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Topics - Tealight

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1
Antarctica / Melt water in Antarctica
« on: December 23, 2016, 03:07:16 PM »
Most of Antarctica is far too cold for surface melting in summer, but with global warming more and more regions go periodically above the freezing point. Regions which already experience surface melt will have longer melting periods.

Its time to keep track of these early changes and document if the melt water can form melt lakes like on Greenland or if it flows towards the coast. For the start I attach four images from East Antarctica. Three are upstream of the Amery ice shelf and one is at Cape Ann.


2
Arctic sea ice / Albedo-Warming Potential
« on: September 27, 2016, 09:29:22 AM »
The Albedo-Warming Potential is an attempt to quantify the additional warming from a lower ice cover at the poles. At the moment these calculations don't include cloud cover, therefore it is called "Warming Potential" and not actual warming. However, over six-month weather tends to average out and warm areas correlate well with low ice extend in September. The basis of all calculations is a self-developed global surface radiation model and NSIDC Sea Ice Concentration data.
It is in essence a much better version of my “Quantifying albedo effect / Rating daily area values” topic. In order to present the results better I created my own website and only use links on the forum. If I update my calculations all changes will be applied to this first post too and not scattered across several posts. 

Link to my website CryosphereComputing:
https://sites.google.com/site/cryospherecomputing/warming-potential

The following images are all cumulative results from the last day of the melt season. The end of the astronomical summer to be precise. For daily Animations click on the link below the year. All daily values are also available on my website.

All anomalies are calculated against the 2007-2016 sea ice concentration average.
Red indicates lower albedo and above average warming.
Blue indicates higher albedo and below average warming.
One extra day of peak insulation on open ocean is about 5.7 kWh/m2.
One extra month of peak insulation on open ocean is about 170 kWh/m2.

2007
Daily Animation



2008
Daily Animation


2009
Daily Animation


2010
Daily Animation


2011
Daily Animation



2012
Daily Animation



2013
Daily Animation



2014
Daily Animation



2015
Daily Animation



2016
Daily Animation



Pan Arctic Graphs:




Regional graphs:

https://sites.google.com/site/cryospherecomputing/warming-potential/regional-graphs


Global surface radiation model details:
The model calculates the incoming solar energy per day per m2 for all latitudes between 40N and 90N (0.2 degree steps). Considered are solar zenith angles, the atmospheric reduction (Air mass), Projection effect and water albedo for every 15min interval. If a grid cell has 55% ice concentration, then it is treated as a water area 55% the size of the grid cell.


NSIDC Sea Ice Concentration details:
   Ice concentration average: 2007-2016
   Pole hole ice concentration is calculated from a 2-pixel wide ring around the hole
   Lake ice is ignored to reduce noise
   Pixel Area corrected
   warming potential for each individual pixel (max. 0.44-pixels off from pixel center)

NSIDC Data
Cavalieri, D., C. Parkinson, P. Gloersen, and H. J. Zwally. 1996, updated yearly. Sea Ice Concentrations from Nimbus-7 SMMR and DMSP SSM/I-SSMIS Passive Microwave Data, Version 1. [indicate subset used]. Boulder, Colorado USA: NASA DAAC at the National Snow and Ice Data Center.http://dx.doi.org/10.5067/8GQ8LZQVL0VL.

3
Glaciers / Barnes Ice Cap / Penney Ice Cap
« on: August 26, 2016, 11:59:19 PM »
On the 8th of August most of the snow on Barnes Ice Cap has melted apart from the very top. This reveals an interesting pattern of white parallel lines flowing down the ice cap. Most of these are dried out meltwater streams. Only a few are light blue and have meltwater flowing down.

The pattern reminds me of a skeleton from a prehistoric animal buried in sand or rock.



Click to see full resolution

4
Developers Corner / Arctic sea ice forecast model
« on: June 05, 2016, 08:12:47 PM »
This thread will be used to discuss and improve my arctic sea ice loss forecast model, which is based on my albedo calculations.

Albedo thread: http://forum.arctic-sea-ice.net/index.php/topic,1543.msg79289.html#new


Question : what is that "outgoing kWh" variable and how did you determine it ?
Also, which period did you analyze to determine "the best results so far" ?


So far I only compared my model to recent years, 2007 and later.
The outgoing kWh is based on my heat loss to space calculations. (10 degrees Celsius black body radiation with 35% back radiation) The actual values don't matter so much as the time when this sub-part becomes relevant. It had to match the June cliff losses from end of May to July.

I did not find any significant change in fit by just assuming that thickness does not change.

I think its very important to prevent the model from shooting towards zero area. If for example the area losses are overestimated for a week, then the average thickness will increase and reduce future area losses, because the ice is thicker.  At the moment this function isn't implemented because all losses are based on historic area data and not predicted ones. Maybe thats a big part of the rather large errors for 2008 and 2011.

I'm confused about your 0.000001 factor for snow cover compared to 0.75 for extent-area.
In my experience the snow cover factor should be about 1/4 of the extent-area factor.
Or am I misinterpreting the units on each variable ?

Ha, I made a mistake. All my ice data is in million km2, but my snow area is in km2. So all my land energy calculations were too high by 6 orders of magnitude, which is exactly the number of zeros in the factor.

------------------------
Edit1: I changed the model to use average thickness calculated with my own area values instead of historic area. This reduced the error by around 50%.

Edit2: By using calculated values for (extent - area) instead of historic ones the error reduces even further.

new errors for each year
year   2007   2008   2009   2010   2011   2012   2013   2014   2015
diff   0.35   0.74   0.46   -0.13   -0.27   0.29   -0.33   0.32   0.05
%   12%   25%   13%   -4%   -9%   13%   -9%   9%   2%

5
I wanted to investigate if the arctic albedo is the main factor during a melting season or if warmth from lower latitudes and weather is a bigger factor. On the forum we always talk about preconditioning from melt ponds and ice free areas leading to self-reinforcing melt.

Another motivation was to give each daily area value a weight. A low value in June should be more significant than a low value in September, since most sunlight is already gone by then.

To estimate the albedo I used Cryosphere Today area data, which is prone to show low concentrations in low albedo areas. Normally this is bad to estimate the true sea ice area, but for my calculations it gives a good albedo value. The first image shows an example from 2nd July 2012.

Currently the model is only able to calculate with one latitude for the entire arctic and doesn’t give a perfect representation. However the error isn’t huge since the sea ice area value is most important. A gridded concentration dataset would improve accuracy, but might not be possible in Excel because it requires millions of calculations steps. If I develop a second version, it will consider gridded concentration.

The model calculates the following every half hour for each day: solar zenith angles, the atmospheric reduction (Air mass), Projection effect and albedo for water and snow surfaces.
The final value (kWh/m2) is then multiplied with the water or ice area respectively. See Block diagram for an overview of the calculations.

For simplicity the model assumes clear sky all the time and no energy loss to space. It is not a weather model, just a surface albedo rating.

Bibliography:
A review of snow and ice albedo and the development of a new physically based broadband albedo parameterization, Alex S. Gardner and Martin J. Sharp -https://www.researchgate.net/publication/228755070_A_review_of_snow_and_ice_albedo_and_the_development_of_a_new_physically_based_broadband_albedo_parameterization
http://pveducation.org/
https://en.wikipedia.org/wiki/Solar_irradiance
https://upload.wikimedia.org/wikipedia/en/7/7f/Water_reflectivity.jpg



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