scholarly journals Publisher Correction: Assessing the impact of suppressing Southern Ocean SST variability in a coupled climate model

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Ariaan Purich ◽  
Ghyslaine Boschat ◽  
Giovanni Liguori
Keyword(s):  
Southern Ocean ◽  
Climate Model ◽  
Coupled Climate Model ◽  
Sst Variability ◽  
The Impact

scholarly journals Assessing the impact of suppressing Southern Ocean SST variability in a coupled climate model

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Ariaan Purich ◽  
Ghyslaine Boschat ◽  
Giovanni Liguori
Keyword(s):  
Southern Ocean ◽  
Sea Ice ◽  
Ocean Circulation ◽  
Climate Model ◽  
Southern Annular Mode ◽  
Coupled Climate Model ◽  
Annular Mode ◽  
Sst Variability ◽  
The Impact ◽  
Mean State

AbstractThe Southern Ocean exerts a strong influence on global climate, regulating the storage and transport of heat, freshwater and carbon throughout the world’s oceans. While the majority of previous studies focus on how wind changes influence Southern Ocean circulation patterns, here we set out to explore potential feedbacks from the ocean to the atmosphere. To isolate the role of oceanic variability on Southern Hemisphere climate, we perform coupled climate model experiments in which Southern Ocean variability is suppressed by restoring sea surface temperatures (SST) over 40°–65°S to the model’s monthly mean climatology. We find that suppressing Southern Ocean SST variability does not impact the Southern Annular Mode, suggesting air–sea feedbacks do not play an important role in the persistence of the Southern Annular Mode in our model. Suppressing Southern Ocean SST variability does lead to robust mean-state changes in SST and sea ice. Changes in mixed layer processes and convection associated with the SST restoring lead to SST warming and a sea ice decline in southern high latitudes, and SST cooling in midlatitudes. These results highlight the impact non-linear processes can have on a model’s mean state, and the need to consider these when performing simulations of the Southern Ocean.

scholarly journals Impacts of Broad-Scale Surface Freshening of the Southern Ocean in a Coupled Climate Model

2018 ◽  
Vol 31 (7) ◽  
pp. 2613-2632 ◽  
Author(s):  
Ariaan Purich ◽  
Matthew H. England ◽  
Wenju Cai ◽  
Arnold Sullivan ◽  
Paul J. Durack
Keyword(s):  
Southern Ocean ◽  
Sea Ice ◽  
Ocean Circulation ◽  
Climate Model ◽  
Cmip5 Models ◽  
Coupled Climate Model ◽  
Surface Cooling ◽  
Subsurface Waters ◽  
The Impact ◽  
Scale Surface

The Southern Ocean surface has freshened in recent decades, increasing water column stability and reducing upwelling of warmer subsurface waters. The majority of CMIP5 models underestimate or fail to capture this historical surface freshening, yet little is known about the impact of this model bias on regional ocean circulation and hydrography. Here experiments are performed using a global coupled climate model with additional freshwater applied to the Southern Ocean to assess the influence of recent surface freshening. The simulations explore the impact of persistent and long-term broad-scale freshening as a result of processes including precipitation minus evaporation changes. Thus, unlike previous studies, the freshening is applied as far north as 55°S, beyond the Antarctic ice margin. It is found that imposing a large-scale surface freshening causes a surface cooling and sea ice increase under preindustrial conditions, because of a reduction in ocean convection and weakened entrainment of warm subsurface waters into the surface ocean. This is consistent with intermodel relationships between CMIP5 models and the simulations, suggesting that models with larger surface freshening also exhibit stronger surface cooling and increased sea ice. Additional experiments are conducted with surface salinity restoration applied to capture observed regional salinity trends. Remarkably, without any mechanical wind trend forcing, these simulations accurately represent the spatial pattern of observed surface temperature and sea ice trends around Antarctica. This study highlights the importance of accurately simulating changes in Southern Ocean salinity to capture changes in ocean circulation, sea surface temperature, and sea ice.

scholarly journals The Southern Hemisphere Westerlies in a Warming World: Propping Open the Door to the Deep Ocean

2006 ◽  
Vol 19 (24) ◽  
pp. 6382-6390 ◽  
Author(s):  
Joellen L. Russell ◽  
Keith W. Dixon ◽  
Anand Gnanadesikan ◽  
Ronald J. Stouffer ◽  
J. R. Toggweiler
Keyword(s):  
Carbon Dioxide ◽  
Southern Ocean ◽  
Climate Model ◽  
Deep Ocean ◽  
Global Ocean ◽  
Westerly Winds ◽  
Anthropogenic Carbon ◽  
Warming World ◽  
The Impact ◽  
Anthropogenic Carbon Dioxide

Abstract A coupled climate model with poleward-intensified westerly winds simulates significantly higher storage of heat and anthropogenic carbon dioxide by the Southern Ocean in the future when compared with the storage in a model with initially weaker, equatorward-biased westerlies. This difference results from the larger outcrop area of the dense waters around Antarctica and more vigorous divergence, which remains robust even as rising atmospheric greenhouse gas levels induce warming that reduces the density of surface waters in the Southern Ocean. These results imply that the impact of warming on the stratification of the global ocean may be reduced by the poleward intensification of the westerlies, allowing the ocean to remove additional heat and anthropogenic carbon dioxide from the atmosphere.

