Ocean Circulation and Tropical Variability in the Coupled Model ECHAM5/MPI-OM

Abstract This paper describes the mean ocean circulation and the tropical variability simulated by the Max Planck Institute for Meteorology (MPI-M) coupled atmosphere–ocean general circulation model (AOGCM). Results are presented from a version of the coupled model that served as a prototype for the Intergovernmental Panel on Climate Change (IPCC) Fourth Assessment Report (AR4) simulations. The model does not require flux adjustment to maintain a stable climate. A control simulation with present-day greenhouse gases is analyzed, and the simulation of key oceanic features, such as sea surface temperatures (SSTs), large-scale circulation, meridional heat and freshwater transports, and sea ice are compared with observations. A parameterization that accounts for the effect of ocean currents on surface wind stress is implemented in the model. The largest impact of this parameterization is in the tropical Pacific, where the mean state is significantly improved: the strength of the trade winds and the associated equatorial upwelling weaken, and there is a reduction of the model’s equatorial cold SST bias by more than 1 K. Equatorial SST variability also becomes more realistic. The strength of the variability is reduced by about 30% in the eastern equatorial Pacific and the extension of SST variability into the warm pool is significantly reduced. The dominant El Niño–Southern Oscillation (ENSO) period shifts from 3 to 4 yr. Without the parameterization an unrealistically strong westward propagation of SST anomalies is simulated. The reasons for the changes in variability are linked to changes in both the mean state and to a reduction in atmospheric sensitivity to SST changes and oceanic sensitivity to wind anomalies.

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Stratospheric Communication of El Niño Teleconnections to European Winter

Journal of Climate ◽

10.1175/2009jcli2717.1 ◽

2009 ◽

Vol 22 (15) ◽

pp. 4083-4096 ◽

Cited By ~ 148

Author(s):

C. J. Bell ◽

L. J. Gray ◽

A. J. Charlton-Perez ◽

M. M. Joshi ◽

A. A. Scaife

Keyword(s):

El Niño ◽

General Circulation ◽

El Nino ◽

Southern Oscillation ◽

Polar Vortex ◽

Circulation Model ◽

Active Role ◽

Late Winter ◽

The Mean ◽

Mean State

Abstract The stratospheric role in the European winter surface climate response to El Niño–Southern Oscillation sea surface temperature forcing is investigated using an intermediate general circulation model with a well-resolved stratosphere. Under El Niño conditions, both the modeled tropospheric and stratospheric mean-state circulation changes correspond well to the observed “canonical” responses of a late winter negative North Atlantic Oscillation and a strongly weakened polar vortex, respectively. The variability of the polar vortex is modulated by an increase in frequency of stratospheric sudden warming events throughout all winter months. The potential role of this stratospheric response in the tropical Pacific–European teleconnection is investigated by sensitivity experiments in which the mean state and variability of the stratosphere are degraded. As a result, the observed stratospheric response to El Niño is suppressed and the mean sea level pressure response fails to resemble the temporal and spatial evolution of the observations. The results suggest that the stratosphere plays an active role in the European response to El Niño. A saturation mechanism whereby for the strongest El Niño events tropospheric forcing dominates the European response is suggested. This is examined by means of a sensitivity test and it is shown that under large El Niño forcing the European response is insensitive to stratospheric representation.

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The Effect of a Well-Resolved Stratosphere on Surface Climate: Differences between CMIP5 Simulations with High and Low Top Versions of the Met Office Climate Model

Journal of Climate ◽

10.1175/jcli-d-11-00579.1 ◽

2012 ◽

Vol 25 (20) ◽

pp. 7083-7099 ◽

Cited By ~ 44

Author(s):

S. C. Hardiman ◽

N. Butchart ◽

T. J. Hinton ◽

S. M. Osprey ◽

L. J. Gray

Keyword(s):

