Friday, May 10, 2013

SEA ICE phase changes mimicked by the vertically shifting horizon

~Seeing the thermal effects helps explain the sea ice melt
~ A series of May 2013 days remove the veil from thermal variance mysteries

    In order to establish a 12 melt hour period and prove it, one must record data.  Last few days of photo chemical ice crystals showers slowed the melting period,  for now it lasts about 10 hours a day.  The image sequence below shows a relatively complex drop of the morning horizon as the sun elevation rises.  One may observe the 3 underside phases, freezing (extreme left)  until  steady state 4th from left,  and melting (extreme right).    Underside melting will go on until long wave outgoing radiation become weaker and the ice horizon will rise again in about 10 hours.

    {take sequence to desktop and zoom}   All pictures from land to sea with fixed mount camera.  

Mean time from extreme right melting picture the horizon will drop further and further.

  The total thermal effect from top of sea water column twinned with more intense sun rays on top of ice obliterate atmospheric boundary layers (inversions) created during the night right above the ice.   This shifts the horizon to go lower. During the night, in this case from the much lower midnight sun,  the underside freezes because the net thermal balance favors it, this causes the horizon to rise greatly.    When the sun rises further in elevation ,  sun rays penetrate a thinner and thinner atmosphere, the rays have been less depleted and hit the ice.   The albedo effect theoretically should deflect most of this energy upwards.   But sea ice,  even covered with snow seems to absorb a significant amount of rays, sufficient to change its net thermal balance within 1 hour as seen here,  making it emit more long wave radiation along with short wave deflections (which does not warm air  as much).   We literally see here sea ice thermal emissivity change to the point when the ice 
can't possibly be freezing or accreting.   The underside of the ice is most bombarded with long wave radiation from above and below, thus it melts.

First 12 hour underside melt observed

History in the making:

Same May 10 2013  day, 11 hours later (extreme right picture)  underside ice was still melting.  The day got cloudier a few hours after the beginning of the underside melting.
The clouds were mostly broken stratocumulus at 3000 feet ,  which reduced the impact from photochemical ice crystals (less sun,  less photochemistry).    This reduced sun ray obstructions to surface.   Here seems to be another discovery,  total clear air makes the sea ice more thermally active,  clouds mixed with sunlight reduced wild thermal fluctuations especially in the evening.
This kind of weather is possibly an ideal cold weather sea ice melt accelerator.   At any rate,  after 11 hours of underside melting, the weather was such that I lost the clear horizon, distant snow showers reduced visibility.  However secondary observation spot showed a continuance of the lower horizon.   So for the first time in history, 12 hours of underside melting was observed and nearly completely filmed.   This means that the sea ice at 75 N 95 W is thinning, cracking and vanishing.  Slowly for now, but much faster in no time.  2012 during same May period had consistently smaller melt periods.  The underside ice column also has a significant layer of bottom "soft ice" confirming the visual observations.

wd May10, 2013

Overnight clear sky cooling slows the melt

Clear weather is a double edge sword when it comes to thawing underside sea ice,  this morning (May 12) I measured a later start of melting phase by 46 minutes than from May 10 (above).
Below is a darkened on purpose 1 hour phase change sequence:

The net effect of clear night air was to cool sea ice a great deal more especially with the low midnight sun.  This caused a later freezing to melting phase change,  remains to be seen whether a clear day can counter balance this shift and make the melting period last just as long than previous days.  Clouds with sunshine seem to be the most potent thawing combination.

8 and a half hours later,   apparent underside thawing stopped ,  3.5 hours earlier than previous days,  in cool very clear air.  This is very interesting.  The likely reason is the latent cooling from the clear  night prior,  freezing the soft ice column further than usual.  There was cooler ice to start from, ultimately it was not warmed to previous days balance.  If left to clear air only, the freezing process would last longer in the spring because of the low midnight sun.  Pictures will be placed  up tomorrow.

Clear Sky conundrum, the ice freezes more
~With confirmation of melting phase.

The next few clear days from May 12 were strange and exhilarating.  Turns out that clear skies were indeed not conducive for melting sea ice,  even with the midnight sun
at reasonable elevations.  From May 10 and 11 melting periods of 12 hours or more, day 12 went to 8.5, 13 8 and day 14 even less long.  Despite 24 hours sunshine
and on day 14 warmer temperatures.

