ENSO: El Niño/Southern Oscillation

El Niño is characterized by unusually warm temperatures that move

eastward toward Peru’s coastLa Niña is characterized by

unusually cool temperatures in that same area of the Pacific.

The term “El Niño” is so commonly known that it was combined with the scientific term “Southern

Oscillation” to form the acronym, ENSO, “El Niño-Southern Oscillation”

Why is it called “El Niño”?

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Oscillation?Oscillation is the action of something that

shifts back-and-forth

An oscillating fan cooled the room as it moved to the right and then to the left.

The Southern Oscillation is an alternating pattern of warmer- or cooler-than-normal ocean surface temperatures. Each cycle of the pattern can take years.

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ENSO Anomalies are deviations from normal,

or “nominal”, temperatures Unusually warm temperatures are

shown in red, unusually cold anomalies in blue. Here are the actual temperatures in the top slide, then the anomalous temperatures in the bottom slide.

http://www.cpc.ncep.noaa.gov/products/analysis_monitoring/enso_update/sstanim.shtml

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ENSO in action: a typical El Niño weather pattern Dec-Feb

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ENSO in action: a typical El Niño weather pattern Jun-Aug

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ENSO in action: a typical La Niña weather pattern Dec-Feb

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ENSO in action: a typical La Niña weather pattern Jun-Aug

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ENSO Each cycle can be strong or weak.

• The unusually warmer or cooler temperatures can be a few degrees or several degrees away from what has historically been recorded.

Strong ENSO seasons can result in severe weather disruptions in many areas far from the equatorial (tropical) Pacific• On the next slide, record 3 events caused by an

El Niño event.

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Remember! ENSO is not the normal situation. ENSO cycles are deviations from data

recorded over many years ENSO seems to follow a pattern of

every 2-7 years…but lately has been 3-4 years.

ENSO can last 12-18 months, or LONGER!

Unpredictability is a hallmark of this phenomenon

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Tropical Cyclones

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Tropical Cyclones! Carla-1961 Ike- 2008 Katrina-2005 Rita- 2005 Tropical Storm Allison-2001 Alicia-1983 And …the Great Storm of 1900!

All are tropical cyclones that have affected our region.

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What is a tropical cyclone? It is an area of disturbed weather

(storms) that has a closed circulation in tropical regions and it is not connected to a low pressure frontal boundary. • Closed Circulation means the winds blow

around it in a circular pattern• It has its origins in the tropics• It has low pressure in its center, meaning air

is rising• It is isolated, i.e., not part of a cold front

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Heat from the tropics… Warms the air in the

tropics This warm, humid air

rises Convergence of wind

currents in the ITCZ are believed to start the rising air to spin, causing a cyclonic action

(See where the winds converge, then diverge…this starts the rising air to spin.)

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This heat then… Is carried “aloft”, meaning high into the

atmosphere The core of a tropical cyclone is warmer

than the air surrounding it- that is what makes it “tropical”

It is one method for excess heat to be spread to higher latitudes from the tropics• The enormous amount of water in a tropical

cyclone carries heat with it as the storm moves away from the Inter Tropical Convergence Zone (ITCZ)

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Remote sensing deviceso …are used to detect tropical

cyclones far out at sea o They also track developments

as the storms moveo Such devices as

o Buoys,o Ships,

o Weather Balloons, o Satellites,

o and Aircraft o all play an important role in

measuring the intensities of storms.

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Costliest U.S. Atlantic Hurricanes

Total estimated property damage, 2005 USD 1 MIAMI 1926 $157 billion 2 GALVESTON 1900 $99.4 billion 3 KATRINA 2005 $81.0 billion 4 GALVESTON 1915 $68.0 billion 5 ANDREW 1992 $55.8 billion 6 NEW ENGLAND1938 $39.2 billion 7 CUBA-FLORIDA 1944 $38.7 billion 8 OKEECHOBEE 1928 $33.6 billion 9 DONNA 1960 $26.8 billion 10 CAMILLE 1969 $21.2 billion