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.
Suggested CitationJournal of Climate 26 (2013): 8476–8494
Showing items related by title, author, creator and subject.
Northern hemisphere winter atmospheric transient eddy heat fluxes and the Gulf Stream and Kuroshio–Oyashio Extension variability Kwon, Young-Oh; Joyce, Terrence M. (American Meteorological Society, 2013-12-15)Spatial and temporal covariability between the atmospheric transient eddy heat fluxes (i.e., υ′T′ and υ′q′) in the Northern Hemisphere winter (January–March) and the paths of the Gulf Stream (GS), Kuroshio Extension (KE), ...
Gebregiorgis, Daniel; Hathorne, Ed C.; Giosan, Liviu; Clemens, Steven C.; Nürnberg, Dirk; Frank, Martin (Nature Publishing Group, 2018-11-08)The orbital-scale timing of South Asian monsoon (SAM) precipitation is poorly understood. Here we present new SST and seawater δ18O (δ18Osw) records from the Bay of Bengal, the core convective region of the South Asian ...
Arienzo, Monica; McConnell, Joseph R.; Murphy, Lisa N.; Chellman, Nathan; Das, Sarah B.; Kipfstuhl, Sepp; Mulvaney, Robert (John Wiley & Sons, 2017-07-01)Black carbon (BC) and other biomass-burning (BB) aerosols are critical components of climate forcing, but quantification, predictive climate modeling, and policy decisions have been hampered by limited understanding of the ...