Ice area data is used to estimate the underlying annual melting/freezing cycle.
A short filter is used to remove short term ‘weather’ noise and a small but significant circa 14 days pseudo cyclic variation. The aim being to study the change from year to year without these perturbing effects.
Both melting and freezing periods are determined and a single annual value derived from the average of the melting period and the complement of the freezing period.
The horizontal black line represents the neutral value of AO, that has been shifted up from zero.
The current antarctic melting period is notably shorter than 6 months.
Neither the Arctic nor the Antarctic responded strongly to the significant negative spike in AO in 2010.
Subject to verification and further study.
The may be a fixed time lag in the dating of the melt/freeze lengths.