Seasonal climate summary southern hemisphere (summer 2011–12): a mature La Niña, strongly positive SAM and active MJO

Abstract

Atmospheric and oceanic conditions in the southern hemisphere are reviewed for the austral summer 2011–12, with emphasis given to the Pacific Basin climate indicators and Australian rainfall and temperature patterns. In the Pacific Basin, the La Niña pattern that developed during spring 2011 strengthened in early summer before gradually decaying. It was the weaker of two consecutive, yet quite different, La Niña events following an extremely strong La Niña in 2010–11. A record strong positive Southern Annular Mode was present during December 2011 and January 2012 and an active Madden–Julian Oscillation affected the tropics for much of summer 2011–12, especially in February. Averaged across the country, Australia was wetter and cooler than usual, but there were large regional variations. Parts of the south and tropical north were drier and warmer than average, to some extent due to a less active than normal North Australian Monsoon. While New South Wales was exceptionally cool during the day and wetter than usual, Tasmania was exceptionally warm and drier than usual.