Thanks for pointing this out. The lag-one autocorrelation of the detrended annual series is -0.13 (see image below), well within the 95% confidence interval (shaded area), meaning that it’s not statistically different from zero.

We also show that this is tied to the polar amplification of warming and increased land/ocean thermal contrast, both of which can be tied to human-caused climate change. These mechanisms appear to be enhancing the atmospheric conditions that favor planetary wave resonance.

The substantial observed increase in resonance events is driven not by increases in wave activity but, rather, with increases in the joint occurrence of wave amplitude and phase conditions that support planetary wave resonance.

We found that the average number of resonance events per year has tripled since the advent of adequate upper atmospheric measurements in the mid-20th century, rising from about 1 event per year in 1950 to now about 3 per year.