~Complex system by its vastness, the Arctic atmosphere warmed to #1 despite any clear year to year trend.
~600 mb temperature analysis reveals September 2019 surpassing 2012, despite 2012 having less sea ice at minima.
~Shouldn't 2012 atmosphere have been the warmest one?
|NOAA daily composites, 2012 to 2019 600 mb temperature comparison for September. In a quite amazing contrast of causes, the greatest minima sea ice had a cooler atmosphere. In between 2012 and 2019 seasons had over all much cooler Septembers as well. 600 mb temperature is closest level to represent the average temperature of the entire troposphere. How to explain this disparity?
The Polar Vortex is key, it was much larger spread out over 2 continents, now in 2019 much weakened, it is still there but a much deformed entity. Whereas, in the past it survived the summer, now it almost vanishes. The difference between 2019 and 2018 Polar Vortex was quantified by refraction of the sun disk technique, 2019 had a powerful vortex center nowhere as big and long lasting as 2018. The smaller the vortex the colder it is at center (this was felt by Chicagoans last winter from when the center of the vortex unusually formed deeply south, a very unstable situation, it was a short lived super freeze-up). 2012 for instance had a larger vortex, lasting , barely surviving the summer (a key factor of a great sea ice melt). 2018 was astoundingly dominant for a longer period, healthily survived the sea ice melting season. In fact it vanished in late October. 2013 was the most peculiar of years , there was lots of sea ice extent at minima mid September, but the vortex survived barely very much like 2012 in a split vortices configuration. 2018 had the strongest summer vortex in decades, despite being 4th warmest year for the Northern Hemisphere (a contradiction was it not for its not so vast size). There has been ample evidence of a strong warming over sea ice although faint:
2019 Surface temperatures between 80N an 90N degrees latitude, show an extreme push upwards of temperatures aligning to the 1958-2002 mean especially during the great melt summers. Although it makes sense warmer advection occurs from vast open waters towards remnant sea ice, the DMI summer temperature mean seems counterintuitive, the mean of colder years from decades prior were warmer than during all time low sea ice extent summers, but then again during 50's 60's and 70's sea ice field was laced with multiyear very thick ice islands, it was a different cryo mini world on its own. On these very thick ice floes existed summer time mini lakes, all likely thermally stratified, with warmer water on it's surface, capable of increasing air temperatures well above 0 C at the 2 meter level. With AGW 2019 sea ice field transformed to much younger multi year pack, having had surface water draining more thoroughly avoiding great top of ice water buildups, the summer average surface temperature can be cooler. A more bare top of sea ice, consisting of mainly ice - with a bit of snow - may be influenced by the rule: top of snow (ice) T*** is always colder or equal to surface temp - (rule established by horizon refraction observations). 2 meter air temperatures above water on ice or open sea water would be the only reason why surface air can warm a lot more than 0, after all sea ice does not exist at temperatures greater than 0 C.
This leaves to the not so obvious conclusion - the atmosphere and sea water of the Northern Hemisphere has warmed since 2012 - NASA would say so, but the sea ice minima extent has still not shrunk below 2012. Vast sea ice packs are rather not easily judged by extent alone, but rather by very esoteric circulation patterns and cloud albedo, not necessarily always favorable for clearing the Arctic Ocean. The circulation patterns were rather not good for greater dumping of sea ice during summers since 2012, because of where the remainder sea ice twins with Greenland and causes a circulation pattern unfavorable to dump sea ice towards the North Atlantic. A more open Arctic Ocean Cloud albedo increases mid-summer when there is a great deal more evaporation next to ice ( by more substantial open water and greater heat), sea ice easily helps form low clouds and fog in such circumstances. But the main extent numbers to watch are not only found at minima but at every other period as well:
2012 have been well below, often historically lowest than this 1972-2018 average. It is this fact which proves that the atmosphere has warmed substantially in a mere 7 years. WD October 5, 2019