scholarly journals Biophysical Feedbacks in the Tropical Pacific

2005 ◽  
Vol 18 (1) ◽  
pp. 58-70 ◽  
Author(s):  
Ben Marzeion ◽  
Axel Timmermann ◽  
Ragu Murtugudde ◽  
Fei-Fei Jin
Keyword(s):  
Mixed Layer ◽  
Annual Cycle ◽  
Southern Oscillation ◽  
Heat Budget ◽  
Tropical Pacific ◽  
Shortwave Radiation ◽  
Bjerknes Feedback ◽  
Mean State ◽  
Chlorophyll Concentrations ◽  
The Tropical Pacific

Abstract This study explores the influence of phytoplankton on the tropical Pacific heat budget. A hybrid coupled model for the tropical Pacific that is based on a primitive equation reduced-gravity multilayer ocean model, a dynamic ocean mixed layer, an atmospheric mixed layer, and a statistical atmosphere is used. The statistical atmosphere relates deviations of the sea surface temperature from its mean to wind stress anomalies and allows for the rectification of the annual cycle and the El Niño–Southern Oscillation (ENSO) phenomenon through the positive Bjerknes feedback. Furthermore, a nine-component ecosystem model is coupled to the physical variables of the ocean. The simulated chlorophyll concentrations can feed back onto the ocean heat budget by their optical properties, which modify solar light absorption in the surface layers. It is shown that both the surface layer concentration as well as the vertical profile of chlorophyll have a significant effect on the simulated mean state, the tropical annual cycle, and ENSO. This study supports a previously suggested hypothesis (Timmermann and Jin) that predicts an influence of phytoplankton concentration of the tropical Pacific climate mean state and its variability. The bioclimate feedback diagnosed here works as follows: Maxima in the subsurface chlorophyll concentrations lead to an enhanced subsurface warming due to the absorption of photosynthetically available shortwave radiation. This warming triggers a deepening of the mixed layer in the eastern equatorial Pacific and eventually a reduction of the surface ocean currents (Murtugudde et al.). The weakened south-equatorial current generates an eastern Pacific surface warming, which is strongly enhanced by the Bjerknes feedback. Because of the deepening of the mixed layer, the strength of the simulated annual cycle is also diminished. This in turn leads to an increase in ENSO variability.

scholarly journals Regional impacts of ocean color on tropical Pacific variability

2009 ◽  
Vol 6 (1) ◽  
pp. 243-275 ◽  
Author(s):  
W. Anderson ◽  
A. Gnanadesikan ◽  
A. Wittenberg
Keyword(s):  
El Niño ◽  
El Nino ◽  
Pure Water ◽  
Ocean Color ◽  
Tropical Pacific ◽  
Shortwave Radiation ◽  
Penetration Length ◽  
The Mean ◽  
Mean State ◽  
The Tropical Pacific

Abstract. The role of the penetration length scale of shortwave radiation into the surface ocean and its impact on tropical Pacific variability is investigated with a fully coupled ocean, atmosphere, land and ice model. Previous work has shown that removal of all ocean color results in a system that tends strongly towards an El Niño state. Results from a suite of surface chlorophyll perturbation experiments show that the mean state and variability of the tropical Pacific is highly sensitive to the concentration and distribution of ocean chlorophyll. Setting the near-oligotrophic regions to contain optically pure water warms the mean state and suppresses variability in the western tropical Pacific. Doing the same above the shadow zones of the tropical Pacific also warms the mean state but enhances the variability. It is shown that increasing penetration can both deepen the pycnocline (which tends to damp El Niño) while shifting the mean circulation so that the wind response to temperature changes is altered. Depending on what region is involved this change in the wind stress can either strengthen or weaken ENSO variability.

scholarly journals Cloud–Radiation Feedback as a Leading Source of Uncertainty in the Tropical Pacific SST Warming Pattern in CMIP5 Models

2016 ◽  
Vol 29 (10) ◽  
pp. 3867-3881 ◽  
Author(s):  
Jun Ying ◽  
Ping Huang
Keyword(s):  
Heat Budget ◽  
Tropical Pacific ◽  
Eastern Pacific ◽  
Shortwave Radiation ◽  
Cmip5 Models ◽  
Central Pacific ◽  
Surface Warming ◽  
Sst Warming ◽  
Radiation Feedback ◽  
The Tropical Pacific

