Quiz #1, Part 1 results (You can see the statistics yourself in “My Grades”)

Quizzes, Part 2 Marking rubric posted, with examples from student answers to the Practice Quiz, Part 2 (VISTA homepage  Quizzes link on homepage  Rubric...)

Goals for Today 1.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

RELEVANCE Fisheries 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 shore D. Generally away from shore E. There is no Ekman transport because of the presence of a continent. 12°S

Wind, Ekman transport, geostrophic flow, and coastal upwelling: Peru WIND Ekman transport Higher Lower Geostrophic flow

Along shorelines: Southern hemisphere upwelling Upwelling of deeper water

Along shorelines: Northern hemisphere upwelling

Along shorelines: Northern hemisphere, downwelling Notes

Along shorelines: Coastal upwelling Sea surface temperature, South Africa Blue = cold Red = 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? Peru A. Summer monsoon B. Winter monsoon C. In between summer & winter D. There’s not enough information given Red – high Blue - low

In the open ocean: TAO Project Office/PMEL/NOAA Equatorial upwelling Sea Surface Temperature

In the open ocean: Equatorial upwelling Chlorophyll-a in surface water Blue = Low Green/yellow = High Divergence 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 South America 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)? NOAA High ~30ºS High ~4ºN High ~30ºN Low 0º Low ~10ºN A.To the west  B. To the east  C. To the NE D. To the NW E. 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? NOAA High ~30ºS High ~4ºN High ~30ºN Low 0º Low ~10ºN A.To the west  B. To the east  C. To the NE D. To the NW E. 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

Equatorial upwelling  chlorophyll-a NOAA Divergence Convergence Purple = low chlorophyll-a light blue = higher chlorophyll-a Notes

Southern Ocean: No Lateral Barriers… Notes

JULY Circular wind patterns

Ekman transport under the Bermuda High

Horizontal pressure gradient force Geostrophic flow around a SUBTROPICAL GYRE Coriolis force Geostrophic Flow

North Atlantic Subtropical Gyre South Atlantic Subtropical Gyre Notes

L H IN THE NORTHERN HEMISPHERE (opposite directions in the S. Hem.) Subpolar gyreSubtropical gyre Ocean gyres Notes

(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 – 2000 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 into colder water Cold rings  south into warmer water

G3

Sea surface temperature (SST) February

Surface Air Temperature, January 2003

Sea surface Temperature (SST) August

Winds Drive Surface Currents Currents are Moving Ocean water…

Effect of Coriolis on surface ocean circulation

Ekman Transport 90 o to wind direction convergence

Another Look at Convergence

purple = low chlorophyll-a light blue = higher chlorophyll-a High phytoplankton concentration at equator

Cool SST animations at

Along shorelines: Northern hemisphere upwelling

Along shorelines: California WIND Ekman transport Higher Lower Geostrophic flow

Coastal upwelling Ekman Coastal downwelling

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 H

gravity Ekman Transport How Does Water Flow Around a Hill? Resulting Flow “Around the hill” Trade Winds Coriolis