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Abstract

In-situ near-bottom current measurements, which were collected at a depth of ~5,000 m in the northeastern Pacific (10.5°N, 131.3°W) during 2004–2013, revealed a spectral peak at 25–40 days and showed increased amplitude during La Niña periods. Tropical instability waves (TIWs), which are located at the boundary between the Pacific warm pool and the cold tongue in the equatorial eastern Pacific, exhibit temporal variations similar to those observed by the near-bottom current sensor. Coherence map at 25–40-day periods between gridded satellite-measured sea surface height (SSH) which includes the variation of TIWs, and the near-bottom velocity components exhibits significant values in a wide region of eastern Pacific except along the latitude 10°N, where the coherence phase changes abruptly. It is known that the discontinuity results from a coherent superposition of TIWs with barotropic Rossby waves induced by TIW (BTRW_TIW). We also used 25–40-day bandpass filtered barotropic velocity results from data-assimilated ocean model called GLORYS12V1, which agree well with the filtered in-situ near-bottom currents. The filtered simulated barotropic velocity results showed that they reasonably satisfied the theoretical dispersion relation of BTRW_TIW and exhibited the inter-annual variations which are related to El Niño-southern oscillation (ENSO). We reconfirmed BTRW_TIW propagating northward above 10°N in the northeastern Pacific by in-situ observations firstly with a maximum velocity of approximately 3 cm/s.