Title: The evolution of the equatorial Pacific zonal SST gradient during the twentieth century 1 2 Authors: 3 (original) (raw)
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Journal of Climate, 2009
Decadal variations of very small amplitude [∼0.3°C in sea surface temperature (SST)] in the tropical Pacific Ocean, the genesis region of the interannual El Niño–Southern Oscillation (ENSO) phenomenon, have been shown to have powerful impacts on global climate. Future projections from different climate models do not agree on how this critical feature will change under the influence of anthropogenic forcing. A number of attempts have been made to resolve this issue by examining observed trends from the 1880s to the present, a period of rising atmospheric concentrations of greenhouse gases. A recent attempt concluded that the three major datasets disagreed on the trend in the equatorial gradient of SST. Using a corrected version of one of these datasets, and extending the analysis to the seasonal cycle, it is shown here that all agree that the equatorial Pacific zonal SST gradient has strengthened from 1880 to 2005 during the boreal fall when this gradient is normally strongest. This ...
npj Climate and Atmospheric Science
Changes in the zonal gradients of sea surface temperature (SST) across the equatorial Pacific have major consequences for global climate. Therefore, accurate future projections of these tropical Pacific gradients are of paramount importance for climate mitigation and adaptation. Yet there is evidence of a dichotomy between observed historical gradient trends and those simulated by climate models. Observational records appear to show a “La Niña-like” strengthening of the zonal SST gradient over the past century, whereas most climate model simulations project “El Niño-like” changes toward a weaker gradient. Here, studies of these equatorial Pacific climate trends are reviewed, focusing first on data analyses and climate model simulations, then on theories that favor either enhanced or weakened zonal SST gradients, and then on notable consequences of the SST gradient trends. We conclude that the present divergence between the historical model simulations and the observed trends likely ...
Climate Response of the Equatorial Pacific to Global Warming
Journal of Climate, 2009
of a thesis at the University of Miami. Thesis supervised by Professor Amy C. Clement. No. of pages in text ( 56 ). The climate response of the equatorial Pacific to increased greenhouse gases is investigated using numerical experiments from five climate models participating in the Intergovernmental Panel on Climate Change Fourth Assessment Report. Changes in the heat budget of the surface layer in response to CO 2 doubling (2xCO2) are analyzed in experiments with full-coupled ocean dynamics; and compared to experiments with uncoupled ocean dynamics. In full-coupled experiments, weaker ocean zonal currents driven by a slowing down of the Walker circulation reduce the ocean heat flux divergence throughout the equatorial Pacific. The resulting ocean dynamical heating enhances the surface warming due to increased clear-sky surface radiation in response to
Surface Heat Balance in the Equatorial Pacific Ocean: Climatology and the Warming Event of 1994–95
Journal of Climate, 2001
The surface heat budget in the equatorial Pacific Ocean was investigated through ocean model simulations, both the climatological cycle and the case of the 1994-95 warm event. The dominant processes governing the seasonal cycle of sea surface temperature (SST) vary significantly across the basin. In the western Pacific the annual cycle of SST is primarily in response to net surface heat flux. In the central basin the magnitude of the zonal advection term is comparable to that of the net surface heat flux. In the eastern basin the role of zonal advection is reduced and the vertical mixing and advection are more important. The model estimate of the vertical mixing contribution to the mixed layer heat budget compared well with estimates obtained by analysis of observations using the same diagnostic vertical mixing scheme. During 1994-95 the largest positive SST anomaly was observed in the midbasin and was related initially to reduced latent heat flux due to weak surface winds and later to anomalous zonal advection. In the eastern Pacific where winds were not significantly anomalous throughout 1994-95, only a moderate warm surface anomaly was detected. This is in contrast to strong El Niño events where the SST anomaly is largest in the eastern basin. Overall, the balances inferred from the model forced by Special Sensor Microwave/Imager winds are consistent with the balances derived using tropical atmosphere-ocean moorings data and Reynolds SST.
Geophysical Research Letters, 2006
We present the new alkenone-based sea-surface temperature (SST) records from the eastern equatorial Pacific over the past 150 kyr. Core HY04 (4ºN) at the North Equatorial Countercurrent (NECC) registered the invariant SSTs (25.8-27.2 ºC), whereas core HY06 (0ºN) registered cyclic glacial-interglacial SST variations (22.4-26.1 ºC). Although HY06 alkenone-based SST evolution was almost consistent with the previously published SST records from around the equator, at site HY04 alkenone-and foraminiferal Mg/Ca-based SSTs showed a large difference in the magnitude of LGM SST cooling. We hypothesize that alkenone-based SSTs might not fully express the true magnitude of glacial SST cooling in the NECC, as suggested by the coincidence of higher glacial productivity and unchanged glacial SSTs at site HY04. However, further SST data in the NECC are needed before this can be accepted with any degree of confidence.
Persistent Discrepancies between Observed and Modeled Trends in the Tropical Pacific Ocean
Journal of Climate
The trends over recent decades in tropical Pacific sea surface and upper ocean temperature are examined in observations-based products, an ocean reanalysis and the latest models from the Coupled Model Intercomparison Project phase six and the Multimodel Large Ensembles Archive. Comparison is made using three metrics of sea surface temperature (SST) trend—the east–west and north–south SST gradients and a pattern correlation for the equatorial region—as well as change in thermocline depth. It is shown that the latest generation of models persist in not reproducing the observations-based SST trends as a response to radiative forcing and that the latter are at the far edge or beyond the range of modeled internal variability. The observed combination of thermocline shoaling and lack of warming in the equatorial cold tongue upwelling region is similarly at the extreme limit of modeled behavior. The persistence over the last century and a half of the observed trend toward an enhanced east–...