scholarly journals ENSO Amplitude Changes due to Climate Change Projections in Different Coupled Models

2007 ◽  
Vol 20 (2) ◽  
pp. 203-217 ◽  
Author(s):  
Sang-Wook Yeh ◽  
Ben P. Kirtman
Keyword(s):  
Climate Change ◽  
Tropical Pacific ◽  
Skewed Distribution ◽  
Geophysical Fluid Dynamics Laboratory ◽  
Coupled Models ◽  
Climate Change Projections ◽  
State Changes ◽  
The Mean ◽  
Gfdl Model ◽  
Mean State

Abstract Four climate system models are chosen here for an analysis of ENSO amplitude changes in 4 × CO2 climate change projections. Despite the large changes in the tropical Pacific mean state, the changes in ENSO amplitude are highly model dependant. To investigate why similar mean state changes lead to very different ENSO amplitude changes, the characteristics of sea surface temperature anomaly (SSTA) variability simulated in two coupled general circulation models (CGCMs) are analyzed: the Meteorological Research Institute (MRI) and Geophysical Fluid Dynamics Laboratory (GFDL) models. The skewed distribution of tropical Pacific SSTA simulated in the MRI model suggests the importance of nonlinearities in the ENSO physics, whereas the GFDL model lies in the linear regime. Consistent with these differences in ENSO regime, the GFDL model is insensitive to the mean state changes, whereas the MRI model is sensitive to the mean state changes associated with the 4 × CO2 scenario. Similarly, the low-frequency modulation of ENSO amplitude in the GFDL model is related to atmospheric stochastic forcing, but in the MRI model the amplitude modulation is insensitive to the noise forcing. These results suggest that the understanding of changes in ENSO statistics among various climate change projections is highly dependent on whether the model ENSO is in the linear or nonlinear regime.

scholarly journals Impact of Resolution on the Tropical Pacific Circulation in a Matrix of Coupled Models

2009 ◽  
Vol 22 (10) ◽  
pp. 2541-2556 ◽  
Author(s):  
Malcolm J. Roberts ◽  
A. Clayton ◽  
M.-E. Demory ◽  
J. Donners ◽  
P. L. Vidale ◽  
...  
Keyword(s):  
Coupled Model ◽  
Walker Circulation ◽  
Ocean Model ◽  
Tropical Pacific ◽  
Coupled Models ◽  
Model Stability ◽  
The Mean ◽  
The Impact ◽  
Mean State ◽  
The Tropical Pacific

Abstract Results are presented from a matrix of coupled model integrations, using atmosphere resolutions of 135 and 90 km, and ocean resolutions of 1° and 1/3°, to study the impact of resolution on simulated climate. The mean state of the tropical Pacific is found to be improved in the models with a higher ocean resolution. Such an improved mean state arises from the development of tropical instability waves, which are poorly resolved at low resolution; these waves reduce the equatorial cold tongue bias. The improved ocean state also allows for a better simulation of the atmospheric Walker circulation. Several sensitivity studies have been performed to further understand the processes involved in the different component models. Significantly decreasing the horizontal momentum dissipation in the coupled model with the lower-resolution ocean has benefits for the mean tropical Pacific climate, but decreases model stability. Increasing the momentum dissipation in the coupled model with the higher-resolution ocean degrades the simulation toward that of the lower-resolution ocean. These results suggest that enhanced ocean model resolution can have important benefits for the climatology of both the atmosphere and ocean components of the coupled model, and that some of these benefits may be achievable at lower ocean resolution, if the model formulation allows.

scholarly journals Oxygen minimum zones in the tropical Pacific across CMIP5 models: mean state differences and climate change trends

2015 ◽  
Vol 12 (8) ◽  
pp. 6525-6587 ◽  
Author(s):  
A. Cabré ◽  
I. Marinov ◽  
R. Bernardello ◽  
D. Bianchi
Keyword(s):  
Climate Change ◽  
Tropical Pacific ◽  
Cmip5 Models ◽  
Upper Ocean ◽  
Intermediate Water ◽  
Climate Change Projections ◽  
Oxygen Minimum Zones ◽  
Mean State ◽  
Oxygen Minimum ◽  
The Tropical Pacific

