Lyman et al. (2004) Abstract

Structure of 17-day versus 33-day Tropical Instability Waves in the equatorial Pacific

Lyman, J.M., G.C. Johnson and W.S. Kessler, 2004.

Journal of Physical Oceanography, 37(4), 855-872.
Tropical instability waves (TIWs) within a half-degree of the equator in the Pacific Ocean have been consistently observed in meridional velocity with periods of around 20 days. On the other hand, near 5°N, TIWs have been observed in sea surface height (SSH), thermocline depth, and velocity to have periods near 30 days. Tropical AtmosphereŠOcean (TAO) Project moored equatorial velocity and temperature time series are used to investigate the spatial and temporal structure of TIWs during 3 years of La Ni–a conditions from 1998 through 2001. Along 140°W, where the TIW temperature and velocity variabilities are at their maxima, these variabilities include two distinct TIWs with periods of 17 and 33 days, rather than one broadbanded process. As predicted by modeling studies, the 17-day TIW variability is shown to occur not only in meridional velocity at the equator, but also in subsurface temperature at 2°N and 2°S, while the 33-day TIW variability is observed primarily in subsurface temperature at 5°N. These two TIWs, respectively, are shown to have characteristics similar to a Yanai wave/surface-trapped instability and an unstable first meridional mode Rossby wave. One implication of such a description is that the velocity variability on the equator is not directly associated with the dominant 33-day variability along 5°N.

Download the paper as it appeared in JPO: (3Mb pdf file)

horizontal black line
NOAA logo Dr. William S. Kessler
7600 Sand Point Way NE
Seattle WA 98115 USA
Tel:   206-526-6221
Fax:  206-526-6744
See also:    Kessler home page        Kessler publications         PMEL home page