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On the Variability of Winds, Sea Surface Temperature, and Surface Layer Heat Content in the Western Equatorial Pacific

Michael J. McPhaden and Stanley P. Hayes

NOAA/Pacific Marine Environmental Laboratory, Seattle, Washington

Journal of Geophysical Research, 96, supplement, 3331-3342 (1991)
This paper is not subject to U.S. copyright. Published in 1991 by the American Geophysical Union.

1. Introduction

The western equatorial Pacific is characterized by mean sea surface temperatures that are among the warmest in the world ocean. This region is also characterized by vigorous air-sea interaction, because turbulent heat exchange between the ocean and the atmosphere is a highly nonlinear function of sea surface temperature (SST). In extreme cases, air-sea interactions in the western Pacific may lead to El Nio/Southern Oscillation (ENSO) events, which are coupled ocean-atmosphere phenomena occurring every 4-7 years [Rasmusson and Wallace, 1983]. ENSO has global climatic impacts, some of which can be traced to western Pacific SST anomalies of 1C [e.g., Nicholls, 1985; Palmer and Mansfield, 1984]. These impacts may be predictable months to years in advance, provided that the processes involved in SST change can be understood and reliably modeled.

While it is generally conceded that understanding SST variability is important for understanding and predicting ENSO, little is known quantitatively about the atmospheric and oceanic processes that control this variability. The purpose of this study therefore is to examine the relationship between wind forcing, SST, and surface layer heat content, using data from a near-equatorial moored array along 165E. The analysis is a continuation of that presented by McPhaden [1989] and focuses mainly on time scales of days to months. The period of study coincides with the 1986-1987 ENSO, during which pronounced interannual variations occurred throughout the tropical Pacific (Figure 1) (see also Kousky and Leetmaa [1989]; McPhaden et al., [1990]).

Fig. 1. (a) Average SST and (b) SST anomaly in the western tropical Pacific for December 1986 to October 1987, based on data from the National Meteorological Center [Reynolds, 1988]. Contour interval is 1C in Figure 1a, except that the 29.5C isotherm is shown as dashed curve. Contour interval in Figure 1b is 0.5C, with positive values shown as solid contours and negative values shown as dashed contours. Hatching in Figure 1b indicates regions of negative SST anomaly. The current meter mooring (solid square) and ATLAS moorings (solid diamonds) are also indicated.

The paper is outlined as follows. Section 2 briefly describes the data used in this study. This is followed in section 3 by discussion of the mechanisms that are potentially important in controlling SST and surface layer heat content. In section 4 we describe the spatial structure of temperature and wind variations observed from the moored array. Then in section 5 we discuss how these variations may be related to turbulent heat fluxes across the air-sea interface, vertical advection, and entrainment from the thermocline. Lateral advection in the surface layer is discussed in section 6. Major results and conclusions are summarized in section 7.


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