Quiz #1, Part 1 results

(You can see the statistics yourself in “My Grades”)

Quizzes, Part 2Marking rubric posted, with

examples from student answers to the Practice Quiz, Part 2

(VISTA homepage Quizzes link on homepage Rubric...)

Goals for Today1. PREDICT whether upwelling or downwelling will

occur along a coastline, given surface wind direction

2. PREDICT the direction of wind-driven surface ocean currents anywhere on Earth with any continental configuration.

3. LIST differences between western and eastern boundary currents in subtropical gyres

Hydrosphere II: Surface ocean circulation w/continents

RELEVANCEFisheries Heat transport

Trans-portation

Christopher Duncklee

Digital Vision

Surface Ocean Currents

Marshak, Figure 18.10

Clicker question: The wind often blows from south to north along the coastline of Peru.

Toward what direction is the Ekman transport?

Peru

WIND

A. Generally northward B. Generally southward C. Generally toward the shoreD. Generally away from shoreE. There is no Ekman transport because of the presence of a continent.

12°S

Wind, Ekman transport, geostrophic flow, and coastal upwelling:

Peru

WIND

Ekmantransport

Hig

her

Lo

wer

Geostrophicflow

Along shorelines: Southern hemisphere upwelling

http://ww2010.atmos.uiuc.edu/(Gh)/guides/mtr/eln/upw.rxml

Upwelling of deeper water

Along shorelines: Northern hemisphere upwelling

Along shorelines: Coastal upwelling

Sea surfacetemperature,South Africa

Blue = coldRed = warm

Along shorelines: Coastal upwelling

Chlorophyll,South Africa

Red = more chlorophyll Blue = less chlorophyll

Clicker question: This image shows chlorophyll concentration in the ocean off the Arabian peninsula in a particular season in a particular year. This pattern is related to monsoon circulation in India. WHAT SEASON IS IT IN THIS IMAGE?

PeruA. Summer monsoonB. Winter monsoonC. In between summer & winterD. There’s not enough information given

Red – highBlue - low

In the open ocean:

TAO Project Office/PMEL/NOAA

Equatorial upwelling

Sea Surface Temperature

In the open ocean: Equatorial upwelling

Chlorophyll-ain surface water

Blue = LowGreen/yellow = HighDivergence

Convergence

Convergence

Surface Ocean Currents Equatorial currents

ERROR ALERT! The Equatorial Counter Current should be NORTH of the equator!

Intertropical Convergence Zone (thermal equator)

NOAA

Geographic equator

ITCZ

SouthAmerica

NE Trades

SE Trades

Which direction is the Ekman transport?

Light wind! Rising air!

NOAA

NE Trades

SE Trades

Ekman transport

Light wind!

Where are the convergences and divergences?

Intertropical Convergence Zone (thermal equator)

Equatorial dynamic topography

NOAA

Light wind!

Convergence at ~30ºS

Convergence at ~4ºN

Convergence at ~30ºN

Divergence at 0º

Divergence at ~10ºN

Where are the hills and valleys?

Clicker Question: Toward what direction does the geostrophic current flow under the ITCZ (between about 4°N and 10°N)?

NOAAHigh ~30ºS

High ~4ºN

High ~30ºN

Low 0º

Low ~10ºN

A.To the west

B. To the east

C. To the NED. To the NWE. There’s no

geostrophic current there

Follow-up Clicker Question: Toward what direction does the geostrophic current flow between about 0°N and 4°N?

NOAAHigh ~30ºS

High ~4ºN

High ~30ºN

Low 0º

Low ~10ºN

A.To the west

B. To the east

C. To the NED. To the NWE. There’s no

geostrophic current there

Equatorial dynamic topography

NOAA

Light wind!

High ~30ºS

High ~4ºN

High ~30ºN

Low 0º

Low ~10ºN

Which direction are the geostrophic currents?

Equatorial geostrophic currents

NOAA

North Equatorial Counter Current

North Equatorial Current

South Equatorial Current

JULY

Circular wind patterns

Ekman transport under the Bermuda High

Horizontal pressure gradient force

Geostrophic flow around a SUBTROPICAL GYRE

Coriolisforce

GeostrophicFlow

(Mercier and Le Traon)

Sea surface height:North Atlantic subtropical gyre

Red = High, Blue = low

70 cm0 cm-80 cm

Symmetric(atmospheric winds)

Asymmetric(ocean gyres)

H H

Asymmetrical ocean gyres (N. Hem.)

Western intensification

Steepness of mound sets flow speed

~10 cm/s

~150 cm/s

1000

– 2

000

m

Global dynamic topography

Surface Ocean Currents

Warm and cold currents

Global Sea Surface Temperature

Global Surface Air Temperature, July 2003

• All major ocean currents are geostrophic, responding to pressure gradients that are set up by Ekman transport, which is driven by the wind.

• Upwelling & downwelling, coastal or open ocean• Complex equatorial currents, due to continents• Subtropical gyres:

Warm western boundary currents flow poleward; Cool eastern boundary currents flow equatorward.

• You can apply the same principles to any situation, along a coastline or in the open ocean, to deduce the direction and strength of ocean currents.

Summary: Surface Ocean Circulation

Relevance: food, heat, transportation

In preparation for next lecture…

So far, we have considered only the circulation near the surface of the ocean. The deep ocean also moves. What’s the major driver of deep ocean circulation?

Extra, unused slides below this one

Gulf Stream Warm Core Ring

Gulf Stream Ring formation

Warm rings north intocolder water

Cold rings south intowarmer water

G3

Sea surface temperature (SST)Sea surface temperature (SST)

February

Surface Air Temperature, January 2003Surface Air Temperature, January 2003

Sea surface Temperature (SST)Sea surface Temperature (SST)

August

Winds Drive Surface CurrentsWinds Drive Surface Currents

Currents areMovingOcean water…

Effect of Coriolis on surface ocean Effect of Coriolis on surface ocean circulationcirculation

Ekman Transport 90o to wind direction

convergence

convergence

Another Look at ConvergenceAnother Look at Convergence

purple = low chlorophyll-a light blue = higher chlorophyll-a

High phytoplanktonHigh phytoplanktonconcentration at equatorconcentration at equator

Cool SST animations athttp://svs.gsfc.nasa.gov/vis/a000000/a003300/a003389/index.html

Along shorelines: Northern hemisphere upwelling

http://oceanmotion.org/html/background/upwelling-and-downwelling.htm

Along shorelines:

Cal

iforn

ia

WIND

EkmantransportH

igh

er

Lo

wer

Geostrophicflow

Co

asta

l up

wel

ling

Co

asta

l up

wel

ling

Ekman

Co

asta

l do

wn

wel

ling

Co

asta

l do

wn

wel

ling

Circular wind patterns:

Ekman? Pressure gradient? Geostrophic flow? Ocean currents?

Ekman transport into the middle

This example driven by anticyclonic winds in the N. Hem.

Geostrophic current around a GYRE

Open Univ., Fig. 3.25

H

gravity

Ekman Transp

ort

How Does Water Flow Around a Hill?How Does Water Flow Around a Hill?

Resulting Flow“Around the hill”

Trade Winds

Coriolis