For the InstructorThese student materials complement the Climate of Change Instructor Materials. If you would like your students to have access to the student materials, we suggest you either point them at the Student Version which omits the framing pages with information designed for faculty (and this box). Or you can download these pages in several formats that you can include in your course website or local Learning Managment System. Learn more about using, modifying, and sharing InTeGrate teaching materials.
Unit 3 Reading: From Anomaly to Oscillation
Once enough ocean surface temperature and pressure data are compiled and analyzed, we can distinguish the average, or "normal," condition of the ocean surface from abnormal or anomalous conditions. These anomalies represent departures from the normal condition, which—due to the connection between the ocean and atmosphere—cause variation in regional and global climates. The activities in Unit 3 take you on a tropical Pacific journey from ocean surface temperatures to their anomalies, and finally to the oscillation patterns that impact the lives and fortunes of people around the world.
- understand the mechanics of the El Niño-Southern Oscillation.
- diagram an El Niño event.
- recall examples of how ocean surface oscillations impact ecosystems and people.
Shifts in tropical Pacific SST and precipitation affect wind patterns over much of the globe. Normally trade winds and strong equatorial currents flow toward the west. This process, along with an intense Peruvian current, draws up cool water from beneath the surface of the ocean along the west coast of South America. As El Niño begins, the trade winds weaken, and the equatorial countercurrent strengthens. This creates Kelvin waves, surges of warm water moving eastward. When a Kelvin wave reaches the Americas, it divides and travels north and south along the west coast. The warmer water associated with the Kelvin wave affects local weather conditions along the west coast of the Americas, including an increase in the likelihood of precipitation in the tropics, and shifts in the mid-latitude jet streams.
Topics for further inquiry:
- Do you live in an at-risk area?
- How well is your community prepared for such effects?
Case Study 3.1: Predicting Patterns: What Does La Niña Look Like?
El Niño itself is only one-third of what we call ENSO, or the Southern Oscillation. The other parts of ENSO are the normal condition and La Niña. El Niño is considered the positive condition, and La Niña the negative. (These do not mean "good" and "bad" though! Positive and negative just refer to the pressure states associated with the anomaly.) El Niño has a longer history of study than La Niña, but does not necessarily occur more often.
Case Study 3.2: Exploring ENSO on the Global Stage
Additionally, interactions between different ocean surface anomaly systems can cause the weather conditions we actually experience to vary from those we expect of the oscillation. For example, some expressions of NAO can be quite subtle, depending on the state of ENSO and its impact on the jet stream.