Friday, April 28, 2017

Arctic Snow sublimation physics is very hard to evaluate, but happens to be another very important reason why snow creates deeper cooling.

~ Mid April top centimeter of compact snow takes about 5 days to vaporize
~ Top 1 cm may have wind polished very thin ice only seen by sun reflections
~ Winter importance of inversions

     A mid April day top of snow crust hardened by many days of high winds causing substantial sublimation:

Looks of 40 to 50  cm snow carpet,  near record thickness,  at the South shore of Cornwallis Island Nunavut Canada.  4 or 5 days of moderate at times heavy winds appear to have hardened the snow skin rather than distribute it evenly.  The process is more complex than that,  as this picture suggests,  there is very thin ice over the entire canopy causing a direct reflection of wherever the sun is,  the ice really forms heavily on the thinner snow cover,  where sublimation is stronger,  but here it is not so obvious.  This polished veneer disappears in a few days suggesting it was a very dense crystalline cover.
      Same day. in the dimmer lower direct sun,  there is no reflection on the same slope because the light is less strong,  scattering is spreading out photons more thoroughly throughout a thicker atmosphere,    where at first glance,  ice appears to have formed,  it is again more complex,  a closer look reveals a denser top snow crust or skin. Likely 50 to 60 % hard top, a mix of very fine but compacted crystals,  or a rough precursor to ice.  What happened was intense venting of water vapor by the sublimation process,  the winds caused a vacuum amongst the porous cover which accelerated the vaporization process.   When so, top of skin hardens,  column of snow slightly shrinks causing more sublimation vapor pressure,  a natural version of a cold pressure cooker.

        The great snow cover of 2017 made it difficult to measure sublimation rates,  while windy it snowed as well,  the fields of snow changed shape daily:

  Days of Winds carving the thick snow canopy made for a chaotic surface,  imaging the process which created it.

     There can be several layers of snow crusts in one column,  each crust can be 500 to 600 kg/m3 dense as opposed to the entire column being 400 kg/m3.  Within this top denser crust,  the snow temperature was always colder than standard 2 meter air because of sublimation,  this so happens as as long as there is a snow cover until the sun really is high in the sky.   The solid small snow crystals to water vapor process requires a great deal of energy to happen,  this energy is detected by the temperature drop within or on top of the skin and by conduction on the air immediately above it.  Unfortunately,  sublimation can only be measured  accurately with lab conditions,  the Arctic outside is loaded with varying weather, making sublimation appear different with each possible weather scene,   when in fact it is rather a continuous process.


  Briefly by the numbers,
 
   A 1 cm top of snow column has a density of 500 kg/m3,   there is 5 kg in that layer,    it takes

    3013 (latent heat of sublimation)  w/gr X 5000 gr  = 15.1 million Watts to sublimate it.

      Given a solar constant 1360 w/m2 and given that the atmosphere absorbs  23% ,  albedo on a thick  and dense snow layer  varies between 80 to 90%,

        on a perfect clear April 24 sky day:  5.68 MW/m2 can be absorbed by the top 1 cm skin

But not all of is absorbed,  as with figure 2.23:

http://www.usask.ca/hydrology/papers/Pomeroy_et_al_2001.pdf

      A typical 74.5 degrees latitude North High Arctic day top 1 cm snow may absorbs about 2.84 MWatts per meter square.    Therefore it would take 5.3 days for the top cm to evaporate by direct sun radiation alone, which has been observed as such,  but sublimation heat comes from potentially many other sources,  from the warmer snow,  the warmer air,  back scatter from clouds,  heat from ground or sea ice,  by winds drawing out the heat within the snow or ground column.   It is also very difficult to measure temperature at the surface to air interface due to UV affecting thermistors (coming essay).


   Sublimation is one of the main contributors for near ground or sea ice permanent winter Inversions

     To maintain a loss of temperature of 1 degrees C within the same top 1 cm of dense  crystalline snow, 10,000 watts per square meter would be required,  this is clearly not happening.  I have observed more like a permanent cooling of .1 to .3 C of the air immediately off top of thick snow column,  this means the thickness of snow absorbing heat, rather sublimating,   is very shallow,  vaporization is actually happening in more like terms smaller than a millimeter,  like the shrinking size of the crystals themselves with their micro-surface and total entity vaporize,  if we consider 1 mm surface, meaning 500 grams per square meter,  it would still take about 90 watts per meter square of energy to drop the surface temperature by 0.1 C.  This is what is likely more realistic.