General Circulation ◽

Climate Model ◽

Southern Oscillation ◽

Coupled Model ◽

Circulation Model ◽

Climate Simulation ◽

Reanalysis Dataset ◽

Quasi Biennial Oscillation ◽

Surface Climate ◽

The Impact

Abstract The importance of using a general circulation model that includes a well-resolved stratosphere for climate simulations, and particularly the influence this has on surface climate, is investigated. High top model simulations are run with the Met Office Unified Model for the Coupled Model Intercomparison Project Phase 5 (CMIP5). These simulations are compared to equivalent simulations run using a low top model differing only in vertical extent and vertical resolution above 15 km. The period 1960–2002 is analyzed and compared to observations and the European Centre for Medium-Range Weather Forecasts (ECMWF) reanalysis dataset. Long-term climatology, variability, and trends in surface temperature and sea ice, along with the variability of the annular mode index, are found to be insensitive to the addition of a well-resolved stratosphere. The inclusion of a well-resolved stratosphere, however, does improve the impact of atmospheric teleconnections on surface climate, in particular the response to El Niño–Southern Oscillation, the quasi-biennial oscillation, and midwinter stratospheric sudden warmings (i.e., zonal mean wind reversals in the middle stratosphere). Thus, including a well-represented stratosphere could improve climate simulation on intraseasonal to interannual time scales.

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Improved Climate Simulation by MIROC5: Mean States, Variability, and Climate Sensitivity

Journal of Climate ◽

10.1175/2010jcli3679.1 ◽

2010 ◽

Vol 23 (23) ◽

pp. 6312-6335 ◽

Cited By ~ 761

Author(s):

Masahiro Watanabe ◽

Tatsuo Suzuki ◽

Ryouta O’ishi ◽

Yoshiki Komuro ◽

Shingo Watanabe ◽

...

Keyword(s):

Climate Sensitivity ◽

General Circulation ◽

Southern Oscillation ◽

Circulation Model ◽

Ocean General Circulation Model ◽

Climate Simulation ◽

Mean Fields ◽

Equatorial Ocean ◽

The Mean ◽

The Difference

Abstract A new version of the atmosphere–ocean general circulation model cooperatively produced by the Japanese research community, known as the Model for Interdisciplinary Research on Climate (MIROC), has recently been developed. A century-long control experiment was performed using the new version (MIROC5) with the standard resolution of the T85 atmosphere and 1° ocean models. The climatological mean state and variability are then compared with observations and those in a previous version (MIROC3.2) with two different resolutions (medres, hires), coarser and finer than the resolution of MIROC5. A few aspects of the mean fields in MIROC5 are similar to or slightly worse than MIROC3.2, but otherwise the climatological features are considerably better. In particular, improvements are found in precipitation, zonal mean atmospheric fields, equatorial ocean subsurface fields, and the simulation of El Niño–Southern Oscillation. The difference between MIROC5 and the previous model is larger than that between the two MIROC3.2 versions, indicating a greater effect of updating parameterization schemes on the model climate than increasing the model resolution. The mean cloud property obtained from the sophisticated prognostic schemes in MIROC5 shows good agreement with satellite measurements. MIROC5 reveals an equilibrium climate sensitivity of 2.6 K, which is lower than that in MIROC3.2 by 1 K. This is probably due to the negative feedback of low clouds to the increasing concentration of CO2, which is opposite to that in MIROC3.2.

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Assessing the Quality of Southern Ocean Circulation in CMIP5 AOGCM and Earth System Model Simulations

Journal of Climate ◽

10.1175/jcli-d-19-0263.1 ◽

2019 ◽

Vol 32 (18) ◽

pp. 5915-5940 ◽

Cited By ~ 5

Author(s):

R. L. Beadling ◽

J. L. Russell ◽

R. J. Stouffer ◽

P. J. Goodman ◽

M. Mazloff

Keyword(s):

Southern Ocean ◽

Wind Stress ◽

Ocean Circulation ◽

Climate Models ◽

Dominant Role ◽

Surface Wind ◽

Coupled Model ◽

Observational Uncertainty ◽

Mean State

Abstract The Southern Ocean (SO) is vital to Earth’s climate system due to its dominant role in exchanging carbon and heat between the ocean and atmosphere and transforming water masses. Evaluating the ability of fully coupled climate models to accurately simulate SO circulation and properties is crucial for building confidence in model projections and advancing model fidelity. By analyzing multiple biases collectively across large model ensembles, physical mechanisms governing the diverse mean-state SO circulation found across models can be identified. This analysis 1) assesses the ability of a large ensemble of models contributed to phase 5 of the Coupled Model Intercomparison Project (CMIP5) to simulate observationally based metrics associated with an accurate representation of the Antarctic Circumpolar Current (ACC), and 2) presents a framework by which the quality of the simulation can be categorized and mechanisms governing the resulting circulation can be deduced. Different combinations of biases in critical metrics including the magnitude and position of the zonally averaged westerly wind stress maximum, wind-driven surface divergence, surface buoyancy fluxes, and properties and transport of North Atlantic Deep Water entering the SO produce distinct mean-state ACC transports. Relative to CMIP3, the quality of the CMIP5 SO simulations has improved. Eight of the thirty-one models simulate an ACC within observational uncertainty (2σ) for approximately the right reasons; that is, the models achieve accuracy in the surface wind stress forcing and the representation of the difference in the meridional density across the current. Improved observations allow for a better assessment of the SO circulation and its properties.

