We have reached the short window of opportunity in the arctic when the sun is high (by arctic standards) and relentless. It never sets. In fact, if the arctic was a flat, snowless desert of dry sand at sea level, the constant heating of the sun would make it hot, and warm fronts would head south. As it is the heat is used up warming the sea-ice from roughly -30°C to zero, and in melting the snow atop the ice (which involves turning a lot of the available heat into latent heat, as the water goes through the phase change from solid to liquid.) For roughly three weeks before and after the summer solstice the Pole receives more heat than it loses, and we can expect to see temperatures zoom up to just above freezing, at which point they flatten, as all the heat is consumed by the process of turning solid water to liquid water. There are only slight variations from this pattern, summer after summer, but these variations are interesting.
One interesting fact is that during the depth of winter temperatures drop so low that salt loses its ability to melt snow. Above that temperature (roughly -10°C [+14°F]) the salt forms brine which bores down through the ice, but below those temperatures the salt is exuded from the ice and blows about as a powder. Under certain conditions there can be minute drifts of powdered salt at the sides of fresh, flat frozen leads, during the dead of winter. This salt is mixed in with the powdered snow, and any time a surge of southern air invades the arctic in the winter and temperatures are briefly raised above -10°C, the snow softens due to the salt; then it refreezes, which gives the snow atop the ice a starchy quality, and makes the wind unable to drift it. Then, when temperatures finally rise in the spring, the “melt” begins well before temperatures get back up to freezing (and available heat is consumed, becoming latent heat, before you would think.)
Another thing that has to happen is that the ice itself must warm. There are fascinating charts produced by dedicated scientists that show a cross section of the ice, and temperatures at various depths. At the end of winter the ice is coldest at the top and warmest at the very bottom, but when the ice starts gaining heat from above, there is a period when the ice is coldest in the middle. Then, towards the end of the summer, the ice is at zero where it is melting from above and at -1.7° where it is melting from below. At the start of September the ice can be refreezing from above, at zero, even as it is still melting away from below at -1.7°C (which has fooled me many a time, as I think the thaw is over when it isn’t).
Currently there is little visual evidence the ice is melting, but the air temperatures nudge above freezing at times. Down at lower latitudes, such as at Barrow at 70° north, there is enough of a diurnal variation so that, even though the sun is still up at midnight, it drops low enough to the horizon for frost to form. It touched 40°F a week ago, but was cold enough for snow a day later. The ice is still frozen fast to the shore, and shows no sign of budging despite tides and strong winds, as it is apparently over 20 feet thick. (Double error: First, this is the 2016 graph, and second, I misread the bottom as the bottom-of-the ice. The ice is thicker this year. I don’t know why they haven’t updated. Funding? But no use blaming them for my mistake. [Too rushed.])
I like to google “Barrow Webcam” and then watch the ten-day-animation from the roof of the bank building, for one gets a feeling for the diurnal variation, just watching the snow and frost form and then melt away on the bank building’s roof, at the very bottom of the picture. (Bit of snow left, just to right of vent in midnight picture below.) (Temperature 28°F [-2.2°C] with a strong north breeze of 22 mph.)
The further north you go the less the diurnal variation is, until at the Pole it is absent. O-buoy 14 is still far enough south, at 74° north, for the diurnal effect to be clear. It experienced its first thaw May 25-27
And another June 3
(The little peaks in temperature are caused by what I’ve dubbed BHI (Buoy Heat Islands). In the summer buoys can actually form their own little melt-water pools.)
The milder temperatures often bring north moisture, and fog.
(Fog is interesting, for rather than using up the available heat, it releases available heat in the phase change from vapor to liquid, as it condenses on the side of the cold ice like water on the side of a summertime drink.)
This far south on often sees the counter-intuitive phenomenon of temperatures dropping as the sun comes out. (The landscape has a more rounded look where there had been peaks and sharper features, indicative of the first effects of thaw.)
Further north there are fewer signs of any diurnal effect, and the warming is more usually (but not always) a sign the sun is out. Up at 87° north, across the Pole at Army buoy 2017B, we are seeing a more general slow rise in temperatures, with the ups and downs more due to local conditions than time of day, (and we are sorely missing the visual confirmations of a North Pole Camera). (A plague on those who cut their funding.)
Incidentally, at 2017B the ice has stopped growing thicker, but hasn’t yet started to thin.
Lastly we come to the DMI graph of air temperatures north of 80° latitude. While soaring upwards, it displayed a an interesting blip. First temperatures approached normal, but then sank back below normal, before approaching normal again.
This blip was caused by Byoof (The Beaufort High) being shoved away from Canada and over the Pole, giving the Pole sunny weather, followed by a reappearance of the low “Ralph” at the Pole, creating cloudy weather, followed by Byoof returning.
Obviously there is more to be said about this, but as usual I am strapped for time. I’ll just stick the daily maps below (apologizing for some missing maps.) Hopefully I’ll find time to comment on some ideas I glean from the maps, later.
For those interested in the yearly decent of ice “extent” towards its minimum, the decent is slower than last year and resembles 2014.