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
satellite-measured sea surface height in a wide region of EEP with
maxima approximately 5°N. Simulated deep currents from a
data-assimilated 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.