Abstract The role of the intermodel spread of cloud–radiation feedback in the uncertainty in the tropical Pacific SST warming (TPSW) pattern under global warming is investigated based on the historical and RCP8.5 runs from 32 models participating in CMIP5. The large intermodel discrepancies in cloud–radiation feedback contribute 24% of the intermodel uncertainty in the TPSW pattern over the central Pacific. The mechanism by which the cloud–radiation feedback influences the TPSW pattern is revealed based on an analysis of the surface heat budget. A relatively weak negative cloud–radiation feedback over the central Pacific cannot suppress the surface warming as greatly as in the multimodel ensemble and thus induces a warm SST deviation over the central Pacific, producing a low-level convergence that suppresses (enhances) the evaporative cooling and zonal cold advection in the western (eastern) Pacific. With these processes, the original positive SST deviation over the central Pacific will move westward to the western and central Pacific, with a negative SST deviation in the eastern Pacific. Compared with the observed cloud–radiation feedback from six sets of reanalysis and satellite-observed data, the negative cloud–radiation feedback in the models is underestimated in general. It implies that the TPSW pattern should be closer to an El Niño–like pattern based on the concept of observational constraint. However, the observed cloud–radiation feedback from the various datasets also demonstrates large discrepancies in magnitude. Therefore, the authors suggest that more effort should be made to improve the precision of shortwave radiation observations and the description of cloud–radiation feedback in models for a more reliable projection of the TPSW pattern in future.

scholarly journals Modulation of cross-isothermal velocities with ENSO in the tropical Pacific cold tongue

2021 ◽  
Author(s):  
Anna-Lena Deppenmeier ◽  
Frank O. Bryan ◽  
William Kessler ◽  
LuAnne Thompson
Keyword(s):  
El Niño ◽  
Cold Water ◽  
El Nino ◽  
Southern Oscillation ◽  
Heat Budget ◽  
Vertical Mixing ◽  
Tropical Pacific ◽  
Cold Tongue ◽  
Diabatic Processes ◽  
The Tropical Pacific

AbstractThe tropical Pacific cold tongue (CT) plays a major role in the global climate system. The strength of the CT sets the zonal temperature gradient in the Pacific that couples with the atmospheric Walker circulation. This coupling is an essential component of the El Niño Southern Oscillation (ENSO). The CT is supplied with cold water by the equatorial undercurrent that follows the thermocline as it shoals toward the east, adiabatically transporting cold water towards the surface. As the thermocline shoals, its water is transformed through diabatic processes producing water mass transformation (WMT) that allows water to cross mean isotherms. Here, we examine WMT in the cold tongue region from a global high resolution ocean simulation with saved budget terms that close its heat budget exactly. Using the terms of the heat budget, we quantify each individual component of WMT (vertical mixing, horizontal mixing, eddy fluxes, solar penetration), and find that vertical mixing is the single most important contribution in the thermocline, while solar heating dominates close to the surface. Horizontal diffusion is much smaller. During El Niño events, vertical mixing, and hence cross-isothermal flow as a whole, is much reduced, while during La Niña periods strong vertical mixing leads to strong WMT, thereby cooling the surface. This analysis demonstrates the enhancement of diabatic processes during cold events, which in turn enhances cooling of the CT from below the surface.

scholarly journals Interactions between marine biota and ENSO: a conceptual model analysis

2011 ◽  
Vol 18 (1) ◽  
pp. 29-40 ◽  
Author(s):  
M. Heinemann ◽  
A. Timmermann ◽  
U. Feudel
Keyword(s):  
Southern Oscillation ◽  
Radiation Force ◽  
Ecosystem Model ◽  
Ocean Model ◽  
Tropical Pacific ◽  
Continuation Methods ◽  
Shortwave Radiation ◽  
Enso Cycle ◽  
Marine Biota ◽  
The Tropical Pacific

Abstract. We develop a conceptual coupled atmosphere-ocean-ecosystem model for the tropical Pacific to investigate the interaction between marine biota and the El Niño-Southern Oscillation (ENSO). Ocean and atmosphere are represented by a two-box model for the equatorial Pacific cold tongue and the warm pool, including a simplified mixed layer scheme. Marine biota are represented by a three-component (nutrient, phytoplankton, and zooplankton) ecosystem model. The atmosphere-ocean model exhibits an oscillatory state which qualitatively captures the main physics of ENSO. During an ENSO cycle, the variation of nutrient upwelling, and, to a small extent, the variation of photosynthetically available radiation force an ecosystem oscillation. The simplified ecosystem in turn, due to the effect of phytoplankton on the absorption of shortwave radiation in the water column, leads to (1) a warming of the tropical Pacific, (2) a reduction of the ENSO amplitude, and (3) a prolongation of the ENSO period. We qualitatively investigate these bio-physical coupling mechanisms using continuation methods. It is demonstrated that bio-physical coupling may play a considerable role in modulating ENSO variability.

scholarly journals Regional impacts of ocean color on tropical Pacific variability

