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Andreas T

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Radiative balance in the Arctic
« on: February 15, 2014, 05:15:15 PM »
This is a topic which comes up in other threads (naturally, since we are talking about the consequences of radiative imbalance) but then I can't remember where I read some useful information or discussion so I'll try to make this a collection of links and info on this topic. Help from others appreciated.
ktonine brought up the topic of OLR  [Edit, per request: OLR = Outgoing Longwave (infra-red) Radiation] recently but I can't find the graphs he showed.
IIRC it was surface OLR plotted like this: http://eh2r.blogspot.co.uk/2014/01/count-calories-arctic-sea-ice-needs.html
« Last Edit: June 20, 2016, 11:29:39 AM by Neven »

Andreas T

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Re: OLR in the Arctic
« Reply #1 on: February 15, 2014, 05:45:34 PM »
One thing that strikes me in the infrared imagery AVHRR found on the DMI site
 http://ocean.dmi.dk/arctic/lincoln.uk.php
are the dark i.e. high emission fog / low cloud  areas such as this
http://ocean.dmi.dk/arctic/images/MODIS/Lincoln/201402101251.NOAA.jpg.
 I have to admit I have not made systematic comparisons to other years but it seems to me that the persistent dark streaks I have seen this winter are associated with the relatively warm temperatures on the surface. Yet what is seen in the IR images is not the surface, it is the top of low cloud which is warmer than the ice surface. This warmth is brought in from further south or higher up, adiabatic compression raising temp., this effect can be seen in small scale where fog flows off the Greenland ice to lower elevation.
With cloud cover outgoing longwave radiation from the surface may be high but similar or even higher intensity can come down from the cloudcover. Yet what is going out into space (from where the satellite sees it) is more energy, acting as a negative feedback to the radiative imbalance caused by atmospheric CO2. These are just some thoughts but as a mechanism which dumps heat from the planet via a warming arctic it would be important.
There is much I do not know about this, one element is: how much of the total radiated power/area is represented by what the satelite "sees" in a limited frequency band?
Any suggestions, pointers are appreciated.

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Re: OLR in the Arctic
« Reply #2 on: May 03, 2014, 07:56:15 PM »
IIRC it was surface OLR plotted like this: http://eh2r.blogspot.co.uk/2014/01/count-calories-arctic-sea-ice-needs.html

Andreas,

The NOAA plots at the beginning of the blog post in your link have the label "surface" outgoing longwave radiation, but I think they are actually for the Top of Atmosphere rather than the surface.

The NOAA documentation for interpolated and uninterpolated outgoing longwave radiation suggests that the plotted data are: (1) for the top of atmosphere level, (2) obtained by satellite, (3) obtained by the Advanced Very High Resolution Radiometer (AVHRR), which is the same sensor used for the DMI plots in your second post.  A possible explanation for the term "surface OLR" is that the word "surface" could also refer to the upper surfaces of clouds, as in the first paragraph on this page.
« Last Edit: May 03, 2014, 08:45:53 PM by Steven »

Andreas T

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Re: OLR in the Arctic
« Reply #3 on: June 15, 2014, 07:01:55 PM »
a  recent discussion in the melting season thread brought a number of interesting sources on radiative balance in the arctic
one is free to view here: http://faculty.atmos.und.edu/dong/papers/10.1007_s00382-013-1920-8.pdf
another shown in Chris' comment below
.......

Screen 2010, "The central role of diminishing sea ice in recent Arctic temperature amplification" figure 3 shows the impact of cloud cover changes from 1989 to 2008 in ERA. They find that cloud cover changes over the Arctic are largely a cooling influence.



To quote the legend of that graphic:
Quote
Figure 3 | Impacts of cloud-cover changes on the net surface radiation.
Mean net surface radiation (short-wave plus long-wave) over the 1989–2008
period under cloudy-sky (solid lines) and clear-sky (dotted lines) conditions.
Means are averaged around circles of latitude for winter (a), spring
(b), summer (c) and autumn (d). The fluxes are defined as positive in the
downward direction. Red shading indicates that the presence of cloud has a
net warming effect at the surface. Blue shading indicates that the presence of
cloud has a net cooling effect at the surface. The dashed lines show the
approximate edge of the Arctic basin. Symbols show latitudes where
increases (triangles) and decreases (crosses) in total cloud cover significant
at the 99% uncertainty level are found.