     During spring time, when the ground or ice surface becomes much warmed,  the top of snow sublimation should be stronger.  Thermally speaking this sublimation cooling is eventually overtaken by strong sunshine as observed at the sea ice horizon,  sublimation occurs but there is more external solar forcing masking its signature optical effect.    During the long night,  absent of solar effects,  with no shortwave  radiation,   it would be sensible to believe that top of snow or sea ice temperature would be greater than air right above on most occasions,  especially absent warm air advection,  since the only source of greater heat is from the covered by ice much warmer ocean,  that is not the case,  in fact as soon as sea ice covers sea water completely the entire ocean horizon sustains a higher height than Astronomical Horizon (A.H.) until "first Melt Day",  till well into spring following the long Arctic night :


      High Arctic November 2, 2017,   Northwest Passage pretty much completely frozen, from this moment onwards the sea ice horizon will never lower below Astronomical Horizon.  Here 2.6 Arc minutes above A.H.  .  It is counter intuitive, after all sea ice is less than 30 cm thick,  a lot of heat is escaping from the sea despite the ice shallow sheet.  But there is the process of snow and ice sublimation,  which cools the solid top colder than the air right above, this creates a near permanent inversion causing the horizon to rise.

   at least 1.6 arc minutes above A.H,  nearly 2 dark  months have passed,  the ice is 70 cm thicker than in November picture above this one.  Less radiation escaped to space because of sea ice insulation properties.  Throughout all dark season observations,  not one was at or below A.H.,  all were above.  Indicating a permanent colder top of sea ice than surface air.  This is easier to explain,  there is a colder sea ice layer always maintaining a colder top part,  but that is not always theoretically possible.  Sometimes cold air advection  should overtake a warmer thermal ice imprint,  making surface air colder than top of snow would lower the sea ice horizon below A.H.  ,  this was never observed.  Another reason to posit that snow sublimation always helps maintain an inversion at the interface between ice and air.

     Low surface thermal inversions have a huge impact over weather,  they stop surface moisture from rising reducing cloudiness causing more over all cooling to space,  they create,  no,  they are the reason for winter to exist.  When they vanish it is a sign of summer.   When there is a lot of snow on top of the ground or sea ice,  this literally further cools temperatures,  with solar heat  already reflected back up by very white snow albedo,  also made further colder by snow sublimation.  Although exact temperature numbers about this subject are very difficult to be precise with, a small temperature drop on the surface may implicate a very large over all cooling.  WD April 28, 2017

Saturday, April 8, 2017

Astounding sea ice velocities suggest free flowing sea ice never consolidated

   NASA EOSDIS  recent Worldview,  already having Goodbye Waves Upper Right,  signifying heavy melting from easily broken apart sea ice,  similar to what we usually see in July or August.  This kind of movement  North of Novaya Zemlya makes coming data days confusing,  as it was ever since the great dispersion of the strongest densest Canadian Pack last September.  We have had this event of a miss-judged magnitude,  the lack of a more stable sea ice pack has triggered more fluid movements always giving open water at some point anywhere over the Arctic Ocean,  this helped warm Arctic Ocean air and "invite"  more Cyclones to linger longer, making the warmest Arctic Ocean in recorded history.   These images reflect this warming.  WD April 8,2017

Thursday, April 6, 2017

déjà vu: How Beaufort sea early open water becomes important much later

NOAA HRPT latest visual animation Mainly April 5, 2017.   Beaufort sea water arises from a short winter slumber,  with sea ice measured quite new, about 1 meter thick,  something easily manipulatable by clockwise winds from a small 1030 mb High pressure system.  

2013-2014-2015-2016 and 2017 NASA EOSDIS gives foresight,  we know that 2013-2015 had lesser sea ice Minima extents in September.  We also know 2016 had a very long lasting High Pressure system already raging by April 5.  However, 2017 has the thinner sea ice with similar breaking open sea water as with 2016.  From this vantage point,  we can clearly  make 2017 potentially in league with 2016 early Beaufort sea warming equal or worse by thinner grayer sea ice,  it will not take much wind action to disintegrate the Beaufort pack,  20 degree high solar ray absorption by sea water, likely quite warmer,  does look good for a long boating season .  WD April 6, 2017

Monday, April 3, 2017

Proving snow sublimation being strongly linked to Arctic inversions

~A great deal of energy is necessary to sublimate snow to water vapor.
~This energy likely creates a shallow cooling layer on top of snow surface,  a potential component of air inversions.
~ The process is continuous as long as there is snow,  helps explain the 1st rule of sea ice horizon refraction.