Ocean Science ◽  
2009 ◽  
Vol 5 (3) ◽  
pp. 313-327 ◽  
Author(s):  
W. Anderson ◽  
A. Gnanadesikan ◽  
A. Wittenberg
Keyword(s):  
El Niño ◽  
El Nino ◽  
Pure Water ◽  
Ocean Color ◽  
Tropical Pacific ◽  
Shortwave Radiation ◽  
Penetration Length ◽  
The Mean ◽  
Mean State ◽  
The Tropical Pacific

Abstract. The role of the penetration length scale of shortwave radiation into the surface ocean and its impact on tropical Pacific variability is investigated with a fully coupled ocean, atmosphere, land and ice model. Previous work has shown that removal of all ocean color results in a system that tends strongly towards an El Niño state. Results from a suite of surface chlorophyll perturbation experiments show that the mean state and variability of the tropical Pacific is highly sensitive to the concentration and distribution of ocean chlorophyll. Setting the near-oligotrophic regions to contain optically pure water warms the mean state and suppresses variability in the western tropical Pacific. Doing the same above the shadow zones of the tropical Pacific also warms the mean state but enhances the variability. It is shown that increasing penetration can both deepen the pycnocline (which tends to damp El Niño) while shifting the mean circulation so that the wind response to temperature changes is altered. Depending on what region is involved this change in the wind stress can either strengthen or weaken ENSO variability.

scholarly journals Variability of the Heat and Salt Budget in the Subtropical Southeastern Pacific Mixed Layer between 2004 and 2010: Spice Injection Mechanism

2013 ◽  
Vol 43 (9) ◽  
pp. 1880-1898 ◽  
Author(s):  
Nicolas Kolodziejczyk ◽  
Fabienne Gaillard
Keyword(s):  
Mixed Layer ◽  
Annual Cycle ◽  
Heat Budget ◽  
Salt Content ◽  
Vertical Gradient ◽  
Surface Fluxes ◽  
Surface Velocity ◽  
Shortwave Radiation ◽  
Southeastern Pacific ◽  
Salt Budget

Abstract The mixed layer heat and salt budget in the southeastern subtropical Pacific are estimated using 7 years (2004–10) of Argo-profiling float data, surface fluxes, precipitation, surface velocity data, and wind observations and reanalysis. In this region, the mixed layer heat budget is characterized by a strong annual cycle mainly modulated by the shortwave radiation annual cycle. During the austral fall and winter, the shortwave radiation input minimum is overwhelmed by the heat loss mainly because of the latent heat flux. The mixed layer salt budget also presents a strong annual cycle with a minimum of salt content during the late austral winter. In contrast with the heat budget, the salt budget is mainly driven by the unresolved terms computed as the residual of the budget. Among these missing terms, the most likely candidate is the vertical turbulent mixing as a result of convection caused by the heat surface buoyancy loss and the destabilizing vertical gradient of salinity at the base of the mixed layer. This downward flux of salt at the base of the mixed layer could explain the annual spiciness injection and interannual spiciness variability in the permanent thermocline in the southeastern Pacific.

scholarly journals Sensitivity of ENSO Simulation to the Convection Schemes in the NESM3 Climate System Model: Atmospheric Processes

2021 ◽  
Vol 9 ◽  
Author(s):  
Libin Ma ◽  
Zijun Jiang
Keyword(s):  
Heat Flux ◽  
Southern Oscillation ◽  
Phase Locking ◽  
Tropical Pacific ◽  
Climate System ◽  
Convection Scheme ◽  
Bjerknes Feedback ◽  
Climate System Model ◽  
Convection Schemes ◽  
The Tropical Pacific

The El Niño-Southern Oscillation (ENSO) is the most prominent climate system in the tropical Pacific. However, its simulation, including the amplitude, phase locking, and asymmetry of its two phases, is not well reproduced by the current climate system models. In this study, the sensitivity of the ENSO simulation to the convection schemes is discussed using the Nanjing University of Information Science and Technology Earth System version 3.0 (NESM3) model. Three convection schemes, including the default, the default coupled with the stochastic multicloud model (SMCM), and the default used in the Coupled Model Intercomparison Project Phase 6 (CMIP6), are implemented. The model results reveal that the low-level cloud cover and surface net shortwave radiation are best represented over the tropical Pacific in the model containing the SMCM. The simulations of the ENSO behavior’s response to changes in the convection scheme are not uniform. The model results reveal that the model containing the SMCM performs best in terms of simulating the seasonal cycle of the sea surface temperature anomaly along the equatorial Pacific, the phase locking, and the power spectrum of ENSO but with a modest ENSO amplitude. Compared to the model containing the default convection scheme, the coupling of the default scheme and the SMCM provides a good simulation of the ENSO’s asymmetry, while the model containing the CMIP6 convection scheme outperforms the others in terms of the simulation of the ENSO’s amplitude. Two atmospheric feedback processes were further discussed to investigate the factors controlling the ENSO’s amplitude. The analyses revealed that the strongest positive atmospheric Bjerknes feedback and the thermodynamic damping of the surface net heat flux occurred in the model containing the CMIP6 convection scheme, suggesting that the atmospheric Bjerknes feedback may overwhelm the heat flux damping feedback when determining the ENSO’s amplitude. The results of this study demonstrate that perfectly modeling and predicting the ENSO is not simple, and it is still a large challenge and issue for the entire model community in the future.

