A new observational evidence of generation and propagation of barotropic Rossby waves induced by tropical instability waves in the Northeastern Pacific

Abstract

Tropical instability waves (TIWs) in the equatorial eastern Pacific (EEP) exhibit 25-40-day westward-propagating fluctuations with seasonal and inter-annual variations, which are stronger during July-December and La Niña periods. They likely transfer their energy northward by forming barotropic Rossby waves (BTRWs). Long-term near-bottom current measurements at 10.5°N and 131.3°W during 2004-2013 revealed a spectral peak at 25-40 days, where significant coherences were found with satellitemeasured sea surface height in a wide region of EEP with maxima approximately 5°N. Simulated deep currents from a dataassimilated ocean model concur with the observed near-bottom currents, and both currents vary seasonally and interannually, consistent with the typical characteristics of TIW. Further analyses using 25-40-day bandpass-filtered barotropic velocity data from the model revealed that they reasonably satisfied the theoretical dispersion relation of TIW-induced BTRW (BTRWTIW). We reconfirmed BTRWTIW propagating northward above 10°N in the northeastern Pacific by in-situ observations.