scholarly journals A Station-Based Southern Annular Mode Index from 1884 to 2005

2009 ◽  
Vol 22 (4) ◽  
pp. 940-950 ◽  
Author(s):  
Martin Visbeck
Keyword(s):  
Mass Conservation ◽  
Southern Annular Mode ◽  
Sea Level Pressure ◽  
Subtropical Zone ◽  
Annular Mode ◽  
Continuous Surface ◽  
Pressure Anomaly ◽  
Antarctic Continent ◽  
The Antarctic ◽  
Atmospheric Mass

Abstract Atmospheric pressure observations from the Southern Hemisphere are used to estimate monthly and annually averaged indexes of the southern annular mode (SAM) back to 1884. This analysis groups all relevant observations in the following four regions: one for Antarctica and three in the subtropical zone. Continuous surface pressure observations are available at a number of locations in the subtropical regions since the end of the nineteenth century. However, year-round observations in the subpolar region near the Antarctic continent began only during the 1940–60 period. The shorter Antarctic records seriously compromise the length of a traditionally estimated SAM index. To improve the situation “proxy” estimates of Antarctic sea level pressure anomalies are provided based on the concept of atmospheric mass conservation poleward of 20°S. This allows deriving a longer SAM index back to 1884. Several aspects of the new record, its statistical properties, seasonal trends, and the regional pressure anomaly correlations, are presented.

Winter climate change on the northern and southern Antarctic Peninsula

2020 ◽  
Vol 32 (5) ◽  
pp. 408-424
Author(s):  
Oleksandr M. Evtushevsky ◽  
Volodymyr O. Kravchenko ◽  
Asen V. Grytsai ◽  
Gennadi P. Milinevsky
Keyword(s):  
Time Series ◽  
Surface Temperature ◽  
Antarctic Peninsula ◽  
Southern Annular Mode ◽  
Meridional Wind ◽  
Winter Climate ◽  
Annular Mode ◽  
Temperature Trends ◽  
Pressure Anomaly ◽  
Tropical Sea

AbstractDifferences in the decadal trend in the winter surface temperature in the northern and southern Antarctic Peninsula have been analysed. Time series from the two stations Esperanza and Faraday/Vernadsky since the early 1950s are used. The two time series are strongly correlated only during the 1980s and 1990s when their variability and trends are associated with both the Niño-4 region and Southern Annular Mode impacts. The winter cooling at the Faraday/Vernadsky station contrasts with the winter warming at the Esperanza station during the period of 2006–17. The different temperature trends are accompanied by weak correlations between the temperatures at these two stations. Linearly congruent components of the station temperature trends in 2006–17 indicate a dominant contribution of Southern Annular Mode (tropical sea surface temperature anomalies) to warming (cooling) in the northern (southern) Peninsula. Distinctive impacts of climate modes are observed in combination with the recent deepening of the negative sea-level pressure anomaly to the west of the peninsula and the related change in the zonal and meridional wind components. These factors apparently contribute to the occurrence of the boundary that crosses the peninsula and divides it into sub-regions with warming and cooling.

scholarly journals Rainfall Changes over Southwestern Australia and Their Relationship to the Southern Annular Mode and ENSO

2014 ◽  
Vol 27 (15) ◽  
pp. 5801-5814 ◽  
Author(s):  
Bhupendra A. Raut ◽  
Christian Jakob ◽  
Michael J. Reeder
Keyword(s):  
Southern Oscillation ◽  
Summer Rainfall ◽  
Southern Annular Mode ◽  
Winter Rainfall ◽  
Sea Level Pressure ◽  
Annular Mode ◽  
Southwestern Australia ◽  
Synoptic Conditions ◽  
The Mean ◽  
Rainfall Patterns

