Announcements

1
Announcements
Homework 3 - Due now!
Writing Assignment 2 - Corrected and available to
be picked up
Writing Assignment 3 - Due Tuesday, 8 November.

• Quiz 3 - Next Thursday, 10 November.
• Review session Wed. 9 Nov, 530 - 630 pm in ILC
  140.
• Will cover material since Quiz 2, meaning through
  todays lecture. Essentially, chapters 6-7.
• Will include some of your questions from last
  week and this week. See Study Guides 1 and 2 (by
  this evening) posted on syllabus for sample
  questions.
• Also see lecture note questions posted on
  syllabus.

2
Key Concepts
Global Surface Ocean Circulations Sea level winds
force ocean surface currents
Ocean gyres - large eddy circulations in the
oceans in geostrophic balance
Ocean mixed layer - depth to which wind forcing
is felt in ocean, 30x more heat stored in
seasonal ocean mixed layer than in the atmosphere
Ekman transport - net water motion
(non-geostrophic part) near in the ocean surface
layer driven by Coriolis force, inward around an
anti-cyclonic gyre, outward around a cyclonic gyre
3
Key Concepts
Ocean vertical circulations Upwelling/Downwelling
- vertical motion of water resulting from
convergence or divergence of surface
waters. Convergence ? downwelling, as in center
of anti-cyclonic gyres Divergence ? upwelling, as
along coast of California (coastal upwelling)
Global Conveyor Belt Circulation - ocean heat
transport Thermalhaline circulation - driven by
differences in ocean water density which is
dependent upon temperature (thermal) and salt
content or salinity (haline).
40 of global heat transport from tropics to
poles is carried by ocean currents
4
Global Ocean Circulations
Gyre Circulations

5
Global Ocean Circulations
Ekman spiral
6
Global Ocean Circulations
Ocean upwelling/downwelling within gyres
DH
1000 m surface
DH is greater for convergence zone than for
divergence zone ? ? is greater at 1000 m depth
for convergence zone
DH
1000 m surface
7
Global Ocean Circulations
Coastal Upwelling Rising of cold water from below
due to alongshore wind
8
Global Ocean Circulations
Surface Ocean Currents and Gyres
30W
9
Ocean Water Masses
Ocean water density and water masses
Temperature and salinity (salt content) determine
ocean water density.
Sinking water masses
10
Ocean Conveyor Belt
Conveyor Belt (Thermalhaline) Circulation
40 of global heat transport from tropics to
poles is carried by ocean currents
Cold, salty water sinks in North Atlantic
Colder, fresh water sinks near Antarctica
Heavy water spreads out at bottom of global oceans
Not clear exactly how it resurfaces in Indian and
Pacific Oceans but water must return at surface
to replace North Atlantic and Antarctic water
Lifetime of Conveyor Belt Circulation is 1000
years!
11
Ocean Vertical Structure
Ocean layers Mixed Layer - depth to which wind
mixing occurs in the ocean, ranges from 25 - gt200
m
Thermocline - layer of strong temperature changes
with depth, deeper in winter than in summer
Deep ocean (abyss)
30x more heat stored in seasonal ocean mixed
layer than in the atmosphere - Why?
12
El Niño / La Niña
Tropical Ocean Climate
Ocean Surface Temperature
Sep
Rainfall Over Ocean
Sep
13
El Niño / La Niña
Normal Conditions
Trades blow from east to west
Thermocline is tilted down to the west due to
pile up of water from the trade winds
Walker Circulation
Upwelling of cold water to the east creates a
shallow thermocline in this region
Most convection (stormy weather) occurs over warm
pool
Sep
14
El Niño / La Niña
Ocean Surface Temperature Differences from Normal
El Niño
La Niña
Sep
Warm pool spreads east
Cold tongue spreads west
Sep
Why do we see these changes during each event?
15
El Niño / La Niña
El Niño Conditions
Trades winds slow down, east-west pressure
gradient weakens
2-Cell Walker Circulation
Thermocline flattens due to slower trade winds
Upwelling is reduced in the east also due to
slower trade winds
Sep
Storms move towards central Pacific with warm
water
Equator
Thermocline
120E
80W