Reflection of annual Rossby waves at the maritime western boundary of the tropical Pacific

Abstract

In this study the examination of altimetric sea level time series from the first 17 months of the Geosat Geodetic Mission provides the first evidence of the Rossby wave reflection process operating at the maritime western boundary of the tropical Pacific in both the northern and southern hemispheres. In an earlier study, Tai et al. (1989) analyzed altimetric sea level time series derived from crossover differences during the first 17 months of the Geosat Geodetic Mission from April 1985 to September 1986, finding statistically significant agreement with in situ measurements of sea level differences (i.e., island sea level and relative dynamic height), In the present study, two‐dimensional spectral analysis verified the existence of both off‐equatorial baroclinic Rossby wave activity and equatorial baroclinic Kelvin wave activity in the altimetric sea level data set, establishing also that the annual cycle dominated the variability over this 17‐month period. Next, extended empirical orthogonal function analysis (Graham et al., 1987) determined the evolutionary behavior of the readjustment process that occurred in the sea surface topography on the annual cycle over this 17‐month period. Both the Philippines archipelago in the northern hemisphere and the Solomon archipelago‐Bismarck archipelago‐New Guinea complex in the southern hemisphere were found to reflect incident baroclinic Rossby wave activity of 1‐year period, particularly manifested in the October–April transition, generating equatorial Kelvin wave activity that conducted the annual signal along the equatorial waveguide into the eastern equatorial Pacific. At the eastern boundary of South America, reflection of the incident equatorial Kelvin wave activity was associated with coastal Kelvin wave activity and equatorial‐trapped Rossby wave activity in the equatorial waveguide, the latter propagating back to the west. However, the equatorial‐trapped Rossby wave activity thus generated was not observed to propagate westward past the Galapagos archipelago, a result determined theoretically by Yoon (1981).