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

12. c ~ 200 km/d

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

14. Equatorial Kelvin Waves

16. Satellite altimetry from TOPEX/Poseidon Scenes are 10 days apart

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

18. Equatorial Kelvin Waves

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

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

21. TAO Moorings

22. Yesterday…

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

24. 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

25. 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 30 o Wave speeds increase dramatically towards equator

26. Rossby Waves

29. movie

30. Rossby Waves

32. Propagate zonally from east to west Results from PV conservation Propagation speeds are slow (< 5 cm/s) poleward of 30 o Wave speeds increase dramatically towards equator

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

34. Equatorial Kelvin & Rossby Waves

35. El Niño Conditions

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