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NAO through the eyes of a harbour seal

The North Atlantic, Saturday 7th November


An animated juvenile harbour seal greeted me at a distance somewhat shorter than what his mother would keep as I entered the water yesterday. In between playful dives into the kelp, he threw me engaging glances and tempted himself to come closer still. We were deep inside in a bay, behind a headland, where the impressively large seas caused the kelp to heave many times more than he has ever seen it. Born this summer, I thought his world is un-figuratively being rocked for the first time. It was the first big swell of the winter season, a low pressure system which tracked unwaveringly below Iceland towards our island, its energy manifest as immeasurably large waves on the open coastline, or a more reckonable 2 metres or so wrapping into our well hidden port of refuge.

This will not be the last time his surroundings will be rudely stirred by energies from afar this winter. There will most likely be at least 10-12 more such days where his normally calm habitat, which only ever has its surface tickled by winds will host the unusual phenomena of waves breaking down the length of the point and even more unusually of late, people who come to indulge in this. What is interesting is that according to our best oceanic and atmospheric modelling, were he born in any of the last three years, he might only expect 5 or 6 such days. To impose such orderly logic on such a paradigm of chaos seems a curious exercise, but is accounted for well by the NAO index (North Atlantic Oscillation).

This, at its simplest is a measure of the variation in pressure between the resident Icelandic low pressure system, and the Azores high pressure system, both of which hold fort in the North Atlantic without ever moving too much, especially in winter. Their relative strengths control the westerly winds which incessantly batter Ireland and Northern Europe and a  +NAO year means more westerlies, more rain and more long range swell. The whole system is believed to have links to deep ocean water masses and the El Niño Southern Oscillation among other things.

This year is a predicted + NAO year, and the first week of November is ground truthing this so far with 4 days of swells over seven metres. NAO is not a phenomenon in itself, but a useful way to describe the variation in our weather patterns over entire winters and decades.  A week, month or even winter of unseasonably warm weather does not indicate climate change alone; in fact predictions indicate that a –NAO would actually be the result of such change meaning less westerlies, and lots more cold northerly winds.

As I write, a vessel, too big to be from around here, slips between Clare Island and the coastline intuitively seeking the shelter of Clew Bay, for tomorrow an even bigger swell is forecast. It will be 9 meters, and I would be delighted were the seal to accompany me again tomorrow.


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