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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.
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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
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 • 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)
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
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 = (z + f)/D • Propagation speeds are slow (< 5 cm/s) poleward of 30o • Wave speeds increase dramatically towards equator
Rossby Waves movie
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
Interactions Among Rossby & Kelvin Waves • Kelvin waves can excite Rossby waves • Occurs in equatorial & coastal wave guides • Important for progression of El Nino events