Summer (panel c) shows that clear sky (dotted lines) mean net surface radiation is higher than cloudy, except for north of 80 degN, where ice/ocean albedo feedback does not apply. This has long puzzled me, but it seems it is explainable by the issue raised by K Largo. Over the areas showing the strongest albedo feedback cloudy skies reduce the absorption of insolation, but over areas of high albedo in summer the infrared effect from clouds largely offsets any change in insolation.

.......

Further down from the abstract it is noted that: "Only in midsummer when the sun was highest in the sky did ]CFSW/]Ac surpass ]CFLW/]Ac , indicating that increases in summer cloudiness would cool the surface." This is because the shortwave cooling is dependent upon angle of incidence. SHEBA covered only a region of the Arctic Ocean in Beaufort/Chukchi in over one year. Further north towards the pole solar incidence angles will be lower, and the dominance of SW should be for a lesser part of the year.

SHEBA
http://data.eol.ucar.edu/codiac/projs?SHEBA

Shupe & Intrieri
http://journals.ametsoc.org/doi/pdf/10.1175/1520-0442(2004)017%3C0616%3ACRFOTA%3E2.0.CO%3B2

Andreas T

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Re: OLR in the Arctic
« Reply #4 on: July 18, 2015, 06:23:38 PM »
Although this is not entirely relevant here I am posting this because I only just found this tool in worldview which may be handy for this topic. Whether the IR band used in these satellite images is representative of total outgoing long wave radiation is another question to which I do not know the answer.
The example shown is http://1.usa.gov/1CO8HEf
Beaufort sea 28th May 2015

Andreas T

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Re: OLR in the Arctic
« Reply #5 on: July 25, 2015, 12:43:26 PM »
this is an attempt to move posts from the melting season thread to a new home.

Chris: Actually, I'm suprised that the albedo effect isn't a lot larger than it is.  In order to get the net radiation, you need to subtract off the outgoing IR, which for a 0C blackbody is 315W/m^2.  Using 1120W/m^2 for full sun at the surface including some downwelling IR, maximum radiation at 90N is 445W/m^2.  Most of this incoming radiation is needed just to balance IR loss.  The difference gives maximum radiaitve melting of 3.3 cm ice per day.  The seasonal total is ~2m, with radiative melting ending around August 7.  Yes, this negelects reflection of surface-emitted IR, but it also neglects cloud and surface albedo, which should have a much larger effect.

For comparison 1 k km^3 per 5 days over the Arctic Ocean is around 1.43 cm per day, so peak blackbody melting at the pole exceeds peak PIOMAS melting over the Arctic Ocean by only around a factor of 2.4, which is smaller than I would have expected.  Melting by heat transport is obviously included in PIOMAS but not in the blackbody IR balance.

Jai:  That paramter is exactly zero for Antarctica in winter, so it appears to be shortwave radiative balance only.

This seems a bit oversimplified, especially when you consider that without the existing GHG's, surface temperatures would be on the order of 32C colder than the current global average (14C).

I think your estimate of outbound Black Body radiation at the top of the atmosphere is high by about 70W/M2, but I lack the math right now to work it out.

EDIT:  Found this NASA graphic, which might be instructive.

« Last Edit: July 25, 2015, 12:59:02 PM by Andreas T »

Andreas T

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Re: OLR in the Arctic
« Reply #6 on: July 25, 2015, 01:03:45 PM »
Yes, jdallen, reflection of ~22% of outgoing longwave sounds quite reasonable, but I'm not sure how that contradicts what I said unless you're assuming a total albedo (cloud+surface) under 0.22 which sounds quite low to me.  Yes, the blackbody assumption is a considerable oversimplification, but we're still rapidly running out of positive radiative balance this time of year.

Andreas T

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Re: OLR in the Arctic
« Reply #7 on: July 25, 2015, 01:06:21 PM »
Lots of interesting discussion here, but also a fair bit of confusion so let's try and clear that up.

