Antarctic Sea Ice Index (part 6)

I take a closer look at the relationship between the NSST lower troposphere ocean region temperature anomaly and NOAA’s Antarctic Oscillation Index (AAO)

In part 5 of this series I discovered a fabulous relationship between the South pole lower troposphere ocean anomaly and the Antarctic Oscillation (AAO). Here it is again:

Here we have evidence of a cooler lower troposphere, as measured by the UAH NSST crew, associated with positive-going AAO index, as measured by NOAA. Since these folk know what they are doing it is left to us to figure how they link together and dance over time. Time, then, for one of those cross-correlation function plots methinks!

Fascinating, intriguing and yes, that dirty great negative correlation of r = -0.614 (p<0.001) at a lag of zero years is telling us that the relationship is immediate in effect; that is, a cooler atmosphere and positive-going AAO occur within the same year, there being no sign of any statistically significant lagged effects out to ±12 years. Nice.

Whilst I have my crayons out I might as well run cross-correlation plots for two other major oscillations (PDO, AMO). Here they are:

No joy there, then. Nuffink, nowt and nada. Whatever the Pacific and Atlantic are doing in terms of periodic sea surface temperature variability these patterns are not connecting with the Antarctic oscillation. This doesn’t surprise me because the Antarctic oscillation is a bit of a closed shop: the Antarctic does its own thing. Good to check, though!

A bivariate within-year relationship showing a cooler atmosphere is associated with a positive-going AAO is one thing but stuff changing over time is a different matter – it’s always handy to know where all this is going. To avoid two rather boring time series slides I opted to reach for the linear regression spanner to tell me what has been going on trend-wise over the period 1979 – 2022, and I shall report a statistically insignificant South Pole lower troposphere ocean cooling trend of -0.22°C per century (p=0.368) and a statistically significant positive AAO trend of +1.30 units per century (p=0.010). Let us see what Wiki has to say about the positive-going phase of the AAO:

In its positive phase, the westerly wind belt that drives the Antarctic Circumpolar Current intensifies and contracts towards Antarctica. In winter, a positive phase increases rainfall (including East coast lows) in south-eastern Australia (above Victoria) due to higher onshore flows from the Pacific Ocean, decreases rain in the south-west, and decreases snow in the alpine areas. In spring and summer, a positive phase reduces the chance of extreme heat and increases humid onshore flows, therefore making spring and summer wetter than normal. A positive phase would usually occur more frequently with a La Niña event.

So there you go – there seems to be a trend toward increasing westerly winds bringing both increased and decreased rainfall depending on which bit of Australia you happen to live. Ski resorts might grumble but extreme heat should lessen, with wetter springs.

Sounds fine to me but alarmists will no doubt make a meal of it. At this point Australians have the option of reaching for the superglue and/or tomato soup or pressing on with the happy task of looking at the natural world through less psychotic shades.

Kettle On!