Abstract Since the 1970s, winter rainfall over coastal southwestern Australia (SWA) has decreased by 10%–20%, while summer rainfall has been increased by 40%–50% in the semiarid inland area. In this paper, a K-means algorithm is used to cluster rainfall patterns directly as opposed to the more conventional approach of clustering synoptic conditions (usually the mean sea level pressure) and inferring the associated rainfall. It is shown that the reduction in the coastal rainfall during winter is mainly due to fewer westerly fronts in June and July. The reduction in the frequency of strong fronts in June is responsible for half of the decreased rainfall in June–August (JJA), whereas the reduction in the frequency of weaker fronts in June and July accounts for a third of the total decrease. The increase in rainfall inland in December–February (DJF) is due to an increased frequency of easterly troughs in December and February. These rainfall patterns are linked to the southern annular mode (SAM) index and Southern Oscillation index (SOI). The reduction in coastal rainfall and the increase in rainfall inland are both related to the predominantly positive phase of SAM, especially when the phase of ENSO is neutral.

scholarly journals The 16-Year Periodicity In The Winter Surface Temperature Variations In The Antarctic Peninsula Region

2021 ◽  
Author(s):  
Oleksandr Evtushevsky ◽  
Asen Grytsai ◽  
Oleksiy Agapitov ◽  
Volodymyr Kravchenko ◽  
Gennadi Milinevsky
Keyword(s):  
Surface Temperature ◽  
Sea Level ◽  
Antarctic Peninsula ◽  
Southern Annular Mode ◽  
Meridional Wind ◽  
Environmental Research ◽  
Southwestern Atlantic ◽  
Sea Level Pressure ◽  
Level Pressure ◽  
The Antarctic

Abstract The aim of this work is a comprehensive study of the 16-year periodicity of winter surface temperature in the Antarctic Peninsula (AP) region, described earlier, and its possible source based on weather station records over the 1952–2019 period making use of the Scientific Committee on Antarctic Research (SCAR) Reference Antarctic Data for Environmental Research (READER) database, as well as Fourier and wavelet analysis methods. It is shown that interdecadal oscillation with a period of about 16 years dominates in the northern AP (Esperanza and Orcadas), which is consistent with previous results. The 16-year periodicity is found to closely correlate with the sea level pressure anomaly in the southwestern Atlantic associated with the zonal wave-3 and the Southern Annular Mode patterns. The correlation maximum in the southwestern Atlantic, having the characteristic features of the anticyclonic circulation, affects the surface temperature in the northern AP through the related structure of the zonal and meridional wind anomalies. This effect is weaker to the south, where the Vernadsky station data do not show a regular interdecadal periodicity. Due to the correlated variability in the wave-3 ridges, the pronounced 16-year periods exist also in the surface temperature of southern Australia–New Zealand region, as well as in the zonal mean sea level pressure at 30–50°S. The sea surface temperatures are much less involved in the 16-year oscillation suggesting that atmospheric rather than oceanic processes appear to be more important for its occurrence.

scholarly journals Influence of the Southern Annular Mode on the sea ice-ocean system: the role of the thermal and mechanical forcing

Ocean Science ◽  
2005 ◽  
Vol 1 (3) ◽  
pp. 145-157 ◽  
Author(s):  
W. Lefebvre ◽  
H. Goosse
Keyword(s):  
Sea Ice ◽  
Air Temperature ◽  
Wind Stress ◽  
Southern Annular Mode ◽  
Weddell Sea ◽  
The Other ◽  
Ice Thickness ◽  
Sea Ice Thickness ◽  
Annular Mode ◽  
The Antarctic

Abstract. The global sea ice-ocean model ORCA2-LIM is used to investigate the impact of the thermal and mechanical forcing associated with the Southern Annular Mode (SAM) on the Antarctic sea ice-ocean system. The model is driven by idealized forcings based on regressions between the wind stress and the air temperature at one hand and the SAM index the other hand. The wind-stress component strongly affects the overall patterns of the ocean circulation with a northward surface drift, a downwelling at about 45° S and an upwelling in the vicinity of the Antarctic continent when the SAM is positive. On the other hand, the thermal forcing has a negligible effect on the ocean currents. For sea ice, both the wind-stress (mechanical) and the air temperature (thermal) components have a significant impact. The mechanical part induces a decrease of the sea ice thickness close to the continent and a sharp decrease of the mean sea ice thickness in the Weddell sector. In general, the sea ice area also diminishes, with a maximum decrease in the Weddell Sea. On the contrary, the thermal part tends to increase the ice concentration in all sectors except in the Weddell Sea, where the ice area shrinks. This thermal effect is the strongest in autumn and in winter due to the larger temperature differences associated with the SAM during these seasons. The sum of the thermal and mechaninal effects gives a dipole response of sea ice to the SAM, with a decrease of the ice area in the Weddell Sea and around the Antarctic Peninsula and an increase in the Ross and Amundsen Seas during high SAM years. This is in good agreement with the observed response of the ice cover to the SAM.