Radiation Balance:

(1) Rnet = ((1-a) * SWD) + LWD - LWU

  • a = albedo (in this case, pertinant to shortwave radiation only - lets say 0.2-4.0 micrometers). a * SWD = upward solar radiation.
  • SWD = shortwave radiation, downwards. A function of location and time and atmospheric constituent e.g. water vapor, aerosols, and importantly, clouds
  • LWD = longwave radiation, downwards; a function of atmospheric temperature and radiators like water vapor, clouds, CO2 etc. which determine atmospheric emissivity.
  • LWU = longwave radiation, upwards; function of surface "skin" (i.e. radiant) temperature and surface emissivity

All terms are in units of Watts per meter squared.
Net radiation can be computed for any "surface" whether that be the ice/ocean/land surface or the top of atmosphere (though I have couched things in terms of an ice surface). A black body has an emissivity of 1.0. Snow often considered close to a blackbody. The atmosphere is grey body (i.e. emissivity below 1.0) - see PDF of lecture notes below.
Be careful to consider your spatial and temporal frame of reference when talking about such quantities - are you talking about a particular hour, month, year or decade; are you talking about a point at the pole, the region north of 65N or the entire planet?

Some reference material by Martin Wild at ETH:
https://www1.ethz.ch/iac/edu/courses/master/modules/radiation_and_climate_change/download/Lecture5_2014


Surface energy balance: e.g. for a given ice-atmosphere interface surface:

(2) Rnet = H + E + G

  • H = Sensible heat flux; function of temperature gradient from air to surface, wind speed, stability of atmosphere (+ve towards atmo)
  • E = Latent heat flux to the atmosphere; often thought of as evaporation+sublimation; function of vapor gradient from air to surface, wind speed, stability of atmo (+ve towards atmo)
  • G = flux into the surface. For ice during the melt season, G can be decomposed into a melt flux (which is also a latent flux, though different from E) and a conductive (or diffusive) flux that warms the underlying ice (a function of subsurface temperature & diffusivity properties; the flux that causes the buoy temperature profiles to change). This term will be negative when ice is growing. (+ve into the surface)

Surface radiant temperature (Trad) features in each term of (2). Hence, expand each term and solve for Trad (given all the required inputs/states of SWD, LWD, Tair, humidity, precip, wind, pressure and subsurface temperature). All terms in (2) are in units of Watts per meter squared and the sign convention is given. There are other subtle items such as sub-surface penetration of solar radiation etc. but we'll not go into that.

There is an energy balance at the base of the ice (the ice-ocean interface) but the terms will be of different importance or magnitude and involve a different fluid (sea water) as well as salinity dynamics. Throw a volume between these two energy balances and whacko!, you have yourself a (highly, highly simplified) thermodynamic sea ice model. Now make it all move around properly and you have a neanderthal CICE.


Other item:  Latent heat of fusion (J/kg) compared to heat capacity of (sea) ice (J/kg/K).
L(fusion) : 335000 Joules will melt 1kg of pure ice that is at 0C
Specific heat of pure ice at 0C is 2093 J/kg/K.
So if we removed the same amount of energy from the 1kg 0C ice as would be used to melt it (and it was a completely closed system and the heat capacity did not change with temperature), the ice would now be approx. -160 C. Phase change of H2O involves lots of energy! - vaporization even more so.
Of course, salinity will play a (non-linear) role in these thermodynamic quantities in sea ice, as will temperature - just google it if you want to see the curves.

Old question: I don't know who is using CICE5 for operational forecasting. If I was running an operational system of that sort I'd probably wait until the model has had a good thrashing in the academic community before I switched over from an earlier version.

