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Solar radiation: albedo, scattering, absorption
Gerald Ratzer
December 22, 2024
Solar radiation undergoes several processes as it travels through Earth's atmosphere, including albedo, scattering, and absorption.
These phenomena play crucial roles in the Earth's energy balance and climate system.
## Albedo
Albedo is the fraction of sunlight that is diffusely reflected by a surface or object[9]. It is measured on a scale from 0 (complete absorption) to 1 (complete reflection)[9].
The Earth's overall albedo is approximately 0.29, meaning about 29% of incoming solar radiation is reflected back to space[12].
**Key points about albedo:**
- It varies depending on surface type, with ice and snow having high albedos (80-90%) and water having a low albedo[11].
- Cloud albedo can range from 40% to 90%, significantly affecting Earth's energy balance[3].
- Albedo changes with solar zenith angle, being highest when the sun is near the horizon[4].
## Scattering and Absorption
As solar radiation passes through the atmosphere, it interacts with particles and gases, leading to scattering and absorption processes.
### Scattering
Scattering occurs when particles or gas molecules redirect incoming solar radiation[10]. There are three main types of scattering:
1. Rayleigh scattering: Caused by gases, mainly N2 and O2[2].
2. Mie scattering: Occurs due to aerosol particles and cloud droplets[2].
3. Non Selective scattering: Affects all wavelengths equally[10].
The main difference between Rayleigh and Mie scattering is the direction of the re-emission of the incident solar radiation.
For example, in Rayleigh scattering the light has a symmetrical direction either forward or backward whereas in Mie scattering the light is mainly scattered in the forward direction, depending on the size of the particle.
Scattering reduces the amount of direct solar radiation reaching Earth's surface but increases diffuse radiation[1].
### Absorption
Absorption is the process by which solar radiation is retained by a substance and converted into heat energy[3].
Key aspects of atmospheric absorption include:
- Major absorbers: water vapor, carbon dioxide, ozone, and other trace gases[2]. (I agree with WV, but not the rest)
- Wavelength dependence: Different atmospheric constituents absorb radiation at specific wavelengths[6].
- Vertical distribution: About 3% of solar energy is absorbed in the stratosphere, primarily by ozone[5].
## Impact on Incoming Solar Radiation
The combined effects of albedo, scattering, and absorption significantly modify the incoming solar radiation:
- Approximately 70% of incoming solar energy is absorbed by the Earth system[5].
- 50% is absorbed by the Earth's surface (land and oceans)[5].
- 20% is absorbed by the atmosphere and clouds[5].
- 30% is reflected or scattered back to space[5].
These processes are fundamental to understanding Earth's energy balance and play a crucial role in shaping our planet's climate system.
Citations: [1]
https://geo.libretexts.org/Bookshelves/Geography_(Physical)/The_Physic al_Environment_(Ritter)/04:_Energy_and_Radiation/ 4.03:_Radiation_and_Energy_Balance_of_the_Earth_System/
4.3.01:_The_Radiation_Balance
[2] https://ltb.itc.utwente.nl/580/concept/111247
[3] http://www.physicalgeography.net/fundamentals/7f.html
[4] https://en.wikipedia.org/wiki/Cloud_albedo
[5] https://www.ess.uci.edu/~yu/class/ess15/lecture.6.radiation %20transfer.ESS15.all.pdf
[6]
https://www.atmos.albany.edu/daes/atmclasses/atm100/Notes_files/Cha pter2_EnergyBalance.pdf
[7] https://www.astro.uvic.ca/~tatum/plphot/plphot02.pdf
[8]
https://www.pveducation.org/pvcdrom/properties-of-sunlight/atmospheri c-effects
[9] https://en.wikipedia.org/wiki/Albedo
[10]
https://natural-resources.canada.ca/maps-tools-and-publications/satellite -imagery-elevation-data-and-air-photos/tutorial-fundamentals-remotesensing/introduction/interactions-the-atmosphere/14635
[11] https://www.ces.fau.edu/nasa/module-2/earth-energy-balance.php
[12] https://ugc.berkeley.edu/background-content/reflection-absorptionsunlight/
The red and bold are my additions.
In this respect, the recent video interview of Ned Nikolov by Tom Nelson is important – See Minute 79 about Albedo.
https://www.youtube.com/watch?v=L1GgmBIew9Y
Also, several people (including Lightfoot) have said the IPCC AR5 Energy
Balance is in error – again See Minute 19 at the above link.
Link 11 from the AI response is also good educational material to get the ideas of all the different RTC/HTC components.
https://www.ces.fau.edu/nasa/module-2/earth-energy-balance.php
Numerically, it may not be accurate (not too many numbers in this diagram) – as researchers say the greenhouse effect does not really exist in an open system – no glass to close in our atmosphere! (In the lower right corner – they show three arrows for back radiation – which may be an overstatement.)
My red and bold comments above – point out why you need to look at AI responses with Critical Thinking.
Everything you read – may be true or false or somewhere in between, as demonstrated by the above comments.
Gerald Ratzer.
Attachments area
Preview YouTube video Ned Nikolov: Beyond the Greenhouse Theory | Tom Nelson Pod #268
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Ned Nikolov: Beyond the Greenhouse Theory
Tom Nelson Pod #268