The vertical coherence of the temperature anomalies
from the thermocline downwards (Fig. 15) suggests that
the equatorial Kelvin wave extends downward into the
deep ocean. The 950-dbar anomalies (Fig. 10b) leading
those on the thermocline (Fig. 10a) is reflected by
the vertical tilt (eastward with increasing depth) of the
anomalies in the longitude–depth section This is particularly
apparent in the central and eastern Pacific
during phases 2 and 4–8 (Fig. 15). The vertical wavelength
is estimated to be of the order of 800 m. This
tilt is equivalent to a vertical tilt in the phase lines of
the wave. The sense of the tilt is one of eastward and
upward phase propagation. For an equatorial Kelvin
wave, this implies eastward and downward group velocity
and energy propagation (Gill 1982; Kessler and
McCreary 1993). This is consistent with the forcing of
the Kelvin wave from the surface, by the MJO wind
stress anomalies. However, there does not appear to
be uniform downward propagation. Below about 800 m
depth, the anomaly contours (phase lines of the wave)
tend to become more vertical (e.g., in MJO phase 6 at
120◦W; Fig. 15f).