Long Waves in Ocean Circulation

• Wave response of ocean to transient

conditions such as changes in wind forcing

• Two dominant wave types

– Rossby waves - westward propagating

– Kelvin waves - travel along boundaries

• Space scales of 100’s km & time scales of

a few months to a few years

More Long Waves

• How ocean “communicates” within a

basin

• Kelvin wave pulse is the precursor of an

ENSO event

• Hard to detect from direct field obs due

to the scales involved

• Satellite altimetry though is useful

More Long Waves

• Can be barotropic or baroclinic in nature

Barotropic waves propagate fast (many m/s)

Baroclinic waves are slower (several cm/s)

Kelvin Waves

• Needs boundary or “wave guide” to pile

against

– Coastal boundary

– The equator or “double” Kelvin wave

• Can be wave of depression or elevation

• How ENSO pulse is transmitted in ocean

Kelvin Waves

Wave of

depression

Greatest onshore

Propagates CCW

in a NH basin (CW in SH)

Kelvin Waves

• Simple geostrophic balance (HPF =

CF)

• Propagates into the page

• Wave of depression would go in

same direction

Coastal Kelvin Waves

Coastal Kelvin Waves

Coastal Kelvin Waves

Coastal Kelvin Waves

Coastal Kelvin Waves

Coastal Kelvin Waves

c ~ 200 km/d

Equatorial Kelvin Waves

• Simple geostrophic balance (HPF =

CF)

• Two Kelvin waves “rest” against each

other on equator - double Kelvin

waves

• Propagates to the east

Equatorial Kelvin Waves

Equatorial Kelvin Waves

Equatorial Kelvin Waves

• Satellite altimetry from

TOPEX/Poseidon

• Scenes are 10 days apart

Kelvin Waves

• NH CCW propagation

• SH CW propagation

• Way of building time

cycles into ocean

(climate oscillators)

Equatorial Kelvin Waves

TOGA-TAO Array

• Equatorial array of buoys

• U.S., Japan & French partnership

• http://www.pmel.noaa.gov/tao/

Moorings

• Measure met &

ocean properties

• Thermocline focus

• Real-time data

transmission

• Used in weather &

climate forecasts

TAO Moorings

Yesterday…

Propagates 13,000 km in 4 months - 1.3 m/s

Kelvin Waves

• Needs boundary or “wave guide” to pile

against

– Coastal boundary

– Equatorial boundary or “double” Kelvin

wave

• Can be wave of depression or elevation

• Baroclinic waves travel at 1-2 m/s

Rossby Waves

• Propagate zonally from east to west

• Results from conservation of potential

vorticity, PV = ( + f)/D

• Propagation speeds are slow (< 5 cm/s)

poleward of 30o

• Wave speeds increase dramatically

towards equator

Rossby Waves

Rossby Waves

RossbyWaves

Rossby Waves

movie

Rossby Waves

Rossby Waves

Rossby Waves

• Propagate zonally from east to west

• Results from PV conservation

• Propagation speeds are slow (< 5

cm/s) poleward of 30o

• Wave speeds increase dramatically

towards equator

Interactions Among Rossby & Kelvin

Waves

• Kelvin waves can excite Rossby

waves

• Occurs in equatorial & coastal wave

guides

• Important for progression of El Nino

events

Equatorial Kelvin & Rossby Waves

El Niño Conditions

Interactions Among Rossby & Kelvin

Waves

• Kelvin waves can excite Rossby

waves

• Occurs in equatorial & coastal wave

guides

• Important for progression of El Nino

events