Response of the large‐scale, Southern Hemisphere extratropical atmospheric circulation to extremes of Antarctic sea‐ice concentration in a general circulation model

2001 ◽  
Vol 25 (3) ◽  
pp. 218-238 ◽  
Author(s):  
Marilyn Raphael
Keyword(s):  
Sea Ice ◽  
Atmospheric Circulation ◽  
Southern Hemisphere ◽  
General Circulation Model ◽  
General Circulation ◽  
Large Scale ◽  
Circulation Model ◽  
Sea Ice Concentration ◽  
Antarctic Sea Ice ◽  
Ice Concentration

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.

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 The benefit of using sea ice concentration satellite data products with uncertainty estimates in summer sea ice data assimilation

2015 ◽  
Vol 9 (2) ◽  
pp. 2543-2562
Author(s):  
Q. Yang ◽  
M. Losch ◽  
S. Losa ◽  
T. Jung ◽  
L. Nerger ◽  
...  
Keyword(s):  
Data Assimilation ◽  
Sea Ice ◽  
General Circulation ◽  
Circulation Model ◽  
Data Retrieval ◽  
Data Uncertainty ◽  
Concentration Data ◽  
Sea Ice Concentration ◽  
Uncertainty Estimates ◽  
Ice Concentration

Abstract. We present sensitivity experiments in which the Ocean and Sea Ice Satellite Application Facility (OSISAF) near-real time sea ice concentration data and the recently released Sea Ice Climate Change Initiative (SICCI) data are assimilated during summer. The data assimilation system uses the MIT general circulation model (MITgcm) and a local Singular Evolutive Interpolated Kalman (LSEIK) filter. Atmospheric forcing uncertainties are modelled by using atmospheric ensemble forcing which is taken from the UK Met Office (UKMO) system available through the TIGGE (THORPEX Interactive Grand Global Ensemble) database. When a constant data uncertainty is assumed, the assimilation of SICCI concentrations outperforms the assimilation of OSISAF data in both concentration and thickness forecasts. This is probably because the SICCI data retrieval uses an improved processing algorithms and methodologies. For the assimilation of SICCI data, using the observation uncertainties that are provided with the data improves the ensemble mean state of ice concentration compared to using constant data errors, but does not improve the ice thickness. This is caused by a mismatch between the SICCI concentration and the modelled physical ice concentration. To account for this mismatch the SICCI product should feature larger uncertainties in summer. Consistently, thickness forecasts can be improved by raising the minimum observation uncertainty to inflate the underestimated data error and ensemble spread.

Seasonal Relationships between Large-Scale Climate Variability and Antarctic Sea Ice Concentration

2012 ◽  
Vol 25 (16) ◽  
pp. 5451-5469 ◽  
Author(s):  
Graham R. Simpkins ◽  
Laura M. Ciasto ◽  
David. W. J. Thompson ◽  
Matthew H. England
Keyword(s):  
Climate Variability ◽  
Sea Ice ◽  
Large Scale ◽  
Southern Oscillation ◽  
Principal Component ◽  
Southern Annular Mode ◽  
Enso Cycle ◽  
Sea Ice Concentration ◽  
Antarctic Sea Ice ◽  
Ice Concentration

Abstract The observed relationships between anomalous Antarctic sea ice concentration (SIC) and the leading patterns of Southern Hemisphere (SH) large-scale climate variability are examined as a function of season over 1980–2008. Particular emphasis is placed on 1) the interactions between SIC, the southern annular mode (SAM), and El Niño–Southern Oscillation (ENSO); and 2) the contribution of these two leading modes to the 29-yr trends in sea ice. Regression, composite, and principal component analyses highlight a seasonality in SH sea ice–atmosphere interactions, whereby Antarctic sea ice variability exhibits the strongest linkages to the SAM and ENSO during the austral cold season months. As noted in previous work, a dipole in SIC anomalies emerges in relation to the SAM, characterized by centers of action located near the Bellingshausen/Weddell and Amundsen/eastern Ross Seas. The structure and magnitude of this SIC dipole is found to vary considerably as a function of season, consistent with the seasonality of the overlying atmospheric circulation anomalies. Relative to the SAM, the pattern of sea ice anomalies linked to ENSO exhibits a similar seasonality but tends to be weaker in amplitude and more diffuse in structure. The relationships between ENSO and sea ice also exhibit a substantial nonlinear component, highlighting the need to consider both season and phase of the ENSO cycle when diagnosing ENSO–SIC linkages. Trends in SIC over 1980–2008 are not significantly related to trends in either the SAM or ENSO during any season, including austral summer when the trend in the SAM is most pronounced.

scholarly journals Atmospheric Forcing of Antarctic Sea Ice on Intraseasonal Time Scales

2012 ◽  
Vol 25 (17) ◽  
pp. 5962-5975 ◽  
Author(s):  
James A. Renwick ◽  
Alison Kohout ◽  
Sam Dean
Keyword(s):  
Sea Ice ◽  
Atmospheric Circulation ◽  
Growth Period ◽  
Internal Variability ◽  
Sea Ice Concentration ◽  
Maximum Covariance Analysis ◽  
Antarctic Sea Ice ◽  
Zonal Wavenumber ◽  
Ice Concentration ◽  
Flow Mechanisms

Abstract Intraseasonal relationships between Antarctic sea ice and atmospheric circulation have been investigated using a 29-yr record of pentad-mean Antarctic sea ice concentration and Southern Hemisphere 500-hPa height fields. Analyses were carried out for four sea ice seasons: minimum extent, growth, maximum extent, and decay. Interannual variability was removed from both datasets to focus on intraseasonal variations. Patterns of sea ice variability and linkages to the atmospheric circulation varied markedly with season. The strongest and most coherent relationships were evident during the maximum ice extent period and to a lesser degree during the growth period. At those times of year, the strongest relationships were associated with atmospheric circulation anomalies leading sea ice anomalies by 4 or 5 days, suggesting that variations in the atmospheric circulation force changes in the sea ice field. Ice decreases are generally found in regions of poleward flow and ice increases are found in regions of equatorward flow. Mechanisms appear to be related both to thermal advection and to mechanical forcing, with the relative importance of each varying in space and in time. During the period of maximum ice extent, the leading pattern from a maximum covariance analysis between 500-hPa height and sea ice concentration accounted for 38% of the squared covariance between fields, and the associated time series were correlated at 0.74. The leading patterns of variability exhibit clear zonal wavenumber 3 signatures and appear to be largely a result of internal variability in the extratropical circulation.

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.

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