El Niño/La Niña Events

1. El Niño/La Niña Events • Sort-of periodic oscillation in the sea surface temperature in the Pacific Ocean along the equator • Normal pattern: • western equatorialPacific Ocean warm • eastern equatorialPacific Ocean cool

2. El Niño/La Niña (cont’d) • El Niño pattern: • western equatorial Pacific cooler than usual • eastern equatorial Pacific warmer than usual • so temperature difference between them reduced

3. El Niño/La Niña (cont’d) • Animation of 1997-98 El Niño event(https://www.youtube.com/watch?v=PCT49t648JA) • Graphs shown include: • Ocean surface height vs. time (Jan. 1997- Dec. 1998) • Temperature vs. depth vs. time • Note slosh of warm water eastwardalong the equator to create the El Niño event

4. El Niño/La Niña (cont’d) • La Niña pattern: • opposite of El Niño

5. El Niño/La Niña (cont’d) • Get oscillation between El Niño/La Niña an average of 1-2 times per decade • A La Niña event took place in each of the winters of 2010-2011 and 2011-2012, though they disappeared by mid spring • Yesterday’s sea-surface temperature pattern in the equatorial Pacific(http://www.pmel.noaa.gov/tao/jsdisplay/) • Warmer eastern equatorial Pacific in an El Niño warms the atmosphere there • Raises pressure in upper troposphere there • Increases pressure gradient north of there • Creates southern branch of jet stream in lower midlatitudes • Midlatitude cyclones along jet stream travel farther south than usual • Affects precipitation in parts of North America • Other consequences (often more significant) elsewhere in the globe

6. Global Impacts of El Niño Rainfall and temperature anomalies associated with El Niño events (on the average) In winter and in summer

7. La Niña • La Nina events tend to have a weaker but roughly opposite effect on West Coast weather