Light scattering in the Earth’s atmosphere part 3 – clouds, haze and surface
Previously I have described the light scattering mechanism on the smallest particles of the Earth’s atmosphere, where mainly the Rayleigh Scattering plays a role. Now is the time to round off this whole article and say something more about a different group of elements, that also contributes to the light scattering process. There are bigger particles that build fog and clouds. As an output of this whole light scattering process in the Earth’s atmosphere, we can see the interaction of these all small particles with the Earth’s surface – a ground response.
- MIE SCATTERING
Mie scattering takes place when droplets and light waves are of similar size or these particles are bigger than the light wavelengths. This kind of scattering does not differentiate individual wavelength colors and therefore scatters all wavelength colors the same.
The result is equally scattered initial light coming from the illumination source. In bigger droplets, the scattered light coming from inside cancels each other and what remains is interpreted as reflected and refracted waves. In this case, the spectral composition of the scattered light depends on the scattering angle (Pic. 1).
Pic. 1 Angular distribution of scattered light comparison between Rayleigh and Mie scattering, whereas the direction of incident light remains stable (http://hyperphysics.phy-astr.gsu.edu).
Pic. 2 The Rayleigh and Mie scattering mechanism (http://hyperphysics.phy-astr.gsu.edu).
The common particles causing the Mie scattering are dust, pollen, smoke, and microscopic water droplets, that form clouds. Mie scattering occurs mostly in the troposphere, especially in the atmospheric boundary layer, where often haze is observed.
Pic. 3 The Mie scattering for particles with similar size to light wavelengths (high level of haze concentration). It results in poor visibility; the hills in the picture in the background are located 10 – 30 km away and are barely visible, whereas further mountain ranges 50 km away are invisible. Odrzykoń, Poland
Pic. 4 The Mie scattering for particles with size bigger than light wavelengths (fog). As a result, the visibility range is restricted to less than 1km. Odrzykoń, Poland.
This kind of scattering is very important in meteorological optics with respect to many problems regarding haze and cloud scattering. Mie scattering can change the hue of the sky. Whereas the sky in near-Rayleigh conditions is deep blue, in Mie scattering conditions this color can be washed out depending on the concentration of the big particles in the atmosphere (Pic. 5 – 7).
Pic. 5 The impact of Mie scattering on the sky color (atmo.arizona.edu).
Pic. 6 The sky color difference depends on the concentration of the big particles in the atmosphere: left – in hazy conditions, right – in near-Rayleigh conditions. St. Michel’s Mound, UK (left); Zadar, Croatia (right).
Pic. 7 Extremely high haze concentration in the lower atmosphere makes the sky white-bluish, especially when looking near the solar direction. Łęki Strzyżowskie, Poland.
2. TYNDALL EFFECT
The Tyndall effect is similar both to Rayleigh Scattering and Mie Scattering. The similarity of the Tyndall effect to Rayleigh Scattering lies in the same law, where the intensity of scattered light depends on the fourth power of the frequency. As a result, blue light is scattered much more strongly than red light. This situation refers to particles in a colloid or very fine suspension. Tyndall scattering is more intensive than Rayleigh scattering due to the bigger size of particles involved. If the colloid particles are spheroid then the Tyndall effect can be analyzed in terms of the Mie scattering, which admits particle sizes in the rough vicinity of the wavelength of light. In Earth’s atmosphere, it refers to weather conditions, where the Tyndall Effect can be noticed in foggy or dusty places, which is a good colloid. Sunlight passing through this colloid encounters the individual suspended particles, which scatter and reflect light. These individual suspended particles like water droplets make the headlight beam visible. The amount of scattering depends on the frequency of the light and the density of the particles. When there are no small particles in the air then it is not possible to see a path of light, but when there are enough particles in the air you can see the path of light, that is reflected by them. We can observe it for example in mossy forests or dusty indoors (Pic. 8, 9).
Pic. 8 An example of the Tyndall effect is to be seen in the forest when the Sun shines through a thin fog (weggi.ch).
