Title

On the processes that control sea surface temperature variability in the eastern tropical Pacific

Date of Award

2003

Availability

Article

Degree Name

Doctor of Philosophy (Ph.D.)

First Committee Member

Donald B. Olson, Committee Chair

Second Committee Member

David B. Enfield, Committee Member

Abstract

This study analyzes the processes that control sea surface temperature (SST) variability in the eastern tropical Pacific (ETP), from 10°N through 20°S, and from 120°W to the South American coast. The atmospheric and oceanic fields that play an important role in the oceanic heat balance of the upper layer (30m) are analyzed. The long-term mean and seasonal variability of the wind and thermal fields, and the near-surface circulation have been described for the ETP. A comparison between four wind products shows that the FSU subjectively analyzed pseudo-stress wind is the most suitable product for diagnosing the ocean behavior in the ETP for the 1979--1993 period.The analysis of the heat balance in the upper layer (30m) of the ETP shows that the relative importance of the terms in the heat balance equation has a meridional dependence. Three different regimes have been identified: the north equatorial countercurrent-Intertropical convergence zone (NECC-ITCZ) regime (4°--10°N), the cold tongue-south equatorial current (SEC) one (2°N--4°S), and the slow westward drift (10°--20°S). The processes responsible for the balance in each of the analyzed regimes are shown to be different. Within the NECC-ITCZ area the oceanic term that primarily offsets the warming by the surface heat flux is the vertical diffusive heat flux divergence. The annual average of the horizontal plus vertical diffusive flux is similar to that of the entire Northeastern Pacific warm pool, about -40Wm -2, as estimated by others. In the cold tongue-SEC area the permanent maximum in surface warming by the surface heat flux is balanced primarily by advective cooling (71%) within the upper layer, and secondarily by vertical diffusive cooling (22%), the main contributor to the advective fluxes being the vertical component (upwelling). Lateral diffusion is not an important contributing term because it is very small (5--10Wm -2) due to the reduced horizontal temperature gradients within the 30-m slab (4--8 times smaller than SST gradients derived from a finer grid). South of 10°S the oceanic terms are small and the balance is primarily between the heat storage rate and the surface heat flux all-year round. The large seasonal cycle of SST off Chile and Peru is therefore a direct response to the very large annual variation of solar heating due to the highly seasonal stratocumulus cloud regime.The annual average of the residuals in the heat balance equation is slightly negative, between -5 and -10Wm-2 whereas a nil result is expected by construction. The residual analysis shows that the offset can be easily accounted for by uncertainties in the bulk formulas used to derive the terms in surface heat fluxes, errors due to poor data coverage, and/or underestimation of the cooling by advection or diffusion.

Keywords

Physical Oceanography

Link to Full Text

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