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Impact of surface forcing on Southern Hemisphere atmospheric blocking in the Australia-New Zealand sector

Citation

Ummenhofer, CC and McIntosh, PC and Pook, MJ and Risbey, JS, Impact of surface forcing on Southern Hemisphere atmospheric blocking in the Australia-New Zealand sector, Journal of Climate, 26, (21) pp. 8476-8494. ISSN 0894-8755 (2013) [Refereed Article]


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Copyright Statement

Copyright 2013 American Meteorological Society

DOI: doi:10.1175/JCLI-D-12-00860.1

Abstract

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.

Item Details

Item Type:Refereed Article
Keywords:atmosphere-ocean interaction, atmospheric circulation, Australia, blocking, general circulation models, southern Hemisphere
Research Division:Earth Sciences
Research Group:Atmospheric Sciences
Research Field:Atmospheric Dynamics
Objective Division:Environment
Objective Group:Atmosphere and Weather
Objective Field:Atmospheric Processes and Dynamics
Author:McIntosh, PC (Dr Peter McIntosh)
Author:Pook, MJ (Dr Michael Pook)
Author:Risbey, JS (Dr James Risbey)
ID Code:119116
Year Published:2013
Web of Science® Times Cited:7
Deposited By:Centre for Ecology and Biodiversity
Deposited On:2017-07-26
Last Modified:2017-10-16
Downloads:16 View Download Statistics

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