Pic. 9 An example of the Tyndall Effect indoors, where is caused by dust (Wikimedia.org, Pinterest.org).
3. NON-SELECTIVE SCATTERING
Non-selective scattering occurs in the lower portion of the atmosphere when the particles are much larger than light wavelengths. The non-selective scattering creates a white appearance of the sky and plays the main role in cloud formation. The presence of clouds in the sky creates the cloud cover, which says roughly how much the sky is affected by any kind of cloud (Pic.10). In dense clouds, this dependence is averaged out by varying drop sizes and multiple scattering and the clouds appear white or grey (Pic. 11). Cloud droplets scatter all wavelengths of visible light creating the appearance of a white cloud. The main difference between non-selective scattering and others is the ability to reflect light. The water droplets are much bigger from light wavelengths. Due to this non-selective scattering enables the reflection of the light unlike Mie scattering and Rayleigh Scattering.
Pic. 10 A polarity between non-selective scattering (white cloud) and Rayleigh scattering (blue sky). Big puffy clouds scatter light effectively making the sky around them much brighter (atmo.arizona.edu).
White clouds cool Earth by reflecting some sunlight up into outer space and they warm it by bouncing some sunlight down to the surface (Kassinov et al., 2011).
Pic. 11 Cumulus humilis cloud on the blue sky is a good example of non-selective scattering in conjunction with Rayleigh scattering. Most of the cumulus clouds are dense, so they appear white and grey at once.
Pic. 12 White altocumulus clouds under fair weather conditions, whereas the cumulus below, shaded by altocumulus appears to be grey, even darker than the grey altocumulus base.
Pic. 13 The light scattering by clouds – scheme. White light is scattered in all directions, and some light penetrates to the cloud base (weather.gov.hk).
Pic. 14 Especially in vertically developed clouds we can see a very dark base. As the cloud grows thicker more sunlight is reflected from it and less light can penetrate through it. Małe Pieniny Mts, Poland.
Pic. 15 Relation of light scattering with cloud depth (weather.gov.hk).
The cloud cover affects the diffuse sky radiation. The flux of light is not wavelength-dependent because the fact, cloud droplets are larger than the light’s wavelength and scatter all colors approximately equally (Pic. 16).
Pic. 16 Under an overcast sky, diffuse sky radiation plays the main role in light scattering. Odrzykoń, Poland.
The intensity of direct sunlight varies depending on cloud thickness. It ranges from 1/6 for relatively thin clouds down to 1/1000 under extremely thick storm clouds (Pic. 17).
Pic. 17 The intensity of direct sunlight varies depending on cloud thickness. Odrzykoń, Poland.
Pic. 18 An example of a multicellular thunderstorm, is where a young cumulonimbus with a dark base is growing under an older capillatus, making the sky in grey appearance. The cumulonimbus elements, which could look white in solar beams appear to look much darker because the low portion of light goes through them.
Often the clouds cover the sky partially. There are different sky radiation circumstances. The clear section of the sky will still scatter the light in Rayleigh conditions whereas the cloudy section’s radiation is different. Clouds can bounce a lot of light around. It is noticeable, especially in the case of vertical-developed clouds. These clouds are big puffy white objects, that reflect the sunlight effectively making the sky around them look brighter (Pic. 10). Brighter are also the shadows produced by other clouds located in the vicinity.
This is the answer to why clouds are grey. Sometimes we can see grey clouds shaded by another white cloud floating on a higher level. Then less light is scattered, and therefore cloud appears to be grey. A similar or even more noticeable effect is seen when a cloud grows thicker. Then more sunlight is reflected from it and less light can penetrate through it (Pic. 17-20). Since little sunlight reaches the underside of the cloud, less light is scattered and the cloud base appears grey. Moreover (especially in the cumulus clouds case) water droplets near the cloud base grow larger being in effect a more effective absorber and less effective scatterer more sunlight is either reflected or absorbed before reaching the cloud base. For an observer on the ground below the cloud, the base can look dark grey before the rain begins to fall.
