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Dynamics of seasonal and intraseasonal variability in the eastern equatorial Pacific

Michael J. McPhaden and Bruce A. Taft

NOAA/Pacific Marine Environmental Laboratory, Seattle, Washington

Journal of Physical Oceanography, 18(11), 1713-1732 (1988)
Not subject to U.S. copyright. Published in 1988 by the American Meteorological Society.

1. Introduction

The purpose of this paper is to examine the dynamics of seasonal and intraseasonal variability along the equator in the eastern Pacific using time series measurements of wind, current, and temperature from surface moored buoys. We use the term seasonal to include the semi-annual and annual cycles (i.e., periods of 6 to 12 months) and intraseasonal to include frequencies higher than 2 but lower than 12 cycles per year (cpy) (i.e., periods from 1 up to 6 months). The specific questions that we address are: 1) on what time scales is the near surface equatorial Pacific in equilibrium with the local wind stress? and 2) what is the importance of nonlinearity in the dynamics of equatorial current variability? The data were collected from surface moorings at 110, 124.5, and 140W on the equator from October 1983 to May 1986 as part of the TROPIC HEAT Program (Eriksen 1985) and the Equatorial Pacific Ocean Climate Studies (EPOCS) Program (Hayes et al. 1986). The advantages of these data are that 1) they are synoptic, 2) they are finely resolved in time to allow for filtering (rather than aliasing) of high frequency variability in monthly estimates, 3) they span a period of over two years to allow examination of seasonal variations, and 4) they provide direct measurements of currents so that local accelerations and nonlinear advective effects can be estimated.

The paper is organized as follows. Section 2 provides scientific background on the seasonal dynamics of the eastern equatorial Pacific. Section 3 discusses the mooring data and its processing. Section 4 presents time series plots of winds, currents, temperatures, and dynamic heights. Section 5 describes a diagnosis of the depth integrated zonal momentum (i.e., transport) equation. Section 6 is a summary and discussion of the results.

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