scholarly journals Origin and Pathway of Equatorial 13°C Water in the Pacific Identified by a Simulated Passive Tracer and Its Adjoint*

2009 ◽  
Vol 39 (8) ◽  
pp. 1836-1853 ◽  
Author(s):  
Tangdong Qu ◽  
Shan Gao ◽  
Ichiro Fukumori ◽  
Rana A. Fine ◽  
Eric J. Lindstrom
Keyword(s):  
General Circulation ◽  
Circulation Model ◽  
South Pacific ◽  
Equatorial Region ◽  
Equatorial Pacific ◽  
Western Boundary ◽  
Passive Tracer ◽  
The South ◽  
Mode Water ◽  
Eastern Equatorial Pacific

Abstract The origin and pathway of the thermostad water in the eastern equatorial Pacific Ocean, often referred to as the equatorial 13°C Water, are investigated using a simulated passive tracer and its adjoint, based on circulation estimates of a global general circulation model. Results demonstrate that the source region of the 13°C Water lies well outside the tropics. In the South Pacific, some 13°C Water is formed northeast of New Zealand, confirming an earlier hypothesis on the water’s origin. The South Pacific origin of the 13°C Water is also related to the formation of the Eastern Subtropical Mode Water (ESTMW) and the Sub-Antarctic Mode Water (SAMW). The portion of the ESTMW and SAMW that eventually enters the density range of the 13°C Water (25.8 < σθ < 26.6 kg m−3) does so largely by mixing. Water formed in the subtropics enters the equatorial region predominantly through the western boundary, while its interior transport is relatively small. The fresher North Pacific ESTMW and Central Mode Water (CMW) are also important sources of the 13°C Water. The ratio of the southern versus the northern origins of the water mass is about 2 to 1 and tends to increase with time elapsed from its origin. Of the total volume of initially tracer-tagged water in the eastern equatorial Pacific, approximately 47.5% originates from depths above σθ = 25.8 kg m−3 and 34.6% from depths below σθ = 26.6 kg m−3, indicative of a dramatic impact of mixing on the route of subtropical water to becoming the 13°C Water. Still only a small portion of the water formed in the subtropics reaches the equatorial region, because most of the water is trapped and recirculates in the subtropical gyre.

scholarly journals Subduction of South Pacific Tropical Water and Its Equatorward Pathways as Shown by a Simulated Passive Tracer*

2013 ◽  
Vol 43 (8) ◽  
pp. 1551-1565 ◽  
Author(s):  
Tangdong Qu ◽  
Shan Gao ◽  
Rana A. Fine
Keyword(s):  
South Pacific ◽  
Equatorial Region ◽  
Equatorial Pacific ◽  
Western Boundary ◽  
Passive Tracer ◽  
Tropical Water ◽  
South Pacific Ocean ◽  
Equal Importance ◽  
Equatorial Thermocline ◽  
South Pacific Tropical Water

Abstract This study investigates the subduction of South Pacific Tropical Water (SPTW) and its equatorward pathways using a simulated passive tracer of the consortium Estimating the Circulation & Climate of the Ocean (ECCO). The results show that approximately 5.8 Sv (1 Sv ≡ 106 m3 s−1) of the SPTW is formed in the subtropical South Pacific Ocean within the density range between 24.0 and 25.0 kg m−3, of which about 87% is due to vertical pumping and 13% is due to lateral induction, comparing reasonably well with estimates from climatological data. Once subducted, most SPTW spreads in the subtropical South Pacific. Because of the presence of mixing, some portion of the water is transformed, and its tracer-weighted density steadily increases from an initial value of 24.4 to nearly 25.0 kg m−3 after 13 years of integration. Approximately 42% of the water makes its way into the equatorial Pacific, either through the western boundary or interior pathway. The two equatorward pathways are essentially of equal importance. A large (~70%) portion of the SPTW entering the equatorial region resurfaces in the central equatorial Pacific. The potential impacts of the resurfacing SPTW on the equatorial thermocline and surface stratification are discussed.

scholarly journals Formation Mechanism for Isopycnal Temperature–Salinity Anomalies Propagating from the Eastern South Pacific to the Equatorial Region

2007 ◽  
Vol 20 (7) ◽  
pp. 1305-1315 ◽  
Author(s):  
Masami Nonaka ◽  
Hideharu Sasaki
Keyword(s):  
Formation Mechanism ◽  
General Circulation ◽  
Circulation Model ◽  
South Pacific ◽  
Ocean General Circulation Model ◽  
Equatorial Region ◽  
Sea Surface ◽  
Global Ocean ◽  
Decadal Time Scale ◽  
Isopycnal Surface

