Sunday, May 17, 2015

Sea Ice Thermal Flux Profiles II, as demonstrated by the horizon; thin ice

~A big surprise, very thin sea ice gives a similar horizon to much thicker ice, the instant it is set completely.
~The difference between the two ice profiles help explain thermodynamic action.

   Astounding as it sounds,  thin sea ice raises the horizon a lot as soon as it forms.  Historically, there has been well known weather the day sea ice forms,  the clouds clear along with a common impression of much colder temperatures all around coastal areas.  For obvious reasons thermal variances are difficult to study when sea water turns to sea ice,  although flux studies have been done mainly after sea ice is solid enough to put equipment on it.

   Just after Minima of 2013.  The apparent Arctic wide cooling caused by extraordinary dynamic Gyre stall of ice compaction over the entire Arctic Ocean (except for the Atlantic side) caused an earlier freeze up of McClure and Barrow Strait.   This reduced the usual cloudy autumn from masking the horizon.  Above left picture was on September 21, 2013, with surface temperature -6 C.  Some ice was already present but sea ice formed further afterwards.  Middle picture was September 23, 2013,  sea ice appeared to have formed completely and the horizon rose above true astronomical horizon.  This is simply an exhilarating discovery, it leaves long wave thermal transfer as the principal thermal contributor  of the near surface inversion causing the greater refraction looming.    Further to this (extreme right),   the horizon remained the same or even dropped a little 2 hours later in the evening.    This is another discovery.  Usually a thicker sea ice horizon rises in the evening,  even when cloudy, a stronger evening inversion did not happen when ice was seen bran new.   This lack of horizon rise was observed again multiple times with very thin ice.   I suggest an absent sea ice "cold" core which allows the air to cool faster above top of ice,  while with new ice the higher sun presence at about noon gave greater thermal flux upwards creating a slightly more visible inversion.

   A common problem with very new sea ice analysis is of course caused by fog or clouds.  Natural cooling during autumn causes a great deal of moisture obscurations.  Fortunately 2014 had a brief respite just about the right time,  although not perfect,  the photographic  repetition of 2013  freeze-up was achieved.

    Barrow Strait  can be very complicated by its tidal currents which change substantially during a moon cycle.    But here we can note the same thermal sceneries as witnessed in 2013, 2012, 2011 and 2009.  Capturing a freeze-up with very little clouds is rare.  This is why 2014 and 2013 are featured here,  the other years had some clouds making demonstrations possible with a lot more explanations.  2014 freeze-up took 3 days,  of which day 2 had grey ice which will be dealt with on a subsequent article. Picture of October 1 (extreme left) feature rolling water waves and sea ice bits in a fierce wind storm.  Temperatures ranged from -9 to -12 between Oct 1 and 3.  2014 freeze-up occurred at about -11 C which was a return to regular yearly feature.  except for 2013.    On October 3, Barrow horizon rose substantially despite similar temperatures.  20:07:54 UTC capture (second from left) had new thin ice slightly mangled by winds and tidal currents during its formation.  But at once the horizon rose when sea ice covered all of sea water up to the horizon.  A few hours later the horizon dropped (23:31:26) again likely due to air cooling faster than top of thin ice.  Well frozen with thicker sea ice,  the horizon rose most 15 days later (furtherest right).  the cold ice core started to to grow enough to affect the evening rise, accretion of ice goes in tandem with a more risen horizon.

  Barrow Strait Ice is usually more chaotic than McClure Strait , but concurring to the demo above  the Western view of the Northwest passage had similar refraction effects but on different days:

   October 2, 4 and 18 2014 (from left to right),  sea ice set a day later in McClure Strait and looking at NW passage .  October 3 had grey ice.  The much lowered water horizon (left) rose at freeze-up on (center),  the horizon rose further 2 weeks later indicating the build up of a cold ice core.  The repetition of this looming feature helps explain thermal fluxes instantly.  

  Thin sea ice main feature as giving as high or higher horizon compared with thicker spring time sea ice at noon must be due in large part to thermal long wave heat from the the summer warmed sea causing a weak inversion,    convection stops the moment the sea surface becomes crystalline, the insulation properties of very thin sea ice is simply spectacular.    Sea ice conduction in direct contact with surface air plays a different role in autumn,  likely slightly warming the interface (if at all)  as opposed to cooling the snow/ice with air interface in spring especially in the evening.  The missing core of cold ice is replaced by thermally "hot" sea water reducing evening inversion amplification.  But this feature has been observed to be short lived,  one week or so from onset the stable to slightly lowering horizon in evening changes to heightening as a top of ice cold core becomes more and more resilient and effectively cools the interface faster after warming from the autumnal noon Polar sun. Conduction from very thin sea ice appears to be very poor,  not powerful enough to warm interface air by causing and adiabatic profile which would lower the horizon below astronomical horizon height.   WD May17,2015


Surface energy fluxes of Arctic winter sea ice in Barrow Strait

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