I cannot fathom why DMI 80N was set up so biased
Me either. Terrible idea. Ever look at their own description?
"Since the data are gridded, it is straightforward to deduce the average temperature North of 80 degree North. However, since the model is gridded in a regular 0.5 degree grid, the mean
temperature values are strongly biased towards the temperature in the most northern part of the Arctic! Therefore,
do NOT use this measure as an actual physical mean temperature of the arctic."
http://ocean.dmi.dk/arctic/documentation/arctic_mean_temp_data_explanation_newest.pdfIn other words, the lat lon grid is a completely inappropriate choice of coordinate system here unfit for purpose but the global data came that way so they foolishly used it rather than take a moment to re-grid. A biased average, dependent on coordinate system choice, is scientifically unacceptable, perhaps explaining why DMI 80N analysis has never appeared in a peer-reviewed journal.
Denmark has 5.8m people, a quarter of Los Angeles. What can be expected?
It is merely a ECMWF reanalysis product called ERA40 that you can get anywhere for any place on earth (eg the whole Arctic Ocean basin) as a colored time series map (2D+T data) for the same time span of years. If what you want is ice surface temperature variation or ice temperature profile with thickness, we have satellites and buoy thermistor chains for that.
In the bigger picture, it is a poor idea to believe the state of the Arctic Ocean can be reduced to single numbers. This made some sense in the pre-computer age when journals had minimal ability to dot print even b/w graphics and simple pre-spreadsheet tasks like averaging were tedious. However today analysis of 2D+T displays is preferable as all information is retained, unlike with the single number approach 0D+T.
There's another issue here called pipeline immortality. Once a product algorithm is set up to run unattended, no matter how flawed, that's what it does. The project automator may have moved on or even died but, as long as the institutional electric bill is paid, the daily product continues to be served indefinitely from some nook or cranny in storage. Someone has to actively intervene to take it down. However inaction is a whole lot easier. Innocents come along later on the internet and are
duped.
The 2m amsl level is by far the least accurate atmospheric choice because of topographic effects of rough ice on wind and boundary layer. Ask yourself how many instruments exist offshore actually measuring it for assimilation, typically none. How many 80º+ weather stations on land: 4-5 and diminishing. The Polarstern does not measure it; their mast is at 36m. It is model-driven assumption, not observation.
The case cannot be made that north pole is somehow the "heart" of the Arctic Ocean. It's representative of it in any way becing such an asymmetric basin, both at current sea level and for continental shelf bathymetry. The ice is not centered there at any time of year, the cold pole is not centered there, the geographic center of the the ocean is not there, the last remnant ice will not be located anywhere near it. (In 2016 it was already open water; see Jim H's photo.)
DMI 80 is an inappropriate product for detecting climactic impacts of incipient BOE (
this forum) because it leaves out so much of the open water of the excluded ESS, Chukchi, Beaufort and Laptev where the insolation of large area, low albedo early open water counts the most. The low area NP region is where it matters least because of the lower angle longer path through the atmosphere and poor match to peak insolation even when it is melt pond (this year) or open water.
Thus the Bering Strait is at 65.9º which is 1,234 ignored km below 80º, causing a whole lot of Arctic Ocean to be
left out. Meanwhile 80º north is tainted by its inclusion of the anomalous localized area impacted by incoming Atlantic Waters.
The slides below show the highly variable 80th parallel enclosure on Sept 15 for the years 2012-20. The bottom image shows how poorly this enclosure characterizes actual basin percentages of land, water, ice on that date.