scholarly journals Enhanced glacial discharge from the eastern Antarctic Peninsula since the 1700s associated with a positive Southern Annular Mode

2019 ◽  
Vol 9 (1) ◽  
Author(s):  
W. A. Dickens ◽  
G. Kuhn ◽  
M. J. Leng ◽  
A. G. C. Graham ◽  
J. A. Dowdeswell ◽  
...  
Keyword(s):  
Antarctic Peninsula ◽  
Isotope Composition ◽  
Southern Annular Mode ◽  
Ice Shelf ◽  
Annular Mode ◽  
Ice Shelves ◽  
The North ◽  
North Eastern ◽  
Glacial Discharge ◽  
The Antarctic

Abstract The Antarctic Peninsula Ice Sheet is currently experiencing sustained and accelerating loss of ice. Determining when these changes were initiated and identifying the main drivers is hampered by the short instrumental record (1992 to present). Here we present a 6,250 year record of glacial discharge based on the oxygen isotope composition of diatoms (δ18Odiatom) from a marine core located at the north-eastern tip of the Antarctic Peninsula. We find that glacial discharge - sourced primarily from ice shelf and iceberg melting along the eastern Antarctic Peninsula – remained largely stable between ~6,250 to 1,620 cal. yr BP, with a slight increase in variability until ~720 cal. yr. BP. An increasing trend in glacial discharge occurs after 550 cal. yr BP (A.D. 1400), reaching levels unprecedented during the past 6,250 years after 244 cal. yr BP (A.D. 1706). A marked acceleration in the rate of glacial discharge is also observed in the early part of twentieth century (after A.D. 1912). Enhanced glacial discharge, particularly after the 1700s is linked to a positive Southern Annular Mode (SAM). We argue that a positive SAM drove stronger westerly winds, atmospheric warming and surface ablation on the eastern Antarctic Peninsula whilst simultaneously entraining more warm water into the Weddell Gyre, potentially increasing melting on the undersides of ice shelves. A possible implication of our data is that ice shelves in this region have been thinning for at least ~300 years, potentially predisposing them to collapse under intensified anthropogenic warming.

scholarly journals The Connection between the Southern Annular Mode and a Feature-Based Perspective on Southern Hemisphere Midlatitude Winter Variability

2020 ◽  
Vol 33 (1) ◽  
pp. 115-129 ◽  
Author(s):  
Clemens Spensberger ◽  
Michael J. Reeder ◽  
Thomas Spengler ◽  
Matthew Patterson
Keyword(s):  
Storm Track ◽  
Principal Component ◽  
Southern Annular Mode ◽  
Strong Correlations ◽  
Sea Level Pressure ◽  
Annular Mode ◽  
Rossby Wave Breaking ◽  
The Pacific ◽  
Feature Based ◽  
Consistent Picture

AbstractThis article provides a reconciling perspective on the two main, but contradictory, interpretations of the southern annular mode (SAM). SAM was originally thought to characterize meridional shifts in the storm track across the entire hemisphere. This perspective was later questioned, and SAM was interpreted as a statistical artifact depending on the choice of base region for the principal component analysis. Neither perspective, however, fully describes SAM. We show that SAM cannot be interpreted in terms of midlatitude variability, as SAM merely modulates the most poleward part of the cyclone tracks and only marginally influences the distribution of other weather-related features of the storm track (e.g., position of jet axes and Rossby wave breaking). Instead, SAM emerges as the leading pattern of geopotential variability due to strong correlations of sea level pressure around the Antarctic continent. As SAM correlates strongly both with the pan-Antarctic mean temperature and the meridional heat flux through 65°S, we hypothesize that SAM can be interpreted as a measure of the degree of the (de)coupling between Antarctica and the southern midlatitudes. As an alternative way of characterizing southern midlatitude variability, we seek domains in which the leading EOF patterns of both the geopotential and storm-track features yield a dynamically consistent picture. This approach is successful for the South Pacific. Here the leading variability patterns are closely related to the Pacific–South America pattern and point toward an NAO-like variability.