Abstract. We analyze simulations of the Pacific Ocean oxygen minimum zones (OMZs) from 11 Earth System model contributions to the Coupled Model Intercomparison Project Phase 5, focusing on the mean state and climate change projections. The simulations tend to overestimate the volume of the OMZs, especially in the tropics and Southern Hemisphere. Compared to observations, five models introduce incorrect meridional asymmetries in the distribution of oxygen including larger southern OMZ and weaker northern OMZ, due to interhemispheric biases in intermediate water mass ventilation. Seven models show too deep an extent of the tropical hypoxia compared to observations, stemming from a deficient equatorial ventilation in the upper ocean combined with a too large biologically-driven downward flux of particulate organic carbon at depth, caused by too high particle export from the euphotic layer and too weak remineralization in the upper ocean. At interannual timescales, the dynamics of oxygen in the eastern tropical Pacific OMZ is dominated by biological consumption and linked to natural variability in the Walker circulation. However, under the climate change scenario RCP8.5, all simulations yield small and discrepant changes in oxygen concentration at mid depths in the tropical Pacific by the end of the 21st century due to an almost perfect compensation between warming-related decrease in oxygen saturation and decrease in biological oxygen utilization. Climate change projections are at odds with recent observations that show decreasing oxygen levels at mid depths in the tropical Pacific. Out of the OMZs, all the CMIP5 models predict a decrease of oxygen over most of the surface, deep and high latitudes ocean due to an overall slow-down of ventilation and increased temperature.

scholarly journals Oxygen minimum zones in the tropical Pacific across CMIP5 models: mean state differences and climate change trends

2015 ◽  
Vol 12 (18) ◽  
pp. 5429-5454 ◽  
Author(s):  
A. Cabré ◽  
I. Marinov ◽  
R. Bernardello ◽  
D. Bianchi
Keyword(s):  
Climate Change ◽  
Tropical Pacific ◽  
Cmip5 Models ◽  
Upper Ocean ◽  
Intermediate Water ◽  
Climate Change Projections ◽  
Oxygen Minimum Zones ◽  
Mean State ◽  
Oxygen Minimum ◽  
The Tropical Pacific

Abstract. We analyse simulations of the Pacific Ocean oxygen minimum zones (OMZs) from 11 Earth system model contributions to the Coupled Model Intercomparison Project Phase 5, focusing on the mean state and climate change projections. The simulations tend to overestimate the volume of the OMZs, especially in the tropics and Southern Hemisphere. Compared to observations, five models introduce incorrect meridional asymmetries in the distribution of oxygen including larger southern OMZ and weaker northern OMZ, due to interhemispheric biases in intermediate water mass ventilation. Seven models show too deep an extent of the tropical hypoxia compared to observations, stemming from a deficient equatorial ventilation in the upper ocean, combined with too large a biologically driven downward flux of particulate organic carbon at depth, caused by particle export from the euphotic layer that is too high and remineralization in the upper ocean that is too weak. At interannual timescales, the dynamics of oxygen in the eastern tropical Pacific OMZ is dominated by biological consumption and linked to natural variability in the Walker circulation. However, under the climate change scenario RCP8.5, all simulations yield small and discrepant changes in oxygen concentration at mid depths in the tropical Pacific by the end of the 21st century due to an almost perfect compensation between warming-related decrease in oxygen saturation and decrease in biological oxygen utilization. Climate change projections are at odds with recent observations that show decreasing oxygen levels at mid depths in the tropical Pacific. Out of the OMZs, all the CMIP5 models predict a decrease of oxygen over most of the surface and deep ocean at low latitudes and over all depths at high latitudes due to an overall slow-down of ventilation and increased temperature.

