The Relationship of Weddell Polynya and Open-Ocean Deep Convection to the Southern Hemisphere Westerlies

2014 ◽  
Vol 44 (2) ◽  
pp. 694-713 ◽  
Author(s):  
Woo Geun Cheon ◽  
Young-Gyu Park ◽  
J. R. Toggweiler ◽  
Sang-Ki Lee
Keyword(s):  
Sea Ice ◽  
Southern Hemisphere ◽  
General Circulation ◽  
Deep Convection ◽  
Circulation Model ◽  
Open Ocean ◽  
Weddell Sea ◽  
Warm Water ◽  
Balance Model ◽  
Zonal Winds

Abstract The Weddell Polynya of the mid-1970s is simulated in an energy balance model (EBM) sea ice–ocean coupled general circulation model (GCM) with an abrupt 20% increase in the intensity of Southern Hemisphere (SH) westerlies. This small upshift of applied wind stress is viewed as a stand in for the stronger zonal winds that developed in the mid-1970s following a long interval of relatively weak zonal winds between 1954 and 1972. Following the strengthening of the westerlies in this model, the cyclonic Weddell gyre intensifies, raising relatively warm Weddell Sea Deep Water to the surface. The raised warm water then melts sea ice or prevents it from forming to produce the Weddell Polynya. Within the polynya, large heat loss to the air causes surface water to become cold and sink to the bottom via open-ocean deep convection. Thus, the underlying layers cool down, the warm water supply to the surface eventually stops, and the polynya cannot be maintained anymore. During the 100-yr-long model simulation, two Weddell Polynya events are observed. The second one occurs a few years after the first one disappears; it is much weaker and persists for less time than the first one because the underlying layer is cooler. Based on these model simulations, the authors hypothesize that the Weddell Polynya and open-ocean deep convection were responses to the stronger SH westerlies that followed a prolonged weak phase of the southern annular mode.

Zonal Wave 3 Pattern in the Southern Hemisphere generated by tropical convection

2021 ◽  
Author(s):  
Rishav Goyal ◽  
Martin Jucker ◽  
Alex Sen Gupta ◽  
Harry Hendon ◽  
Matthew England
Keyword(s):  
Sea Ice ◽  
Atmospheric Circulation ◽  
Southern Hemisphere ◽  
Ocean Circulation ◽  
General Circulation ◽  
Deep Convection ◽  
Circulation Model ◽  
Hadley Cell ◽  
Wave Source ◽  
The Tropics

Abstract A distinctive feature of the Southern Hemisphere (SH) extratropical atmospheric circulation is the quasi-stationary zonal wave 3 (ZW3) pattern, characterized by three high and three low-pressure centers around the SH extratropics. This feature is present in both the mean atmospheric circulation and its variability on daily, seasonal and interannual timescales. While the ZW3 pattern has significant impacts on meridional heat transport and Antarctic sea ice extent, the reason for its existence remains uncertain, although it has long been assumed to be linked to the existence of three major land masses in the SH extratropics. Here we use an atmospheric general circulation model to show that the stationery ZW3 pattern is instead driven by zonal asymmetric deep atmospheric convection in the tropics, with little to no role played by the orography or land masses in the extratropics. Localized regions of deep convection in the tropics form a local Hadley cell which in turn creates a wave source in the subtropics that excites a poleward and eastward propagating wave train which forms stationary waves in the SH high latitudes. Our findings suggest that changes in tropical deep convection, either due to natural variability or climate change, will impact the zonal wave 3 pattern, with implications for Southern Hemisphere climate, ocean circulation, and sea-ice.

scholarly journals On the deep convection events and Antarctic Bottom Water formation in ocean reanalysis products

2017 ◽  
Author(s):  
Wilton Aguiar ◽  
Mauricio M. Mata ◽  
Rodrigo Kerr
Keyword(s):  
General Circulation ◽  
Bottom Water ◽  
Deep Convection ◽  
General Circulation Models ◽  
Open Ocean ◽  
Weddell Sea ◽  
Antarctic Bottom Water ◽  
Ocean Reanalysis ◽  
Ocean General Circulation Models ◽  
Bottom Water Formation

Abstract. Deep convection in open ocean polynyas are common sources of error on the representation of Antarctic Bottom Water (AABW) formation in Ocean General Circulation Models. Even though those events are well described in non-assimilatory ocean simulations, recent appearance of open ocean polynya in Estimating the Circulation and Climate of the Ocean Phase II reanalysis product raises a question if this spurious event is also found in state-of-art reanalysis products. In order to answer this question, we evaluate how three recently released high-resolution ocean reanalysis form AABW in their simulations. We found that two of them (ECCO2 and SoSE) create AABW by open ocean deep convection events in Weddell Sea, showing that assimilation of sea ice has not been enough to avoid open ocean polynya appearance. The third reanalysis – My Ocean University Reading – actually creates AABW by a rather dynamically accurate mechanism, depicting both continental shelf convection, and exporting of Dense Shelf Water to open ocean. Although the accuracy of the AABW formation in this reanalysis allows an advance in represent this process, the differences found between the real ocean and the simulated one suggests that ocean reanalysis still need substantial improvements to accurately represent AABW formation.

