Today we’re going to delve into the application of surf science in the Arctic. If you’re not already familiar with the basics of how the best surf is created then perhaps you might first wish to take a detour to the StormSurf “Wave Basics” article:
Wind waves, though rideable, are not the optimal type of wave one likes to ride. Swells are much better. Wind waves are only the raw material that swells are made from. But, the more energy wind waves accumulate while being driven by wind, the greater the likelihood they will transform into a swell. Enough energy and the swell can travel the entire circumference of the globe with only a slow decay in size!
During a typical open ocean winter storm, one could expect to see winds of 45-55 kts blowing over 600-1000 nautical miles for 36 hours. In such a storm, the average highest wind waves (or ‘seas’) commonly reach 30-35 ft towards the center of the fetch area and produce a swell with a period of 17-20 secs.
Regular readers may recall that on August 24th 2014 we revealed this WaveWatch III “surf forecast” for the Beaufort Sea, which lies off the north coast of Alaska and the Canadian Northwest Territories (i.e. top center of the map):
and noted that the 2 meter waves depicted:
Have blasted past Point Barrow and are currently heading straight for the Beaufort Sea Marginal Ice Zone.
Here’s a video from the University of Washington’s Applied Physics Laboratory which explains that the Marginal Ice Zone is:
The area between declining unbroken sea ice and the expanding area of open water.
The theoretical significance of such swells has been discussed in a number of academic papers recently. Take for example these extracts from “Swell and sea in the emerging Arctic Ocean” by Jim Thomson from the University of Washington and W. Erick Rogers from the US Naval Research Laboratory. Note first of all that the authors distinguish between “wind seas” and “swells” as follows:
Pure wind seas have a wave age less than one, indicating that the wind is driving the waves, and these points cluster largely below the Pierson–Moskowitz limit. Swells have a wave age greater than one, indicating that the waves are outrunning the wind.
They then go on to use some more terms very familiar to the average surfer:
Ocean surface waves (sea and swell) are generated by winds blowing over a distance (fetch) for a duration of time. In the Arctic Ocean, fetch varies seasonally from essentially zero in winter to hundreds of kilometers in recent summers. Using in situ observations of waves in the central Beaufort Sea, combined with a numerical wave model and satellite sea ice observations, we show that wave energy scales with fetch throughout the seasonal ice cycle. Furthermore, we show that the increased open water of 2012 allowed waves to develop beyond pure wind seas and evolve into swells. The swells remain tied to the available fetch, however, because fetch is a proxy for the basin size in which the wave evolution occurs. Thus, both sea and swell depend on the open water fetch in the Arctic, because the swell is regionally driven. This suggests that further reductions in seasonal ice cover in the future will result in larger waves, which in turn provide a mechanism to break up sea ice and accelerate ice retreat.
It is possible that the increased wave activity will be the feedback mechanism which drives the Arctic system toward an ice-free summer. This would be a remarkable departure from historical conditions in the Arctic, with potentially wide-ranging implications for the air-water-ice system and the humans attempting to operate there.
In practice there were several more swells that impacted the Beaufort Sea marginal ice zone over the course of the next couple of weeks. Here’s what the charts looked like, as visualised by MagicSeaweed.com rather than NOAA:
Note that on the right of each set of three is a depiction of the period of the waves in question. As StormSurf points out:
Chop tends to have a period ranging from 3-8 seconds. That is, there is anywhere from 3-8 seconds between each wave crest. Wind waves range from 9-12 seconds. Ground swells range from 13-15 seconds, and strong ground swells have a period anywhere from 16-25 or more seconds.
Thus the final swell on September 7th was actually the best of the bunch, with a small area of waves over 10 feet in height and with a period of over 9 seconds. According to StormSurf those are merely “wind waves” and not yet a full blown “swell”. To give you a feel for such waves here’s what some “wind waves” hitting the beach at Barrow looked like on September 4th 2014:
Next here’s another video that reveals what effect those series of waves had on the sea ice in the Beaufort Sea:
whilst here is the swell produced by the “Great Arctic Cyclone” of early August 2012, also mentioned in passing by Thomson and Rogers:
As you can see, if you’re a surfer used to tracking swells across the world’s oceans at least, whilst the September 2012 swell was indeed rather more substantial than those we have looked at in 2014, with a height in excess of 20 feet, the period was too short to qualify as a full blown swell and it was in fact directed away from the ice edge rather than towards it. Here’s what that 2012 swell looked like once it reached Barrow:
All of which does rather make one wonder what might happen if a slightly longer period swell directed at the ice edge in the Beaufort Sea were to occur at some point in the not too distant future? Whilst we all wait with bated breath to discover what that future holds for the sea ice in the Arctic, not to mention the beach at Barrow, here’s another video about the 2014 Marginal Ice Zone Program, which summarises the year’s campaign as a whole:
Note that Craig Lee says that:
We had very little wave activity. It was surprisingly calm when we were out there in the Araon, both when we were in the ice and in the open water. There just wasn’t much wind, and so there weren’t very many surface waves.
However at least one of the “robots” he refers to did discover some significant wave activity. Here’s a visualisation of SWIFT 11‘s record of significant wave height as it floated across the Beaufort Sea in the summer of 2014:
I don’t know about you, but I don’t think I would describe 4.5 meter waves as “surprisingly calm”, especially in the Arctic!