Long Waves in Ocean Circulation

1. 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

2. 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

3. More Long Waves • Can be barotropic or baroclinic in nature Barotropic waves propagate fast (many m/s) Baroclinic waves are slower (several cm/s)

4. 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

5. Kelvin Waves Wave of depression Greatest onshore Propagates CCW in a NH basin (CW in SH)

6. Kelvin Waves • Simple geostrophic balance (HPF = CF) • Propagates into the page • Wave of depression would go in same direction

7. Coastal Kelvin Waves

8. Coastal Kelvin Waves

9. Coastal Kelvin Waves

10. Coastal Kelvin Waves

11. Coastal Kelvin Waves

12. Equatorial Kelvin Waves • Simple geostrophic balance (HPF = CF) • Two Kelvin waves “rest” against each other on equator - double Kelvin waves • Propagates to the east

13. Equatorial Kelvin Waves

14. Equatorial Kelvin Waves

15. Equatorial Kelvin Waves • Satellite altimetry from TOPEX/Poseidon • Scenes are 10 days apart

16. Kelvin Waves • NH CCW propagation • SH CW propagation • Way of building time cycles into ocean (climate oscillators)

17. Equatorial Kelvin Waves

18. TOGA-TAO Array • Equatorial array of buoys • U.S., Japan & French partnership • http://www.pmel.noaa.gov/tao/

19. Moorings • Measure met & ocean properties • Thermocline focus • Real-time data transmission • Used in weather & climate forecasts

20. TAO Moorings

21. Yesterday…

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

23. 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

24. 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

25. Rossby Waves

26. Rossby Waves

27. RossbyWaves

28. Rossby Waves movie

29. Rossby Waves

30. Rossby Waves

31. 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

32. Interactions Among Rossby & Kelvin Waves • Kelvin waves can excite Rossby waves • Occurs in equatorial & coastal wave guides • Important for progression of El Nino events

33. Equatorial Kelvin & Rossby Waves

34. El Niño Conditions

36. Interactions Among Rossby & Kelvin Waves • Kelvin waves can excite Rossby waves • Occurs in equatorial & coastal wave guides • Important for progression of El Nino events