Circumpolar Deep Water Circulation and Variability in a Coupled Climate Model

2006 ◽  
Vol 36 (8) ◽  
pp. 1523-1552 ◽  
Author(s):  
Agus Santoso ◽  
Matthew H. England ◽  
Anthony C. Hirst
Keyword(s):  
Southern Ocean ◽  
Southern Hemisphere ◽  
Time Scales ◽  
North Atlantic ◽  
Deep Water ◽  
Climate Model ◽  
Coupled Climate Model ◽  
Circumpolar Deep Water ◽  
The North ◽  
The North Atlantic

Abstract The natural variability of Circumpolar Deep Water (CDW) is analyzed using a long-term integration of a coupled climate model. The variability is decomposed using a standard EOF analysis into three separate modes accounting for 68% and 82% of the total variance in the upper and lower CDW layers, respectively. The first mode exhibits an interbasin-scale variability on multicentennial time scales, originating in the North Atlantic and flowing southward into the Southern Ocean via North Atlantic Deep Water (NADW). Salinity dipole anomalies appear to propagate around the Atlantic meridional overturning circulation on these time scales with the strengthening and weakening of NADW formation. The anomaly propagates northward from the midlatitude subsurface of the South Atlantic and sinks in the North Atlantic before flowing southward along the CDW isopycnal layers. This suggests an interhemispheric connection in the generation of the first CDW variability mode. The second mode shows a localized θ−S variability in the Brazil–Malvinas confluence zone on multidecadal to centennial time scales. Heat and salt budget analyses reveal that this variability is controlled by meridional advection driven by fluctuations in the strength of the Deep Western Boundary and the Malvinas Currents. The third mode suggests an Antarctic Intermediate Water source in the South Pacific contributing to variability in upper CDW. It is further found that NADW formation is mainly buoyancy driven on the time scales resolved, with only a weak connection with Southern Hemisphere winds. On the other hand, Southern Hemisphere winds have a more direct influence on the rate of NADW outflow into the Southern Ocean. The model’s spatial pattern of θ−S variability is consistent with the limited observational record in the Southern Hemisphere. However, some observations of decadal CDW θ−S changes are beyond that seen in the model in its unperturbed state.

scholarly journals Transient Response of the Southern Ocean to Changing Ozone: Regional Responses and Physical Mechanisms

2017 ◽  
Vol 30 (7) ◽  
pp. 2463-2480 ◽  
Author(s):  
William J. M. Seviour ◽  
Anand Gnanadesikan ◽  
Darryn Waugh ◽  
Marie-Aude Pradal
Keyword(s):  
Southern Ocean ◽  
Climate Model ◽  
Cold Water ◽  
Deep Convection ◽  
Weddell Sea ◽  
Freshwater Flux ◽  
Surface Salinity ◽  
Sea Ice Concentration ◽  
Climate Model Simulations ◽  
The Impact

The impact of changing ozone on the climate of the Southern Ocean is evaluated using an ensemble of coupled climate model simulations. By imposing a step change from 1860 to 2000 conditions, response functions associated with this change are estimated. The physical processes that drive this response are different across time periods and locations, as is the sign of the response itself. Initial cooling in the Pacific sector is driven not only by the increased winds pushing cold water northward, but also by the southward shift of storms associated with the jet stream. This shift drives both an increase in cloudiness (resulting in less absorption of solar radiation) and an increase in net freshwater flux to the ocean (resulting in a decrease in surface salinity that cuts off mixing of warm water from below). A subsurface increase in temperature associated with this reduction in mixing then upwells along the Antarctic coast, producing a subsequent warming. Similar changes in convective activity occur in the Weddell Sea but are offset in time. Changes in sea ice concentration also play a role in modulating solar heating of the ocean near the continent. The time scale for the initial cooling is much longer than that seen in NCAR CCSM3.5, possibly reflecting differences in natural convective variability between that model (which has essentially no Southern Ocean deep convection) and the one used here (which has a large and possibly unrealistically regular mode of convection) or to differences in cloud feedbacks or in the location of the anomalous winds.

