ceans
Lecture 13. Global Wind Patterns and the OEOM
• 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.