As most readers know, clouds are still poorly understood and under-represented in climate models. This new research may help.
From: DOE/Pacific Northwest National Laboratory
Effect of cloud-scattered sunlight on earth’s energy balance depends on wavelength of light
Accounting for wavelength effects will likely improve climate models
RICHLAND, Wash. — Atmospheric scientists trying to pin down how clouds curb the amount of sunlight available to warm the earth have found that it depends on the wavelength of sunlight being measured. This unexpected result will help researchers improve how they portray clouds in climate models.
Additionally, the researchers found that sunlight scattered by clouds — the reason why beachgoers can get sunburned on overcast days — is an important component of cloud contributions to the earth’s energy balance. Capturing such contributions will increase the accuracy of climate models, the team from the Department of Energy’s Pacific Northwest National Laboratory reported in Geophysical Research Letters earlier this month.
“The amount of the sun’s energy that reaches the earth’s surface is the main driver of the earth’s temperature. Clouds are one of the least understood aspects of climate change. They can block the sun, but light can also bounce off one cloud into another cloud’s shadow and increase the solar energy hitting earth,” said PNNL atmospheric scientist Evgueni Kassianov.
White clouds
Clouds both cool down and warm up the earth’s surface. They cool the earth by reflecting some sunlight up into outer space, and they warm it by bouncing some sunlight down to the surface. Overall, most clouds have a net cooling effect, but atmospheric scientists need to accurately measure when they cool and warm to produce better climate models that incorporate clouds faithfully.
But it’s a hard number to get. Fair-weather clouds are big puffy white objects that bounce a lot of light around. They can make the sky around them look brighter when they’re there, but they float about and reform constantly. Cloud droplets and aerosol particles in the sky — tiny bits of dirt and water in the air that cause haziness — scatter light in three dimensions, even into cloud shadows.
To determine the net cloud effect, researchers need two numbers. First they need to measure the total amount of sunlight in a cloudy sky. Then they need to determine how bright that sky would be without the clouds, imagining that same sky to be blue and cloudless, when aerosols are in charge of a sky’s brightness. The difference between those numbers is the net cloud effect.
Rainbow energy
Researchers have traditionally estimated the net cloud effect by measuring a broad spectrum of sunlight that makes it to the earth’s surface, from ultraviolet to infrared. But clouds are white — that’s because the large water droplets within them scatter light of all colors almost equally in the visible spectrum, the part of the electromagnetic spectrum that includes the colors of the rainbow.
On the other hand, aerosols — both within clouds and in the open sky — bounce different-colored light unequally. Broadband measurements that fail to distinguish color differences might be covering up important details, the researchers thought.
Instead of taking one broadband measurement that covers everything from ultraviolet to infrared, Kassianov and crew wanted to determine how individual wavelengths contribute to the net cloud effect. To do so, the team used an instrument that can measure brightness at four different wavelengths of color — violet, green, orange, red — and two of infrared.
In addition, this instrument, a spectral radiometer at DOE’s Atmospheric Radiation Measurement Climate Research Facility located on the southern Great Plains in Oklahoma, allowed the team to calculate what the brightness would be if the day sported a cloudless, blue sky. The spectral measurements taken by the radiometer can be converted into the amount and properties of aerosols. Then aerosol properties can be used to calculate clear blue sky brightness.
Clouds Gone Wild
Comparing measured values for cloudy sky to the calculated values for clear sky, the researchers found that, on average, puffy fair-weather clouds cool down the earth’s surface by several percent on a summer day. Although clouds cool overall, two components that the researchers looked at — from direct and scattered sunlight — had opposite effects.
The direct component accounts for the shade provided by clouds and cools the earth. The second component accounts for the sunlight scattered between and under clouds, which makes the sky brighter, warming the earth.
“The sunlight scattered by clouds can heat the surface,” said Kassianov. “We all know that we can still get sunburned on cloudy days. This explains why.”
In the Oklahoma summer, the scattered-light effect measured by the researchers could be quite large. For example, if a cloud passed over the instrument, the measured cloudy sky brightness exceeded calculated clear sky value by up to 30 percent. Kassianov attributes that large difference to scattered sunlight being “caught on tape” by the radiometer.
