Observations of Large-Scale Ocean–Atmosphere Interaction in the Southern Hemisphere

2008 ◽  
Vol 21 (6) ◽  
pp. 1244-1259 ◽  
Author(s):  
Laura M. Ciasto ◽  
David W. J. Thompson
Keyword(s):  
Southern Hemisphere ◽  
Seasonal Variations ◽  
Large Scale ◽  
Southern Oscillation ◽  
Southern Annular Mode ◽  
Heat Fluxes ◽  
Ocean Atmosphere ◽  
Ocean Atmosphere Interaction ◽  
Atmosphere Interaction ◽  
Sst Anomalies

Abstract The authors provide a detailed examination of observed ocean–atmosphere interaction in the Southern Hemisphere (SH). Focus is placed on the observed relationships between variability in SH extratropical sea surface temperature (SST) anomalies, the Southern Annular Mode (SAM), and the El Niño–Southern Oscillation (ENSO). Results are examined separately for the warm (November–April) and cold (May–October) seasons and for monthly and weekly time scales. It is shown that the signatures of the SAM and ENSO in the SH SST field vary as a function of season, both in terms of their amplitudes and structures. The role of surface turbulent and Ekman heat fluxes in driving seasonal variations in the SAM- and ENSO-related SST anomalies is investigated. Analyses of weekly data reveal that variability in the SAM tends to precede anomalies in the SST field by ∼1 week, and that the e-folding time scale of the SAM-related SST field anomalies is at least 4 months. The persistence of the SAM-related SST anomalies is consistent with the passive thermal response of the Southern Ocean to variations in the SAM, and seasonal variations in the persistence of the SAM-related SST anomalies are consistent with the seasonal cycle in the depth of the ocean mixed layer.

Interannual Extremes in New Zealand Precipitation Linked to Modes of Southern Hemisphere Climate Variability

2007 ◽  
Vol 20 (21) ◽  
pp. 5418-5440 ◽  
Author(s):  
Caroline C. Ummenhofer ◽  
Matthew H. England
Keyword(s):  
New Zealand ◽  
Climate Variability ◽  
Southern Hemisphere ◽  
Large Scale ◽  
Southern Oscillation ◽  
Rainfall Variability ◽  
Heat Fluxes ◽  
Ekman Transport ◽  
The South ◽  
Climate Modes

Abstract Interannual extremes in New Zealand rainfall and their modulation by modes of Southern Hemisphere climate variability are examined in observations and a coupled climate model. North Island extreme dry (wet) years are characterized by locally increased (reduced) sea level pressure (SLP), cold (warm) sea surface temperature (SST) anomalies in the southern Tasman Sea and to the north of the island, and coinciding reduced (enhanced) evaporation upstream of the mean southwesterly airflow. During extreme dry (wet) years in South Island precipitation, an enhanced (reduced) meridional SLP gradient occurs, with circumpolar strengthened (weakened) subpolar westerlies and an easterly (westerly) anomaly in zonal wind in the subtropics. As a result, via Ekman transport, anomalously cold (warm) SST appears under the subpolar westerlies, while anomalies of the opposite sign occur farther north. The phase and magnitude of the resulting SST and evaporation anomalies cannot account for the rainfall extremes over the South Island, suggesting a purely atmospheric mode of variability as the driving factor, in this case the Southern Annular Mode (SAM). New Zealand rainfall variability is predominantly modulated by two Southern Hemisphere climate modes, namely, the El Niño–Southern Oscillation (ENSO) and the SAM, with a latitudinal gradation in influence of the respective phenomena, and a notable interaction with orographic features. While this heterogeneity is apparent both latitudinally and as a result of orographic effects, climate modes can force local rainfall anomalies with considerable variations across both islands. North Island precipitation is for the most part regulated by both local air–sea heat fluxes and circulation changes associated with the tropical ENSO mode. In contrast, for the South Island the influence of the large-scale general atmospheric circulation dominates, especially via the strength and position of the subpolar westerlies, which are modulated by the extratropical SAM.

