More on Persistence

I suspect that not everyone finds this as interesting as I do, but nevertheless here's a follow-up on seasonal temperature persistence in and around Alaska, this time from a map perspective.  Using ERA5 reanalysis data, I calculated the correlation of consecutive monthly temperature anomalies from 1950 through 2020, with the linear trend (specific to each month) removed.  A positive correlation means that the sign of the anomaly (i.e. above or below trend) tends to persist from one month to the next, but a negative correlation indicates that it tends to reverse.

It is usually a safe rule of thumb that weather and climate anomalies tend to be "persistent" even over land - there is a positive autocorrelation - so it's a surprise to see that the overall correlation is slightly negative for a portion of east-central Alaska and an adjacent zone in northwestern Canada.

This is actually the only place on the planet that has a negative month-to-month correlation, according to ERA5 data for this particular historical period.  There are plenty of regions with very low correlations, but this small region just to the north of Eagle is the only place with inverse persistence.  Here's a map for the Northern Hemisphere extratropics.

The tendency for temperature anomalies to reverse sign is mostly found in the winter for interior and eastern Alaska.  Here's the December-January correlation:

The rest of the year is added below.  The maps confirm the observation I made in the previous post: for the state as a whole, persistence is very much heightened in April-May and in July-August.  One might say those pairs of months are temperature twins: they tend to resemble each other in terms of departure from normal.

The other striking point is how much higher persistence is in summer than in winter for the maritime southern regions, and for late summer and early autumn near the Arctic Ocean.  Clearly the warm season temperature anomalies are dominated by slowly-varying ocean temperature regimes in locations close to open water, whereas relatively chaotic atmospheric flow patterns tend to control the month-to-month temperature changes during winter or over ice-covered ocean.