“Sunlight scattered by three-dimensional, irregular clouds is responsible for the observed large difference. The one-dimensional cloud simulations currently used in large-scale climate models don’t capture this diffuse light,” said Kassianov.
Aerosols’ Day in the Sky
The team also found that the effect changed depending on the measured visible-spectrum wavelength, and whether the light was direct or scattered.
With direct light, the cooling caused by clouds was weakest on the violet end of the spectrum and strongest at infrared. With scattered light, warming caused by clouds was also weakest at violet and the strongest at infrared. Overall, the least cooling and warming occurred at violet, and the most cooling and warming occurred at infrared.
Because large droplets in clouds scatter sunlight almost uniformly across the spectrum, the clouds themselves can’t be the reason why different wavelengths contribute differently to the net cloud effect. Compared to cloud droplets, aerosols are more than 100 times smaller and scatter wavelengths differently. These results suggest that aerosols — which not only cause haziness but contribute to cloud formation as well — are responsible for the wavelength differences, something researchers need to be aware of as they study clouds in the sky.
“If you want to study how aerosols and clouds interact,” said Kassianov, “you need to look in the region of the spectrum where aerosol effects are significant. If you want to fish, you go where the fish are biting.”
This work was supported by the U.S. Department of Energy Office of Science.
Pacific Northwest National Laboratory is a Department of Energy Office of Science national laboratory where interdisciplinary teams advance science and technology and deliver solutions to America’s most intractable problems in energy, national security and the environment. PNNL employs 4,900 staff, has an annual budget of nearly $1.1 billion, and has been managed by Ohio-based Battelle since the lab’s inception in 1965. Follow PNNL on Facebook, LinkedIn and Twitter.
Reference: Kassianov E., Barnard J., Berg L.K., Long C.N., and C. Flynn, Shortwave Spectral Radiative Forcing of Cumulus Clouds from Surface Observations, Geophys Res Lett, April 2, 2011, DOI 10.1029/2010GL046282 (http://www.agu.org/pubs/crossref/2011/2010GL046282.shtml).
Abstract:
The spectral changes of the shortwave total, direct and diffuse cloud radiative forcing (CRF) at surface are examined for the first time using spectrally resolved all-sky flux observations and clear-sky fluxes. The latter are computed applying a physically based approach, which accounts for the spectral changes of aerosol optical properties and surface albedo. Application of this approach to 13 summertime days with single-layer continental cumuli demonstrates: (i) the substantial contribution of the diffuse component to the total CRF, (ii) the well-defined spectral variations of total CRF in the visible spectral region, and (iii) the strong statistical relationship between spectral (500 nm) and shortwave broadband values of total CRF. Our results suggest that the framework based on the visible narrowband fluxes can provide important radiative quantities for rigorous evaluation of radiative transfer parameterizations and also can be applied for estimation of the shortwave broadband CRF.
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“Fair-weather clouds are big puffy white objects …” – are these serious scientists? Or do they think we’re too stupid to understand what they are purporting to study, and need to be told in baby language?
Words fail me …
I’ve done alot of work on Albedo (which is how much sunlight is reflected back to space by clouds, ground, water and Ice).
Something which is not that commonly understood is that clouds only reflect about 25% on average of the sunlight that hits them back to space.
A large high thunderstorm which is deep blue underneath will reflect as much as 75% of the sunlight (letting UV through at least), but the thin high cirrus clouds let most of the light through or reflect much of it back to the Earth’s surface at some angle.
On average the Earth is about 65% cloud covered (although this number varies widely depending on the method used to estimate it) but the clouds only contribute about 16% to 17% to the Earth’s Albedo of 29.83%.
Most surfaces, including cloud-covered ones are in the same relative range (8% to 35%) reflection – enough similarity that it doesn’t make much difference.
The surface that is the most important, the big make or break surface, is “Ice and Snow” which can be as high as 85% (cloud covered or not). The Ice and Snow extent on the planet is the big driver of Albedo (and in essence, the climate, in my opinion). It is the surface which varies the most from the Earth average.
Why did it get so cold in the Ice Ages, when the actual sunlight hitting the surface of the Earth was about the same as today and even a little higher. It is because all the extra Ice and Snow, starting out initially only in the high latitudes, reflects just that little extra sunlight.