Investigating the impact of the Southern Annular Mode on ice-shelf basal melt in Antarctica using a regional ocean model forced by reanalysis data

2021 ◽  
Author(s):  
Deborah Verfaillie ◽  
Charles Pelletier ◽  
Hugues Goosse ◽  
Nicolas Jourdain ◽  
Vincent Favier ◽  
...  
Keyword(s):  
Sea Ice ◽  
Ice Sheet ◽  
Southern Annular Mode ◽  
Polar Regions ◽  
High Latitudes ◽  
Ice Shelf ◽  
Sea Level Pressure ◽  
The Past ◽  
The Antarctic ◽  
The Impact

<p>The climate of polar regions is characterized by large fluctuations and has experienced dramatic changes over the past decades. In the high latitudes of the Southern Hemisphere, the patterns of changes in sea ice and ice sheet mass, in particular, are more complex than for the Northern Hemisphere. Some regions have warmed less than the global average with some sea-ice advance, in particular in the Ross Sea, while other regions such as the Bellingshausen Sea have warmed significantly and displayed sea-ice loss. The Antarctic Ice Sheet has also lost mass in the past decades, with a spectacular thinning and weakening of ice shelves, i.e., the floating extensions of the grounded ice sheet. Despite recent advances in observing and modelling the Antarctic climate, the mechanisms at the origin of those trends are very uncertain because of the limited amount of observations and the large biases of climate models in polar regions, in concert with the large internal variability prevailing in the Antarctic. One of the most important atmospheric modes of climate variability in the Southern Ocean is the Southern Annular Mode (SAM), which represents the position and the strength of the westerly winds. During years with a positive SAM index, lower sea level pressure at high latitudes and higher sea level pressure at low latitudes occur, resulting in a stronger pressure gradient and intensified Westerlies. However, the current knowledge of the impact of these fluctuations of the Westerlies on the Southern Ocean and Antarctic cryosphere is still limited. Some efforts have been devoted over the past few years to the impact of the SAM on the Antarctic sea ice and the surface mass balance of the ice sheet from an atmospheric-specific perspective. Recently, a few studies have focused on the local impact on ice-shelf basal melt in specific regions of Antarctica. However, to our knowledge, there is no such study of the impact of the SAM on ice-shelf basal melt at the pan-Antarctic scale. In this communication, we will address this issue by using simulations performed with the regional ocean and sea-ice model NEMO-LIM3.6 at a spatial resolution of 0.25° forced by the ERA5 reanalysis over the period 1979-2018 CE. The impact of both the annular and the non-annular components of the SAM on ice-shelf basal melt will be assessed through regressions and correlations between the seasonal or annual averages of the SAM index and the ice-shelf basal melt.</p>

scholarly journals Skillful Seasonal Prediction of the Southern Annular Mode and Antarctic Ozone

2014 ◽  
Vol 27 (19) ◽  
pp. 7462-7474 ◽  
Author(s):  
William J. M. Seviour ◽  
Steven C. Hardiman ◽  
Lesley J. Gray ◽  
Neal Butchart ◽  
Craig MacLachlan ◽  
...  
Keyword(s):  
Polar Vortex ◽  
Seasonal Prediction ◽  
Southern Annular Mode ◽  
Significant Advance ◽  
Seasonal Forecasts ◽  
Austral Spring ◽  
Stratospheric Polar Vortex ◽  
Annular Mode ◽  
The North ◽  
The Antarctic