    The first rule of sea ice horizon refraction may as well be called the first rule of snow covered horizons,   a paper from J. W. Pomeroy and E. Brun have directly found top of snow colder than surface air:

http://www.usask.ca/hydrology/papers/Pomeroy_et_al_2001.pdf

   Refer to graphs on page 89.   Where boreal forest top of ground snow or air slightly above it was always colder than surface air.    Although they did not highlight this feature in this paper, this confirms what happens in the Arctic as well.  A boreal forest heavily snow clad horizon should be quite similar to sea ice horizons.

   Remains to identify the reason or reasons.   What creates a skin surface to be colder than either air or what is below a skin surface?  It is counter intuitive,  but sublimation seems to fit the bill, it happens as long as there is snow,  when so there would be an endothermic process involved,  which infers a drop in temperature.

   
   A 5X closer look, March 31 2017  top of Arctic snow,  easily capable of carrying the weight of a person with very little sinking,  the top layer can be as dense as 40 to 60%, implying the presence of ice.  At first mid afternoon top of snow appears dense ,  a few hours of sun seems to spring up vertically elongated snow rods.  The mobile viewing apparatus sank more at the third picture without weight pressure applied,  suggesting and expansion of spacing between the grains  -as seen here - likely in part caused by more water vapor.   Eventually the lower sun rays appeared to influence the return of snowflakes closer together.

  Despite high density snow,  there is a lot of air within a column of snow 1 meter high (3rd picture).  It is a greater source of water vapor than with a shallower layer of snow which gives a warmer subdermal temperature. The top of a snow column is a conduit to air,  of which sublimation occurs continuously.   This requires a lot of energy which should be detected by loss of temperature:

    Throughout the modestly March 31 windy day (10-14 knots),  surface temperatures in blue,  measured by ventilated high precision thermistor,  were always warmer than top of snow skin subdermal (in brown,  equally measured by high precision thermistor).   Just below snow skin was even colder snow,  at least on this day, being more a function of permeation,  or the basic long lasting surface air temperature imprint which varies day by day,  24 hours before surface air had much colder temperatures.  Heat was transferred to the top of snow mainly from the warmer air and from solar radiation fueling  the vaporization of snow to water vapor.

     During no winds clear March 24 afternoon,  the surface temperature difference vs snow skin subdermal was far greater,  by 2 C,  this suggests the best way to measure sublimation is when there is no air turbulence, when thermal mixing is much reduced, allowing for top of snow thermal stratification to be enhanced.  If there was another reason for colder snow skin,  this matter would have been brought out by differing weather conditions,  if there is an esoteric radiative cooling effect, independent of winds,  we would have a similar subdermal skin cooling,  windy or not.    Optical observations also confirm lesser horizon elevation boosts when  it is very windy.

     Applied on the totally white snow covered Arctic scale,  the primary reasons for persistent winter inversions may be caused by the colder ground or sea ice with radiation escaping to space twinned with the sublimation of snow which is a continuous process until the sun is high enough in the sky to warm up top of snow surface, in spite of continuing sublimation,  the extra heat compensates and appears to cancel sublimation cooling, triggering an even greater loss of snow cover without outside temperatures being well above 0 C.   Since the end of 2017 long night,  the Northwest Passage by Cornwallis Island had often a great deal of diurnal ice fog bursts,  which may be explained by the presence of significantly above normal snow cover generating more water vapor,  sublimating vapor adds to Arctic air bromine chemical mix always capped at the near permanent inversion peak temperature usually varying at about 800 meters in late March early April.

     Snow column substitution experiment
        A way to separate a possible thermal radiance cooling effect from sublimation would be to remove a portion of the snow column with a body warm enough to affect the snow skin temperature  immediately above.  I used a 9.3 liter sealed container having a liquid,  mainly consisting water,  made a cavity once filled with snow,  placing  the sealed  container with +27.7 C liquid within,  cover the exposed side of container with snow and measure subdernal skin temperature above an undisturbed  10 cm layer of snow separating the skin and top of container.

         A few meters away from this experiment,  there was the regular high precision thermistor subdermal measurement which regularly showed a +.4 C skin cooling vs surface air,  lower than measurements made March 24 and 31,  because it was very windy, high winds above 10 m/s removed all chances of extensive stratification.   The subdermal temperatures above the container were always equal or slightly warmer than surface air,  the opposite result above a complete snow column.  This implies a warmed top snow layer without a skin cooling effect.   Snow sublimation was highly likely occurring but the heat supplied by the liquid container overwhelmed the drop in temperature required to vaporize snow,  similarly to when the sun is high enough and masks sublimation cooling.
  
