I don’t know any other way to put it: this season’s Snow Bunting banding has been a disaster. Consider the numbers: at this same date in 2010, we had banded 619 (total for the whole Winter – 985); at this date in 2011, we had banded 1,074 (Winter total – 2,844); so far this year we have banded only 33! And it’s not just us: David Lamble, who bands in the Fergus area and who banded just under 7,000 last Winter, has banded only 200 so far this season. So what’s going on?
To try to answer this, I’ve had to take a crash course in major weather systems. We’ve all become acquainted with El Nino and its effects on Summer weather conditions but few of us have even heard of the Arctic Oscillation [AO] (or the North Atlantic Oscillation [NAO] which is a part of it), a system that impacts our Winter conditions.
A quick Google search of “arctic oscillation” brings a wealth of information. Just below is a good, quick and easy explanation from EarthLabs of AO with diagrams.
(EarthLabs is a collaborative effort by individuals at the Center for Science Teaching and Learning at TERC in Cambridge, Massachusetts and the Science Education Resource Center (SERC) at Carleton College in Northfield, Minnesota.)
How the Arctic Oscillation Works
Let’s start with the basics. Air moves from one place to another around the world because of air pressure. In some places, the air is thicker, or more dense, than it is in other places. When this happens, we say the air pressure is higher. Air moves from areas of higher pressure to areas of lower pressure, creating wind.
The Arctic Oscillation is the movement of air back and forth between the North Pole area and areas farther south (for example the middle of the U.S.). Sometimes the air pressure is higher in the south than it is in the north. When this happens, warmer air pushes north and keeps the really cold Arctic air in the Arctic. This is called the “positive phase” of the Arctic Oscillation. During a positive phase of the Arctic Oscillation, wind and water currents draw warmer, saltier water farther into the Arctic than usual. Other times, the air pressure is higher in the Arctic than it is further south, so the cold air moves south. This is called the “negative phase.” During the negative phase, strong surface winds maintain a powerful clockwise gyre (circular current) around the north pole, which helps to keep colder, fresher water more evenly distributed at high latitudes. The Arctic Oscillation is a little more complex than this basic description, but this is basically how it works. The AO typically seesaws between its positive and negative phase over three-to-seven-year periods.
This Winter we’re in the midst of a very strong – in fact, a record “extreme” – positive cycle resulting in the very mild and snow-free conditions we’ve been experiencing. Interestingly, this has followed two Winters of record extreme negative values, which brought us cold weather and lots of snow. This is highlighted below by an excerpt from Dr. Jeff Masters’ wonderful weather blog: Weather Underground.
Wild swings in the December Arctic Oscillation
This winter’s remarkable AO/NAO pattern stands in stark contrast to what occurred the previous two winters, when we had the most extreme December jet stream patterns on record in the opposite direction (a strongly negative AO/NAO). The negative AO conditions suppressed westerly winds over the North Atlantic, allowing Arctic air to spill southwards into eastern North America and Western Europe, bringing unusually cold and snowy conditions. The December Arctic Oscillation index has fluctuated wildly over the past six years, with the two most extreme positive and two most extreme negative values on record. Unfortunately, we don’t understand why the AO varies so much from winter to winter, nor why the AO has taken on such extreme configurations during four of the past six winters. Climate models are generally too crude to make skillful predictions on how human-caused climate change may be affecting the AO, or what might happen to the AO in the future. There is research linking an increase in solar activity and sunspots with the positive phase of the AO. Solar activity has increased sharply this winter compared to the past two winters, so perhaps we have seen a strong solar influence on the winter AO the past three winters. Arctic sea ice loss has been linked to the negative (cold) phase of the AO, like we observed the previous two winters. Those winters both had near-record low amounts of sunspot activity, so sea ice loss and low sunspot activity may have combined to bring a negative AO.
It will be interesting to see what the rest of the Winter brings. But one thing is for sure: without any snow, we will not be getting Snow Buntings.