In a less scientific and more subjective manner, I too wonder over how light bounces about. You can get a worse sunburn when working in the sun when there are white clouds about, than you can on a cloudless day. I suppose the sunlight reflects off the sides of the clouds the same way it bounces and burn you when it reflects off shimmering water.
I once stood behind a landscape painter, and he pointed out that the underside of a puffy cloud over distant pines had the slightest tint of green, while the underside of a similar cloud over distant wheat had the slightest tint of yellow.
Light is bouncing all over the place. If you could mark down all the vectors they would resemble swirling straws, especially as clouds are always moving and changing their shapes.
I’m glad I’m not mathematically inclined, and have no need to mark down all the vectors. It leaves me free to simply stand in awe.
Bill Illis said
“The surface that is the most important, the big make or break surface, is “Ice and Snow” which can be as high as 85% (cloud covered or not). The Ice and Snow extent on the planet is the big driver of Albedo (and in essence, the climate, in my opinion). It is the surface which varies the most from the Earth average.”
I’m not so sure because one has to change the temperature trend BEFORE the changes in snow and ice cover can occur. Certainly once present the snow and ice has a strong positive feedback effect on any increase in albedo from another cause for the reason you say but that something else has to kick start the process.
So I’ll continue with the view that total global cloud quantities are the initial driving agent for albedo and everything else follows.
I did not see anything about day and night. Its pretty simple, clouds cool during the day and keep the heat in at night.
When you are a climate researcher looking only at temperatures averaged over a day, and then averaged over a month I guess you forget little things like night and day.
Yep, more junk science. It is amazing that, even in made-up pseudo-science, climate scientists remain firmly “a priori” in their reasoning. The climate scientist says “Assume a spherical cloud made of the finest white stuff, assume the standard numbers for radiation from the sun, and calculate what happens as the radiation passes through the cloud.” Apparently, when they try empirical research their minds remained trapped by their Tinker-Toy imaginations. And the stuff about clouds increasing the radiation that reaches Earth’s surface is nonsense. I guess they are talking about the clouds that are out to the left or right of the Earth, as seen from the sun.
The actual empirical research has to answer two big questions: One is “Where are the clouds?” and Two is “Under what conditions are the clouds there?” In other words, what are the natural regularities that constitute cloud phenomena on Earth? A good starting place would be Central Florida because we have this fabulous cloud show every summer. Every afternoon, you can see the Thunder Heads rolling in. If you are in Orlando, they come from the East. If you are in Tampa, they come from the West. Sometime between three and five PM the showers begin. The temperature drops by as much as ten degrees and the evening is very pleasant. Will the Warmista someday account for cloud behavior over Central Florida? It is highly unlikely, as it would constitute more empirical research than the sum total of all empirical research they have done so far.
And I am so sick of the excuse that Earth’s climate is so complicated. Give me a break. Is it more complicated than energy transfers in the nucleus of an Uranium atom? I don’t think so. Yet those matters were mastered by a bunch of guys who were still reeling from the suffering of the Great Depression, all of whom chain-smoked and enjoyed good whiskey. The reason we do not understand the natural regularities that drive cloud phenomena on the surface of the Earth is that we have not done the research and the little research that has been submitted has been done by bozos. As proof, I bet not one of them recognizes the universally know observational term “Thunder Head.” My mother had taught it to me by the time I was three.
Anthony is far too kind in his title to this post. Instead of “still tweaking,” I suggest “still Tinker-Toying.”
Nonegatives says:
April 23, 2011 at 7:53 pm
The fact that CO2 and H2O absorb different wavelengths of light has been known for a while now. Did they just now figure out that clouds are actually water vapor?
Clouds are droplets. vapor is individual molecules. where ever you’ve got droplets, you’ve got additional degrees of freedom capable of absorbing and emitting continuum like a solid or liquid black body radiator versus a discrete spectrum like an atom or molecule.
They’ve “discovered” that different wavelengths interact in different ways with different kinds of clouds?
What will the “discover” next? The freezing point of water?
Bill Illis says:
April 24, 2011 at 6:02 am
“Something which is not that commonly understood is that clouds only reflect about 25% on average of the sunlight that hits them back to space.
…
On average the Earth is about 65% cloud covered (although this number varies widely depending on the method used to estimate it) but the clouds only contribute about 16% to 17% to the Earth’s Albedo of 29.83%.
