Like a stone skimming across the water creates ripples on the surface, perturbations in the oceans form waves that propagate. These waves may be small-scale ripples formed by the wind or large-scale planetary waves, which we call Kelvin or Rossby waves depending on their origin and direction. Planetary waves transport heat and energy across the oceans. We can detect them using satellite altimetry data because they cause small variations in sea level (of the order of ten centimeters). They can be clearly seen by mapping the oceans at regular intervals or in longitude-time diagrams, where the phenomenon is even more striking. Longitude-time diagrams show sea level variations over time along an east-west axis, at a given latitude. Ocean waves appear in these diagrams as a series of straight lines.

Websites on this subject:

• Waves the size of the ocean (Museums teaching planet Earth)