WD April 2-4 2017

Sunday, March 26, 2017

Consequential applications #2, where is sea ice melting today?

~                                           Ts=Ttsi

       When the mean daily surface temperature is equal to the mean daily top of sea ice temperature,
net melting is occurring.



NOAA daily composites March 23 2017. Skin temperature (left) surface air temperature (right). Barents sea area,  vicinity Franz Josef lands Russia,  there is a band where Ts=Ttsi ,  or Ttsi is a bit warmer than surface temperature,  I usually would consider this as within margin of error from Satellite acquisition, I consider the mean  Ttsi= Ts there.   



Skin temperature areas marked in black where the likely melting is occurring.  


JAXA map,  2 days later,  March 25 2017.  Shows indeed melting where Ts=Ttsi

WD March 26, 2017


Consequential applications gained from the First Rule of Sea Ice Horizon Refraction

~Far from  exotic "interesting mirages" ,  the first rule of sea ice refraction theorized from multiple horizon observations gives many key climate applications.

~                                                      Ts>=Ttsi
              implies a warming sea ice surface automatically gives warmer surface air.

~ The very reason for winter Arctic surface based inversions  can only last till
sun rays become vertical enough to cancel them at the source,  the "skin" surface.

   1987's  spring was very cold,  it was well pre 1998 onwards steeper summer demise of  Arctic sea ice volume and extent.


We notice NOAA ESRL "surface skin" temperatures with same color scales Mean Composite March 1 to 15 1987 followed by 2017.   The first deep signal gathered here is how massively colder Arctic Ocean ice pack was in 1987,  nearly all of the Arctic Ocean in deep purple, with 238 Kelvin at the Pole,  246 degrees  Kelvin at its periphery.  Note the red zone North of Atlantic ocean,  warmer than 264 kelvin,  this is the only common mean temperature with these 2 periods 30 years apart.  2017 has geographically much warmer skin temperatures,  reflecting the thinner sea  ice locations.



 Since the prime refraction rule posits surface air temperature always warmer than "skin temperature"
the surface air from 1987 to 2017 warmed proportionally while always warmer than sea ice ,  again only the extreme North Atlantic has had similar temperatures between 1987 and 2017.   Since 1987 same period interval,  the North Pole area warmed  14 to 20 C exactly where the thinner ice is today.

     The key source of this rule is at top of ice or snow skin,  its temperature follows the surface air temperature trends.   Top of thinner sea ice is much warmer than thick sea ice.  Therefore the air has warmed along with the advent of thinner sea ice by substantial average margins.  This absolutely implies a current much thinner near North Pole sea ice pack,  while very thick multiyear ice North of Ellesmere and adjoining Islands are now the last remnants of a once much thicker Polar ocean pack spread out all the way to Russia.
 
      Like a mirror,  top of sea ice temperatures varies with surface air in tandem,  if ice becomes warmer so does the air, the top skin is always cooler for rather simple and complex reasons,  to be explained on another essay.  Only solar forcing,  an external input of energy,  with especially higher elevation sun rays,  warm the top of ice/snow to render sea ice to air interface isothermal. However,  now you can study indirectly where the thinner ice is with mere temperature maps because of the relation between top of ice and surface air deduced from the prime refraction rule.  WD March 26,2017


Monday, March 20, 2017

First rule of sea ice horizon refraction proven.

~Ts>=Ttsi,  Surface temperature is always greater or equal than top of sea ice temperature
~ Recommendation for buoy thermistors:  measure in the shade
~ This rule is useful for calibrating remote sensing skin temperatures
~ Top of snow layer is coldest day or night,  cloudy or sunny

   One of the greatest features observed at the sea ice horizon is seen when the Astronomical Horizon is reached,  this doesn't happen at any other time then when the air above it is isothermal.  Above sea ice air can't be isothermal without downward solar flux equal or greater to the upward.  This horizon altitude is only attained mainly in the Spring when solar radiation cancels the cooling done by top of sea ice deeply frozen over the long Polar winter.   During the long Arctic Night,  the Astronomical Horizon was never observed,  the horizon always was above A.H...