A Simple Parameterization of Ice Leads In a General Circulation Model, and the Sensitivity of Climateto Change in Antarctic Ice Concentration

1990 ◽  
Vol 14 ◽  
pp. 266-269 ◽  
Author(s):  
Ian Simmonds ◽  
W.F. Budd
Keyword(s):  
Sea Ice ◽  
General Circulation Model ◽  
General Circulation ◽  
Sensible Heat Flux ◽  
Weighted Average ◽  
Circulation Model ◽  
Open Water ◽  
Weddell Sea ◽  
Antarctic Sea Ice ◽  
Ice Leads

We present a simple parameterization of the effect of open leads in a general circulation model of the atmosphere. We consider only the case where the sea ice distribution is prescribed (i.e., not interactive) and the fraction of open water in the ice is also prescribed and set at the same value at all points in the Southern Hemisphere and a different value in the Northern Hemisphere. We approximate the distribution of sea ice over a model “grid box” as a part of the box being covered by solid ice of uniform thickness and the complement of the box consisting of open water at a fixed -1.8 C. Because of the nonlinearity in the flux computations, separate calculations are performed over the solid sea ice and over the open leads. The net fluxes conveyed to the atmosphere over the grid box are determined by performing the appropriate area-weighted average over the two surface types. We report on an experiment designed to assess the sensitivity of the modelled climate to the imposition of a 50% concentration in the winter Antarctic sea ice. Significant warming of up to 6°C takes place in the vicinity of and above the Antarctic sea ice and is associated with significant changes in the zonal wind structure. Pressure reductions are simulated over the sea ice, being particularly marked in the Weddell Sea region, and an anomalous east-west aligned ridge is simulated at about 60°S. Very large changes in the sensible heat flux (in excess of 200 Wm−2) are simulated near the coast of Antarctica.

Improved sea-ice prediction in the Weddell Sea using sea-ice thickness initialization

2021 ◽  
Author(s):  
Yushi Morioka ◽  
Doroteaciro Iovino ◽  
Andrea Cipollone ◽  
Simona Masina ◽  
Swadhin Behera
Keyword(s):  
Sea Ice ◽  
General Circulation ◽  
Climate Models ◽  
Circulation Model ◽  
Weddell Sea ◽  
Ice Thickness ◽  
Austral Spring ◽  
Sea Ice Concentration ◽  
Sea Ice Thickness ◽  
The Antarctic

<p>Skillful sea-ice prediction in the Antarctic Ocean remains a big challenge due to paucity of sea-ice observations and insufficient representation of sea-ice processes in climate models. This study demonstrates that the Antarctic sea-ice concentration (SIC) prediction is significantly improved using a coupled general circulation model (SINTEX-F2) in which the model’s SIC and sea-ice thickness (SIT) are initialized with the ocean/sea-ice reanalysis product (C-GLORSv7). It is found that the wintertime SIT initialization adds positive values to the prediction skills of the summertime SIC, most effectively in the Weddell Sea where the SIT climatology and variability are the largest among the Antarctic Seas. Examination of the SIT balance during low sea-ice years of the Weddell Sea shows that negative SIT anomalies initialized in June retain the memory throughout austral winter (July-September) owing to horizontal advection of the SIT anomalies by sea-ice velocities. The negative SIT anomalies continue to develop in austral spring (October-December) owing to more incoming solar radiation via ice-albedo feedback and the associated warming of mixed layer. This results in further sea-ice decrease during austral summer (January-March). Concomitantly, the model reasonably reproduces atmospheric circulation anomalies in the Amundsen-Bellingshausen Seas as well as the Weddell Sea during the development of the negative sea-ice anomalies. These results provide solid evidence that the wintertime SIT initialization benefits skillful summertime sea-ice prediction in the Antarctic Seas.</p>

The Role of Oscillating Southern Hemisphere Westerly Winds: Southern Ocean Coastal and Open-Ocean Polynyas

