Wave propagation in the central equatorial Pacific Ocean

Kathleen Ann Donohue, University of Rhode Island


Wave variability in the central equatorial Pacific is investigated using a five-year data set of dynamic height near 160$\sp\circ$W between 9$\sp\circ$S and 10$\sp\circ$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$\sp\circ$N.^ A $2{1\over2}$-layer model of the tropical Pacific Ocean (109.125$\sp\circ$E-77.031$\sp\circ$W by 20$\sp\circ$S-20$\sp\circ$N with $0.703125\sp\circ \times .5\sp\circ$ resolution) is used to investigate the generation mechanism for the intraseasonal dynamic-height variability observed near 6$\sp\circ$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$\sp\circ$N dynamic height is most likely caused by shear between the South Equatorial Current and the North Equatorial Countercurrent. ^

Subject Area

Physical Oceanography

Recommended Citation

Kathleen Ann Donohue, "Wave propagation in the central equatorial Pacific Ocean" (1995). Dissertations and Master's Theses (Campus Access). Paper AAI9633482.