Nuovo giorno in Heven
You don't need to be a scientist to see a link between snow cover (black line) and the North Atlantic Oscillation (red line)
© 2015 - Luzian Schmassmann
Snow reflects up to 95% of the suns energy, versus an average 30% for the rest of the Earth's surface. No wonder snow cover can influence atmospheric circulation.
© 2015 - NASA
How the North Atlantic Oscillation (NAO) describes the atmospheric conditions that influence our surf.
Fifteen years ago we first decoded wave model data in a way that allowed us to score more surf. That began an obsession with finding connections that allow a glimpse of the surfing future. With our 16 day forecast about as forward looking as a deterministic model could usefully be we've started digging deeper. It's well known the El Nino can predict, to some extent, the winter wave climate in the North Pacific, but what might offer us a similar glimpse into the season ahead for the North Atlantic?
If you want to read about the North Atlantic climate you'll see a lot of research papers around the North Atlantic Oscillation. This climate mode, literally the difference in pressure between the Azores and Iceland, describes in a general sense the overall atmospheric conditions and particularly the strength and location of the prevalent band of Westerly winds that dominates in the North Atlantic. The NAO doesn't so much predict these winds as offer a simple index for describing them, which itself can be compared with other climate or weather phenomena to see if we can find connections.
For European surfers it'll come as no surprise that there's a clear link between the NAO and wave heights in our waters. There are numerous papers referencing this and the results are fairly easy for us to reproduce. Given we know our swell is created by westerly winds over the ocean's surface there's a clear mechanism for this connection, but this doesn't offer us a predictor. So our search was for things that predicted the NAO. We've been bouncing this conversation around with anyone who'd listen but it was ex-MSW intern and meteorologist Luzian Schmassmann who found a fascinating bit of research attempting to connect snowfall over Europe and Asia in October to winter changes in the NAO. We figured that if there was a connection between snowfall (or actually the rate that snow accumulated) and the NAO and a link between the NAO and surf then perhaps we could cut out the middle man. Luzian not only proved a connection, but fascinatingly it seems to outperform the sort seasonal numerical modelling that drives the long range winter forecasts that weather agencies produce. To give a better understanding of what this might mean for surfers we caught up with him to discuss the work:
How did this project come about?
"The first time I’d read something about the connection between winter NAO and the winter wave heights in the North Atlantic was actually during my internship at Magicseaweed a few years ago. I remember the discussions we had about the possibility of seasonal wave forecasts: If there is a good way to predict the whole winter NAO. The key moment was when I saw a presentation at the University of Innsbruck about seasonal forecasting of the winter NAO with the help of the SAI, an index describing the rate of accumulation of snowfall across Eurasia."
How might Eurasian snow cover be influencing the climate?
"Snow cover changes the surface albedo - how reflective the land surface is - and this does change the way the land heats and cools. Because pressure systems are created by warm air rising and cool air sinking there is a relationship between albedo, the Siberian High and broader atmospheric circulation. I did reach back directly to Judah Cohen, responsible for the original research, on why exactly the rate of change of snowfall was important rather than overall snow cover and he suggested it may also be the case that snowfall accumulation was simply a good proxy for the overall atmospheric circulation. Ultimately, knowing there's a provable connection means we don't have to fully understand the nuances of the mechanism to start to create a better seasonal forecast."
You mentioned that you found a stronger correlation with the average for the whole winter than with any particular month – presumably this means we can still expect a huge day to day variation in conditions?
"Yes that’s absolutely correct. Predicting high probabilities for small mean winter wave heights doesn’t mean that there’s no possibility for a couple of huge swells during this winter. The reason for stronger correlation with the seasonal average is the high variability between the months for the different investigated years. Every surfer will know just how much the North Atlantic can vary, even in the depths of winter."
Seasonal forecasting is often a statistics game but surfers, like everyone else, tend to be influenced as much by a few key events as average swell heights. How might surfers make use of this information?
"There are other seasonal forecasting methods which don’t use the statistics. My study showed that the use of simple statistics often outperformed the complex numerical predictions of the ECMWF, that’s awesome and does mean this is something surfers can use to understand the likelihood of outsized waves in some areas.
Of course, if there’s a winter with the biggest Nazaré waves ever seen, then it’s hard to believe that the overall winter wave heights could be smaller than normal. For the interpretation of the new forecasting method it’s important to make a step back and watch the whole winter, not only one extreme event. The question is what kind of surf forecasts do you want to have? If you want to predict daily wave heights three months in advance, this method will not be very useful! It's also useless for anyone wanting to know how big the waves are going to be during their one week surf trip. While I didn't find strong links for the West Coast of France or Portugal there was still a correlation and the strongest results came in predicting the average winter wave height and period for big wave areas like the West coast of Ireland. I’m sure that this could be interesting for surfers exploring these areas for a whole winter. It could also be a useful tool for things like risk management of extreme flooding in a coastal area."
How does the connection you found here for the North Atlantic compare with the sort of correlations with El Nino effects in the North Pacific?
"El Nino is another league. There are tons of scientists who have investigated the relationship between the El Nino and the wave climate in the Pacific. From a surfer's view, these influences on the waves of Hawaii and California are probably more exciting than the effect of the SAI on the wave climate in the Norwegian Sea or Ireland. Nevertheless, this study showed that there are strong connections between the snow in Eurasia and the waves in different areas in the North Atlantic, and that’s pretty cool if you're there and not in Hawaii."
Does connecting something so seemingly obscure as Eurasian snow cover with surf conditions hint that there may be other factors with a huge influence we've yet to discover?
"Well the fact that snow cover and its albedo have a big influence on the atmospheric conditions is not new. But the findings that the autumnal rate of Eurasian snow cover accumulation has such a strong influence on the winter waves in the North Atlantic is impressive, though. However, there are a lot of other factors, which affect the atmospheric conditions and the wave climate, respectively. But a lot of these factors couldn’t be used for such simple method to predict seasonal forecasts. That’s basically the interesting thing about this study. To obtain such a good result with these relative simple couplings and models."
Most importantly what does the current snow cover tell us about the likely upcoming season for European surfers?
"The SAI from October 2015 was +2.0. This means that there was a fast accumulation of snow in Eurasia during October. This index leads to more southerly storm tracks over the whole winter and correlates with a negative NAO pattern (see above). For the North East Atlantic this generally means average wave heights are more likely to be smaller than usual and for the Canaries, for example, larger than usual. Of course this is an average over the season so we can still expect a range of conditions and no doubt significant winter surf at both at times."
The website of Judah Cohen gives more information about his research.
Luzian can be found lurking around Swiss river waves and writing for Wave Up Magazine.
Any questions please ask me below or on twitter and I'll do my best to answer.