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ENSO Amplitude Modulation Associated with the Mean SST Changes in the Tropical Central Pacific Induced by Atlantic Multidecadal Oscillation

Journal of Climate ◽

10.1175/jcli-d-14-00018.1 ◽

2014 ◽

Vol 27 (20) ◽

pp. 7911-7920 ◽

Cited By ~ 49

Author(s):

In-Sik Kang ◽

Hyun-ho No ◽

Fred Kucharski

Keyword(s):

Observational Data ◽

Wind Stress ◽

General Circulation ◽

Southern Oscillation ◽

Coupled Model ◽

Circulation Model ◽

Atlantic Multidecadal Oscillation ◽

Positive Phase ◽

Central Pacific ◽

Easterly Wind

Abstract The mechanism associated with the modulation of the El Niño–Southern Oscillation (ENSO) amplitude caused by the Atlantic multidecadal oscillation (AMO) is investigated by using long-term historical observational data and various types of models. The observational data for the period 1900–2013 show that the ENSO variability weakened during the positive phase of the AMO and strengthened in the negative phase. Such a relationship between the AMO and ENSO amplitude has been reported by a number of previous studies. In the present study the authors demonstrate that the weakening of the ENSO amplitude during the positive phase of the AMO is related to changes of the SST cooling in the eastern and central Pacific accompanied by the easterly wind stress anomalies in the equatorial central Pacific, which were reproduced reasonably well by coupled general circulation model (CGCM) simulations performed with the Atlantic Ocean SST nudged perpetually with the observed SST representing the positive phase of the AMO and the free integration in the other ocean basins. Using a hybrid coupled model, it was determined that the mechanism associated with the weakening of the ENSO amplitude is related to the westward shift and weakening of the ENSO zonal wind stress anomalies accompanied by the westward shift of precipitation anomalies associated with the relatively cold background mean SST over the central Pacific.

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The Equatorial Pacific Cold Tongue Bias in a Coupled Climate Model

Journal of Climate ◽

10.1175/2008jcli2205.1 ◽

2008 ◽

Vol 21 (22) ◽

pp. 5852-5869 ◽

Cited By ~ 19

Author(s):

Vasubandhu Misra ◽

L. Marx ◽

M. Brunke ◽

X. Zeng

Keyword(s):

General Circulation ◽

Low Frequency ◽

Coupled Model ◽

Circulation Model ◽

Equatorial Pacific ◽

Cold Tongue ◽

Equatorial Pacific Ocean ◽

Time Step ◽

Coupling Interval ◽

The Mean

Abstract A set of multidecadal coupled ocean–atmosphere model integrations are conducted with different time steps for coupling between the atmosphere and the ocean. It is shown that the mean state of the equatorial Pacific does not change in a statistically significant manner when the coupling interval between the atmospheric general circulation model (AGCM) and the ocean general circulation model (OGCM) is changed from 1 day to 2 or even 3 days. It is argued that because the coarse resolution of the AGCM precludes resolving realistic “weather” events, changing the coupling interval from 1 day to 2 or 3 days has very little impact on the mean coupled climate. On the other hand, reducing the coupling interval to 3 h had a much stronger impact on the mean state of the equatorial Pacific and the concomitant general circulation. A novel experiment that incorporates a (pseudo) interaction of the atmosphere with SST at every time step of the AGCM was also conducted. In this unique coupled model experiment, the AGCM at every time step mutually interacts with the skin SST. This skin SST is anchored to the bulk SST, which is updated from the OGCM once a day. Both of these experiments reduced the cold tongue bias moderately over the equatorial Pacific Ocean with a corresponding reduction in the easterly wind stress bias relative to the control integration. It is stressed from the results of these model experiments that the impact of high-frequency air–sea coupling is significant on the cold tongue bias. The interannual variation of the equatorial Pacific was less sensitive to the coupling time step between the AGCM and the OGCM. Increasing (reducing) the coupling interval of the air–sea interaction had the effect of weakening (marginally strengthening) the interannual variations of the equatorial Pacific Ocean. It is argued that the low-frequency response of the upper ocean, including the cold tongue bias, is modulated by the atmospheric stochastic forcing on the coupled ocean–atmosphere system. This effect of the atmospheric stochastic forcing is affected by the frequency of the air–sea coupling and is found to be stronger than the rectification effect of the diurnal variations of the air–sea interaction on the low frequency. This may be a result of a limitation in the coupled model used in this study in which the OGCM has an inadequate vertical resolution in the mixed layer to sustain diurnal variations in the upper ocean.