The Role of the Indonesian Throughflow in the Indo–Pacific Climate Variability in the GFDL Coupled Climate Model

2007 ◽  
Vol 20 (11) ◽  
pp. 2434-2451 ◽  
Author(s):  
Qian Song ◽  
Gabriel A. Vecchi ◽  
Anthony J. Rosati
Keyword(s):  
Indian Ocean ◽  
Interannual Variability ◽  
Tropical Indian Ocean ◽  
Tropical Pacific ◽  
Equatorial Pacific ◽  
Indonesian Throughflow ◽  
Enso Events ◽  
State Changes ◽  
The Mean ◽  
Mean State

Abstract The impacts of the Indonesian Throughflow (ITF) on the tropical Indo–Pacific climate, particularly on the character of interannual variability, are explored using a coupled general circulation model (CGCM). A pair of CGCM experiments—a control experiment with an open ITF and a perturbation experiment in which the ITF is artificially closed—is integrated for 200 model years, with the 1990 values of trace gases. The closure of the ITF results in changes to the mean oceanic and atmospheric conditions throughout the tropical Indo–Pacific domain as follows: surface temperatures in the eastern tropical Pacific (Indian) Ocean warm (cool), the near-equatorial Pacific (Indian) thermocline flattens (shoals), Indo–Pacific warm-pool precipitation shifts eastward, and there are relaxed trade winds over the tropical Pacific and anomalous surface easterlies over the equatorial Indian Ocean. The character of the oceanic changes is similar to that described by ocean-only model experiments, though the amplitude of many features in the tropical Indo–Pacific is amplified in the CGCM experiments. In addition to the mean-state changes, the character of tropical Indo–Pacific interannual variability is substantially modified. Interannual variability in the equatorial Pacific and the eastern tropical Indian Ocean is substantially intensified by the closure of the ITF. In addition to becoming more energetic, El Niño–Southern Oscillation (ENSO) exhibits a shorter time scale of variability and becomes more skewed toward its warm phase (stronger and more frequent warm events). The structure of warm ENSO events changes; the anomalies of sea surface temperature (SST), precipitation, and surface westerly winds are shifted to the east and the meridional extent of surface westerly anomalies is larger. In the eastern tropical Indian Ocean, the interannual SST variability off the coast of Java–Sumatra is noticeably amplified by the occurrence of much stronger cooling events. Closing the ITF shoals the eastern tropical Indian Ocean thermocline, which results in stronger cooling events through enhanced atmosphere–thermocline coupled feedbacks. Changes to the interannual variability caused by the ITF closure rectify into mean-state changes in tropical Indo–Pacific conditions. The modified Indo–Pacific interannual variability projects onto the mean-state differences between the ITF open and closed scenarios, rectifying into mean-state differences. These results suggest that CGCMs need to reasonably simulate the ITF in order to successfully represent not just the mean climate, but its variations as well.

scholarly journals Ubiquity of human-induced changes in climate variability

2021 ◽  
Vol 12 (4) ◽  
pp. 1393-1411
Author(s):  
Keith B. Rodgers ◽  
Sun-Seon Lee ◽  
Nan Rosenbloom ◽  
Axel Timmermann ◽  
Gokhan Danabasoglu ◽  
...  
Keyword(s):  
Climate Change ◽  
Climate Variability ◽  
Climate Adaptation ◽  
Southern Oscillation ◽  
System Modeling ◽  
Greenhouse Warming ◽  
Earth System ◽  
Wide Range ◽  
State Changes ◽  
Mean State

Abstract. While climate change mitigation targets necessarily concern maximum mean state changes, understanding impacts and developing adaptation strategies will be largely contingent on how climate variability responds to increasing anthropogenic perturbations. Thus far Earth system modeling efforts have primarily focused on projected mean state changes and the sensitivity of specific modes of climate variability, such as the El Niño–Southern Oscillation. However, our knowledge of forced changes in the overall spectrum of climate variability and higher-order statistics is relatively limited. Here we present a new 100-member large ensemble of climate change projections conducted with the Community Earth System Model version 2 over 1850–2100 to examine the sensitivity of internal climate fluctuations to greenhouse warming. Our unprecedented simulations reveal that changes in variability, considered broadly in terms of probability distribution, amplitude, frequency, phasing, and patterns, are ubiquitous and span a wide range of physical and ecosystem variables across many spatial and temporal scales. Greenhouse warming in the model alters variance spectra of Earth system variables that are characterized by non-Gaussian probability distributions, such as rainfall, primary production, or fire occurrence. Our modeling results have important implications for climate adaptation efforts, resource management, seasonal predictions, and assessing potential stressors for terrestrial and marine ecosystems.