2018 ◽  
Vol 31 (3) ◽  
pp. 1053-1073 ◽  
Author(s):  
Woo Geun Cheon ◽  
Chang-Bong Cho ◽  
Arnold L. Gordon ◽  
Young Ho Kim ◽  
Young-Gyu Park
Keyword(s):  
Southern Ocean ◽  
Sea Ice ◽  
Southern Hemisphere ◽  
Ross Sea ◽  
Deep Ocean ◽  
Open Ocean ◽  
Weddell Sea ◽  
Wind Forcing ◽  
Westerly Winds ◽  
Southern Hemisphere Westerly Winds

Abstract An oscillation in intensity of the Southern Hemisphere westerly winds is a major characteristic of the southern annular mode. Its impact upon the sea ice–ocean interactions in the Weddell and Ross Seas is investigated by a sea ice–ocean general circulation model coupled to an energy balance model for three temporal scales and two amplitudes of intensity. It is found that the oscillating wind forcing over the Southern Ocean plays a significant role both in regulating coastal polynyas along the Antarctic margins and in triggering open-ocean polynyas. The formation of coastal polynya in the western Weddell and Ross Seas is enhanced with the intensifying winds, resulting in an increase in the salt flux into the ocean via sea ice formation. Under intensifying winds, an instantaneous spinup within the Weddell and Ross Sea cyclonic gyres causes the warm deep water to upwell, triggering open-ocean polynyas with accompanying deep ocean convection. In contrast to coastal polynyas, open-ocean polynyas in the Weddell and Ross Seas respond differently to the wind forcing and are dependent on its period. That is, the Weddell Sea open-ocean polynya occurs earlier and more frequently than the Ross Sea open-ocean polynya and, more importantly, does not occur when the period of oscillation is sufficiently short. The strong stratification of the Ross Sea and the contraction of the Ross gyre due to the southward shift of Antarctic Circumpolar Current fronts provide unfavorable conditions for the Ross Sea open-ocean polynya. The recovery time of deep ocean heat controls the occurrence frequency of the Weddell Sea open-ocean polynya.

scholarly journals On deep convection events and Antarctic Bottom Water formation in ocean reanalysis products

Ocean Science ◽  
2017 ◽  
Vol 13 (6) ◽  
pp. 851-872 ◽  
Author(s):  
Wilton Aguiar ◽  
Mauricio M. Mata ◽  
Rodrigo Kerr
Keyword(s):  
Sea Ice ◽  
Bottom Water ◽  
Deep Convection ◽  
Open Ocean ◽  
Weddell Sea ◽  
Ocean Dynamics ◽  
Antarctic Bottom Water ◽  
Ocean Reanalysis ◽  
Reanalysis Product ◽  
Warm Deep Water

Abstract. Open ocean deep convection is a common source of error in the representation of Antarctic Bottom Water (AABW) formation in ocean general circulation models. Although those events are well described in non-assimilatory ocean simulations, the recent appearance of a massive open ocean polynya in the Estimating the Circulation and Climate of the Ocean Phase II reanalysis product (ECCO2) raises questions on which mechanisms are responsible for those spurious events and whether they are also present in other state-of-the-art assimilatory reanalysis products. To investigate this issue, we evaluate how three recently released high-resolution ocean reanalysis products form AABW in their simulations. We found that two of the products create AABW by open ocean deep convection events in the Weddell Sea that are triggered by the interaction of sea ice with the Warm Deep Water, which shows that the assimilation of sea ice is not enough to avoid the appearance of open ocean polynyas. The third reanalysis, My Ocean University Reading UR025.4, creates AABW using a rather dynamically accurate mechanism. The UR025.4 product depicts both continental shelf convection and the export of Dense Shelf Water to the open ocean. Although the accuracy of the AABW formation in this reanalysis product represents an advancement in the representation of the Southern Ocean dynamics, the differences between the real and simulated processes suggest that substantial improvements in the ocean reanalysis products are still needed to accurately represent AABW formation.

scholarly journals A Simple Parameterization of Ice Leads In a General Circulation Model, and the Sensitivity of Climateto Change in Antarctic Ice Concentration

1990 ◽  
Vol 14 ◽  
pp. 266-269 ◽  
Author(s):  
Ian Simmonds ◽  
W.F. Budd
Keyword(s):  
Sea Ice ◽  
General Circulation Model ◽  
General Circulation ◽  
Sensible Heat Flux ◽  
Weighted Average ◽  
Circulation Model ◽  
Open Water ◽  
Weddell Sea ◽  
Antarctic Sea Ice ◽  
Ice Leads