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Test and evaluation of a simple parameterization to enhance air-sea coupling in a global coupled model

Satellite Oceanography and Meteorology ◽

10.18063/som.v3i3.739 ◽

2018 ◽

Vol 3 (3) ◽

Author(s):

Fanghua Xu 1

Keyword(s):

Wind Stress ◽

Ocean Circulation ◽

Southern Oscillation ◽

Current System ◽

Surface Wind ◽

Coupled Model ◽

Global Ocean ◽

Western Boundary ◽

Surface Wind Stress ◽

Gyre Circulation

A simple temperature-dependent wind stress scheme is implemented in National Center for Atmospheric Research (NCAR) Community Earth System Model (CESM), aiming to enhance positive wind stress and sea surface temperature (SST) correlation in SST-frontal regions. A series of three-year coupled experiments are conducted to determine a proper coupling coefficient for the scheme based on the agreement of surface wind stress and SST at oceanic mesoscale between model simulations and observations. Afterwards, 80-year simulations with/without the scheme are conducted to explore its effects on simulated ocean states and variability. The results show that the new scheme indeed improves the positive correlation between SST and wind stress magnitude near the large oceanic fronts. With more realistic surface heat flux and wind stress, the global SST biases are reduced. The global ocean circulation represented by barotropic stream function exhibits a weakened gyre circulation close to the western boundary separation, in agreement with previous studies. The simulation of equatorial Pacific current system is improved as well. The overestimated El Niño Southern Oscillation (ENSO) magnitude in original CESM is reduced by ~30% after using the new scheme with an improved period.

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Internal Atmospheric Dynamics and Tropical Indo-Pacific Climate Variability

Journal of the Atmospheric Sciences ◽

10.1175/jas3449.1 ◽

2005 ◽

Vol 62 (7) ◽

pp. 2220-2233 ◽

Cited By ~ 48

Author(s):

Ben P. Kirtman ◽

Kathy Pegion ◽

Saul M. Kinter

Keyword(s):

Autoregressive Model ◽

Null Hypothesis ◽

General Circulation ◽

Coupled Model ◽

Circulation Model ◽

Atmospheric Dynamics ◽

Ocean Dynamics ◽

Tropical Eastern Pacific ◽

Stochastic Forcing ◽

Sst Variability

Abstract One possible explanation for tropical sea surface temperature (SST) interannual variability is that it can be accurately described by a linear autoregressive model with damped coupled feedbacks and stochastic forcing. This autoregressive model can be viewed as a “null hypothesis” for tropical SST variability. This paper advances a new coupled general circulation model (CGCM) coupling strategy, called an interactive ensemble, as a method to test this null hypothesis. The design of the interactive ensemble procedure is to reduce the stochastic variability in the air–sea fluxes applied to the ocean component while retaining the deterministic component of the coupled feedbacks. The interactive ensemble procedure uses multiple realizations of the atmospheric GCM coupled to a single realization of the ocean GCM. The ensemble mean of the atmospheric GCM fluxes are applied to the ocean model thereby significantly reducing the variability due to internal atmospheric dynamics in the air–sea fluxes. If the null hypothesis is correct, the SST variability is reduced, and the autoregressive model defines how much the variability should be reduced. To test the null hypothesis, the interactive ensemble procedure is applied to a heuristic coupled model. Then the heuristic coupled model is used to interpret the CGCM interactive ensemble results with respect to (i) SST variance and (ii) how the amplitude of atmospheric internal dynamics depends on the evolving background SST anomaly. There are significant regions where the heuristic model fails to reproduce the CGCM results, suggesting that aspects of tropical Indo-Pacific variability in the CGCM cannot be explained by damped coupled feedbacks and stochastic forcing. These regions are largely coincident with regions of large convective anomalies. Surprisingly, significant regions were found in the tropical eastern Pacific where the variability due to internal ocean dynamics cannot be neglected.

