Regional Oceanography II OEAS 604

Lecture Outline

1) Pacific Ocean circulation2) Antarctic circulation 3) Climate cycles4) Atmosphere-ocean coupling Chapters 8,9 – KnaussChapter 10 – Talley et al.

• Quiz – Tuesday, 10 November– Geostrophic balance – Ekman dynamics and upwelling– Frictional boundary layers– Wind-driven gyres

Annual Mean Wind Field Westerlies – 30-60 latitudeTrade Winds – from eastIntertropical Convergence Zone (Doldrums)

East and west basins

Connection to Arctic andSouthern Ocean

Arctic connectionrestricted by the Aleutian Islands andBering Strait

Bottom WaterPathways

Different varieties along western and eastern sides of basin

Limited across basinexchange

No deep water formation in north Pacific

Pacific Ocean Current Structure

• Subtropical gyres in both hemispheres– Eastern and western boundary currents

• Subpolar gyre in northern hemisphere• Equatorial current system• Connection to Arctic • Connection to Southern Ocean

Western Boundary CurrentsKuroshio, East AustraliaCurrent

Eastern Boundary CurrentsCalifornia CurrentPeru/Chile Current

Equatorial Current SystemNorth Equatorial CurrentEquatorial Countercurrent South Equatorial Current

Subpolar GyreNorth Pacific CurrentAlaska Current/StreamOyashio

ME - Mindanao Eddy; HE- Halmahera Eddy

Equatorial Current StructureBanded structure

Undercurrentshallow

Upwelling

Temperature section along Equator in Pacific Ocean

Warm Pool

Thermocline slopes upward from west to east

Cold Tongue

SST – Eastern Pacific Ocean

Cold Tongue

Kuroshio – sheds eddies as moves across Pacific

Bering Sea – Current Pattern

Climate Change is associated with changes in the air temperature of the Earth

Temperature changes are caused by

• changes in heat input from the sun• exchange of heat between the ocean and

atmosphere (mostly) • changes in the motion of heat through the ocean

and atmosphere, and • changes in the radiation properties of the

atmosphere

These changes lead to various physical, chemical and biological changes throughout the earth

Milankovitch cycles

• Are variations in the orbit of the earth with times scales of 20,000 to 100,000 years

• Changes in the orbit eccentricity, tilt of earth’s rotation axis, and precession of earth’s orbit

• Affect the length of time for the various seasons

• Length of the year remains constant

• Affects the shortwave radiation to the earth

Ocean-Atmosphere Coupling

• Some variations are caused by internal feedbacks between the atmosphere and ocean or within the atmosphere

• Many of these variations are described by indexes of various kinds

• Best understood is the El Niño/Southern Oscillation (ENSO)

ENSO• Associated with changes in the equatorial Pacific • Originally defined as a change of pressure difference

between Darwin, Australia and Tahiti (southern oscillation index or SOI)

• Change in strength of south Pacific Trade winds (east to west winds)

• Winds cause water to move to the west leaving lower water off South America and higher water off South Asia

• Low water off South America allows upwelling to bring cool, nutrient rich water to the surface

• Reduced winds leaves warm water in the east, no nutrients upwelled, reduced productivity, and poor fish harvest (El Niño)

Walker Circulation

ENSO• Water temperature affects atmospheric convection

which changes the air mass distribution (and pressure)

• Warm ocean events are El Niño - associated with Christmas season off South America

• Cold ocean events (La Niña, anti-El Niño, el viejo)

• El Niño means cooler and wetter winters in the US SE• La Niña means dryer conditions in the US SE• Other influences around the world

ENSO index based on ocean temperature in the central Pacific Ocean

SOI Index Atmospheric Pressure Difference

https://www.ncdc.noaa.gov/teleconnections/enso/indicators/sea-temp-anom.php?begmonth=5&begday=1&begyear=2015&endmonth=8&endday=26&endyear=2015

Other Indexes• Annular Modes (Southern Annular mode, SAM)

o Changes in North-South pressure o increase/decrease in winds

• North Atlantic Oscillation (NAO)o Change in Azores-Iceland pressure differenceo Changes in N Atlantic wind strength and storm track

• Pacific Decadal Oscillation (PDO)o W Pacific cool SST, SE Pacific warm SSTo 20 to 30 year period

• all indexes are available at NOAA climate prediction center (www.cpc.ncep.noaa.gov)

Southern Annular Mode (SAM)Southern Ocean

Positive NAO - Eastern US wetter and stronger winter storms

Negative NAO - Eastern US has drier and colder air

Pacific Decadal Oscillation - PDO

Gille, J Climate (2008)

Temperature trends in Southern Ocean Top 1000 m

Levitus GRL, 2005. Global ocean heat content change 1955 to 2003, 0-3000 m

Sorkosz et al. (2012, J. Climate)

IPCC (2007)

Overturning in the Subpolar North Atlantic Program (OSNAP)

RAPID array at 26N – UK program for monitoring MOC

Next Class• Ocean Waves

– Chapters 10 and 11 , Knauss