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ENSO El Nino & La Nina Reference Cheat Sheet
A printable reference covering ENSO states, El Nino, La Nina, sea surface temperature anomalies, Southern Oscillation Index, and teleconnections for grades 9-12.
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ENSO, the El Nino Southern Oscillation, is a repeating climate pattern in the tropical Pacific Ocean that affects weather around the world. This cheat sheet helps students compare El Nino, La Nina, and neutral conditions using ocean temperatures, winds, pressure, and rainfall patterns. It is useful for interpreting climate maps, seasonal forecasts, and real-world impacts such as droughts, floods, and hurricane activity. The most important ENSO indicators are sea surface temperature anomalies in the central and eastern equatorial Pacific, trade wind strength, and air pressure differences across the Pacific. El Nino usually means warmer-than-average water in the eastern or central tropical Pacific, while La Nina usually means cooler-than-average water there. These ocean changes shift tropical rainfall and jet stream patterns, creating teleconnections that influence regions far from the Pacific.
Key Facts
- ENSO stands for El Nino Southern Oscillation, a coupled ocean-atmosphere pattern in the tropical Pacific.
- El Nino conditions occur when sea surface temperature anomalies in the Nino 3.4 region are at least +0.5 degrees Celsius for several overlapping 3-month periods.
- La Nina conditions occur when sea surface temperature anomalies in the Nino 3.4 region are at most -0.5 degrees Celsius for several overlapping 3-month periods.
- Sea surface temperature anomaly = observed sea surface temperature - long-term average sea surface temperature.
- During El Nino, trade winds often weaken, warm surface water shifts eastward, and rainfall increases over the central or eastern tropical Pacific.
- During La Nina, trade winds often strengthen, cold upwelling increases near South America, and rainfall shifts farther west toward Indonesia and Australia.
- The Southern Oscillation Index compares air pressure near Tahiti and Darwin, with negative values often linked to El Nino and positive values often linked to La Nina.
- Teleconnections are climate links in which ENSO changes tropical Pacific heating and shifts weather patterns in distant regions.
Vocabulary
- ENSO
- ENSO is the El Nino Southern Oscillation, a climate pattern involving linked changes in tropical Pacific ocean temperatures and atmospheric circulation.
- El Nino
- El Nino is the warm phase of ENSO, usually marked by unusually warm sea surface temperatures in the central and eastern equatorial Pacific.
- La Nina
- La Nina is the cool phase of ENSO, usually marked by unusually cool sea surface temperatures in the central and eastern equatorial Pacific.
- Sea Surface Temperature Anomaly
- A sea surface temperature anomaly is the difference between the measured ocean surface temperature and the long-term average for that location and time of year.
- Trade Winds
- Trade winds are persistent tropical winds that usually blow from east to west across the equatorial Pacific.
- Teleconnection
- A teleconnection is a climate connection where changes in one region, such as the tropical Pacific, influence weather patterns far away.
Common Mistakes to Avoid
- Confusing El Nino with simply hot weather is wrong because El Nino is defined by Pacific Ocean temperature anomalies and atmospheric changes, not by local temperature alone.
- Using one warm month to declare El Nino is wrong because ENSO classification depends on sustained anomalies over overlapping 3-month periods.
- Forgetting the anomaly part of sea surface temperature is wrong because ENSO is based on departure from the long-term average, not the raw water temperature.
- Assuming ENSO impacts are identical everywhere is wrong because teleconnections vary by region, season, event strength, and other climate patterns.
- Thinking La Nina is just the opposite of El Nino in every location is wrong because some impacts reverse clearly while others are weaker, shifted, or inconsistent.
Practice Questions
- 1 The long-term average sea surface temperature in part of the Nino 3.4 region is 26.8 degrees Celsius, and the observed temperature is 27.6 degrees Celsius. What is the sea surface temperature anomaly, and does it suggest warming or cooling?
- 2 A 3-month Nino 3.4 anomaly is -0.8 degrees Celsius. If this pattern continues for several overlapping seasons, which ENSO state is most likely?
- 3 Tahiti pressure is relatively high compared with Darwin pressure, producing a positive Southern Oscillation Index. Is this more commonly associated with El Nino or La Nina?
- 4 Explain why an ocean temperature change in the tropical Pacific can affect rainfall or temperature patterns thousands of kilometers away.