~In a short time span Arctic spring and autumn days have shortened.
~A very good reason why Northern Hemisphere circulation is changing aside from warming temperatures: thinner sea ice.
~ This can be visually observed multiple ways, all to to with atmospheric refraction.
The latest Arctic warming can be summed up in 3 periods by sunset tardiness, of which some part of the sun disk can be seen well below the astronomical horizon (A.O. : horizon seen if there was no atmosphere). In the High Arctic Cornwallis Island some sun disks parts have been seen lower than -3 degrees (that is 3 degrees of arc below astronomical horizon). Furthermore when seen so much below the A.O. under the violet sky, sunsets shift Northwards quite a lot, prolonging the day. 3 recent periods of concern would certainly be 2001-2005 , the last thicker ice years, 2005-2010 intermediate warming/thinning of sea ice, 2011 to 2021 severe thinning years, of which the first period had 6 Month of March sunsets 2 degrees below astronomical horizon, the intermediate period had 3, the longest lasting period of 11 March months had only 3, this is a serious decline in optical properties caused by sea ice and air interface. Visually this can be studied in greater details, although I have no illusions about how convincing these images can be, atmospheric refraction is very poorly understood, I'll endeavor to explain nevertheless:
March 20, 2021. At first the sun appears red and reddish throughout, by moisture, March 2021 had more snow, more encroaching Pacific cyclones, than perhaps in the entire observation period of 2001 to 2020. This sequence has been captured in a brief cooling build up period between cyclonic storms. The sea ice at horizon is also at thinnest recorded levels. The sunset was not tardy, -1.39 degrees below A.O. . The main feature of interest is the lack of laminas, the lack of roundness. At end you see the beginning of purple sky light. Basically there was no great temperature gains near the surface upwards. This makes for a rather ordinary (for the Arctic) sunset.
March 19, 2009, much drier air, therefore much cooler over all winter, on this moment -35 C surface.
These impressive presence of laminas are a feature of a colder atmospheric processing, these occur when there is layers of warmer air above, but with very cold interface between sea ice and air in light or no winds. These laminas rose undisturbed by strong winds, forming multiple thermal layers in stable air, again a feature of a long time cooled surface facing the rising heat and sun as winter ends and spring begins.
March 19,2010. a windier sunset, but with great thermal rate difference, it was -33 C a few hours back, at this sequence it was -23 C causing a lapse rate favoring an extreme late sunset, indeed 1.93 degrees below the horizon. Warm air advection is one cause of sunset tardiness by reasons of refraction optics. The cold ice did not warm up instantly, as the air just above changed, for this to happen in greater winds, the sea ice must be thick and sluggish in warming.
One may not conclude a great Climate Change with one observation moment, rather it be known, the entire EH2r corpus of data, likely 10,000 individual sunset sun disk observations, which have gradually evolved into mundane sunsets rather than exciting colorful, extremely strange, lines upon lines stretching to "fire on the ice" sun line before dusk. What we are witnessing is the signs of drastic warming affecting all visual aspects of land, sea and even winter. WD April 6 2021