Impact of surface forcing on Southern Hemisphere atmospheric blocking in the Australia–New Zealand sector
Ummenhofer, Caroline C.
McIntosh, Peter C.
Pook, Michael J.
Risbey, James S.
MetadataShow full item record
KeywordAustralia; Southern Hemisphere; Atmosphere-ocean interaction; Atmospheric circulation; Blocking; General circulation models
Characteristics of atmospheric blocking in the Southern Hemisphere (SH) are explored in atmospheric general circulation model (AGCM) simulations with the Community Atmosphere Model, version 3, with a particular focus on the Australia–New Zealand sector. Preferred locations of blocking in SH observations and the associated seasonal cycle are well represented in the AGCM simulations, but the observed magnitude of blocking is underestimated throughout the year, particularly in late winter and spring. This is related to overly zonal flow due to an enhanced meridional pressure gradient in the model, which results in a decreased amplitude of the longwave trough/ridge pattern. A range of AGCM sensitivity experiments explores the effect on SH blocking of tropical heating, midlatitude sea surface temperatures, and land–sea temperature gradients created over the Australian continent during austral winter. The combined effects of tropical heating and extratropical temperature gradients are further explored in a configuration that is favorable for blocking in the Australia–New Zealand sector with warm SST anomalies to the north of Australia, cold to the southwest of Australia, warm to the southeast, and cool Australian land temperatures. The blocking-favorable configuration indicates a significant strengthening of the subtropical jet and a reduction in midlatitude flow, which results from changes in the thermal wind. While these overall changes in mean climate, predominantly forced by the tropical heating, enhance blocking activity, the magnitude of atmospheric blocking compared to observations is still underestimated. The blocking-unfavorable configuration with surface forcing anomalies of opposite sign results in a weakening subtropical jet, enhanced midlatitude flow, and significantly reduced blocking.
Author Posting. © American Meteorological Society, 2013. This article is posted here by permission of American Meteorological Society for personal use, not for redistribution. The definitive version was published in Journal of Climate 26 (2013): 8476–8494, doi:10.1175/JCLI-D-12-00860.1.
Showing items related by title, author, creator and subject.
Strong depth-related zonation of megabenthos on a rocky continental margin (∼700–4000 m) off southern Tasmania, Australia Thresher, Ronald E.; Althaus, Franziska; Adkins, Jess F.; Gowlett-Holmes, Karen; Alderslade, Phil; Dowdney, Jo; Cho, Walter W.; Gagnon, Alexander C.; Staples, David; McEnnulty, Felicity; Williams, Alan (Public Library of Science, 2014-01-22)Assemblages of megabenthos are structured in seven depth-related zones between ~700 and 4000 m on the rocky and topographically complex continental margin south of Tasmania, southeastern Australia. These patterns emerge ...
Thresher, Ronald E.; Rintoul, Stephen R.; Koslow, J. Anthony; Weidman, Christopher R.; Adkins, Jess F.; Proctor, Craig (American Geophysical Union, 2004-04-13)Chemical analysis of deepwater octocorals collected at 1000 m depth off southern Australia indicates long-term cooling, beginning in the mid-18th century. This cooling appears to reflect shoaling of isotherms along the ...
Planktonic Larval Duration, age and growth of Ostorhinchus doederleini (Pisces: Apogonidae) on the southern Great Barrier Reef, Australia Kingsford, Michael J.; Finn, M. D.; O’Callaghan, M. D.; Atema, Jelle; Gerlach, Gabriele (2013-09-15)Cardinalfishes (Apogonidae) are abundant on corals reefs, but there are few data on demography to understand trophodynamics and population dynamics. Ostorhinchus doederleini is a small and abundant apogonid on the Great ...