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Interactive Feedback between the Tropical Pacific Decadal Oscillation and ENSO in a Coupled General Circulation Model

Journal of Climate ◽

10.1175/2009jcli2782.1 ◽

2009 ◽

Vol 22 (24) ◽

pp. 6597-6611 ◽

Cited By ~ 47

Author(s):

Jung Choi ◽

Soon-Il An ◽

Boris Dewitte ◽

William W. Hsieh

Keyword(s):

General Circulation ◽

Circulation Model ◽

Tropical Pacific ◽

Thermocline Depth ◽

Coupled General Circulation Model ◽

The Mean ◽

The Stability ◽

Interactive Feedback ◽

Mean State ◽

The Tropical Pacific

Abstract The output from a coupled general circulation model (CGCM) is used to develop evidence showing that the tropical Pacific decadal oscillation can be driven by an interaction between the El Niño–Southern Oscillation (ENSO) and the slowly varying mean background climate state. The analysis verifies that the decadal changes in the mean states are attributed largely to decadal changes in ENSO statistics through nonlinear rectification. This is seen because the time evolutions of the first principal component analysis (PCA) mode of the decadal-varying tropical Pacific SST and the thermocline depth anomalies are significantly correlated to the decadal variations of the ENSO amplitude (also skewness). Its spatial pattern resembles the residuals of the SST and thermocline depth anomalies after there is uneven compensation from El Niño and La Niña events. In addition, the stability analysis of a linearized intermediate ocean–atmosphere coupled system, for which the background mean states are specified, provides qualitatively consistent results compared to the CGCM in terms of the relationship between changes in the background mean states and the characteristics of ENSO. It is also shown from the stability analysis as well as the time integration of a nonlinear version of the intermediate coupled model that the mean SST for the high-variability ENSO decades acts to intensify the ENSO variability, while the mean thermocline depth for the same decades acts to suppress the ENSO activity. Thus, there may be an interactive feedback consisting of a positive feedback between the ENSO activity and the mean state of the SST and a negative feedback between the ENSO activity and the mean state of the thermocline depth. This feedback may lead to the tropical decadal oscillation, without the need to invoke any external mechanisms.

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Impact of Systematic GCM Errors on Prediction Skill as Estimated by Linear Inverse Modeling

Journal of Climate ◽

10.1175/jcli-d-20-0209.1 ◽

2020 ◽

Vol 33 (23) ◽

pp. 10073-10095

Author(s):

Ingo Richter ◽

Ping Chang ◽

Xue Liu

Keyword(s):

General Circulation ◽

Circulation Model ◽

Equatorial Pacific ◽

Prediction Skill ◽

Statistical Prediction ◽

Equatorial Atlantic ◽

Sst Variability ◽

Inverse Models ◽

Tropical Sea ◽

Mean State

Statistical prediction of tropical sea surface temperatures (SSTs) is performed using linear inverse models (LIMs) that are constructed from both observations and general circulation model (GCM) output of SST. The goals are to establish a baseline for tropical SST predictions, to examine the extent to which the skill of a GCM-derived LIM is indicative of that GCM’s skill in forecast mode, and to examine the linkages between mean state bias and prediction skill. The observation-derived LIM is more skillful than a simple persistence forecasts in most regions. Its skill also compares well with some GCM forecasts except in the equatorial Pacific, where the GCMs are superior. The observation-derived LIM is matched or even outperformed by the GCM-derived LIMs, which may be related to the longer data record available for GCMs. The GCM-derived LIMs provide a fairly good measure for the skill achieved by their parent GCMs in forecast mode. In some cases, the skill of the LIM is actually superior to that of its parent GCM, indicating that the GCM predictions may suffer from initialization problems. A weak-to-moderate relation exists between model mean state error and prediction skill in some regions. An example is the eastern equatorial Atlantic, where an erroneously deep thermocline reduces SST variability, which in turn affects prediction skill. Another example is the equatorial Pacific, where skill appears to be linked to cold SST biases in the western tropical Pacific, which may reduce the strength of air–sea coupling.

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