Link here

http://eh2r.blogspot.ca/2015/05/dedicated-sea-ice-model-proofing.html

   for the first formal hypothesis in May 2015,   which included the first ever Sea Horizon Evolution sketch given the various seasonal temperature profiles:

   Sea ice in green becomes dominant in winter,  but only in spring can we observe the Astronomical
Horizon (in orange) coinciding with the horizon (in black horizontal line associated with the temperature profile).   Prior to that,   another very important feature dominates:   top of sea ice  is always colder than surface air.     This gives a near permanent high horizon height,  till the sun warms top of ice and in turn warms the air immediately above,  then as the sun gradually rises higher day by day the horizon finally drops to A.H.  But this higher than A.H.  period needed data.

    On one occasion I used Arctic sea ice buoys during the dark season to prove this optical rule in April 2016:

http://eh2r.blogspot.ca/2016/04/sea-ice-refraction-prime-rule-top-of_28.html

      During the dark season,  top of buoy thermistors were always colder  than surface air.
Then we needed further in situ observations:



Nice sunny High Arctic day, in the snow drift shade atop a 1 meter high snow column density .36,  the temperature of the top of snow was -32.3.
measured with a high precision Omega monitor attached to  very sensitive Thermistor rated +-0.1 C.  
A few meters away , the ventilated 2 meter surface temperature was -30.2 .


 In the sun above or below snow ,  the thermistor warms rapidly to -29.3 in a few seconds.

Still outside ,  1 minute later the thermistor keeps on warming to well above -27 C.  The sun affects the thermistor greatly. Just like sea ice buoy thermistors embedded in snow.

   Top of snow column being about 1 meter above ground,  mid way down sideways,  a shade reading is stable at -26.7 C.  Like sea ice, the ground was warmer.
10 cm above ground the snow column is even warmer,  again in the shade,  -25.7 C.  This is a sea ice proxy.  The ground was warmer than the air....

     After several days of data,  it doesn't matter whether it is sunny or cloudy,  day or night or whether the temperature trends warmer or colder,  the temperature of top of snow column in the shade (or during evening) was always colder than the surface air.   Thus proving the first rule of sea ice horizon refraction.   I await warmer days.

  And now for top of sea ice measurements:

Day after,  March 21 2017,  outside temperature  was -28 to -29 C above sea ice with no 2 meter high ventilated surface reading,  the picture above is snow over sea ice temperature measured within a snow drift shade, -30.2 C.    By the ventilated screen, 3 kilometers away 46 meters ASL,  outside temperature was -30 C with top of snow -34 C (in the shade).  Sea ice surface here was about 40  cm below.   Top of sea ice snow was 4 degrees warmer than top of land snow.   This helps explain why the coldest Arctic air formations usually occur over land and or in the not so distant past,  over very thick sea ice. 

Right by thermistor in the sun.  As warm as -26.8 C.

     Direct vertical probing,  -25.3 C in the shade,  a few centimeters below the surface layer,  sea ice snow was warmer than land snow.
Right by vertical probe hole,  snow skin subdermal was -30.4 C,  colder than surface air and the snow column just below it,  there may be lateral light scattering affecting the deeper reading.  

     A small tide crack,  2 meters deep,  sensor is about 30 cm from surface in open air,  the temperature was -20.8 C.   These openings are very common over the Arctic Ocean,  the heat injection they give should be quite huge since there are hundreds of thousands such openings.

   The first rule of sea ice horizon refraction is well confirmed by this model/ sat observations,  basically suggests that NOAA/ESRL needs refining especially near coastal sea ice areas,  this anomaly looks the same since last time I checked:

http://eh2r.blogspot.ca/2016/05/remote-sensing-vs-refraction-prime-sea.html




WD March 21-22 2017.










Monday, March 13, 2017

Rogue Polar vortices, one meets a Cyclone and closes down the Northeast Coast of North America

~NWWO strikes again,  leaves a last taste of wild temperature variations.
~ A rogue vortex came from afar


      We pay attention to coming storm named Stella which will cause havoc,  first it is primarily a coastal Cyclone heading  Northeastwards along the USA coast:

https://www.wunderground.com/blog/JeffMasters/all-eyes-on-east-coast-as-big-snowmaker-looms-for-tuesday

     But it meets an "Upper level Low"  as skillfully described by Dr Masters.  But this Low,  a vortex,  born from an offshoot of a massive but short lived cold spell from Central Ellesmere Island at about March 8,  when surface temperatures were more or less unusually normal for this time of the year.  As we follow its progress with 700 mb upper air temperatures,  we can see the gradual meanderings of the coldest air in the Northern Hemisphere,  a spin off vortex,  eventually ended up centered near Montreal.  But tonight the Ellesmere origin of this has warmed 17 C,  leaving vortices in its waning vanishing coldness.  The size and or variations gyrations of the coldest air zones,  quite smaller than usual, marked this winters outlook significantly,  favoring a continuous incursion of Pacific and Atlantic Cyclones to shield the Arctic Ocean from the normal long night lost of heat to space, there is always still a great chance for severe cooling given a lack of clouds by Anticyclones,  this is how great Northern Hemisphere winters were made, but the winter factory shrunk.   WD March 13, 2017

Friday, March 3, 2017

Varying thermal fluxes as portrayed by sea ice horizons.