We present a simple parameterization of the effect of open leads in a general circulation model of the atmosphere. We consider only the case where the sea ice distribution is prescribed (i.e., not interactive) and the fraction of open water in the ice is also prescribed and set at the same value at all points in the Southern Hemisphere and a different value in the Northern Hemisphere. We approximate the distribution of sea ice over a model “grid box” as a part of the box being covered by solid ice of uniform thickness and the complement of the box consisting of open water at a fixed -1.8 C. Because of the nonlinearity in the flux computations, separate calculations are performed over the solid sea ice and over the open leads. The net fluxes conveyed to the atmosphere over the grid box are determined by performing the appropriate area-weighted average over the two surface types.We report on an experiment designed to assess the sensitivity of the modelled climate to the imposition of a 50% concentration in the winter Antarctic sea ice. Significant warming of up to 6°C takes place in the vicinity of and above the Antarctic sea ice and is associated with significant changes in the zonal wind structure. Pressure reductions are simulated over the sea ice, being particularly marked in the Weddell Sea region, and an anomalous east-west aligned ridge is simulated at about 60°S. Very large changes in the sensible heat flux (in excess of 200 Wm−2) are simulated near the coast of Antarctica.

scholarly journals Internal Ocean Dynamics Control the Long-Term Evolution of Weddell Sea Polynya Activity

2021 ◽  
Vol 3 ◽  
Author(s):  
Jonathan W. Rheinlænder ◽  
Lars H. Smedsrud ◽  
Kerim H. Nisanciouglu
Keyword(s):  
Sea Ice ◽  
Deep Convection ◽  
Vertical Mixing ◽  
Open Ocean ◽  
Weddell Sea ◽  
Ocean Dynamics ◽  
Heat Reservoir ◽  
Ice Dynamics

Open-ocean polynyas effectively couple the ocean and atmosphere through large ice-free areas within the sea-ice cover, release vast quantities of oceanic heat, and impact deep ocean ventilation. Changes in polynya activity, particularly in the Weddell Sea, may be key to longer time-scale climate fluctuations, feedbacks and abrupt change. While changes in the occurrence of Weddell Sea polynyas are generally attributed to changes in the atmospheric surface forcing, the role of internal ocean dynamics for polynya variability is not well-resolved. In this study we employ a global coupled ocean-sea ice model with a repeating annual atmospheric cycle to explore changes in Weddell Sea water mass properties, stratification and ocean circulation driven by open-ocean polynyas. During the 1300-year long simulation, two large polynyas occur in the central Weddell Sea. Our results suggest that Weddell polynyas may be triggered without inter-annual changes in the atmospheric forcing. This highlights the role of ocean processes in preconditioning and triggering open-ocean polynyas on multi-centennial time-scales. The simulated polynyas form due to internal ocean-sea ice dynamics associated with a slow build-up and subsequent release of subsurface heat. A strong stratification and weak vertical mixing is necessary for building the subsurface heat reservoir. Once the water column turns unstable, enhanced vertical mixing of warm and saline waters into the surface layer causes efficient sea ice melt and the polynya appears. Subsequent, vigorous deep convection is maintained through upwelling of warm deep water leading to enhanced bottom water formation. We find a cessation of simulated deep convection and polynya activity due to long-term cooling and freshening of the subsurface heat reservoir. As subsurface waters in the Southern Ocean are now becoming warmer and saltier, we speculate that larger and more persistent Weddell polynyas could become more frequent in the future.

scholarly journals Summertime sea-ice prediction in the Weddell Sea improved by sea-ice thickness initialization

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Yushi Morioka ◽  
Doroteaciro Iovino ◽  
Andrea Cipollone ◽  
Simona Masina ◽  
Swadhin K. Behera
Keyword(s):  
Sea Ice ◽  
General Circulation ◽  
Climate Models ◽  
Circulation Model ◽  
Weddell Sea ◽  
Ice Thickness ◽  
Austral Spring ◽  
Sea Ice Concentration ◽  
Sea Ice Thickness ◽  
The Antarctic

AbstractSkillful sea-ice prediction in the Antarctic Ocean remains a big challenge due to paucity of sea-ice observations and insufficient representation of sea-ice processes in climate models. Using a coupled general circulation model, this study demonstrates skillful prediction of the summertime sea-ice concentration (SIC) in the Weddell Sea with wintertime SIC and sea-ice thickness (SIT) initializations. During low sea-ice years of the Weddell Sea, negative SIT anomalies initialized in June retain the memory throughout austral winter owing to horizontal advection of the SIT anomalies. The SIT anomalies continue to develop in austral spring owing to more incoming solar radiation and the associated warming of mixed layer, contributing to further sea-ice decrease during late austral summer-early autumn. Concomitantly, the model reasonably reproduces atmospheric circulation anomalies during austral spring in the Amundsen-Bellingshausen Seas besides the Weddell Sea. These results provide evidence that the wintertime SIT initialization benefits skillful summertime sea-ice prediction in the Antarctic Seas.

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