El Nino Flashcards
What is an El Nino?
El Niño is a warming of the waters in the equatorial east Pacific, which can have significant impacts on the weather across large parts of the globe.
It may also affect the intensity of individual extreme weather events.
El Niño also results in perhaps the most well known atmospheric teleconnection pattern, which causes different weather patterns in different places
Economic Impacts of El Nino
Negative impact on fishing because there is less upwelling of nutrient rich cold water which attracts fish
Seabirds that feed on fish also suffer, along with other parts of the coastal ecosystem
Ocean thermocline
The temperature of ocean water falls rapidly as depth increases
Due to a quick dissipation of the warmth of sunlight`
What is Southern Oscillation?
The Southern Oscillation refers to changes in surface pressure patterns in the Southern Pacific Ocean between Tahiti and Darwin, Australia.
When water is warmer, pressure over Darwin is lower
When water is colder, pressure over Tahiti is lower
Equatorial easterly winds alternately weaken and strengthen in response to the SO
What is the Souther Oscillation Index?
Strong Negative correlation between the pressures at these two locations. The index is a subtraction between two pressures
When index is positive, we are in a La Nina
When it is negative, we are in an El Nino
What is the normal weather pattern on the south pacific (Walker Circulation)? What conditions cause an El Nino?
Normally, sea surface temperature is about 14°F higher in the Western Pacific than the waters off South America.
This is due to the trade winds blowing from east to west along the equator allowing the upwelling of cold, nutrient rich water from deeper levels off of South America.
Once every few years, the normal pattern ‘breaks down’, and winds travel from West to East. Pressure decreases in the eastern high and increases in the western low, causing trade winds to weaken.
Because of this, 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.
Global Consequences of El Nino
Since the effects of El Nino are global, there are huge costs associated. A good amount of damage is associated with fires in areas of lush vegetation.
Droughts in Australia and Indonesia
Warm, rainy weather in the eastern Pacific and South America
May also cause the spread of disease because droughts may turn rivers into pools which increase breeding of mosquitos
What is a La Nina?
Opposite of El Nino
There is higher than average pressure in the eastern Pacific and lower than average pressure in the western Pacific, which causes stronger than normal easterly trade winds.
This increases upwelling of cold water, which causes colder than normal water temperatures of the coast of South America.
What is the Jetstream?
The polar jet stream (wind maximum) flows along the boundary of warm and cold air and makes it stronger than average
So these high winds have been deflected away from populated areas
The subtropical jet stream creates weak hurricanes and wet conditions
Why are we so good at seasonally forecasting El Nino?
Most of the positive skill exhibited in seasonal forecasting comes from persistent sea surface temperature anomalies The ocean tends to retain unusual temperatures for extended periods of time
