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.

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

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

Chapter 5, Unnumbered Figure 1, Page 130 Labeled

Chapter 5, Unnumbered Figure 1, Page 131 Labeled

General Atmospheric Circulation Figure 6.12

General Atmospheric Circulation Figure 6.12

Global Barometric Pressure Figure 6.10

Global Barometric Pressure Figure 6.10

June–July ITCZ Figure 6.11

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

Location of Polar Front and Sub-Polar Low Pressure

March 13, 1993

Chapter 5, Figure 5.19 Labeled

Chapter 5, Figure 5.18 Labeled

Monsoonal Winds Figure 6.20

Major Ocean Currents Figure 6.21

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

El Niño-Southern Oscillation

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.

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

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

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

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

El Niño (Warm Phase ENSO)

Piura - Perú

The rainfall in Piura and El Niño 1997-98 1982-83 1992 2002 1972 1987

1997 e-mail from Anton Seimon in Peru

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

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

1997-98 El Niño 2015-16 El Niño 1982-83 El Niño 1998-99 La Niña

Chacaltaya Glacier 2003 Disappeared in 2009 2016 Source: http://news.bbc.co.uk/2/hi/americas/6496429.stm

Francou et al. 2004

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

ENSO Links http://www.cpc.ncep.noaa.gov/products/analysis_monitoring/enso_update/sstanim.shtml http://www.cpc.ncep.noaa.gov/products/analysis_monitoring/enso_advisory/ensodisc.html