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 El Niño in a Coupled Climate Model: Sensitivity to Changes in Mean State Induced by Heat Flux and Wind Stress Corrections

2007 ◽  
Vol 20 (10) ◽  
pp. 2273-2298 ◽  
Author(s):  
Hilary Spencer ◽  
Rowan Sutton ◽  
Julia M. Slingo
Keyword(s):  
Heat Flux ◽  
Wind Stress ◽  
El Niño ◽  
General Circulation ◽  
El Nino ◽  
Seasonal Forecasts ◽  
Coupled Models ◽  
The Mean ◽  
Flux Corrections ◽  
Mean State

Abstract Here the factors affecting the mean state and El Niño variability in the Third Hadley Centre Coupled Ocean–Atmosphere General Circulation Model (HadCM3) are examined with and without heat flux or wind stress corrections. There is currently little confidence in the prediction of El Niño for seasonal forecasts or climate change due to the inaccuracies in coupled models. If heat flux or wind stress corrections could reduce these biases then forecasts might be improved. Heat flux corrections have unexpected effects on both the mean state and variability of HadCM3. HadCM3 is found to be very sensitive to the corrections imposed. If heat flux corrections are imposed Tropics wide then easterlies in the eastern equatorial Pacific are increased leading to localized steep east–west gradients in the thermocline or “thermocline jumps,” which appear to suppress propagation of heat from the west to the east and hence suppress strong El Niños so that ENSO variability is weak. In contrast, if heat flux corrections are imposed only within 10° of the equator, an atmospheric teleconnection from the cold subtropical SST biases intensifies the ITCZ and weakens the equatorial easterlies. As a result, the thermocline jumps are flattened and strong El Niños occur very frequently. Neither heat flux correction procedure improves the representation of El Niño. Wind stress corrections alone have a small impact on the coupled model. Some of the SST warm biases are reduced, but the variability is not altered significantly.

Season-Dependent Forecast Skill of the Leading Forced Atmospheric Circulation Pattern over the North Pacific and North American Region*

2012 ◽  
Vol 25 (20) ◽  
pp. 7248-7265 ◽  
Author(s):  
XiaoJing Jia ◽  
Hai Lin ◽  
June-Yi Lee ◽  
Bin Wang
Keyword(s):  
Atmospheric Circulation ◽  
North Pacific ◽  
Circulation Pattern ◽  
Tropical Pacific ◽  
Atmospheric Circulation Pattern ◽  
Potential Predictability ◽  
The North ◽  
The Mean ◽  
The North Pacific ◽  
Mean State

Abstract Multimodel ensemble (MME) seasonal forecasts are analyzed to evaluate numerical model performance in predicting the leading forced atmospheric circulation pattern over the extratropical Northern Hemisphere (NH). Results show that the time evolution of the leading tropical Pacific sea surface temperature (SST)-coupled atmospheric pattern (MCA1), which is obtained by applying a maximum covariance analysis (MCA) between 500-hPa geopotential height (Z500) in the extratropical NH and SST in the tropical Pacific Ocean, can be predicted with a significant skill in March–May (MAM), June–August (JJA), and December–February (DJF) one month ahead. However, most models perform poorly in capturing the time variation of MCA1 in September–November (SON) with 1 August initial condition. Two possible reasons for the models’ low skill in SON are identified. First, the models have the most pronounced errors in the mean state of SST and precipitation along the central equatorial Pacific. Because of the link between the divergent circulation forced by tropical heating and the midlatitude atmospheric circulation, errors in the mean state of tropical SST and precipitation may lead to a degradation of midlatitude forecast skill. Second, examination of the potential predictability of the atmosphere, estimated by the ratio of the total variance to the variance of the model forecasts due to internal dynamics, shows that the atmospheric potential predictability over the North Pacific–North American (NPNA) region is the lowest in SON compared to the other three seasons. The low ratio in SON is due to a low variance associated with external forcing and a high variance related to atmospheric internal processes over this area.

