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1607058 
Journal Article 
The link between cut-off lows and Rossby wave breaking in the Southern Hemisphere 
Ndarana, T; Waugh, DW 
2010 
1 
Quarterly Journal of the Royal Meteorological Society
ISSN: 0035-9009
EISSN: 1477-870X 
136 
649 
869-885 
WOS:000279407000004 
The climatological link between cut-off low (COL) pressure
systems that occur from 20 to 50 degrees S and Rossby wave breaking (RWB) in the Southern
Hemisphere (SH) is examined for 1979-2008. It is shown that COLs are associated with either RWB
events (89%) or with potential vorticity (PV) intrusions where there is north south advection of
high-PV air (11%). In the vast majority of COLs, the RWB events occur upstream, on or before the
day of the COL formation. The evolution of the PV, geopotential heights, static stability,
absolute vorticity and temperature advection fields during the COLs are consistent with the
formation of high-PV anomalies that induce cyclonic circulations as predicted by theory. RWB
plays a key role in producing the split flow associated with COLs in the SH, which in turn
produces absolute vorticity anomalies by shear-curvature vorticity conversion, and creates static
stability anomalies. The COLs associated with RWB at 330 K are deeper and more persistent than
those associated with 350 K RWB and surface processes differ depending on the isentropic surface
on which the associated RWB occurs. The seasonality of the RWB and COLs are similar, and is
linked to the seasonal march of the westerly jets. Copyright (C) 2010 Royal Meteorological
Society 
potential vorticity anomaly; potential vorticity intrusion; jet stream