Andreas T

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Re: OLR in the Arctic
« Reply #8 on: July 25, 2015, 01:45:33 PM »
following Oren's and Neven's suggestions I have quoted some of the posts from the melting season thread to copy them here.
Now I can have my own comment on this:
jdallen; the difference between the EBAF chart and blaine's figure is that the 0deg are more likely found at ground level. Since the chart shows monthly average it includes the tops of clouds which are much colder. Use the IR band on EOSDIS as I have described above to see how these temperatures vary for high clouds (cold) and low clouds (fog can be warmer than the ice below it)
Radiation of long wave IR down to the ground is dependent on temp of cloud bottom and can be equal, lower or higher than ice surface temp.
This isn't an external input generally unless warm air is advected and forms relatively warm clouds over the cold surface layer, but in the arctic it can lead to higher surface temperatures under clouds than under clear sky. Clear sky has much less down welling LW while outgoing LW is fairly constant (ice surface temps in summer are pretty constant (in Kelvin). incoming SW is of course higher under clear sky but as the incident angle falls it becomes less while outgoing LW is just a function of temperature.
See diurnal fluctuations in buoy air temperatures south of 80N. When the sky is clear temps drop below 0C when there are clouds they can stay more level above 0C
The other important issue is: where is the radiation emitted or absorbed. Water is largely transparent to the SW coming in (dependent on suspended solids and gases) So clear water absorbs it gradually over a thick layer, ice over a shorter thickness and snow also not purely at its surface (I don't know enough but clearly it has some translucent behaviour)
Outgoing LW is emitted at the very surface because water is not transparent at those frequencies.
This doesn't alter radiative balance but it does determine how surface temperatures respond to it and where the energy goes. Water warmed over a greater depth shows a smaller temperature rise.  That warmed water needs to be convected to the ice/ water interface to cause melting, and that takes time.
This is meant as additional aspects to Blizzard of Oz's comment which I find a  good outline of the physics

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Re: OLR in the Arctic
« Reply #9 on: July 25, 2015, 03:36:33 PM »
Thanks for moving the comments, Andreas. I'll move the thread to another category.
Il faut comparer, comparer, comparer, et cultiver notre jardin

Andreas T

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Re: OLR in the Arctic
« Reply #10 on: April 07, 2016, 09:29:52 PM »
I'm quoting from another thread to make it easier to find again
when sunlight returning to the arctic is discussed I often get the impression that the outgoing longwave radiation is overlooked. When skies are clear a lot of radiation is going out, sunshine has to make up for that loss before the surface stops cooling. This is why ice volume grows until the end of April. Only when incoming radiation exceeds outgoing, does warming start,  apart from heat convected to the Arctic of course. Albedo plays an important part in this because albedo is high for snow and ice reflecting much of the incoming radiation, but albedo is low (snow and ice have high emissivity at 10micrometer) for the long wavelengths at which thermal radiation is going out.
The plots below are small and colour scales not easy to distiguish but I haven't found better ones. http://earthobservatory.nasa.gov/IOTD/view.php?id=35555

Andreas T

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Re: radiative balance in the arctic
« Reply #11 on: April 24, 2016, 05:35:41 PM »
looking around for data on radiation balance I found this from the CERES EBAF validation page
https://ceres-tool.larc.nasa.gov/cave/cave which are monthly averages for Barrow, Alaska

it shows reflection of incoming shortwave with high albedo until June
outgoing longwave is probably mostly a function of temperature of the surface
incoming (at the surface) longwave should be a function of cloudiness and temperature of the clouds

The balance for April is slightly positive I would say from reading values out of the graph to get a rough idea of magnitude: +25 to 30 for SW and -20 for LW
If anybody can point me to better data I would be grateful

edit: I found a page where CERES EBAF (surface fluxes calculated from TOA observations) data can be displayed in maps for chosen lat / lon ranges
https://ceres-tool.larc.nasa.gov/ord-tool/jsp/EBAFSFCSelection.jsp
« Last Edit: July 01, 2016, 07:08:03 PM by Andreas T »

Andreas T

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Re: radiative balance in the arctic
« Reply #12 on: June 19, 2016, 09:35:26 AM »
some very interesting papers found by A-team and posted on another thread are confirming the role of radiation balance in the initial surface melting which lowers albedo and increases uptake of incoming shortwave.
Quote
ultimate driver is thermodynamic. How much heat enters the arctic. Direct heat in is a question of albedo, clouds hurt, reflective ice hurts, clear skies maximize, blue waters maximize.
Just so we are all clear on the research results (#2343) applicable to the Arctic Ocean and Greenland, clouds can and sometimes do make melt worse than straight sunlight. Indeed, heat transfer from moist imported clouds is the dominant driver of early melt of the Arctic Ocean, not sunlight through clear skies.