Most surfaces, including cloud-covered ones are in the same relative range (8% to 35%) reflection – enough similarity that it doesn’t make much difference.
”
Bill,
I think you’re way off base. Not even K&T97, trenberth’s tinkertoy effort are that off the mark. liquid h2o is going to run an albedo of under 0.04 and that’s over 70% of the surface. Most of your ice & snow are at high latitudes that have much less incoming insolation. The numbers are more like 24% of the incoming tsi is reflected by the clouds, not 24% of the incoming tsi impinging on the clouds or of the total albedo. We’re talking around 0.24*341 = 82 w/m^2 of cloud reflection. To that, add around 24w/m^2 of atmospheric scattering and a ground contribution of 14 w/m^2 for a total of around 120 w/m^2 of albedo reflection or an albedo value of 0.35 or 35%. These numbers are values from 1957, J. London and are discussed in Introduction to Theoretical Meteorology by S.L. Hess, 1959.
Your number of 29.83% albedo is also interesting and wrong. Albedo is a variable, almost totally dependent upon cloud cover and upon the makeup of cloud particulates. Over two recent decades, it is known to have varied by nearly 10%. While it would seem that an albedo measurement of 35% from 1957 would indicate serious accuracy problems, that is not necessarily the case. It well could have been 35.0% back in 1957, 30.5% in 1996, and 29.8% in 2008, averaged over a year or two for each.
As for trenberth and K&T97, they used 0.62 cloud cover fraction for their simple model composed of two layers of opaque clouds, referred to by emissivity = 1 – meaning optically thick, and by high clouds with low coverage area and emissivity = 0.6. Unfortunately, in their paper, they used the term clear sky for the condition of no clouds, yet used the cloudy condition to mean 62% cloud cover rather than to mean total cloud cover in normal convention which can be combined with clear sky to yield the net result with a simple weighted average of 0.38 clear and 0.62 cloudy.
“unexpected result”
Press-release writers always paint scientists as lacking intuition about reality.
–
“To determine the net cloud effect, researchers need two numbers. First they need to measure the total amount of sunlight in a cloudy sky. Then they need to determine how bright that sky would be without the clouds, imagining that same sky to be blue and cloudless, when aerosols are in charge of a sky’s brightness. The difference between those numbers is the net cloud effect.”
Need info about the PATTERN too, as that affects flow… Hint…
–
“clouds in white reveal landmass shapes”
…which is why folks should start cluing in to widespread misconceptions (including at WUWT) about AMO.
Lot of (seemingly exclusive?) focus on albedo ….doesn’t cloud do anything else besides reflect light?!…
With an eye for continental-maritime contrast, the distribution of continents on the globe, and the position of the [magically powerful in some minds] North Atlantic in the context of the global distribution of continents, carefully compare:
1) http://icecap.us/images/uploads/AMOTEMPS.jpg
2) Figure 10:
Carvalho, L.M.V.; Tsonis, A.A.; Jones, C.; Rocha, H.R.; & Polito, P.S. (2007). Anti-persistence in the global temperature anomaly field. Nonlinear Processes in Geophysics 14, 723-733.
http://www.uwm.edu/~aatsonis/npg-14-723-2007.pdf
http://www.icess.ucsb.edu/gem/papers/npg-14-723-2007.pdf
Hydrology is a function of absolutes, NOT anomalies. I suggest blinking between the upper & lower panels of figure 6 here for related insight:
Trenberth, K.E. (2010). Changes in precipitation with climate change.
http://www.cgd.ucar.edu/cas/Trenberth/trenberth.papers/ClimateChangeWaterCycle-rev.pdf
Temperature-precipitation relations seasonally reverse sign over large portions of the globe.
High amplitude regional variance (think continental-maritime heat-capacity contrast) leverages “global” averages, particularly during periods of interannual synchronicity [which show nonrandom relations with solar variables across a range of timescales from semi-annual through interannual to multidecadal].
