Clouds' effect on sunlight energy at Earth's surface depends on the wavelength of light

May 09, 2011
Spectral radiometers measuring sunlight wavelengths in the sky over Oklahoma at DOE’s ARM Climate Research facility.

Bouncing around from cloud to cloud, and down to Earth, sunlight's warmth is both enhanced and blocked by clouds. Atmospheric scientists from Pacific Northwest National Laboratory found that clouds' overall effect on the amount of sunlight available to warm the earth depends on the wavelength of sunlight being measured. Their unexpected findings show that the sunlight scattered by clouds is an important component of cloud contributions to Earth's energy balance.

The influence of clouds on both warming and cooling the earth is one of the least understood aspects of climate change. This research will provide atmospheric scientists with new information to improve how they portray clouds in climate models. Knowing how clouds contribute to the earth's will enhance our ability to accurately model and predict .

Clouds both cool and warm the earth's surface. They cool the earth by bouncing sunlight back into the atmosphere; they warm it by bouncing light down to Earth's surface. The net cloud effect is what scientists need to obtain. To do that, they measured the total amount of sunlight in a cloudy day. Then, they determined the amount of energy contained in the sunlight in a cloudless, blue sky. The difference was the net cloud effect. To find out if the individual colors of light contribute to the net cloud effect, the research team measured brightness with a spectral radiometer from DOE's Facility in Oklahoma. The team found that the net cloud effect changed depending on the measured visible-spectrum wavelength, and whether the sunlight was direct or scattered. Their results also suggest that aerosols, those tiny bits of dust or pollution in clouds and the sky, are responsible for the wavelength differences. Thus, clouds alone are not responsible for the different wavelengths contribution to the net cloud effect.

Scientists will use developed long- and short-term data sets from several sites around the world, along with the approach suggested by this research, to estimate the wavelength changes of the total cloud impact to improve information on the radiative properties of and clouds in large-scale .

Explore further: Tropical Storm Odile taken on by two NASA satellites

More information: Kassianov EI, et al. "Shortwave spectral radiative forcing of cumulus clouds from surface observations," Geophysical Research Letters, Vol. 38, L07801, 5 pp., 2011, doi:10.1029/2010GL046282.

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GSwift7
1 / 5 (1) May 09, 2011
I wonder if it would make sense to measure the temperature of objects at ground level? For example, you could have temperature measurements inside a car? It doesn't say in the above whether they are doing daytime only or both day and night measurements, but I would think both would be important, as well as seasonal differences to see if a longer versus shorter day makes a difference. I'm sure it would be helpful to correlate the temperature of ocean surface water with cloud cover also, however wind conditions and humidity play a big part in that too, so it wouldn't be easy, but it should be possible.
Na_Reth
not rated yet May 09, 2011
it really depends on the clouds temperature and density and particle make up....
And the layers of clouds...
ted208
1 / 5 (1) May 09, 2011
Quick somebody should let the IPPC know this, it's what skeptical scientist have been saying for years!

They found that clouds' overall effect on the amount of sunlight available to warm the earth depends on the wavelength of sunlight being measured. Their unexpected findings show that the sunlight scattered by clouds is an important component of cloud contributions to Earth's energy balance.
It's the Sun and Clouds with Co2 plays a tiny part in global warming or cooling cycle!
GSwift7
1 / 5 (1) May 10, 2011
I have a small joke about the wording of the article. They said:
clouds' overall effect on the amount of sunlight available to warm the earth depends on the wavelength of sunlight being measured


I hate to say this, but the overall effect remains the same whether you measure it correctly or not. :) I know it's just a wording thing and they didn't mean it that way, but I couldn't pass that one up.

To NaReth:
it really depends on the clouds temperature and density and particle make up....
And the layers of clouds...


That's a good point: LAYERS, plural. The above article doesn't say whether they tried to deal with multiple layers of clouds or not. Clouds are just such a PITA to study, measure and model.
GSwift7
1 / 5 (1) May 10, 2011
Here's an interesting paper from the journal Astronomy and Astrophysics that will probably not get an article here on physorg.

http://www.aanda....emid=129

They are careful to say that there's no reason to prefer their results over the results of different techniques becuase there's not any sure way to determine which method yields the most accurate results.

IF this is the most correct method then it doesn't leave much wiggle room for human caused climate change. However, as usual, I must say that I have a hard time choosing to believe a new study when it contradicts all the previous work. Read with caution and a doubting mind.