and provides researchers with a greater understanding of the effects of El Niño and La Niña on sea ice.
Scientists may use these findings in global climate models to gauge past, present and future climate changes.
"Understanding how changes in the temperature in the different ocean basins will affect sea ice is an important part of the puzzle in understanding climate sensitivity," Rind said.

NOAA ISSUES UNSCHEDULED EL NIÑO ADVISORY
El Niño Makes a Comeback

Sept. 13, 2006 — Scientists at the NOAA Climate Prediction Center reported today that El Niño conditions have developed in the tropical Pacific and are likely to continue into early 2007. Ocean temperatures increased remarkably in the equatorial Pacific during the last two weeks. "Currently, weak El Niño conditions exist, but there is a potential for this event to strengthen into a moderate event by winter," said Vernon Kousky, NOAA's lead El Niño forecaster.
Some impacts from the developing El Niño are already evident in the pattern of tropical precipitation. During the last 30 days, drier-than-average conditions have been observed across all of Indonesia, Malaysia and most of the Philippines, which are usually the first areas to experience ENSO-related impacts. This dryness can be expected to continue, on average, for the remainder of 2006.
Also, the development of weak El Niño conditions helps explain why this Atlantic hurricane season has been less active than was previously expected. El Niño typically acts to suppress hurricane activity by increasing the vertical wind shear over the Caribbean Sea region. However, at this time the El Niño impacts on Atlantic hurricanes are small. "We are still in the peak months of the Atlantic hurricane season, and conditions remain generally conducive for hurricane formation," said Gerry Bell, NOAA's lead seasonal hurricane forecaster.
Typical El Niño effects are likely to develop over North America during the upcoming winter season. Those include warmer-than-average temperatures over western and central Canada, and over the western and northern United States. Wetter-than-average conditions are likely over portions of the U.S. Gulf Coast and Florida, while drier-than-average conditions can be expected in the Ohio Valley and the Pacific Northwest.
The term El Niño refers to the large-scale ocean-atmosphere climate phenomenon linked to a periodic warming in sea surface temperatures across the central and east-central equatorial Pacific (between approximately the date line and 120 degrees west). El Niño represents the warm phase of the El Niño/Southern Oscillation, or ENSO, cycle, and is sometimes referred to as a Pacific warm episode. El Niño originally referred to an annual warming of sea surface temperatures along the west coast of tropical South America.