scholarly journals Pacific Climate Change and ENSO Activity in the Mid-Holocene

2009 ◽  
Vol 22 (4) ◽  
pp. 923-939 ◽  
Author(s):  
J. C. H. Chiang ◽  
Y. Fang ◽  
P. Chang
Keyword(s):  
Annual Cycle ◽  
Climate Changes ◽  
Southern Oscillation ◽  
Asian Summer Monsoon ◽  
Coupled Model ◽  
Tropical Pacific ◽  
Orbital Forcing ◽  
Frequency Entrainment ◽  
Asian Summer ◽  
The Tropical Pacific

Abstract The authors argue that a reduction to the stochastic forcing of the El Niño–Southern Oscillation (ENSO) wrought by Pacific-wide climate changes in response to mid-Holocene (6000 BP) orbital forcing is a viable hypothesis for the observed reduction of ENSO activity during that time. This conclusion is based on comprehensive analysis of an intermediate coupled model that achieves significant reduction to ENSO variance in response to mid-Holocene orbital forcing. The model’s excellent simulation of the tropical Pacific interannual variability lends credibility to the results. Idealized simulations demonstrate that the mid-Holocene influence is communicated to the tropical Pacific largely via climate changes outside of the tropical Pacific, rather than from insolation changes directly on the tropical Pacific. This is particularly true for changes to the ENSO, but also with changes to the cold tongue annual cycle. Previously proposed mechanisms for teleconnected mid-Holocene ENSO changes, including forcing of ENSO by a strengthened Asian summer monsoon and an increase in the annual cycle forcing on the tropical Pacific leading to a reduction in ENSO activity by frequency entrainment, do not appear to occur in these simulations. Rather, the authors show that the modeled mid-Holocene climate exhibits a pronounced reduction in Pacific meridional mode activity that has been recently shown to be a forcing on ENSO, though the reasons for this reduction are still to be explained. The contrasting nature of the results compared to previous studies highlights the effect of the prevailing ENSO paradigm on this problem. By showing that an externally forced ENSO model is equally capable of explaining mid-Holocene ENSO reduction as its nonlinear, weakly chaotic counterpart, it is demonstrated that the mid-Holocene ENSO data point cannot yet discriminate between these two paradigms of ENSO.

Successive Modulation of ENSO to the Future Greenhouse Warming

2008 ◽  
Vol 21 (1) ◽  
pp. 3-21 ◽  
Author(s):  
Soon-Il An ◽  
Jong-Seong Kug ◽  
Yoo-Geun Ham ◽  
In-Sik Kang
Keyword(s):  
General Circulation ◽  
Southern Oscillation ◽  
General Circulation Models ◽  
Tropical Pacific ◽  
Greenhouse Warming ◽  
Delayed Response ◽  
Subsurface Temperature ◽  
Climate System Model ◽  
The Mean ◽  
The Tropical Pacific

Abstract The multidecadal modulation of the El Niño–Southern Oscillation (ENSO) due to greenhouse warming has been analyzed herein by means of diagnostics of Intergovernmental Panel on Climate Change (IPCC) Fourth Assessment Report (AR4) coupled general circulation models (CGCMs) and the eigenanalysis of a simplified version of an intermediate ENSO model. The response of the global-mean troposphere temperature to increasing greenhouse gases is more likely linear, while the amplitude and period of ENSO fluctuates in a multidecadal time scale. The climate system model outputs suggest that the multidecadal modulation of ENSO is related to the delayed response of the subsurface temperature in the tropical Pacific compared to the response time of the sea surface temperature (SST), which would lead a modulation of the vertical temperature gradient. Furthermore, an eigenanalysis considering only two parameters, the changes in the zonal contrast of the mean background SST and the changes in the vertical contrast between the mean surface and subsurface temperatures in the tropical Pacific, exhibits a good agreement with the CGCM outputs in terms of the multidecadal modulations of the ENSO amplitude and period. In particular, the change in the vertical contrast, that is, change in difference between the subsurface temperature and SST, turns out to be more influential on the ENSO modulation than changes in the mean SST itself.

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