Seasonal climate summary southern hemisphere (spring 2007): La Niña finally takes hold

Atmospheric and oceanic conditions in the southern hemisphere are reviewed for the austral spring of 2007. Particular emphasis is given to the Australian and Pacific regions. The transition from El Niño conditions in 2006 to La Niña conditions in 2007 took approximately ten months, arriving in early to mid-spring. Sea-surface temperatures in the central to eastern equatorial Pacific were generally cool for the season, as was the subsurface, while the Southern Oscillation Index gradually rose, reaching near one standard deviation above normal by season’s end. Despite the La Niña conditions, mean temperatures remained warm over Australia, with spring 2007 being the third warmest since high-quality records commenced in 1950. Rainfall was very low early in the season, but by November central and eastern Australia received aboveaverage totals. This rainfall did little to alleviate the six-year drought for the agriculturally vital Murray-Darling Basin. In the Antarctic, the sea-ice area of 15.2 million km2 was the largest area observed for any month since the sea-ice pack was first observed in its entirety by satellites in 1979, and appeared consistent with changing circulation patterns. The Antarctic ozone hole reached an area of 25.1 million km2; considerably less than the record 2006 area but still well above the 1979- 2006 mean peak value of just under 21 million km2 .