ceans

Lecture 13. Global Wind Patterns and the O

EOM

• Dra ocean surface inthe

• The• In g revailing wind• Pol o ocean currents

mo parable amount ofhea

• Thi des, while coolingthe

• In t the warm GulfStr s a strong jetstre torms) along theAtl

Global Wind Patterns and the Oceans

g from wind exerts a force called ‘wind stress’ on the direction of the wind. currents in the upper ocean are driven by the windeneral, they tend to flow in a similar direction to the peward currents are warm; equatorward currents cold, sve heat from the tropics toward the poles, doing a comt transport as occurs in the atmosphere.s heat transport helps warm the climate of higher latitu tropics.he winter, strong temperature contrasts occur betweeneam and the cold interior of N America. This produceam and a ‘storm track’(region of particularly intense santic coast of N America.

WW site

Current Sea-Surface Temperatures

Unisys W

• Alomecol

• Thi(anby

OM

Upwelling

ng the Pacific coast in the sum-r, ocean temperatures stay quited, particularly off N California.s is due to upwelling of coldd nutrient-rich) water inducedthe prevailing N winds.

E

g

• Wi• Co ).• Co• Fog rlying air.

How Alongshore Winds Make Upwellin

nd ‘stress’ pushes surface water southward.riolis force deflects surface water to the right (offshoreld subsurface water upwells to take its place. or persistent low cloud often forms in the chilled ove

EOM

• We pics. A ther-mo deep waters

• Pre surface waters onthe thermocline isdee

x’s denote TAO buoyocean temperaturemeasurements.

Equatorial upwelling

ll below the ocean surface, it is icy-cold even in the trocline separates the warm surface waters from the cold vailing tropical easterly winds tend to pile up the warm west side of ocean basins, so the equatorial W Pacific p (200 m) while the E Pacific thermocline is shallow.

TAO WWW site

• Eas

- th- su ances wind stress.- In ward- In ward- To elled at equator.- T

• If w ng and no sourceof c

• If t cools SST.

terly winds also induce ‘equatorial upwelling’ since

e easterly winds push on the ocean surface.rface currents adjust so Coriolis force on the water bal the northern hemisphere, the resulting current is north the southern hemisphere, the resulting current is south replace the diverging surface water, cold water is upw

his lowers SST along the equator.inds change to westerly, there is equatorial downwelliold water, so SST remains warm even near equator.

he thermocline is shallow (E Pacific), upwelling easily

Current (SH)

Current (NH)

CF

CF

Wind stress

Wind stress

A co

Norm• Wa

surPac

• StrPac

• EaswaPac

• Southeupw

• La and equatorialcoo

TAO WWW site

El Nino / Southern Oscillation (ENSO)

upled tropical atmosphere-ocean phenomenon

al conditionsrmest water, low surface pres-e and persistent T-storms in Wific

ong subtropical highs in Eificterly winds and cool upwelled

ter along the equator in Eifictherly prevailing winds off

Peruvian coast produce coldelling, good fishing.

Nina is an intensification of the east winds, upwellingling.

nt’:

• Cenwa

• Stomo(the

• Traerly

• OffandNinand

• The fluences theent

TAO WWW site

Every few years- an ‘El Nino’ or ‘warm eve

tral equatorial Pacific oceanrmsrms and low surface pressureve to central and east Pacific Southern Oscillation).de winds and coastal south- winds weaken Peru, upwelling diminishes ocean surface warms (an Elo event), leading to fish dieoff ocean warming. changed tropical Pacific wind and pressure patterns in

ire tropics and much of the midlatitudes.

O cific, off Peru.

The mega-El Nino of 1997-1998

cean 3-5°C warmer than normal along equator in E Pa

Unisys WWW site

• Oc cific.

The La Nina of 1998-1999

ean 2°C colder than normal along equator in central Pa

ina

ino

sure)

lling andg La Nina,e strong along

ENSO over the last 20 years

La N

El N

Nino 3 SST anomaly (2S-2N, 90-150 W)

Southern Oscillation (Tahiti-Darwin pres

During El Nino, Tahiti to Darwin PGF is weak, kieast winds and upwelling along the equator. DurinT-D PGF is strong, so east winds and upwelling arthe equator, promoting cold SST.

k

ds

The ENSO Ocean-Atmosphere Feedbac

ocean temperature pattern

surface pressure pattern, storms, win

ocean currents and upwelling pattern

With e equatorialPacifi tmosphere Ocean)buoy atellite and othermeas rable skill up to ayear

monitoring of the temperature in the upper ocean in thc and the atmosphere using NOAA’s TAO (Tropical A

array, currently run out of PMEL here in Seattle, and surements, we can now forecast an El Nino with considein advance.