Vertically propagating equatorial waves obey the
dispersion relation c = N/m, where c is the phase
speed, N is the buoyancy frequency and m is the vertical
wavenumber (Gill, 1982). The mean density stratification
was calculated from the Argo temperature and
salinity data and gave N 0.017 s−1 in the thermocline.
Using the observed phase speed of c = 2.5 m s−1,
the theoretical vertical wavenumber is m = 7×10−3 m−1
and the corresponding vertical wavelength is 2/m =
900 m, consistent with the estimated observed vertical
wavelength of 800 m. However, the stratification weakens
considerably with depth to around N 4×10−3 s−1
at a depth of 500 m, with a correspondingly much larger
vertical wavelength of approximately 4000 m. Hence,
the vertical wavelength would be expected to increase
with depth, with the consequence that phase lines would
tilt back towards the vertical. This is consistent with
the structures described above.
Vertically propagating equatorial waves obey thedispersion relation c = N/m, where c is the phasespeed, N is the buoyancy frequency and m is the verticalwavenumber (Gill, 1982). The mean density stratificationwas calculated from the Argo temperature andsalinity data and gave N 0.017 s−1 in the thermocline.Using the observed phase speed of c = 2.5 m s−1,the theoretical vertical wavenumber is m = 7×10−3 m−1and the corresponding vertical wavelength is 2/m =900 m, consistent with the estimated observed verticalwavelength of 800 m. However, the stratification weakensconsiderably with depth to around N 4×10−3 s−1at a depth of 500 m, with a correspondingly much largervertical wavelength of approximately 4000 m. Hence,the vertical wavelength would be expected to increasewith depth, with the consequence that phase lines wouldtilt back towards the vertical. This is consistent withthe structures described above.
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