Sorry for the bad link. Trenberth’s 2010 draft appears to have been removed from the directory, but here’s the recently published article — see figure 6:
Trenberth, K.E. (2011). Changes in precipitation with climate change. Climate Research 47, 123-138. doi: 10.3354/cr00953.
http://www.int-res.com/articles/cr_oa/c047p123.pdf
Just curious. It seems there should be more water transported out of the lakes and oceans and up to the clouds if things heat up. The phase change to gas will cool the surface and deposit heat wherever the clouds form as they phase change from gas to liquid. Then the heat is a bit closer to exiting the earth than it was when it was on the earth’s surface.
Thinking simply, it would seem if the earth were to heat up, there would be more water evaporation, as the atmosphere heats up the clouds will be higher, etc.
I have no idea whether this is an “in the noise” effect or actually makes a difference. Anyone know?
For example, if a cloud passed over the instrument, the measured cloudy sky brightness exceeded calculated clear sky value by up to 30 percent. Kassianov attributes that large difference to scattered sunlight being “caught on tape” by the radiometer.
“Sunlight scattered by three-dimensional, irregular clouds is responsible for the observed large difference. The one-dimensional cloud simulations currently used in large-scale climate models don’t capture this diffuse light,” said Kassianov.
Incredible! They are still modelling clouds in one dimension. I thought that was where they were 30 years ago. I could do that on my PC.
It has been calculated that a change of 2% in the effect of clouds could outweigh all that is being attributed to CO2. They now realise that in some areas they are off by 30% . Well that’s solved AGW, we can all go home now.
Unexpected ?! They have just worked out that reflection and diffraction are wavelength dependant. I learnt that at the age of 14 in my first year of physics lessons. Have climate modellers never seen a prism??
I suppose if you are only doing 1D modelling you cannot account for either so it never mattered to them.
>>
cba says:
April 24, 2011 at 9:46 am
Unfortunately, in their paper [KT97], they used the term clear sky for the condition of no clouds, yet used the cloudy condition to mean 62% cloud cover rather than to mean total cloud cover in normal convention which can be combined with clear sky to yield the net result with a simple weighted average of 0.38 clear and 0.62 cloudy.
<<
After KT97 calculates the 62% cloud cover value, the term “cloudy” is ambiguous in the rest of the paper. The diagram (Fig. 7) probably should state that 62% cloudiness is assumed. However, they don’t make it that easy for us.
Notice how they calculate the IR window:
“The estimate of the amount leaving via the atmospheric window is somewhat ad hoc. In the clear sky case, the radiation in the window amounts to 99 W m-2, while in the cloudy case the amount decreases to 80 W m-2, showing that there is considerable absorption and re-emission at wavelengths in the so-called window by clouds. The value assigned in Fig. 7 of 40 W m-2 is simply 38% of the clear sky case, corresponding to the observed cloudiness of about 62%.”
Did you notice the subtle error in the math? If “cloudy” here means 62%, then the value in Fig. 7 should be 80 W m-2. If, instead, they mean “cloudy” is 100% (and that’s implied because they proceed with an interpolation), then they should interpolate between 99 W m-2 and 80 W m-2 which gives us about 87 W m-2. They actually interpolate between 99 W m-2 and 0 W m-2. In that case, the value should be about 38 W m-2. Why did they round up to 40 W m-2? If you’re looking for a missing heat flow, then here is about 2.38 W m-2 that they lost through rounding error.
The cloudy case of 80 W m-2 is apparently some other cloudiness value (not 100% and not 62%).
Jim
Amongst other flaws in this paper, and in answer to some of the comments in this thread, one cannot quantify the net effect of clouds the way they measured it one way or the other regardless of the accuracy of their measurements.
To arrive at something meaningful, the same cloud has to be evaluated for net effect under different circumstances. For example, I saw several comments to the effect that a low altitude cloud has an obvious cooling effect as anyone standing outside when a cloud crosses the sun can tell you. This is highly misleading but it is only a single context.
That same cloud, should it hand around until after sunset, will have a warming effect on the surface below. Perhaps more accurately, it will slow the rate of cooling of the surface below. Similarily, cloud cover in the depths of winter in high latitude has a net warming effect (or less cooling depending on how you want to view it) during both day and night. As anyone from a harsh winter climate can tell you, a bright blue sky on a July morning means it will be a very hot day. A bright blue sky on a January morning means go back to bed because it is -40 degrees outside.