This seems counterintuitive because the top of the cloud reflects a portion of the sunlight back into space and so that energy never has the opportunity to warm the ice or ocean, whereas no clouds mean more solar energy reaches the surface.

However for thinner clouds like we have been seeing this spring*, quite a bit of the solar radiation does make it to the surface, either directly or after rounds of elastically scattering within the cloud. A portion of it is taken up and the rest reflected, some back up to the clouds to be partly back-scattered down again and so forth.

The counterintuitive part is where the heat (absorbed shortwave fraction) re-emits at longer wavelengths per the graybody spectrum appropriate to the ~0º C ice/water surface. The cloud is no longer transparent to this upwelling infrared so absorbs and re-radiates some of it downward. This amounts to an efficient near-surface greenhouse effect for low thin liquid-containing clouds.

After folding in all the transmissivity coefficients, the net result can be more heating of ice than would have happened had straight sunlight came down on high albedo ice or reflective water at the unfavorably oblique angles appropriate to spring/summer and Arctic latitudes.

Decades of in situ polar radiometric observations published by D Perovich and others have quantitated this for various conditions:

The Radiation Budget of Sea Ice during the Springtime Melt
http://tinyurl.com/gwsmcd8

Such clouds are very common over the Arctic and Greenland:

G Cesani 2012
http://onlinelibrary.wiley.com/doi/10.1029/2012GL053385/abstract

The remarkable Greenland melt event of 12 July 12 even melted dry facies at Summit Station, 3216 m). The decisive effect was not clear skies from a stagnant ridge as initially thought:

Bennartz 2013
http://www.nature.com/nature/journal/v496/n7443/abs/nature12002.html

"Here we show that low-level clouds consisting of liquid water droplets, via their radiative effects, played a key part in this melt event by increasing near-surface temperatures.

At the critical surface melt time, the clouds were optically thick enough and low enough to enhance the downwelling infrared flux at the surface. At the same time they were optically thin enough to allow sufficient solar radiation to penetrate through them and raise surface temperatures above the melting point.

Outside this narrow range in cloud optical thickness, the radiative contribution to the surface energy budget would have been diminished, and the spatial extent of this melting event would have been smaller.

We further show that these thin, low-level liquid clouds occur frequently, both over Greenland and across the Arctic, being present around 30–50% of the time... Global climate models fail in simulating the Arctic surface energy budget because they under-predict the formation of optically thin liquid clouds at supercooled temperatures"

Hanna 2013
http://onlinelibrary.wiley.com/doi/10.1002/joc.3743/full

"In 2012, as in recent warm summers since 2007, a blocking high pressure feature, associated with negative NAO conditions, was present in the mid-troposphere over Greenland for much of the summer. This circulation pattern advected relatively warm southerly winds over the western flank of the ice sheet, forming a ‘heat dome’ over Greenland that led to the widespread surface melting."

van Tricht 2016 free full
http://www.nature.com/ncomms/2016/160112/ncomms10266/full/ncomms10266.html

"The main drivers of Greenland ice sheet runoff remain poorly understood. Here we show that clouds enhance meltwater runoff by about one-third relative to clear skies, using a unique combination of active satellite observations, climate model data and snow model simulations. This impact results from a cloud radiative effect of 29.5 Wm2.

Contrary to conventional wisdom, however, the Greenland ice sheet responds to this energy through a new pathway by which clouds reduce meltwater refreezing as opposed to increasing surface melt directly, thereby accelerating bare-ice exposure and enhancing meltwater runoff. The high sensitivity of the Greenland ice sheet to both ice-only and liquid-bearing clouds highlights the need for accurate cloud representations in climate models.

The dominating effect depends strongly on cloud properties such as vertically integrated ice and liquid water contents that determine cloud optical depth and emissivity, in addition to cloud temperature, sun position and surface albedo.