~A few examples.
~Clouds help discern 2 distinct albedo reactions.

  At stake is this graph done by very capable mathematician Tamino,  essentially portraying total sky albedos given various weather possibilities:

   At latitude 75 degrees North we will deal with zenith angles  70 to 90 degrees.  Essentially the 2
blue lines.   Knowing Tamino's thorough laser dedication to exactitude,  this graph likely represents the standard  widely used Albedo reference numbers.   Note the "clear sky over bright sea ice"  vs "cloud over bright sea ice"  small 10% difference.  We deal here with these 2 features.  Keep in mind the actual horizontal view largely contradicts this.  If there is albedo reflecting clouds at Local Apparent Noon, the horizon view is dramatically different than with "clear sky albedo" consistently and repeatedly,  incoming sun rays become very deflected,  leaving a dramatic difference in horizon heights, either at Local Apparent Noon  or especially seen easier later as the sun lowers to the horizon.  A complete cloud cover  leaves the horizon altitude in a steady state of flux, as opposed to "clear sky albedo"  which enables the observer to witness various thermal effects un-impeded.  This implies that back radiation from bottom of clouds leave sea ice in neither extremes of cooling or warming.  Therefore heat which could be gained from direct sunshine is lost.  During the dark Arctic long night, clouds do just the opposite,  a lot of heat is not lost to space,  while during the long Arctic midnight sun days, persistent strong albedo clouds prevent a great deal of melting.

      The integrated albedos (graph above) perspective may be an erroneous concept.  Albedo layers  should  be calculated individually layer by layer following the sun ray path.  The idea of merging albedo layers is good, but 50% seems too low given the greater cloud cover when sea ice cools the warming summer surface.

   During the Arctic sea ice melt season there can be up to 4 stratocumulus decks stacked on top of each other.  It is the most common Arctic cloud,  with small water droplets 10 micrometers in diameter, there is also often wide ranging fog banks becoming stratus and reverting back to fog in long lasting cycles. Summer time viewing of sea ice from the vantage point of High Resolution satellite pictures is almost always a tasking job:

"Cloud albedo varies from less than 10% to more than 90% and depends on drop sizes, liquid water or ice content, thickness of the cloud, and the sun's zenith angle. The smaller the drops and the greater the liquid water content, the greater the cloud albedo, if all other factors are the same.

Low, thick clouds (such as stratocumulus) primarily reflect incoming solar radiation, causing it to have a high albedo, whereas high, thin clouds (such as Cirrus) tend to transmit it to the surface but then trap outgoing infrared radiation, causing it to have low albedo. It contributes to the greenhouse effect.[1][2]" wikipedia


       The presence of extensive multi layered cloud spreads,  often covering the entire Arctic Ocean for weeks, certainly brings up the cloud albedo value well above the 50% mark.  On occasions,  such as during summer 2007,   with persistent anticyclones, next to land and moving northwards,  shatter clouds important ice protective vail,  plummeting the ice pack to melt rapidly.  

    One primary reference for 50% integrated albedo was the Sheba project,  although the vanishing albedo is correct interpretation of latest melt trends, the nature of sea ice albedo is less variable than cloud cover. 

An annual cycle of Arctic surface cloud forcing at SHEBA , JOURNAL OF GEOPHYSICAL RESEARCH: SUBMITTED JANUARY 19, 2001 

   Sheba Albedo graph has been cited in other journals namely:  http://www.pnas.org/content/111/9/3322.full

   While the data proved interesting,  the said research ship location in summer 1998, Beaufort Chukchi seas, which by coincidence marked the beginning of the greater melting summers to come: 

       The open water footprint amongst sea ice at minima in 1998 suggests there was a great deal of insolation leaving mostly atmospheric absorption and sea ice albedo to reduce the melt otherwise with the full force of nearly direct sunlight and of course lesser total albedo.   