The “net effect” of cloud cover not only is governed by the properties of the cloud, but also by the environment the cloud is in. Sometimes it warms and sometimes it cools despite being the exact same cloud. As a result, you can’t point your fancy meters at the clouds in one spot on earth in one season and come to any meaningfull conclusions about net effect on a global and annual basis.
Worst of all, nothing I wrote just now is anything that hasn’t been known and understood for decades. While I welcome the fact that what they are talking about may now actually get included in climate models as it should have from day one, their own research amounts to putting lipstick on a pig and calling it a discovery of something new. The only thing that is new is the lipstick.
Wyatt, M.G.; Kravtsov, S.; & Tsonis, A.A. (2011). Atlantic Multidecadal Oscillation and Northern Hemisphere’s climate variability. Climate Dynamics. doi: 10.1007/s00382-011-1071-8.
…haven’t yet found a free link, but having read this recent paper fairly carefully, I would say it will eventually stimulate a lot of discussion.
Some connected material is available:
Wyatt, M.G.; Kravtsov, S.; & Tsonis, A.A. (2011). Poster: Atlantic Multidecadal Oscillation and Northern Hemisphere’s climate variability.
https://pantherfile.uwm.edu/kravtsov/www/downloads/WKT_poster.pdf
Also:
http://pielkeclimatesci.wordpress.com/2011/04/21/guest-post-atlantic-multidecadal-oscillation-and-northern-hemisphere%E2%80%99s-climate-variability-by-marcia-glaze-wyatt-sergey-kravtsov-and-anastasios-a-tsonis/
Important Highlight:
Mainstream acknowledgement of NPI pivot:
“PNA participates in all synchronizations.” – Wyatt, Kravtsov, & Tsonis
(more on why this is significant at a later date…)
Dr. Judith Curry mentioned the article at Climate Etc. [ http://judithcurry.com/2011/04/21/week-in-review-42211/ ] and it received (quite interestingly) minimal attention, but she has not yet introduced a technical thread devoted specifically to the article. Certainly the current absence of a free version of the article puts a serious chill on the potential for open public discussion, so I support her restraint as sensibly prudent if this is the rationale for delay.
Jim Masterson says:
April 24, 2011 at 1:46 pm
jim,
I’m a bit distracted this afternoon so I’m having trouble following some of your comments. I don’t buy anything KT claims unless I can duplicate it. I haven’t gone over KT97 for a while – not since I discovered at least some of their numbers for cloudy skies are already weighted for 62%. It may well be that some of them are not.
I’m using a 1d model for looking at the spectral content and total power. I’ve just done a very simple cloud model for LWIR that looks like it might actually work. It simply assumes that an optically thick cloud in the LWIR will result in total absorption and a continuum thermal emission at the cloud top (and bottom). I’ve got a lot of digging to find LWIR spectral graphs from the TOA for cloudy conditions again. I think it’s in the ballpark for total output emission at the TOA (or tropopause) .
One of the KT97 problems is the overestimate of surface reflections escaping to the TOA. It’s high by over a factor of 2 from some other sources and this permits them to underestimate cloud and atmospheric effects. They also seem to ignore atmospheric scattering separately from clouds – actually, it’s probably about as much now as the overestimate of the ground reflection. If the 30w/m^2 were the 38% clear sky portion and with 70% of the surface being h2o at about 0.04 reflectivity, the result would give the average surface reflectivity for land as being around 0.78 – which could only happen with fresh snow over all land, lol. 0.085 albedo average is for oceans being about 0.04 albedo and land mass being 0.19 average albedo and that provides 30w/m^2 reflection in clear skies. for 38% clear skies, that reduces down to about 11 w/m^2 which is more in line with the 13.6w/m^2 for J. London and for some other references I’ve seen.
davidmhoffer says:
April 24, 2011 at 2:15 pm
“Amongst other flaws in this paper, and in answer to some of the comments in this thread, one cannot quantify the net effect of clouds the way they measured it one way or the other regardless of the accuracy of their measurements.”
The clouds that we so love in summer here in Central Florida appear on the horizon about 11:00 AM or so and arrive about 3:00 PM or so. They are bearing rain which drops the temperature as much as ten degrees and produces a very pleasant evening. The clouds hang around but do not cause the temperature to increase.