CloudSat and CALIPSO data suggest liquid-bearing clouds that contain both ice and (supercooled) liquid water are present 28% of the time, consistent with other work showing that such clouds are prevalent throughout the Arctic."

*You can see that on the 367 Modis over the Beaufort because floe details are still visible, ie sunlight has passed through the clouds, reflected off the ice, passed through the clouds again and reached the satellite sensors at sufficient levels for imaging despite absorption and scattering at each step.
« Last Edit: July 01, 2016, 07:08:49 PM by Andreas T »

Andreas T

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Re: radiative balance in the arctic
« Reply #13 on: June 19, 2016, 01:37:20 PM »
and another one by guess who:
Quote
let's not forget the new paper looking at long wave radiation and finding that 'opaque' skies are better than 'clear skies' for imparting energy to the snow/ice below?

only as it relates to melt onset. Warm, moist air is better at getting the ice/snow surface to melt for the first time .. After melt onset, short-wave radiation is more effective at building up melting momentum if I've interpreted the paper correctly.
Not if that new paper is the one below. This research only addresses melt onset. There is a single very familiar sentence midway on sunlight being ineffectual until melt (or whatever) has decreased albedo, not any comparison of effectiveness. Clouds are complex and counterintuitive.

It reminds me of the record July 2012 melt-out of Greenland -- that too is attributed to cloud cover (of just the right kind), not sunny skies. And this year's shocking melt came far too early for such attribution. http://tinyurl.com/zp6xhha

Melt onset over Arctic sea ice controlled by atmospheric moisture transport
J Mortin ... JC. Stroeve et al
http://tinyurl.com/j2q2hs5 free full

The timing of melt onset affects the surface energy uptake throughout the melt season. Yet the processes triggering melt and causing its large interannual variability are not well understood. Here, we show that melt onset over Arctic sea ice is initiated by positive anomalies of water vapor, clouds, and air temperatures that increase the downwelling longwave radiation (LWD) to the surface. The earlier melt onset occurs, the stronger are these anomalies. Downwelling shortwave radiation (SWD) is smaller than usual at melt onset, indicating that melt is not triggered by SWD.

When melt occurs early, an anomalously opaque atmosphere with positive LWD anomalies preconditions the surface for weeks preceding melt. In contrast, when melt begins late, clearer than usual conditions are evident prior to melt. Hence, atmospheric processes are imperative for melt onset. It is also found that spring LWD increased during recent decades, consistent with trends towards an earlier melt onset.

The seasonal transition from winter to summer plays an important role for the Arctic climate. The timing of sea ice melt onset affects the energy absorbed by the surface throughout the summer melt season, because after melt begins, the albedo continues to decrease until either the sea ice is completely melted and disappears or freeze-up has begun.

Over multi year ice, for any day melt begins earlier, additional energy sufficient to melt 3 cm of sea ice during the melt season is absorbed [Perovich et al., 2007]. Since melt onset has been occurring successively earlier over the last few decades, the energy uptake over the Arctic Ocean in summer has increased by an amount large enough to melt about 1 m of ice over a recent 5-year period [Stroeve 2014 http://tinyurl.com/h5zurgz].

This additional energy warms the ocean during summer, leading to a substantially later fall freeze-up and a warmer lower atmosphere in the fall.Hereby the atmospheric circulation, both within and outside of the Arctic region, may be altered
...
At a specific site and a certain year, the melt onset was found to be triggered by moist, warm air masses associated with synoptic-scale weather systems that augmented the atmospheric energy fluxes to the surface... Arctic melt onset is weakly linked to two atmospheric circulation indicators, the Arctic oscillation and the 500-hPa height.

The increased cloudiness leads to a reduction of downwelling shortwave radiation at the surface (SWD). These findings imply that the enhanced greenhouse effect associated with more [imported, non-local] moisture and clouds in the atmosphere is crucial for the timing of the melt onset over sea ice. Further, SWD in itself seems of minor importance for triggering melt.

