1. Oceanic Circulation and ENSO
Current Weather 
Finish Idealized Global Circulation  
Seasonal and Regional Modification
Oceanic Circulation
El Niño-Southern Oscillation
For Next Class: Bring Questions
Reminder: Exam I on Friday (9/13)! Review Sheet is posted on AsUlearn.

3. Idealized Global Circulation Model
ITCZ – Inter-Tropical Convergence Zone
STHP – Sub-Tropical High Pressure
SPLP – Sub-Polar Low Pressure
PHP – Polar High Pressure

4. Seasonal Patterns
Location of the sun’s noon-time vertical rays (i.e., where the sun is directly overhead) helps to control the position of the ITCZ
Northern Hemisphere summer, ITCZ and all of the wind and pressure belts migrate to the north
North Hemisphere winter, ITCZ and all of the wind and pressure belts migrate to the south

5. Chapter 5, Unnumbered Figure 1, Page 130 Labeled

6. Chapter 5, Unnumbered Figure 1, Page 131 Labeled

7. General Atmospheric Circulation
Figure 6.12

8. General Atmospheric Circulation
Figure 6.12

9. Global Barometric Pressure
Figure 6.10

10. Global Barometric Pressure
Figure 6.10

12. June–July ITCZ
Figure 6.11

13. Rossby Waves
Giant meanders in upper-level wind patterns: can range from small to large (zonal to meridional flow)
Figure 6.16

14. Location of Polar Front and Sub-Polar Low Pressure

15. March 13, 1993

16. Chapter 5, Figure 5.19 Labeled

17. Chapter 5, Figure 5.18 Labeled

18. Monsoonal Winds
Figure 6.20

19. Major Ocean Currents
Figure 6.21

20. ENSO What is ENSO and why is it important?
What are the three major phases of ENSO?

21. El Niño-Southern Oscillation

22. ENSO
ENSO is a coupled phenomenon, depending on feedbacks between the ocean and the atmosphere.
Changes in the oceanic sea surface temperatures (SSTs) drive changes in atmospheric circulation which feedback and further alter the ocean.

23. El Niño-Southern Oscillation
Coupling of the ocean and atmosphere in the tropical Pacific Ocean
El Niño (warm-phase of ENSO): above average sea-surface temperatures
La Niña (cold-phase of ENSO): below average sea-surface temperatures
La Nada (ENSO-neutral): average sea-surface temperatures

24. ENSO Neutral Conditions in the Tropical Pacific
Contrast between relatively high air pressure over the central and eastern tropical Pacific and relatively low air pressure over the western tropical Pacific ultimately drives the trade winds
Walker Circulation: east-west oriented atmospheric circulation across the equatorial Pacific
© AMS

25. ACCION 2013: Climate variability
Coastal upwelling
Andes
Cold water
Warm water
Thermocline
Temperature
Depth
Trade winds
Ekman transport
Figure: University of Washington

27. ENSO
Warm Phase
With the onset of El Niño, air pressure falls over the eastern tropical Pacific and rises over the western tropical Pacific
Trade winds slacken in the western and central equatorial Pacific
Warm surface waters in the eastern tropical Pacific reduces upwelling
© AMS

28. El Niño (Warm Phase ENSO)

30. Piura - Perú

31. The rainfall in Piura and El Niño
1992
2002
1972
1987

32. 1997 e-mail from Anton Seimon in Peru

33. El Niño, La Niña, and the Southern Oscillation
Cold Phase
During La Niña, surface waters are colder than usual over the central and eastern tropical Pacific and somewhat warmer than usual over the western tropical Pacific
Lower than usual SST in the east topical Pacific inhibit rainfall while higher than usual SST in the west enhance rainfall
© AMS

34. Positive feedback between ocean and atmosphere (Bjerknes 1969)
ACCION 2013: Climate variability
Positive feedback between ocean and atmosphere (Bjerknes 1969) 1
1. Warming 2
2. Displacement of convection 3
3. Weakening of easterly winds 4
4. Eastward currents and deepening of thermocline
Peru
Australia
Thermocline
Figura: NOAA PMEL

37.
El Niño
El Niño
El Niño
La Niña

40. Chacaltaya Glacier 2003 Disappeared in 2009 2016
Source:

41. Francou et al. 2004

42. ENSO Impacts in Central Andes
El Niño (warm-phase ENSO) is typically associated with warm and more variable precipitation, leading to glacier retreat
low albedo bare ice is exposed to intense tropical sun at higher temperatures
La Niña (cold-phase ENSO) is typically associated with cool and sometimes wetter conditions, leading to glacier advance
high albedo fresh snow covers most glacier surfaces, cloud cover is increased, and temperatures are lower

43. ENSO Links