Wave propagation in the central equatorial Pacific Ocean

Wave variability in the central equatorial Pacific is investigated using a five-year data set of dynamic height near 160{dollar}spcirc{dollar}W between 9{dollar}spcirc{dollar}S and 10{dollar}spcirc{dollar}N. Variability is divided into four period ranges: two intraseasonal bands (one with periods between 80 and 100 days, and the other between 30 and 50 days), interweekly (9 to 12 days) and intraweekly (periods less than 7 days). Wavenumber and frequency estimates computed within each of these bands fall near the dispersion curves for various linear equatorial waves: Kelvin waves in the 80-100 day intraseasonal band, Rossby waves in the 30-50 day intraseasonal band, Rossby-gravity waves in the interweekly band and first- and second-meridional-mode inertia-gravity waves in the intraweekly band. Frequency-domain empirical orthogonal functions reveal the meridional structure of the dynamic-height field associated with each wave. These structures resemble those of the identified linear wave categories in each case with one exception: the intraseasonal 30-50 day wave meridional structure does not resemble a Rossby wave, but is asymmetric about the equator with a strong peak at 6{dollar}spcirc{dollar}N.; A {dollar}2{lcub}1over2{rcub}{dollar}-layer model of the tropical Pacific Ocean (109.125{dollar}spcirc{dollar}E-77.031{dollar}spcirc{dollar}W by 20{dollar}spcirc{dollar}S-20{dollar}spcirc{dollar}N with {dollar}0.703125spcirc times .5spcirc{dollar} resolution) is used to investigate the generation mechanism for the intraseasonal dynamic-height variability observed near 6{dollar}spcirc{dollar}N. A simulation of equatorial circulation is produced by forcing the model with mean-monthly wind-stress climatology. Two westward-propagating waves appear in the upper layer in the central and eastern portion of the model basin. An off-equatorial wave with period of 36 days and wavelength of 1300 km has a meridional structure similar to that of the 30-50 day intraseasonal wave observed in the ocean: asymmetric with respect to the equator with larger amplitudes in the northern hemisphere. The second wave with period of 15 days and wavelength 1100 km appears similar to a Rossby-gravity wave. In the simulation and in the ocean, the variability seen in the 6{dollar}spcirc{dollar}N dynamic height is most likely caused by shear between the South Equatorial Current and the North Equatorial Countercurrent.