Abstract Using a set of seasonal hindcast simulations produced by the Met Office Global Seasonal Forecast System, version 5 (GloSea5), significant predictability of the southern annular mode (SAM) is demonstrated during the austral spring. The correlation of the September–November mean SAM with observed values is 0.64, which is statistically significant at the 95% confidence level [confidence interval: (0.18, 0.92)], and is similar to that found recently for the North Atlantic Oscillation in the same system. Significant skill is also found in the prediction of the strength of the Antarctic stratospheric polar vortex at 1 month average lead times. Because of the observed strong correlation between interannual variability in the strength of the Antarctic stratospheric circulation and ozone concentrations, it is possible to make skillful predictions of Antarctic column ozone amounts. By studying the variation of forecast skill with time and height, it is shown that skillful predictions of the SAM are significantly influenced by stratospheric anomalies that descend with time and are coupled with the troposphere. This effect allows skillful statistical forecasts of the October mean SAM to be produced based only on midstratosphere anomalies on 1 August. Together, these results both demonstrate a significant advance in the skill of seasonal forecasts of the Southern Hemisphere and highlight the importance of accurate modeling and observation of the stratosphere in producing long-range forecasts.

Linkage of the South Asian High to the Southern Annular Mode during the Boreal Summer

2014 ◽  
Vol 962-965 ◽  
pp. 1404-1409
Author(s):  
Jian Zhang ◽  
Yan You Guo ◽  
Cheng Shan Wang
Keyword(s):  
South Asian ◽  
Surface Wind ◽  
Southern Annular Mode ◽  
Boreal Summer ◽  
South Asian High ◽  
Interhemispheric Interaction ◽  
The South ◽  
Sea Level Pressure ◽  
Annular Mode ◽  
The Relationship

The linkage of the South Asian High (SAH) to the southern annular mode (SAM) during the boreal summer is addressed. The results show that the SAH correlated well with the Southern Hemispheric subtropical high (SSH) and SAM, which exhibits that their recent positive trends are associated with each other. During the positive SAH anomalies years, roughly speaking, the sea level pressure (SLP) and the zonal surface wind (u10) are analogous to that of the positive SAM phase, but they also show an anomalous zonal-wave-3-like (ZW3-like) pattern over the mid latitudes. The surface temperature (ST) variations are not similar to the SAM. Nevertheless, these changes are related with the anomalous cyclones and meridional surface wind (v10). The relationship between the SAH and SAM is also a manifestation of the interhemispheric interaction, and this study contributes to the understanding of the global change.

scholarly journals Influence of the Southern Annular Mode on the sea ice-ocean system: the role of the thermal and mechanical forcing

2005 ◽  
Vol 2 (3) ◽  
pp. 299-329 ◽  
Author(s):  
W. Lefebvre ◽  
H. Goosse
Keyword(s):  
Sea Ice ◽  
Air Temperature ◽  
Wind Stress ◽  
Southern Annular Mode ◽  
Weddell Sea ◽  
Ice Thickness ◽  
Sea Ice Thickness ◽  
Annular Mode ◽  
Mechanical Forcing ◽  
The Antarctic

Abstract. The global sea ice-ocean model ORCA2-LIM is used to investigate the impact of the thermal and mechanical forcing associated to the Southern Annular Mode (SAM) on the Antarctic sea ice-ocean system. To do so, the model is driven by idealized forcings based on regressions of the wind stress and the air temperature to SAM. The wind-stress component strongly affects the overall patterns of the ocean circulation with a northward surface drift, a downwelling at about 45° S and an upwelling in the vicinity of the Antarctic continent when SAM is positive. On the other hand, the thermal forcing has a negligible effect on the ocean currents. For sea ice, both the wind-stress (mechanical) and the air temperature (thermal) components have a significant impact. The mechanical part induces a decrease of the sea ice thickness close to the continent and a sharp decrease of the mean sea ice thickness in the Weddell sector. In general, the sea ice area also diminishes, with a maximum decrease in the Weddell Sea. On the contrary, the thermal part tends to increase the ice concentration in all sectors except in the Weddell Sea, where the ice area shrinks. This thermal effect is the strongest in autumn and in winter due to the larger temperature differences associated with SAM during these seasons. The sum of the thermal and mechaninal effects gives a dipole response of sea ice to the SAM, with a decrease of the ice area in the Weddell Sea and around the Antarctic Peninsula and an increase in the Ross and Amundsen Seas during high SAM years. This is in good agreement with the observed response of the ice cover to SAM.

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