Abstract Equatorward propagation of temperature–salinity (or spiciness) anomalies on an isopycnal surface emanating from the eastern subtropical South Pacific and their formation mechanism are investigated based on a hindcast simulation with an eddy-resolving quasi-global ocean general circulation model. Because of density-compensating meridional distributions of temperature and salinity, the meridional density gradient is weak at the sea surface in the eastern subtropical South Pacific. With these mean fields, cool sea surface temperature anomalies (SSTAs) can make the outcrop line of an isopycnal surface migrate equatorward more than 5° and induce warm and salty anomalies on the isopycnal surface. Subducted warm, salty anomalies propagate to the equatorial region over approximately 5 yr and may influence equatorial isopycnal temperature–salinity anomalies. Although the associated effects are unclear, if these anomalies could further induce warm eastern equatorial SSTAs that are positively correlated with eastern South Pacific SSTAs, opposite sign temperature–salinity anomalies would be formed in the subtropical South Pacific, and a closed cycle having a decadal time scale might be induced.

scholarly journals Near-Annual SST Variability in the Equatorial Pacific in a Coupled General Circulation Model

2005 ◽  
Vol 18 (21) ◽  
pp. 4454-4473 ◽  
Author(s):  
Renguang Wu ◽  
Ben P. Kirtman
Keyword(s):  
General Circulation ◽  
Circulation Model ◽  
Equatorial Pacific ◽  
Near Surface ◽  
Boreal Spring ◽  
Eastern Equatorial Pacific ◽  
Zonal Advection ◽  
The Mean ◽  
Annual Mode ◽  
Sst Anomalies

Abstract Equatorial Pacific sea surface temperature (SST) anomalies in the Center for Ocean–Land–Atmosphere Studies (COLA) interactive ensemble coupled general circulation model show near-annual variability as well as biennial El Niño–Southern Oscillation (ENSO) variability. There are two types of near-annual modes: a westward propagating mode and a stationary mode. For the westward propagating near-annual mode, warm SST anomalies are generated in the eastern equatorial Pacific in boreal spring and propagate westward in boreal summer. Consistent westward propagation is seen in precipitation, surface wind, and ocean current. For the stationary near-annual mode, warm SST anomalies develop near the date line in boreal winter and decay locally in boreal spring. Westward propagation of warm SST anomalies also appears in the developing year of the biennial ENSO mode. However, warm SST anomalies for the westward propagating near-annual mode occur about two months earlier than those for the biennial ENSO mode and are quickly replaced by cold SST anomalies, whereas warm SST anomalies for the biennial ENSO mode only experience moderate weakening. Anomalous zonal advection contributes to the generation and westward propagation of warm SST anomalies for both the westward propagating near-annual mode and the biennial ENSO mode. However, the role of mean upwelling is markedly different. The mean upwelling term contributes to the generation of warm SST anomalies for the biennial ENSO mode, but is mainly a damping term for the westward propagating near-annual mode. The development of warm SST anomalies for the stationary near-annual mode is partially due to anomalous zonal advection and upwelling, similar to the amplification of warm SST anomalies in the equatorial central Pacific for the biennial ENSO mode. The mean upwelling term is negative in the eastern equatorial Pacific for the stationary near-annual mode, which is opposite to the ENSO mode. The development of cold SST anomalies in the aftermath of warm SST anomalies for the westward propagating near-annual mode is coupled to large easterly wind anomalies, which occur between the warm and cold SST anomalies. The easterly anomalies contribute to the cold SST anomalies through anomalous zonal, meridional, and vertical advection and surface evaporation. The cold SST anomalies, in turn, enhance the easterly anomalies through a Rossby-wave-type response. The above processes are most effective during boreal spring when the mean near-surface-layer ocean temperature gradient is the largest. It is suggested that the westward propagating near-annual mode is related to air–sea interaction processes that are limited to the near-surface layers.

scholarly journals Inter-annual tropical Pacific climate variability in an isotope-enabled CGCM: implications for interpreting coral stable oxygen isotope records of ENSO

2013 ◽  
Vol 9 (1) ◽  
pp. 741-773 ◽  
Author(s):  
T. Russon ◽  
A. W. Tudhope ◽  
G. C. Hegerl ◽  
M. Collins ◽  
J. Tindall
Keyword(s):  
Oxygen Isotope ◽  
General Circulation ◽  
Climate Models ◽  
Circulation Model ◽  
Equatorial Pacific ◽  
Stable Oxygen Isotope ◽  
Ocean Climate ◽  
Eastern Equatorial Pacific ◽  
Stable Oxygen ◽  
Pacific Climate Variability