First on day 13, I have confirmed a melting phase.  If sea ice is one solid block of uniform ice and for example there is no melting going on when there is more sun rays hitting it, the horizon should drop continuously,  without interruption similar to what it does at night,  raises continuously in direct relation with the lowering elevation of the sun.   Inversions are such that there is no limit to the horizon rise,  if there is less and less rays the surface to air interface inversion becomes stronger and stronger.  Causing a form of looming,  the sea ice well frozen looses most of its energy to space,  since the ice is at same thickness the only variable is the long wave radiation escaping to space.  Theoretically with the one block of ice getting warmer as the sun rises, at local apparent noon,  when the sun is at daily zenith,   the horizon should be lowest,  it was not observed as doing so.   The horizon reaches a steady point and stays there,  similar to boiling water, when the temperature reaches 100 C it stays there until all water evaporates.  Likewise with sea ice,  the underside melts,   a new thermal balance is reached where the horizon stays at constant elevation.  What likely happens was triggered by the changing nature of the sea ice column when water melts on its underside the ice column is not the same.   Its a mix where sea water is part of the process, at that moment there is  a much larger body of  matter to exchange heat with.   Unlike 1.7 meters sea ice, this sea water may be considered as having infinite thermal capacity,  therefore there is a lull in the lowering of the horizon.  Its the same as air interfacing with open water ,  a thermal exchange causes a fixed horizon level, only to be changed when especially the air temperature just above varies.  A similar effect occurs when the sea temperature becomes different.  But as seen below,  especially places like Redondo beach California,  a small difference between sea and surface air temperature doesn't shift the horizon a whole lot.     Sea ice is unlike the sea surface because it is insulated and may be considered a body separate from the sea until it starts melting in the underside.

Bottoming out of dropping horizon:
The first picture from left until 4th spans nearly 3 hours at about the same horizon height, 
despite the pre and post local apparent noon sun.   Very similar to sea to air horizon when the sun can't heat the sea significantly enough to make a shift.  The furtherest picture right was equally fascinating, this phase change occurred significantly earlier than previous days, 1 hour earlier,  despite clear blue sky compared to cloudy weather.

   Although this sequence just above (repeated twice more),  represents a better understanding of what is going on under the ice surface,  the last one furtherest right was puzzling.  Why would there be more freezing on a sunny clear day?  The next 3 days were clear,  it seems the ice was made warmer by clouds,  then sea ice cooled dramatically at first clear night,   slower on the next following days.
The freezing period was progressively longer,  with subsequent clear nights and days of May 13 and 14.  Even though the temperatures were 5 degrees warmer on the 14th.
From 12 hours of melting in clouds,  the freezing became stronger  in each subsequent clear air day because there was an adiabatic process which evolved from weaker to stronger,  since the air above was relatively still cold,  the adiabatic process on the 14th was equally more unstable.  In the fall,  particularly over wide open Arctic water,  adiabatic air profiles favors surface cooling.   Only the higher 24 hour sun can compensate for the heat loss from adiabatic process,  likely as records show end of May at 75 N.  When clear air will likely give melting longer than 12 hours.   The other discovery here is equally important,  partially cloudy weather has been the greatest factor increasing melt times, so far....WD May 15, 2013

Returning clouds stops sea ice night cooling
Subsequent clear nights of May 12,13 and 14 amazingly slowed the melting process until the 14th when there appears to be a gain in late melt time from Local Apparent Noon.
May 15 late AM. at first it was cirrus,   approaching from the southwest,
then lower clouds from a small cyclonic system.  The results were interesting,
the high clouds gave similar horizons than with clear skies, at first,  then the horizon never bottomed out for long afterwards (line in yellow).  In the evening,  the usual sudden rise of horizon from long wave radiation loss to space slowed a great deal compared to preceding day, so this means a lesser extent of cooling. Resuming the longer  melting period especially for tomorrow, since the night is cloudy.  I'd expect an extensive melt period nearing 12 hours if there is partial skies again.   We shall see...WDMay 15, 2013

Low clouds exceed 12 hours melting again.

Night of 15-16 was cloudy ,  day 16 equally so.  Fortunately late evening gave ideal conditions to study,  mostly cloudy but with a clear  horizon.  Instead of the usual rebound with clear or high cirrus,  the horizon  remained low indicating a likely 12 hour melt day.    Again broken clouds peppered with sun breaks gave the maximum thawing effect.  This great method of observing the Thermal balance of sea ice shows an elegance in heat exchanges.   A continuity,  a follow up from the consequence of the previous day and night.  Clear days cool the ice more than warm it,  until the midnight sun becomes higher in the sky.  Cloudy days prop up the thermal influence from sea heat, bouncing back from cloud bottoms instead of escaping to space.  The clouds reflect back the heat from the sea ,  which as the graphs above show,  does not bottom the horizon elevation as much as the sun during a clear blue day.  But overcast conditions are lethal for sea ice growth,  something
most specialists always knew,  but not for the fact that clear skies- not at the North Pole -  give a strong diurnal thermal variation favoring ice accretion. WD May 16,2013

What happens when the sky is mixed 50% blue?  

