Wind Trends

In last week's post, I noted that Alaska's 10-year running mean precipitation is at a record high, reflecting the fact that the state's climate has become generally wetter in recent decades.  It's common knowledge that temperatures have also increased on a timescale of several decades, especially in the Arctic.  But what about wind?  Are there any notable multi-decadal trends in wind speed for Alaska?

The question of climate trends is not as straightforward for wind, because there is no good long-term "ground truth" data for wind speeds; measurement practices have changed too much over the years.  We have to rely on retrospective estimates from a model, which in my case means the ERA5 reanalysis from the European modeling center.  So take the following results with a pinch of salt.

First we can observe that last year was apparently the windiest year in many decades for Alaska as a whole (according to ERA5); and it was particularly windy over western regions:

This wasn't just caused by one windy month; 6 of 12 months saw statewide winds at least 5% above normal, and January and August were particularly windy.  Only one month - September - was notably calm compared to normal.

Does this reflect a long-term trend towards greater winds?  No: ERA5 data indicates no significant trend over Alaska's land area, and if anything it suggests an absence of windy years in the last 20-30 years.  2024 was quite anomalous compared to the previous couple of decades:

Here's a look at the 75-year change in annual mean wind speed, using a linear trend, and including 2024:

The results in the complex terrain of southern Alaska are highly variable and probably not representative of the actual trends at populated valley-level locations.  (The ~30km horizontal resolution of the ERA5 data is far too coarse to handle complex terrain.)  There's a marginal hint of decreasing wind speeds across parts of the interior, but clearly the model shows increased wind speed across the near-coastal waters of the Bering Sea as well as more widely in the Arctic Ocean.

The seasonal breakdown of the trends shows a few interesting results - see below.  First, the largest percent increase in wind for the Bering, Chukchi, and Beaufort Seas is found in winter, although the Arctic waters have also become more windy in summer and autumn, if the model is to be believed.  The winter trend of increasing wind is also evident across the western land area and the northern interior.  However, it seems that the North Slope and the northern interior have become less windy in autumn, and there is a distinct trend toward less windy summers in the southwestern interior and Bristol Bay region.

The rising wind trends over the Arctic and Bering waters may have more than one cause.  First, there seems to be a trend toward greater storminess over the Bering Sea in winter; the two maps below show the multi-decadal difference of 500mb heights (top) and MSLP (bottom) for 1950-1990 versus 1991-2024.  This is consistent with the December-February wind increase extending inland across northwestern Alaska and the northern interior.

But the general warming trend in the Arctic is also a direct cause of rising wind speeds across the Arctic waters, because the surface-based temperature inversion has weakened, allowing more atmospheric momentum to mix down to the surface.  This effect is pronounced in autumn, when sea ice loss has been dramatic (see the Sep-Nov map above).  Here's a paper from last year on this topic:

https://www.nature.com/articles/s43247-024-01428-1

As for the summer wind decrease in southwestern Alaska, this is probably related to increasing high pressure and fair-weather "ridging" over the Bering Sea at that time of year.  In contrast, the Arctic Ocean seems to have become more stormy, especially in the Eastern Hemisphere.

So far this year, we've seen a very windy January - one of the windiest on record statewide (2024 was the windiest) - but February and March were somewhat less windy than normal.  It will be interesting to see if we have another windy summer, following last summer's record high wind statewide.  I see some reasons to believe the high-latitude summer patterns could indeed be similar to last summer - but more on that another time.