Barotropic Rossby Waves Radiating from Tropical Instability Waves in the Pacific Ocean

Abstract

Tropical instability waves are triggered by instabilities of the equatorial current systems, and their sea level signal, with peak amplitude near 58N, is one of the most prominent features of the dynamic topography of the tropics. Cross-spectral analysis of satellite altimetry observations shows that there is sea level variability in the Pacific Ocean as far north as Hawaii (i.e., 208N) that is coherent with the sea level variability near 58N associated with tropical instability waves. Within the uncertainty of the analysis, this off-equatorial variability obeys the dispersion relation for nondivergent, barotropic Rossby waves over a fairly broad range of periods (26-38 days) and zonal wavelengths (98-238 of longitude) that are associated with tropical instability waves. The dispersion relation and observed wave properties further suggest that the waves are carrying energy away from the instabilities toward the North Pacific subtropical gyre, which, together with the observed coherence of the sea level signal of the barotropic waves with that of the tropical instability waves, suggests that the barotropic Rossby waves are being radiated from the tropical instability waves. The poleward transport of kinetic energy and westward momentum by these barotropic Rossby waves may influence the circulation in the subtropics.

Spectral signatures of the tropical Pacific dynamics from model and altimetry: a focus on the meso-/submesoscale range

“…In accordance with observations (Willet et al, 2006;Lee et al, 2018), the modeled TIWs are defined by periods and zonal wavelengths in the range of 15-40 days and 800-2000 km, respectively. They have a meridional propagation with northward and southward motions roughly balanced, which is a hallmark of standing meridional modes for TIWs as seen in Lyman et al (2005) and Farrar (2008Farrar ( , 2011 and earlier work (Fig. 4d).…”

Evidence for the Maintenance of Slowly Varying Equatorial Currents by Intraseasonal Variability

“…The simplest example is a barotropic wave for which the horizontal velocity components are vertically uniform. Such waves are known to exist in the equatorial ocean and to be excited by tropical instability waves near the surface (Farrar, ). Such a wave, having a large meridional scale, will interact with and be advected by the deep jets that have a smaller meridional scale.…”

Observation of first and second baroclinic mode Yanai waves in the ocean

“…Although the period of oceanic Yanai wave is longer (about 10-20 days), the observational evidence of its eastward group-velocity has not been reported because until recently the spatial and temporal resolutions of satellite and in situ data were insufficient to explicitly describe the propagation of the wave packet. This situation has begun to change because of the multiple satellite launches in recent years, and the most recent satellite altimetry products are shown to be able to well resolve the signal of oceanic equatorially trapped waves including Yanai waves and to describe their observed dispersion relations (Wakata, 2007;Farrar, 2008Farrar, , 2011Shinoda et al, 2009;Shinoda, 2010).…”