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Tomoki Tozuka, Motoki Nagura, and Toshio Yamagata

Abstract

The sea surface temperature (SST) in the western Arabian Sea upwelling region is known to influence the amount of precipitation associated with the Indian summer monsoon. Thus, understanding what determines the SST in this region is an important issue. Using outputs from an ocean general circulation model with and without strong damping in the eastern equatorial Indian Ocean, this study examines how the reflection of semiannual Kelvin waves at the eastern boundary of the Indian Ocean may influence the western Arabian Sea upwelling region. The downwelling Kelvin waves generated in boreal spring are reflected at the eastern boundary and reach the western equatorial Indian Ocean as reflected Rossby waves about 6 months later. The resulting westward current along the equator in the western equatorial Indian Ocean transports warmer water to the western Arabian Sea upwelling region. Thus, the SST in this region becomes colder especially in boreal fall without the reflected Rossby waves. These results are further supported by the analysis of the mixed layer temperature balance. Surprisingly, vertical processes do not contribute to the SST difference, even though the thermocline becomes shallower without the downwelling Rossby waves. This is because the mixed layer is shoaling rapidly from September to November, and there is basically no entrainment of water from below. In contrast, the reflected Rossby waves do not have large impacts on the SST in other seasons mainly because the zonal SST gradient is not as strong and/or the amplitude of Rossby waves is weaker.

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Rui Xin Huang and Qi Wang

1. Introduction Many studies on climate change have been focused on the link between the subtropics and Tropics. This link was first identified through tracer studies in 1970 and 1980. Fine and her colleagues have analyzed the tritium data and found a local tritium maximum around 140°W along the equator, which they rightly attributed to the ventilation of the subtropical water via subduction (e.g., Fine et al. 1987 ; McPhaden and Fine 1988 ). This link has been discussed in many recent

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Alexey Fedorov, Marcelo Barreiro, Giulio Boccaletti, Ronald Pacanowski, and S. George Philander

permanently warm conditions with absent zonal SST gradient along the equator (“permanent El Niño” in the case of the Pacific; e.g., Fedorov et al. 2006 ) prevail in the Tropics. What is the connection between the wind-driven and thermohaline components of the oceanic circulation? Although some studies of the THC give the impression that the Gulf Stream is exclusively one of its features, this current will be absent should the wind stop blowing (to the extent that its volume transport is proportional to

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A. J. G. Nurser, Robert Marsh, and Richard G. Williams

α E = − ρ −1 dρ / dT = 2.5 × 10 −4 K −1 , a density influx of 10 −6 kg s −1 m −2 is equivalent to a heat outflux of ∼17 W m −2 . As expected, there is a net gain of density generally north of a zero line running from 10°N, 60°W to 45°N, 10°W and a loss south of it. This surface flux is the sum of the climatological fluxes and the relaxation (29) . In comparison, the climatological density flux shown in Fig. 9b shows a greater density loss in the Tropics and has a zero line that lies

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James A. Carton, Gennady Chepurin, Xianhe Cao, and Benjamin Giese

moored currents. In summary, these comparisons show that the analysis explains 25%–35% of the observed tide-gauge sea level variance at longer than annual frequencies. The root-mean-square difference of observed minus analysis sea level in the Tropics (15°S–15°N) lies in the range of 3.1–4.0 cm, increasing somewhat in midlatitudes. A second study ( Chepurin and Carton 1999 ) compares the control analysis temperature with that of six other basin- to global-scale analyses ( White 1995 ; Levitus et al

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Scott C. Doney, Steve Yeager, Gokhan Danabasoglu, William G. Large, and James C. McWilliams

signal from the model arises because of dynamic adjustments to surface wind forcing and resulting advective redistribution of upper-ocean heat and salt content, consistent with previous findings (e.g., Stammer 1997 ; Fu 2003 ). The hindcast simulation reproduces well the dominant space/time patterns of SSH variability seen in the T/P data, particularly in the Tropics. The agreement of principal component time series is quite encouraging, with temporal model–data correlations of 0.99 and 0.98 for

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Sydney Levitus

. The Indian Ocean exhibits a largeannual cycle in meridional Ekman volume flux. Ekman upwelling in the tropics of the Atlantic and Pacificoccurs from June through November. The maximum upward vertical Ekman volume flux slightly exceeds 2.5sverdrup in the Pacific and 1.0 sverdrup in the Atlantic and occurs centered around 10-N in each ocean.1. Introduction We have used monthly climatological estimates ofwind stress over the world ocean prepared by Hellerman and Rosenstein (1983) to compute Ekman

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Jian Zhao and William Johns

. Figure 2 shows the distribution of the AMOC anomaly with respect to latitude and month. The most significant seasonal variability takes place in the tropical Atlantic region with 11-Sverdrup (Sv; 1 Sv ≡ 10 6 m 3 s −1 ) peak-to-peak amplitude and a maximum (minimum) in boreal winter (fall). Outside of the tropics, the amplitudes are much weaker (4–6 Sv), and the phases are also different from that in the tropical ocean. While the Northern Hemisphere subtropics have a broad maximum in boreal summer

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Abraham H. Oort and Thomas H. Vonder Haar

tabular form. As was known before, the storage of heat in the oceansis found to dominate the energy storage in the combined atmosphere-ocean-land-cryosphere system. Inthe tropics, large changes in oceanic heat storage are found in the 10-N-20-N belt with a maximum in springand a minimum in late summer. The main new finding of this study is that the inferred oceanic heat transports appear to undergo very large seasonal variations especially in the tropics. Between 10-N and 20-N,maximum northward

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Gerald A. Meehl

subtropical convergence zones which move closest to the equator during the respective winters in eachhemisphere. Net annual v-component surface flow at the equator is northward. Zonally averaged u-component currents have greatest seasonal variance in the tropics with strongest westward currents in the winterhemisphere. An ensemble of ocean currents measured by buoys and current meters compares favorably withOCDS data in spite of widely varying time and space scales. The OCDS currents and directly

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