Have you heard of El Niño? 1. Yes, and I have a good understanding of the concept. 2. No. 3. Yes, but I really do not understand the concept.

Have you heard of the Southern Oscillation? 1. Yes, and I have a good understanding of the concept. 2. No. 3. Yes, but I really do not understand the concept.

Have you ever been in an El Niño? 1. Yes. 2. No. 3. I am not sure.

Background First, let’s consider what the normal distribution of sea surface temperatures are.

Background Oceanic surface temperature are largely governed by a combination of solar radiation and surface wind patterns

Background Surface currents bring cool waters up along the west coast of South America

Cold Water lies beneath the surface. Why? Units: 35 0 / 00 means 35 parts salt out of 1000 STABLE on average

Origins of El Niño Spanish for ‘Christ Child’ Originally used by fishermen along the coast of Peru and Ecuador in referring to a warm ocean current appearing near Christmas and lasting a few months

El Niño Fish are less abundant during these warm periods because there is less ‘upwelling’ of cold nutrient-rich water Fishermen spend more time with their families

El Niño During some years, however, the water remains especially warm and the break in the fishing season extends into May The term ‘El Niño’ has become reserved for these extreme events

So what makes El Niño unique?  During an El Niño, the trade winds weaken  This allows the warm pool of surface water in the western tropical Pacific to extend farther east, to the Peruvian coast.  Warm water suppresses upwelling of cold, nutrient rich water from below. Occurs every 3-7 years, a result of complex air- sea interaction in tropical Pacific

So what makes El Niño unique?

Why study El Niño? Association with unusual weather patterns that affect much of the world and persist for a season or more Ocean surface temperatures may affect the intensity of individual extreme weather events El Niños are becoming more frequent: the two strongest on record have occurred during the past 20 years

Why study El Niño? Since the effects of El Nino are global in nature, the costs can be astronomical. A large portion of the costs are often associated with fires in areas of relatively lush vegetation.

Why study El Niño? Increased oceanic surface temperatures can mean stronger and wetter storms for some parts of the world.

El Niño’s economic impact Economic impact on Peruvian fishing is negative Seabirds that feed on fish also suffer, along with other parts of the coastal ecosystem

More recent El Ninos About two dozen El Ninos have occurred during the past century Most raised the ocean temperatures along the South American coast and in a belt extending 9,000 km westward in the South Pacific The strongest events were and with SSTs raised by 3-4 deg C

The most recent El Niño Southern Oscillation Index (as of August 31, 2010):

Southern Oscillation (SO) SO is a sea-saw variation of surface pressure between western and eastern equatorial Pacific Equatorial easterlies alternately weaken and strengthen in response to SO

Normal weather pattern in the South Pacific: Eastern region has little precipitation because of downward motion near the high Western region has precipitation because of upward motion near the low

DARWIN AND TAHITI SOI = ‘Tahiti – Darwin’ pressure SOI > 0 La Nina/typical SOI < 0 El Nino Darwin Tahiti Two locations: large longitude difference small latitude difference long time record

When the atmospheric pressure rises in the eastern Pacific, it falls in the western Pacific and vice-versa Southern Oscillation is the ‘seesaw’ of pressure in the South Pacific El Niño and the Southern Oscillation (ENSO)‏

Southern Oscillation index El Nino La Nina‘Tahiti – Darwin’ La Nina El Nino

So how exactly does El Niño impact the weather?

The Walker Circulation

El Niño Conditions The easterly trade winds weaken (or even reverse) The warm waters of the western tropical Pacific come sloshing back to the east because the trade winds are too weak to sustain the tilted sea level

El Niño Conditions The warm waters of the western tropical Pacific come sloshing back to the east because the trade winds are too weak to sustain the tilted sea level

Changes to the Walker circulation during an El Niño

El Niño Conditions The upwelling or rising of the cold nutrient-rich waters off the South American coast ceases The upward motion, clouds and precipitation moves eastward into the central and eastern Pacific

Transition from El Niño to La Niña

An animation of sea-surface height, as compared With El Niño Nino index: ( (

El Nino has global consequences Droughts in Australia and Indonesia Warm, rainy weather in the eastern Pacific and South America

Wild Fires can be a particular problem in Indonesia During wildfires during the El Nino event, over 24.1 million acres were burned

Wild Fires can be a particular problem in Indonesia The massive forest fire in Indonesia in 1997 is estimated to have released between 0.81 and 2.57 gigatonnes of Carbon Dioxide into the atmosphere, which is between 13-40% of the annual carbon dioxide emissions from burning fossil fuels.

Wild Fires also represent a huge health hazard. At one point, the pollution index of the region reached 839. To put a relative point to this number, a pollution index of 300 is the equivalent of smoking 20 cigarettes a day. The smoke, during one time, blanketed an area that was larger than the continental United States.

Wildfires and Drought in Australia Another region severely impacted by droughts and wildfires during an El Nino event is Australia. The droughts have a severe impact on agriculture, mainly in the form of an inability to feed livestock.

Wildfires and Drought in Australia Also, without the shrubs and pasture land, dust and particulate matter become a significant problem.

Flooding and disease In areas of flooding, water borne diseases become a significant issue. For instance, consider cholera in Peru.

Disease and El Nino In very humid climates, droughts may turn rivers into strings of pools, preferred breeding sites of other types of mosquito.

El Niño has a large impact on North American weather, including a reduction in Atlantic Ocean hurricane activity, because of the very strong upper-level winds that produce too much wind shear for a hurricane to continue to exist up below

The 1998 Ice Storm in Montreal was associated with a record-breaking El Niño

Gyakum and Roebber 2001 (Monthly Weather Review)‏ Roebber and Gyakum 2003 (Monthly Weather Review)‏

Freezing rain accumulation

Effects in California Effects in California include storm surge and coastal erosion, as well as the possibility of floods and landslides

La Niña Opposite to El Niño Higher than average pressure in the eastern Pacific and lower than average pressure in the western Pacific

La Niña

Stronger than normal easterly trade winds Colder than normal ocean temperatures off of South America Flooding in Australia and Indonesia

Impacts of La Niña

La Niña

What are the current conditions in the Pacific Ocean? A modest La Nina…..

Predicting El Nino

ENSO and seasonal foreacsts It turns out, that most of the positive skill exhibited in seasonal forecasting comes from persistent sea surface temperature anomalies.

Seasonal Forecasts The reason that we can make seasonal predictions when we have El Nino is that the slowly varying sea- surface temperature anomalies “force” a response in the atmosphere. In much the same way, climate models can predict changes in our climate that are “forced” by increases in carbon dioxide. However there are “unforced” modes of atmospheric variability that are significantly harder to predict.

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