Well we have another chance to develop our thickness estimate algorithm soon. Core ice temperature is dropping to levels where we thought we had some reasonable estimates last year. I have doubts though.
Looking at T78 data the deployment report (1) states the ice was 1.52m thick with 2cm of fresh snow on aug23. Thermistor buoy sensors are 2cm apart so we can't really detect snow at that point but we are also given the sensor id of the air/snow interface as 33. Great. So the bottom of the ice on that day was at sensor 110.
The temperature profile then was almost flat by winter standards but a more detailed look shows the ice thickness quite well. (2)
Thermistors 33 and 110 have been marked roughly at the beginning of the animation(3) and again on nov22 when the temperature profile shows them clearly (with a short pause both times). There is not much additional thickening since then.
So my doubt is this. Did the ice melt quickly during end of august/september or has it been 1.5m thick and possibly porous all the time but took 3 months to cool down again?
added T78 drift path(4)
It's nice to have the actual thermistor air-snow and ice-water numbers at deployment.
Looking at the animation, it appears like there was massive bottom melt, and then re-thickening.
This is what I would expect in general with the given temperature profile.
At first, ice top is warmer than at the bottom. This surely brings about bottom melt, as heat trickles from above and the salt water eats away from below, and I think would also depend on the rate of drag of the ice over the water.
The image from Aug 23 clearly shows ice-water interface at thermistor 110.
Next, the temp profile is flat. My understanding is that the bottom would still be melting, albeit at a much slower pace.
The image from Sep 13 seems to be the last day of top melt, as well as the ice having a cold core again (cold gradient from the middle to the bottom).
Eventually, the ice top is colder than the ice bottom, with a gradient appearing through the ice. From this point on the ice starts bottom freezing and it's easier to spot where the ice ends.
The image from Sep 21 in my opinion shows the ice-water interface at around thermistor 55.
The image from Oct 15 seems to show the ice-water interface at thermistor 70.
The end of the animation again shows the ice to exceed thermistor 110.
Admittedly these are just generalizations, since I can't put any quantitative expectations as to the rates of melting and freezing. The rates do depend on the steepness of the warm or cold gradient though. Therefore I would not expect a whole lot of bottom melting, also given the rather late date of deployment. However, eyeing the animation, it would appear as if the bottom melted all the way to thermistor 55. Some possible explanations:
* Bottom was higher than thermistor 110 to begin with, with 110 being some protruding edge. However, the animation data does support this initial placement for the ice-water interface.
* Melting did not actually reach thermistor 55, though I can't see any other explanation for the cold gradient ending where it ends on Sep 23, except that it was the ice-water edge.
* The ice was extremely mobile which enhanced bottom melt way beyond what the temp profile would suggest. This can be checked by looking at T78 drift.
* The ice has not cooled enough for the gradient to reach the ice-water interface.
* My intuition for rates of bottom melt is disconnected from reality (very probable).
All in all, a very interesting mystery, with wider implications. If indeed ice can bottom-melt so quickly at the end of the season, we are not so far away from blue ocean as the extent extrapolations seem to suggest.
Following up on Tbuoy thickness estimates. Here is an update of
T78 temperature profiles, the blue line, with the Heat120 temperatures overlaid in black. A bit confusing in this format so some explanation:
Heat120 records the change in temperature after heating each thermistor for 120secs. The idea being that air, snow, ice and water will heat differing amounts, allowing us to see which is which. Some further interpretation is required.
Again thermistors 33 and 110 have been marked roughly at the beginning of the animation, marking the thickness of the ice the day after deployment date when the first heat120 cycle ran on aug24.
30 days later on sep22 the heat cycle shows a similar thickness but I think by now this is mostly rotten ice from bottom 'not quite' melt. Could perhaps be described as phase changing. This ice would probably be no match for an icebreaker or a heavy storm but just about maintains its integrity to the end of the season.
Skip to day 60 and we see a similar thickness but we can see the ice state changing from the surface downwards as the weather cools during October. Surface temperature on oct21 was about -20C.
By day 88, nov20 the ice is happy again, phase change back at depth almost complete and the heat cycle perhaps shows some signs of bottom thickening, also marked, optimistically, at thermistor160.
After that even a fertile imagination struggles to interpret small changes in temperature though I made a guess at day126, dec28 at thermistor170. Perhaps SimonF32's analysis will show more.
So 170-33 time 2cm is 2.74m, a possible increase of 1.2m.
I'd be interested in other interpretations.
Apologies for removing the 2 temperature scales. It was necessary for the overlay.
The warmer Heat cycle temps in the final frame are interesting....
Added t78 location, not far from the
shear lineand amsr2 awi v103 for more detail.
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