Calculation using separate step by step not integrated albedos:

Entire Arctic ice melt calculation using best albedo data available separately,  suggests a correct interpretation of the physics,  in a simple equation I call ASIMP,  Arctic Sea Ice Melt Potential

   ASIMP = Area of entire Arctic Ocean X TOA TSI  for Arctic Ocean  6 months from spring equinox to fall equinox X average summer sea ice albedo X Atmospheric Absorption factor X Average cloud albedo  / sea ice latent heat of fusion.

Using 

Arctic Ocean sea ice area:  14E6 km2 
Top Of Atmosphere average TSI for same area for Equinox to Equinox 70 to 90 N=  257 247 W/m2
  (equinox calculation closely matching known TSI graph median)
Clear Sky Albedo (sea ice albedo) =  50%
Atmospheric Absorption = 23%
Average cloud albedo over the summer = 80 % 
(1) Sea ice latent heat of fusion =   2.95e17 j/km3   U.N. fisheries and agriculture department
  (with density 0.89 t/m3 U.N, 1% salinity at -2 C according to Doctor Ono's chart)

     Gives ASIMP = 15,081 km3 (calculated mar 7, 2017) close to the actual POMAS latest summer melt 17,500 km3.   (77% cloud albedo is needed to make  ASIMP equal to 2016 summer melt). These variables were at first taken from different sources, I did not try to fit with known melts,  and they need be perfected, leaving the greatest yearly variation to cloud albedo.    This reformulation calculation gives a fairly interesting estimate.  

----------Arctic "clear sky albedo" vs cloud albedo effects:

   Series pictures displaying different sky conditions and resulting thermal flux action at the sea ice horizon.  If horizon outgoing thermal heat is equal to incoming Astronomical Horizon is achieved.
All pictures mostly above A.H. indicating net thermal loss from the sea,  those at A.H.  will be indicated.   None can be below A.H,.

   On all pictures,  top left:  date time, top right:  general sky condition,  lower left: temperature wind speed with narration, lower right: sea ice horizon elevation (2.6' is astronomical horizon) below is sun elevation in degrees.

     Dominant  Low cloud albedo

     Clear Air Albedo

     Arctic Ice Fog

   Mixed albedos , warmed sea ice

   Clear sky , warmed sea ice

    Clear sky albedo, sea ice "wall"  , maximum horizon height boosts, large diurnal thermal variations

     Clear sky albedo

   Horizon low clouds,  mixed albedo, clear at camera, cloudy away above sun beam path

    Clear sky albedo with some distant mid day dissipating later ice fog 

   Clear sky albedo , mid day distant ice fog and clouds

Mostly cloud albedo with light snow

Clear sky albedo,  all sea ice albedo.  

Clear sky albedo, all sea ice albedo

Early fog then cloudy albedo
 More to come...

Sunday, February 19, 2017

Summer greater cloudiness thermal flux mystery resolved

~Has huge implications with respect to sea ice melt season.
~ Partial cloud cover reduces sea ice albedo,  this was captured by horizon refraction method.


"Spectral albedo and transmittance of thin young Arctic sea ice "

by

Torbjørn Taskjelle1, Stephen R. Hudson2, Mats A. Granskog2, Marcel Nicolaus3, Ruibo Lei4, Sebastian Gerland2, Jakob J. Stamnes1, and Børge Hamre1 1

at

http://onlinelibrary.wiley.com/doi/10.1002/2015JC011254/abstract

 A most interesting paper,  well apt study with respect to greater current thinner sea ice conditions, has made at least 2 major discoveries:  

15 cm sea ice has :

"Integrated albedo and transmittance for photosynthetically active radiation (400–900 nm) were in the range 0.17–0.21 and 0.77– 0.86, respectively. The average albedo and transmittance of the total solar radiation energy were 0.16 and 0.51, respectively. V"

     That is a rather big discovery-observation,  it means that thin sea ice even with a bit of snow has 4 to 4.5 times less albedo than thicker ice,  likely in excess of 1 meters thickness.  

   The rather much larger discovery:

"Under a cloudy sky we found molecular oxygen absorption bands in the atmosphere to favor light traveling less obliquely and thus slightly increase the fraction of light penetrating the ice within these bands compared to the penetration of light at wavelengths outside the bands. For large solar zenith angles, a cloud layer was found to increase the ice transmittance at all wavelengths, because it shifts the average direction of the light toward the vertical."