Abyssal Ocean Warming and Salinification after Weddell Polynyas in the GFDL CM2G Coupled Climate Model

2015 ◽  
Vol 45 (11) ◽  
pp. 2755-2772 ◽  
Author(s):  
Hannah Zanowski ◽  
Robert Hallberg ◽  
Jorge L. Sarmiento
Keyword(s):  
Southern Ocean ◽  
Climate Model ◽  
Deep Ocean ◽  
Weddell Sea ◽  
Coupled Climate Model ◽  
Composite Event ◽  
Recent Warming ◽  
Time Period ◽  
Ocean Properties

AbstractThe role of Weddell Sea polynyas in establishing deep-ocean properties is explored in the NOAA Geophysical Fluid Dynamics Laboratory’s (GFDL) coupled climate model CM2G. Using statistical composite analysis of over 30 polynya events that occur in a 2000-yr-long preindustrial control run, the temperature, salinity, and water mass changes associated with the composite event are quantified. For the time period following the composite polynya cessation, termed the “recovery,” warming between 0.002° and 0.019°C decade−1 occurs below 4200 m in the Southern Ocean basins. Temperature and salinity changes are strongest in the Southern Ocean and the South Atlantic near the polynya formation region. Comparison of the model results with abyssal temperature observations reveals that the 1970s Weddell Polynya recovery could account for 10% ± 8% of the recent warming in the abyssal Southern Ocean. For individual Southern Ocean basins, this percentage is as little as 6% ± 11% or as much as 34% ± 13%.

scholarly journals The impact of equilibrating hemispheric albedos on tropical performance in the HadGEM2‐ES coupled climate model

2016 ◽  
Vol 43 (1) ◽  
pp. 395-403 ◽  
Author(s):  
Jim M. Haywood ◽  
Andy Jones ◽  
Nick Dunstone ◽  
Sean Milton ◽  
Michael Vellinga ◽  
...  
Keyword(s):  
Climate Model ◽  
Coupled Climate Model ◽  
The Impact

Global Climate Model Simulations of Natural Aerosols over the Southern Ocean

2021 ◽  
Author(s):  
Yusuf Bhatti ◽  
Laura Revell ◽  
Adrian McDonald ◽  
Jonny Willaims
Keyword(s):  
Southern Ocean ◽  
Dimethyl Sulfide ◽  
Climate Model ◽  
Global Climate ◽  
Global Climate Model ◽  
Cloud Formation ◽  
Sulfate Aerosols ◽  
Climate Model Simulations ◽  
Aerosol Cloud Interactions ◽  
The Impact

<p>We studied sulfate aerosols over the Southern Ocean using the atmosphere-only climate model HadGEM3-GA7.1. The model contains biases in the aerosol seasonal variability over the Southern Ocean (40°S to 60°S), which cascade to uncertainties in aerosol-cloud interactions. Aerosols over the Southern Ocean are primarily natural in origin, such as sea spray aerosol and sulfate aerosol formed by phytoplankton-produced dimethyl sulfide (DMS).</p><p>The current sulfate chemistry scheme implemented in the model simplifies the oxidation pathways for DMS, which has been identified as a major source of the seasonal bias present. The simulations performed here incorporate a comprehensive sulfate scheme in both the gas and aqueous-phase. An intermediate complexity biogeochemical dynamic model, MEDUSA, simulated a global climatology of seawater DMS, which is compared with a seawater DMS observational dataset from 2011. We compared the seasonality of sulfate aerosols over the Southern Ocean, and the global distribution using the two seawater DMS climatologies. Simulated aerosols over the Southern Ocean were evaluated against satellite and in-situ observations. The results show the impact of seawater DMS on sulfate aerosols and their influence on cloud formation.</p>

scholarly journals Impact of increasing Antarctic ice-shelf melting on Southern Ocean hydrography

2012 ◽  
Vol 58 (212) ◽  
pp. 1191-1200 ◽  
Author(s):  
Caixin Wang ◽  
Keguang Wang
Keyword(s):  
Southern Ocean ◽  
Bottom Water ◽  
Climate Model ◽  
Ice Shelf ◽  
Ocean Climate ◽  
Deep Waters ◽  
Qualitative Understanding ◽  
The Difference ◽  
Ocean Climate Model ◽  
The Impact

AbstractSouthern Ocean hydrography has undergone substantial changes in recent decades, concurrent with an increase in the rate of Antarctic ice-shelf melting (AISM). We investigate the impact of increasing AISM on hydrography through a twin numerical experiment, with and without AISM, using a global coupled sea-ice/ocean climate model. The difference between these simulations gives a qualitative understanding of the impact of increasing AISM on hydrography. It is found that increasing AISM tends to freshen the surface water, warm the intermediate and deep waters, and freshen and warm the bottom water in the Southern Ocean. Such effects are consistent with the recent observed trends, suggesting that increasing AISM is likely a significant contributor to the changes in the Southern Ocean. Our analyses indicate potential positive feedback between hydrography and AISM that would amplify the effect on both Southern Ocean hydrography and Antarctic ice-shelf loss caused by external factors such as changing Southern Hemisphere winds.

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