Same graph as previous day except for purple line representing May 17.A mixed sky shifted the horizon all over the place.  There was at first mainly cirrus which gave practically the same horizon heights as clear skies, bottoming slightly higher than a clear blue day.  Than at evening the clouds, even cirrus moved away,  causing an abrupt change of phase from melting to freezing.  Afterwards the sky dome changed appearance
with a mix of low clouds and cirrus taking turns over the filmed horizon light rays path.
When low clouds dominated the horizon dropped, when cirrus covered the ray path
the horizon rose.   wd May 17, 2013

Horizon BOTTOM elevation confirms a deep water column source of energy

May 18,  measured the horizon at Local Apparent Noon ,  2.43' above a fixed point again, as often as the sun is 30 degrees high and there is no clouds  or just high Cirrus.
It is a wonderful repeated observation confirming the under sea ice is melting.  Sea water temperature can be considered a constant,  only the sea ice and surface air changes in nature.   So today,  a warm sunny day of spring,  has warmer temperatures than preceding days,  by more than 10 degrees C.  Yet the bottom LAN horizon is a constant?
Something is making it so:

The horizon can drop further than 2.43',  this is a 1.73' arc minute September 2010 open water example. It can lower even more.

Consider again the sea ice one single ice sheet,  uniform in density,  1.8 meters thick,
from direct sun rays it's horizon should lower and lower along with the rising towards noon high zenith sun.  In the High Arctic it does so daily.  But then the horizon stops lowering,  remains at near constant elevation only to rise when the sun is about 25 degrees on its diurnal course towards the midnight lower in the sky sun.    If perfectly insulated from sea water, the top of the sea ice should reach a thermal balance similar to the picture ( just above, with 1.73' above fixed point),  but it doesn't.  Something is moderating the course of events.  And that is the sea water thermal signal mixed with the ice thickness which now doesn't appear to change,  for that to happen something must give,  this something has to be melting sea ice.  The energy gained by sun rays twin with heat energy from the sea, merge to melt underside ice keeping the horizon constant.  Water replaces bottom ice, this should make the horizon lower but it doesn't,  because sea water does not change in temperature (just like the ice next to it),  there is a vertical displacement of water just melted.  Being replaced by  constant temperature water from the much thicker water column.  When the sun energy is insufficient to compensate for thermal radiation escaping to space, the ice bottom refreezes,  insulating the ice further, lengthening the insulation from top of sea column to top of sea ice.  This changes the structure of the surface to air interface  immediately above the ice.  wd May 18,2013

New horizon bottom,  the ice melted until the skies cleared

May 14                                        May 20                                May 22
A long series of cloudy days eventually reduced the horizon elevation to about 2.13' above a fixed marker point.  On  May 22 with clear afternoon sunshine,  the low horizon was repeated.  This means that the ice thinned, or the column of soft bottom ice has gotten even thicker.     May 14 had 2.86' horizon, May 20 2.13' and May 22,  after cloud effect,  the horizon , even with high sun all day,  the same horizon was 4.32' all at about the same some position in the sky.  

    On May 22 the same low horizon with a strong sun above 30 degrees elevation,
resumed the horizon with low clouds achieved the day prior.  This new refraction bottom  is likely due to a new state of the the nature of the sea ice,  either thinner or physically altered by  a different softer to hard ice ratio.   Warmer temperatures did not play a major role in this change.    It is the net balance of thermal rays,  namely Long Wave Radiation which created these interesting changes.  WD May 22 , 2013

May25 3 PM left, later past midnight right,  even with much milder temperatures the solar diurnal effect still takes place, especially with clear skies.  The sun at 6.4 degrees 
at midnight is by far weaker and not capable of melting underside ice.  At this late time there is freezing even at -7 C with about 2 meter sea ice.  Long wave radiation escapes to space, particularly from the top of the sea water column, cooling occurs bottom side gets coldest as opposed to earlier warmest.  There is a couple of interesting effects,  namely 
a 6 degree sun in  February noon gave a much lower horizon.    There is resonance with the sun ray intensities,  if the rays lessen in total photons the horizon rises,  the opposite is true even during much colder weather.    A sun 6 degrees from the South at noon usually has a lower horizon than with a 6 degree midnight sun.  There seems to be a photon momentum effect., but its likely because the ice cools further from a warmer point than from a much colder state of total weighted temperature.   

WD May 26,2013

For a better understanding please read below:

Data gathered from Optical Refraction above sea ice. An introduction