This very important observation/conclusion solves a once puzzling Horizon Refraction mystery
found in the High Arctic Nunavut Canada:









All these spring April to May 2011 horizon sequences,  one day per row, from shortly after Local Apparent Noon towards end of Arctic day till sunset,   have one thing in common,  clear skies and rising horizon from afternoon to evening.  This is explained by sea ice approximately 1.5 meters thick mostly covered with snow 10-20 cm,  stretching all the way well beyond the horizon line, and the lowering sun as evening progressed.  Transmittance of solar energy,  said to be much reduced by albedo as much as 90%,  with only 10% transmittance of short wave sunlight.  

       However weakened by the very sun ray reflectiveness of sea ice and snow cover,  the surface of sea ice temperature became equal to surface air after Local Apparent Noon,  with Astronomical Horizon held as long as the sun further warmed the ice.  Then after,  as the sun elevation lowered,  the surface of sea ice and snow cooled along with air interface by conduction,   while the air immediately above (a few meters above the surface to air interface) remained warmer, this caused surface inversions becoming steeper as the sun descended further.  We can judge the thickness of sea ice by the horizon rebound height.  From April (top sequence) to May (bottom) the ice thickened,  hence by conduction,  the mid or coldest layer of sea ice  embedded within its column cooled the top of sea ice quicker than the rate of cooling of air having a much lower heat capacity.


These observations are a constant feature unless clouds (sometimes winds) play havoc with the thermal fluxes: 

May 17 2011.  a fine sunny noon Astronomical Horizon (extreme left) ,  yet the horizon line largely stayed steady afterwards,  because low clouds covered sky thereafter.  One reason for the steady horizon, Taskjelle, T., S. R. Hudson et all suggest that the albedo of sea ice itself may be weakened by sun rays hitting the ice more perpendicularly,  the other explanation is the well known  lessening of energy escaping to space,  long wave radiation bouncing back and forth from cloud bottom to top of sea ice.   The former implies a neat possibility of extra but slight transmittance gain of energy to sea ice by albedo change,  combined with clouds causing a lack of surface cooling,  confirmed by the multitude of persistent near Astronomical  Horizon height horizons observed,  which of course means a significant drop or cancellation of sea ice accretion.  

And so on May 2 , 2011 the horizon height never changed at all,  this despite the clouded sun 30.8 degrees elevation (left) giving the same energy or horizon thermal flux result as when the still covered sun was 10.81 degrees elevation later in the evening.  This seem to contradict basic thermal evaluations until we consider that the light getting through the later evening cloud horizon gap  (right) has had an impact,  reducing the cooling if not slightly increasing the net warming,  because the sea ice albedo changed from more vertically directed photons hitting the icy/snowy surface.  This kind of late evening horizon observation was not at all rare.  


 Conclusion and also in appreciation:

     A strange phenomena was perceived throughout many evening horizon refraction observations,  in Southwest Cornwallis Island,  Nunavut Canada,  there was a lesser rise of horizon,  no change in height or even a drop in horizon heights,  unexplained by any other mean but an assumption that the distant horizon had different weather.  

         But a paper written by Taskjelle, T., S. R. Hudson et all  revealed a likely change in albedo of sea ice increasing transmittance of thermal rays reflected by clouds redirecting the rays at a lesser zenith angle.  This explains a couple of very interesting horizon refraction observations,  namely when cloudy there is definitely a greater thermal transfer to sea ice because of cloud cover,  but also in addition by the reflection of rays at a lower zenith angle (higher horizon elevation) .  The two,  cloud cover and more direct ray bombardment of sea ice explains the lower sea ice horizon when cloudy,  and especially when partially cloudy.  Horizon refraction observations shortly after local apparent noon during fully sunny skies have similar horizon heights than when cloudy (usually lowest during clear air).  With overcast conditions towards sunset time, the lack of horizon rise as always observed with clear air,  suggests more energy towards sea ice despite a lower sun elevation.  However, there is more energy transferred to sea ice, lesser escaping it,  when cloudy,  this has a huge over all accretion/melting  impact needed to be considered.  

          The over all melting of 2016 Arctic sea ice,  2nd place in extent,  surprised many considering the greater cloudiness by persistent  Cyclones during much of June and July,   sometimes not so opaque,  which I called "see through".   More vertical redirection of sun rays usually low most times during the Arctic horizon summer may indeed give more melting than calculated.   

      Finally the effect of lowering horizon with partially cloudy  skies when nearing sunset time should have a Norwegian name given the discovery of reduction albedo as discovered by Taskjelle, T., S. R. Hudson et all...   


      WDFebruary 19, 2017