The polar vortex, a river of air that circles Antarctica in the austral winter, is essential.

It was their third attempt over three seasons, all in 2012, including an austral winter attempt in August.

And more than this again; the temperature had fallen sensibly: this was probably a forewarning of the austral winter.

We suggest that the first thermocline warming corresponds to heat transport of southern Pacific shallow overturning circulation driven by June ( austral winter) insolation maximum.