During the 2003–2006 study period, the Pacific basin
was mainly in a weak El Ni˜no state. This could potentially
have biased the results, as the characteristics
of the oceanic equatorial Kelvin waves can change as
El Ni˜no events progress (Roundy and Kiladis 2006).
Again, once a longer term Argo data set becomes available,
this can be investigated.