~ Made different by lack of surface snow
~ Interpretations from multi-coupled thermal systems made simple by one horizontal line.
First sea ice underside melt (FM) happens after the long Arctic night when there was
a continuous accretion of sea ice only interrupted by passing warm Arctic Cyclones. Following Polar long night sunrise, the sea ice horizon is always observed elevated compared to true astronomical horizon which occurs when the sea (ice/land) surface temperature is equal to the air immediately above. The main characteristic of the first underside melt is that it is observed never lower than true astronomical horizon unless the entire ice column temperature is greater than surface air. In Arctic Spring, sea ice is a "heat sink" because it tends to be always colder than sea ice and air, but when there is no longer thermal emissions from ice towards air, the underside melts. This gives an apparent "noon" pause in horizon height variations until the sun lowers in the evening, the horizon appears to rise greatly at every sunset or lower sun (when there is a midnight sun). The process usually continues the next sunny or even cloudy days until complete melting happens.
From FM observation onwards the underside melt is usually observed to last gradually longer day by day, lasting a few minutes on the first day, eventually taking on hours as spring progresses. From FM onwards, sea ice may vanish if warmer air, water and sun rays focus on the colder ice column. Once the ice gone, the horizon may be observed lower than true astronomical horizon, this happens when surface air temperature is colder than sea surface temperature.
This refraction based observation method helps analyze the true nature of the sea ice to air interface - it is an instant analysis of thermal geophysics spanning a huge distance.
It is foremost the over all encapsulation of the winter climate just freshly past;
We look back, and find out the significance in yearly first melt dates.
2010 (top spring photo) had El-Nino during winter, FM's don't happen earlier because it's warmer, rather a matter of all thermal physics, from sea water, ice thickness, ice colour, snow coverage, air temperature, solar radiation, cloud cover, near surface convection/inversions, aerosols and finally the location of the Cold temperature North Pole over winter/spring. 2010 had a particular first melt aftermath, excepting 2012, stronger and longer than the others. Over all sea ice was thinner. 2011 (2nd from top) had nowhere as warm a winter as 2012, the first melt was captured April 15, with following extremely consistent progressive melt periods (continuing all the way to a large minima decrease). 2012 was fascinating by earlier tendencies of near first melt occurrences by late February, it occurred on March 12, along with subsequent regular strong melting, as strong as 2010. But the clue for a great sea ice melt to come is in the tendencies towards the true astronomical horizon especially very early on. 2013 had very inconsistent post FM underside melting. Again the first date of true astronomical horizon did not matter as much as what happens before and after the recorded date. March 19 was early , but what followed marked the September sea ice minima in advance, there was no strong consistent underside thawing, despite regular adiabatic near refraction observations. Another clue of a very cloudy Arctic summer to come. Projecting the future Arctic climate more precisely requires multiple sets of different observation events.
2014 post mortem:
April 3 2014, no sign of any first melt, was late compared to previous year, local apparent noon picture (left) has just as high an horizon as 3 hours later. Vertical vertice horizontal lines are spaced 3.3 minutes of arc apart. 2014 was the year of the Polar Vortex made popular by weather medias. But what mattered was the location of the coldest atmosphere in the world. During Spring 2014, it was right over Cornwallis Island Nunavut Canada where the pictures were taken.
What a difference a week makes. I interpreted this late FM (right) as the return of burgeoning anticyclonic activity, in part true, but it was equally the presence of the Cold Temperature North Pole, lesser clouds and aerosols. But subsequent daily melting was more consistent than post FM 2013.
2015 breaking news from the sea ice horizon:
March 26 2015, NW passage first melt with some early tendencies nearing true astronomical horizon starting 2 weeks prior. Horizon height (left) is equal to whence the temperature of sea water and surface air was equal on september 10 2014 (right), the same horizon height has returned announcing melting and the open iceless sea to come.
Next week: the meaning of all this with respect to Northern Hemisphere coming summer weather and Arctic ice minima projection.. WD April12 ,2015
Post a Comment