scholarly journals Boreal summer intraseasonal oscillation in a superparameterized GCM: effects of air-sea coupling and ocean mean state

2020 ◽  
Author(s):  
Yingxia Gao ◽  
Nicholas P. Klingaman ◽  
Charlotte A. DeMott ◽  
Pang-Chi Hsu
Keyword(s):  
Intraseasonal Oscillation ◽  
Phase Relationship ◽  
Atmospheric Model ◽  
Boreal Summer ◽  
Coupled Models ◽  
Boreal Summer Intraseasonal Oscillation ◽  
Taylor Diagram ◽  
The Indian Ocean ◽  
The Mean ◽  
Mean State

Abstract. The effect of air-sea coupling on the simulated boreal summer intraseasonal oscillation (BSISO) is examined using atmosphere—ocean-mixed-layer coupled (SPCAM3-KPP) and uncoupled configurations of the Super-Parameterized (SP) Community Atmospheric Model, version 3 (SPCAM3). The coupled configuration is constrained to either the observed ocean mean state or the mean state from the SP coupled configuration with a dynamic ocean (SPCCSM3), to understand the effect of mean state biases on the BSISO in the latter. All configurations overestimate summer mean subtropical rainfall and its intraseasonal variance. All configurations simulate realistic BSISO northward propagation over the Indian Ocean and western Pacific, in common with other SP configurations. Constraining SPCAM3-KPP to the SPCCSM3 mean state reduces the overestimated BSISO variability, but also weakens BSISO propagation. Using the SPCCSM3 mean state also introduces a one-month delay to the BSISO seasonal cycle compared to SPCAM3-KPP with the observed ocean mean state, which matches well with the reanalysis. The phase relationship between intraseasonal rainfall and sea surface temperature (SST) is captured by all coupled models, but with a shorter delay between suppressed convection and warm SST relative to the reanalysis. Prescribing the 31-day smoothed SSTs from the SPCAM3-KPP simulations in SPCAM3 worsens the overestimated BSISO variance. This suggests that air-sea coupling improves the amplitude of the simulated BSISO. Based on a Taylor diagram, SPCCSM3 mean state SST biases and air-sea coupling both lead to higher simulated BSISO fidelity, largely due to their ability to suppress the overestimated subtropical BSISO variance.

scholarly journals Global Model selection for evaluation of Climate Change projections in the Eastern Tropical Pacific Seascape

2017 ◽  
pp. 67-81
Author(s):  
Hugo G. Hidalgo ◽  
Eric J. Alfaro
Keyword(s):  
Climate Change ◽  
Model Selection ◽  
20Th Century ◽  
General Circulation ◽  
Tropical Pacific ◽  
Global Model ◽  
Model Ensemble ◽  
Eastern Tropical Pacific ◽  
Climate Change Projections ◽  
Selection For

Two methods for selecting a subset of simulations and/or general circulation models (GCMs) from a set of 30 available simulations are compared: 1) Selecting the models based on their performance on reproducing 20th century climate, and 2) random sampling. In the first case, it was found that the performance methodology is very sensitive to the type and number of metrics used to rank the models and therefore the results are not robust to these conditions. In general, including more models in a multi-model ensemble according to their rank (of skill in reproducing 20th century climate) results in an increase in the multi-model skill up to a certain point and then the inclusion of more models degrades the skill of the multi-model ensemble. In a similar fashion when the models are introduced in the ensemble at random, there is a point where the inclusion of more models does not change significantly the skill of the multi-model ensemble. For precipitation the subset of models that produces the maximum skill in reproducing 20th century climate also showed some skill in reproducing the climate change projections of the multi-model ensemble of all simulations. For temperature, more models/simulations are needed to be included in the ensemble (at the expense of a decrease in the skill of reproducing the climate of the 20th century for the selection based on their ranks). For precipitation and temperature the use of 7 simulations out of 30 resulted in the maximum skill for both approaches to introduce the models. Citation: Hidalgo, H. & E.J. Alfaro. 2012. Global Model selection for evaluation of climate change projections in the Eastern Tropical Pacific Seascape. Rev. Biol. Trop. 60 (Suppl. 3): 67-81. Epub 2012 Dec 01.

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