Abstract. Water isotope-enabled coupled atmosphere/ocean climate models allow for exploration of the relative contributions to coral stable oxygen isotope (δ18Ocoral) variability arising from Sea Surface Temperature (SST) and the isotopic composition of seawater (δ18Osw). The unforced behaviour of the isotope-enabled HadCM3 Coupled General Circulation Model affirms that the extent to which inter-annual δ18Osw variability contributes to that in model δ18Ocoral is strongly spatially dependent, ranging from being negligible in the eastern equatorial Pacific to accounting for 50% of δ18Ocoral variance in parts of the western Pacific. In these latter cases, a significant component of the inter-annual δ18Osw variability is correlated to that in SST, meaning that local calibrations of the effective local δ18Ocoral–SST relationships are likely to be essential. Furthermore, the relationship between δ18Osw and SST in the central and western equatorial Pacific is non-linear, such that the interpretation of model δ18Ocoral in the context of a linear dependence on SST alone may lead to overestimation (by up to 20%) of the SST anomalies associated with large El-Niño events. Intra-model evaluation of a salinity-based pseudo-coral approach shows that such an approach captures the first-order features of the model δ18Osw behaviour. However, the utility of the pseudo-corals is limited by the extent of spatial variability seen within the modelled slopes of the temporal salinity–δ18Osw relationship.

Decadal Sea Level Variability in the South Pacific in a Global Eddy-Resolving Ocean Model Hindcast

2008 ◽  
Vol 38 (8) ◽  
pp. 1731-1747 ◽  
Author(s):  
Yoshi N. Sasaki ◽  
Shoshiro Minobe ◽  
Niklas Schneider ◽  
Takashi Kagimoto ◽  
Masami Nonaka ◽  
...  
Keyword(s):  
Sea Level Rise ◽  
Sea Level ◽  
General Circulation ◽  
Decadal Variability ◽  
Southern Oscillation ◽  
Circulation Model ◽  
South Pacific ◽  
The South ◽  
Sea Level Variability ◽  
The Impact

Abstract Sea level variability and related oceanic changes in the South Pacific from 1970 to 2003 are investigated using a hindcast simulation of an eddy-resolving ocean general circulation model (OGCM) for the Earth Simulator (OFES), along with sea level data from tide gauges since 1970 and a satellite altimeter since 1992. The first empirical orthogonal function mode of sea level anomalies (SLAs) of OFES exhibits broad positive SLAs over the central and western South Pacific. The corresponding principal component indicates roughly stable high, low, and high SLAs, separated by a rapid sea level fall in the late 1970s and sea level rise in the late 1990s, consistent with tide gauge and satellite observations. These decadal changes are accompanied by circulation changes of the subtropical gyre at 1000-m depth, and changes of upper-ocean zonal current and eddy activity around the Tasman Front. In general agreement with previous related studies, it is found that sea level variations in the Tasman Sea can be explained by propagation of long baroclinic Rossby waves forced by wind stress curl anomalies, if the impact of New Zealand is taken into account. The corresponding atmospheric variations are associated with decadal variability of El Niño–Southern Oscillation (ENSO). Thus, decadal sea level variability in the western and central South Pacific in the past three and half decades and decadal ENSO variability are likely to be connected. The sea level rise in the 1990s, which attracted much attention in relation to the global warming, is likely associated with the decadal cooling in the tropical Pacific.

scholarly journals Inter-annual tropical Pacific climate variability in an isotope-enabled CGCM: implications for interpreting coral stable oxygen isotope records of ENSO

2013 ◽  
Vol 9 (4) ◽  
pp. 1543-1557 ◽  
Author(s):  
T. Russon ◽  
A. W. Tudhope ◽  
G. C. Hegerl ◽  
M. Collins ◽  
J. Tindall
Keyword(s):  
Oxygen Isotope ◽  
General Circulation ◽  
Climate Models ◽  
Circulation Model ◽  
Equatorial Pacific ◽  
Stable Oxygen Isotope ◽  
Model Interpretation ◽  
Eastern Equatorial Pacific ◽  
Stable Oxygen ◽  
Pacific Climate Variability

Abstract. Water isotope-enabled coupled atmosphere–ocean climate models allow for exploration of the relative contributions to coral stable oxygen isotope (δ18Ocoral) variability arising from sea surface temperature (SST) and the isotopic composition of seawater (δ18Osw). The unforced behaviour of the isotope-enabled HadCM3 coupled general circulation model suggests that the extent to which inter-annual δ18Osw variability contributes to that in model δ18Ocoral is strongly spatially dependent, ranging from being negligible in the eastern equatorial Pacific to accounting for 50% of δ18Ocoral variance in parts of the western Pacific. In these latter cases, a significant component of the inter-annual δ18Osw variability is correlated to that in SST, meaning that local calibrations of the effective local δ18Ocoral–SST relationships are likely to be essential. Furthermore, the relationship between δ18Osw and SST can be non-linear, such that the model interpretation of central and western equatorial Pacific δ18Ocoral in the context of a linear dependence on SST alone leads to overestimation (by up to 20%) of the SST anomalies associated with large El Niño events. Intra-model evaluation of a salinity-based pseudo-coral approach shows that such an approach captures the first-order features of the model δ18Osw behaviour. However, the utility of the pseudo-corals is limited by the extent of spatial variability seen within the modelled slopes of the temporal salinity–δ18Osw relationship.