After melt is initiated, however, the importance of the SWD increases as the albedo of the sea-ice surface decreases and more solar radiation is absorbed by the surface.
« Last Edit: July 01, 2016, 07:09:03 PM by Andreas T »

Andreas T

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Re: radiative balance in the arctic
« Reply #14 on: June 19, 2016, 02:17:16 PM »
In the Mortin et al paper there is this graph which shows decadal trends for different days of the year but looking how downwelling longwave radiation correllates to other factors I would say it is basically the 850hPa temperature modified by the cloud water content which drives the changes (as a qualitative take home message) or am I very much off the mark?
The actual temperature of the "cloud bottom" would be a better parameter if it is known of course.
« Last Edit: July 01, 2016, 07:09:17 PM by Andreas T »

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Re: Radiative balance in the Arctic
« Reply #15 on: July 02, 2016, 12:28:04 PM »
Thanks for consolidating this important topic.
Is temperature distribution vertically in the atmosphere relevant here?  i.e., does temperature anomaly at different heights give an indication of changes in radiative balance?  iirc, Chris R has posted such graphs on his Dosbat blog and elsewhere on the forum.

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Re: Radiative balance in the Arctic
« Reply #16 on: July 04, 2016, 01:41:34 AM »
Yes, Iceman, even the stratosphere comes into play in the Arctic. Sudden stratospheric warmings are followed by radiative cooling induced subsidence over the Arctic. In 2013 a massive high formed over the pole in February after the intense SSW in January. It helped bring on the sea ice recovery after the sea ice extent crash of summer 2012.

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Re: Radiative balance in the Arctic
« Reply #17 on: July 05, 2016, 09:46:15 PM »
copying from another thread again:
background for second graph here   http://www1.lsbu.ac.uk/water/water_vibrational_spectrum.html#d


Even in clear water at normal incidence most of the energy uptake of the solar spectrum is in the top 2-5 metres.

There is a strong dependence on wavelength.



In the figure, a value of 0.01 cm^-1 means it loses most of its energy within the first metre. (1 - 1/e for clear water at normal incidence, which is 63% from memory.) As shown, this corresponds to about the wavelength boundary between red light and infrared light.

Only for some of the yellow light and for green, blue, violet and UV light can most of the energy flux pass 5 metres, even for clear water at normal incidence. In sum, that still accounts for less than half of the energy in sunlight.

The large infrared component, normally comprising around half the energy at sea level, gets largely absorbed in the top centimetres.

So most of the energy uptake is surely in the top 2-5 metres in Arctic waters, which may also not always be clear and with most of the sunlight arriving at much shallower angles.

« Last Edit: July 05, 2016, 10:49:45 PM by Andreas T »

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Re: Radiative balance in the Arctic
« Reply #18 on: July 23, 2016, 01:56:06 PM »
This paper is useful here because it looks at where the incoming shortwave ends up when not reflected http://epic.awi.de/31931/1/nicolaus-2012-grl_2012GL053738.pdf


Andreas T

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Re: Radiative balance in the Arctic
« Reply #19 on: March 05, 2017, 05:24:31 PM »
to keep relevant posts where they can be found again:
Generally in agreement, two points to dispute:

  .... There have been 5 low maximum years so they might be the best comparison. These were 11, 12, 13, 14 and 16. In those years ice gained an average of 2.25 to maximum from day 60. Average melt was 18.13. Using those numbers for this year we get a maximum of 20.95 and a minimum of 2.82.
    Doesn't account for detrending: see graphs upthread.  Because the trend is steeper for losses than for gains, statistically we would expect a lower minimum than on basis of averaging the low-max years.

   ... there are three big negative feedbacks always at play in the Arctic- lower insolation, lower temperature and lower ice transport to the melt zones.
    Insolation is potentially a positive, not negative feedback (by latitude) around the solstice.  Granted this could be negated by a fourth feedback: increased cloud cover owing to higher atmospheric moisture, in turn from higher SSTs and more open water.

image credit: http://geography.name/insolation-over-the-globe/


plus two charts I posted in that context from
https://ceres-tool.larc.nasa.gov/ord-tool/srbavg
to show insolation in the arctic and the effect of albedo, note the polynya at the southern end of Nares and  melted areas in north east Greenland in the IR + shortwave balance
« Last Edit: March 05, 2017, 05:37:54 PM by Andreas T »