Do you think any of this will ever get addressed by climate scientists studying the effects of clouds on climate and temperature? I have a feeling that it is just way too real for them to even consider addressing it. It is just a hornet’s nest for them. The darn clouds are not spherical, not fluffy, not white, low flying, dripping with moisture, and repeat this process all summer, which is May 1 to October 1 in Central Florida.
Terry says:
April 24, 2011 at 2:32 am
It is basic undergrad level spectroscopy that scattering is a function of wavelength and aerodynamic diameter, that also has big implications for directional scattering. I am staggered that this is not the case.
==========================================================
Me too. I don’t see how you can talk about light scattering in the atmosphere without some reference to Mie theory, which to me includes both Mie scattering and Rayleigh scattering. After all, Rayleigh scattering of visible sunlight off nitrogen molecules is why the sky is blue. The wavelength in relation to areodynamic diameter of the particle is all important in the amount and direction of scattered light.
FYI: Here is the abstract of the actual paper:
GEOPHYSICAL RESEARCH LETTERS, VOL. 38, L07801, 5 PP., 2011
doi:10.1029/2010GL046282
Shortwave spectral radiative forcing of cumulus clouds from surface observations
E. Kassianov
Pacific Northwest National Laboratory, Richland, Washington, USA
J. Barnard
Pacific Northwest National Laboratory, Richland, Washington, USA
L. K. Berg
Pacific Northwest National Laboratory, Richland, Washington, USA
C. N. Long
Pacific Northwest National Laboratory, Richland, Washington, USA
C. Flynn
Pacific Northwest National Laboratory, Richland, Washington, USA
The spectral changes of the shortwave total, direct and diffuse cloud radiative forcing (CRF) at surface are examined for the first time using spectrally resolved all-sky flux observations and clear-sky fluxes. The latter are computed applying a physically based approach, which accounts for the spectral changes of aerosol optical properties and surface albedo. Application of this approach to 13 summertime days with single-layer continental cumuli demonstrates: (i) the substantial contribution of the diffuse component to the total CRF, (ii) the well-defined spectral variations of total CRF in the visible spectral region, and (iii) the strong statistical relationship between spectral (500 nm) and shortwave broadband values of total CRF. Our results suggest that the framework based on the visible narrowband fluxes can provide important radiative quantities for rigorous evaluation of radiative transfer parameterizations and also can be applied for estimation of the shortwave broadband CRF.
>>
cba says:
April 24, 2011 at 5:02 pm
. . . I’m having trouble following some of your comments.
<<
That’s about par for most of my posts.
>>
I’m using a 1d model for looking at the spectral content and total power.
<<
Interesting. I, too, have a 1d model, but it’s duplicating the KT97 heat flows.
Jim
This is crazy. Photographers have known this since before the First World War (that’s why they used to carry so many slightly different yellow and orangeish filters), and the lowered contrast on cloudy days was often utilized for studio portraits. This is bleeding-edge science? A 1930s-era Weston photographic meter would have told the same story — though not, of course, peer-reviewed or tax-funded…
RE: Ed Barbar says:
April 24, 2011 at 11:53 am
The transport of warmth, as latent heat, from the surface to altitudes twice as high as Mount Everest, where the latent heat is released as vapor becomes liquid, and more heat is released as liquid becomes solid, is an obvious and huge “safety valve,” allowing the cooling of over-heated places. Think about how thunderstorms bloom up over heated plains, and how hurricanes swirl up over heated oceans.
Surely this is included in models. It is likely the reason some expected there to be a huge increase in big hurricanes. The simplistic model had to do something with all the extra heat it was creating.
The problem is that reality is far more complex than anything our puny minds can create. Compared to reality, models are like Haiku.
I have seen complex discussions concerning where exactly, in a cloud, the latent heat is released. In the middle? Where humidity is 100%? Or at the very “skin” of a cloud, where humidity is less than 100%? (It makes a difference, for latent heat released at the “skin” of a cloud escapes upwards to outer space more easily.)
Any one of these complex discussions can make a big difference in a model. A little pebble can start a big avalanche.
Not that we shouldn’t try to model our atmosphere. However people need to be a lot more humble while doing so. Also, when people do discover some tiny aspect of how the atmosphere works, they need to stop making grand pronouncements, as if they have discovered the Rosetta Stone, or proven the world will end next Tuesday.