The impact of a changing southern hemisphere annular mode on Antarctic Peninsula summer temperatures

• Published in: Journal of Climate
• Main Authors: Marshall, G.J., Orr, A., van Lipzig, N., King, J.C.
• Format: Article in Journal/Newspaper
• Language: English
• Published: 2006
• Subjects: Antarctic; Antarctic Peninsula; Larsen Ice Shelf; The Antarctic; Antarc*; Ice Shelf
• Online Access: https://www.vliz.be/imisdocs/publications/283801.pdf

Since the mid-1960s, rapid regional summer warming has occurred on the east coast of the northern Antarctic Peninsula, with near-surface temperatures increasing by more than 2°C. This warming has contributed significantly to the collapse of the northern sections of the Larsen Ice Shelf. Coincident with this warming, the summer Southern Hemisphere Annular Mode (SAM) has exhibited a marked trend, suggested by modeling studies to be predominantly a response to anthropogenic forcing, resulting in increased westerlies across the northern peninsula.Observations and reanalysis data are utilized to demonstrate that the changing SAM has played a key role in driving this local summer warming. It is proposed that the stronger summer westerly winds reduce the blocking effect of the Antarctic Peninsula and lead to a higher frequency of air masses being advected eastward over the orographic barrier of the northern Antarctic Peninsula. When this occurs, a combination of a climatological temperature gradient across the barrier and the formation of a föhn wind on the lee side typically results in a summer near-surface temperature sensitivity to the SAM that is 3 times greater on the eastern side of the peninsula than on the west. SAM variability is also shown to play a less important role in determining summer temperatures at stations west of the barrier in the northern peninsula (~62°S), both at the surface and throughout the troposphere. This is in contrast to a station farther south (~65°S) where the SAM exerts little influence.