Seasonal climate summary for the southern hemisphere (winter 2017): exceptionally warm days for Australia

2019 ◽  
Vol 69 (1) ◽  
pp. 331
Author(s):  
David J. Martin ◽  
Skie Tobin
Keyword(s):  
South America ◽  
Southern Hemisphere ◽  
Large Scale ◽  
Southern Oscillation ◽  
Southern Annular Mode ◽  
Austral Winter ◽  
Atmospheric Circulation Patterns ◽  
Circulation Patterns ◽  
The Indian Ocean ◽  
Hemisphere Winter

This is a summary of the southern hemisphere atmospheric circulation patterns and meteorological indices for austral winter 2017; an account of seasonal rainfall and temperature for the Australian region is also provided. The El Niño–Southern Oscillation was neutral during winter 2017, as was the Indian Ocean Dipole. A positive Southern Annular Mode influenced the climates of southern hemisphere countries at times during winter. Despite the lack of large-scale ocean influences, mean temperatures for the season were very much above average across large areas of Australia, New Zealand, southern Africa and South America. Precipitation during the season was below average across much of Australia, South Africa and western areas of Chile and Argentina, but above average in some southern and eastern areas of South America.

scholarly journals Southern Hemisphere Synoptic Behavior in Extreme Phases of SAM, ENSO, Sea Ice Extent, and Southern Australia Rainfall

2008 ◽  
Vol 21 (21) ◽  
pp. 5566-5584 ◽  
Author(s):  
Alexandre Bernardes Pezza ◽  
Tom Durrant ◽  
Ian Simmonds ◽  
Ian Smith
Keyword(s):  
Sea Ice ◽  
Southern Hemisphere ◽  
High Latitude ◽  
Large Scale ◽  
Southern Oscillation ◽  
Southern Annular Mode ◽  
Sea Ice Extent ◽  
Antarctic Sea Ice ◽  
Rainfall Anomalies ◽  
Western Side

Abstract The association between Southern Hemisphere cyclones and anticyclones and the El Niño–Southern Oscillation (ENSO), southern annular mode (SAM), Antarctic sea ice extent (SIE), and rainfall in Perth and Melbourne is explored. Those cities are, respectively, located in the southwestern and southeastern corners of Australia, where substantial decreasing rainfall trends have been observed over the last decades. The need for a more unified understanding of large-scale anomalies in storm indicators associated with the climate features itemized above has motivated this study. The main aim is to identify cyclone-anomalous areas that are potentially important in characterizing continental rainfall anomalies from a hemispheric perspective, focusing on midlatitude Australia. The study covers the “satellite era” from 1979 to 2003 and was conducted for the southern winter when midlatitude rainfall is predominantly baroclinic. The results indicate a well-organized hemispheric cyclone pattern associated with ENSO, SAM, SIE, and rainfall anomalies. There is a moderate large-scale, high-latitude resemblance between La Niña, negative SAM, and reduced SIE in some sectors. In particular, there is a suggestion that SIE anomalies over the Indian Ocean and Western Australia sectors are associated with a large-scale pattern of cyclone/anticyclone anomalies that is more pronounced over the longitudes of Australia and New Zealand. Spatial correlation analysis suggests a robust link between cyclone density over the sectors mentioned above and rainfall in Perth and Melbourne. Statistical analyses of rainfall and SIE show modest correlations for Perth and weak correlations for Melbourne, generally corroborating the above. It is proposed that SAM and SIE are part of a complex physical system that is best understood as a coupled mechanism, and that their impacts on the circulation can be seen as partially independent of ENSO. While SAM and SIE have greater influence on the circulation affecting rainfall in the western side of Australia, ENSO is the dominant influence on the eastern half of the country. A contraction of the sea ice seems to be accompanied by a southward shift of high-latitude cyclones, which is also hypothesized to increase downstream cyclone density at midlatitudes via conservation of mass, similarly to what is observed during the extreme positive phase of the SAM. These associations build on previous developments in the literature. They bring a more unified view on high-latitude climate features, and may also help to explain the declining trends in Australian rainfall.

Biogenic aerosol in central East Antarctic Plateau as a proxy for the ocean-atmosphere interaction in the Southern Ocean

2021 ◽  
pp. 151285
Author(s):  
Silvia Becagli ◽  
Christian Marchese ◽  
Laura Caiazzo ◽  
Virginia Ciardini ◽  
Luigi Lazzara ◽  
...  
Keyword(s):  
Southern Ocean ◽  
Antarctic Plateau ◽  
Ocean Atmosphere ◽  
Ocean Atmosphere Interaction ◽  
Atmosphere Interaction
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