scholarly journals The Role of Air-Sea Coupling on November-April Intraseasonal Rainfall Variability Over the South Pacific

2021 ◽  
Author(s):  
Sunil Kumar Pariyar ◽  
Noel Keenlyside ◽  
Wan-Ling Tseng ◽  
Huang Hsiung Hsu ◽  
Ben-jei Tsuang
Keyword(s):  
General Circulation ◽  
Rainfall Variability ◽  
Phase Relationship ◽  
Coupled Model ◽  
Circulation Model ◽  
South Pacific ◽  
Ocean Model ◽  
The South ◽  
The Impact

Abstract We investigate the impact of resolving air-sea interaction on the simulation of the intraseasonal rainfall variability over the South Pacific using the ECHAM5 atmospheric general circulation model coupled with the Snow-Ice-Thermocline (SIT) ocean model. We compare the fully coupled simulation with two uncoupled ECHAM5 simulations, one forced with sea surface temperature (SST) climatology and one forced with daily SST from the coupled model. The intraseasonal rainfall variability over the South Pacific is reduced by 17% in the uncoupled model forced with SST climatology and increased by 8% in the uncoupled simulation forced with daily SST, suggesting the role of air-sea coupling and SST variability. The coupled model best simulates the key characteristics of two intraseasonal rainfall modes over the South Pacific with reasonable propagation and correct periodicity. The spatial structure of the two rainfall modes in all three simulations is very similar, suggesting these modes are primarily generated by the dynamics of the atmosphere. The southeastward propagation of rainfall anomalies associated with two leading rainfall modes in the South Pacific depends upon the eastward propagating MJO signals over the Indian Ocean and western Pacific. Air-sea interaction seems crucial for such propagation as both eastward and southeastward propagations are substantially reduced in the uncoupled model forced with SST climatology. The simulation of both eastward and southeastward propagations improved considerably in the uncoupled model forced with daily SST; however, the periodicity differs from the coupled model. Such discrepancy in the periodicity is attributed to the changes in the SST-rainfall relationship with weaker correlations and the nearly in-phase relationship.

scholarly journals Impact of South Pacific Subtropical Dipole Mode on the Equatorial Pacific

2018 ◽  
Vol 31 (6) ◽  
pp. 2197-2216 ◽  
Author(s):  
Jian Zheng ◽  
Faming Wang ◽  
Michael A. Alexander ◽  
Mengyang Wang
Keyword(s):  
El Niño ◽  
General Circulation ◽  
El Nino ◽  
Critical Role ◽  
Circulation Model ◽  
South Pacific ◽  
Equatorial Pacific ◽  
Central Pacific ◽  
Trade Winds ◽  
Wes Feedback

Previous studies have indicated that a sea surface temperature anomaly (SSTA) dipole in the subtropical South Pacific (SPSD), which peaks in austral summer (January–March), is dominated by thermodynamic processes. Observational analyses and numerical experiments were used to investigate the influence of SPSD mode on the equatorial Pacific. The model is an atmospheric general circulation model coupled to a reduced-gravity ocean model. An SPSD-like SSTA was imposed on 1 March, after which the model was free to evolve until the end of the year. The coupled model response showed that warm SSTAs extend toward the equator with northwesterly wind anomalies and then grow to El Niño–like anomalies by the end of the year. SPSD forcing weakens southeasterly trade winds and propagates warm SSTAs toward the equator through wind–evaporation–SST (WES) feedback. Meanwhile, relaxation of trade winds in the eastern equatorial Pacific depresses the thermocline and upwelling. Eastward anomalous currents near the equator cause warm horizontal advection in the central Pacific. Further experiments showed that thermodynamic coupling mainly acts on but is not essential for SSTA propagation, either from the subtropics to the equator or westward along the equator, while oceanic dynamic coupling alone also appears to be able to initiate anomalies on the equator and plays a critical role in SSTA growth in the tropical Pacific. This is consistent with observational analyses, which indicated that influence of WES feedback on SSTA propagation associated with the SPSD is limited. Finally, the warm pole close to the equator plays the dominant role in inducing the El Niño–like anomalies.

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