Pic. 19 The light scattering mechanism in multicellular thunderstorm cloud, where: 1 – direct solar beam, 2 – the white appearance of the external parts of the sunlit clouds, 3 – light firstly scattered by cloud surface headed sunwards, 4 – the grey appearance of the clouds, shaded by other clouds, 5 – light secondly scattered by shaded clouds or their parts, 6 – light portion penetrating the cloud, 7 – the smallest light portion, that penetrates to cloud base, making it the most darker. Look also on the edges of these clouds, which are to be seen brighter than the middle due to the brightest shadows produced by other clouds in the vicinity.
Pic. 20 Cumulonimbus cloud reflecting the light scattered by the cloud’s top, down to the darkest base. Odrzykoń, Poland.
The spectral character of the radiation emanating from the bottom of the cloud also depends on the spectral character of the radiation illuminating the cloud, both at the bottom from the irradiance of the ground and the top from the direct attenuated solar radiation and the Rayleigh scattered skylight. Its intensity and spectral character, therefore, will depend on the surface albedo, the cloud thickness and type, and the solar zenith angle.
In low-light conditions like moonlight or twilight, the mechanism remains the same. the clouds are the brightest when headed towards the incident light and the darkest beyond (Pic. 21).
Pic. 21 Cumulus clouds are seen in twilight conditions with the brightest parts headed toward twilight glow and dark base. Odrzykoń, Poland.
4. THE INTERACTION OF LIGHT WITH SMALL PARTICLES AND SURFACE
White light is a mix of wavelengths. We can see the interaction of light both with the surface and the medium, which is our atmosphere. Obviously, the Earth’s atmosphere consists of a few layers and separate mediums with different densities. We are focusing mainly on the lower layer – the troposphere. When the light ray hits the surface we have a reflection of this ray of light. As we know most of the surfaces are coarse, which causes the scattering of this simple ray of light. In the outcome, this ray of light reverberates in a few different directions. Moreover, the color of the surface can decide (in the case of white light) or modify the color of scattered light.
Pic. 22 The interaction of white light with the surface. Considerating a white light (the easiest example) in interaction with the surface can produce optical effects as follows: a) specular reflection, b) lustrous reflection by paper with a slightly rough surface, c) diffuse reflection from the whitewashed wall, where no absorption d) diffuse reflection with the absorption of the shorter wavelengths at a painted yellow wall (Flammer et al., 2013).
The situation is straightforward for sunlight, which appears to be white. When reflected from for instance orange surface gives us orange light scattering, etc (Pic. 20). The surface color depends on the chemical elements, that are built up. These chemical elements run the process where light meets an electron it is “shaken” at the frequency of the light. As a result, the electron sends out light with the same frequency in any direction. Thus light scattering takes place (Flammer et al, 2013). According to quantum theory: when an atom absorbs a UV photon or a photon of visible light, the energy of that photon can excite one of the atom’s electrons to a higher energy level. This moment is known as transition. In order for a transition to occur, the energy of the photon absorbed must be greater than or equal to the difference in energy between the 2 energy levels. Once the electron is in the excited, higher energy level, it is in a more unstable position than it was when it was in its relaxed, ground state. As such the electron will quickly fall back down to the lower energy level and in doing so, it emits a photon with an energy equal to the difference in energy levels.
The simplified scheme of the transition process can be seen in the previous article.
Pic. 23 Each object is built with a different chemical element, that incurs an individual transition process. Finally, we can see the surfaces in different colors. Zilina, Slovakia.
5. OPTICAL EFFECTS RELATED TO LIGHT SCATTERING
There are at least a few optical effects related to light scattering. I will not describe all of them perfectly today, because I am going to prepare a separate article about them.
Optical effects with clouds:
Cloud presence can produce a phenomenon related to light scattering. First of all when clouds are close to the Sun or Moon can create the diffraction phenomenon, which is iridescence for clouds built by tiny water droplets and halo for clouds built by small ice crystals. Then we can see the halo phenomenon.
Pic. 24 The halo phenomenon caused by cirrostratus clouds.
Pic. 25 Circumhorizontal arc (wikimedia.org).
Common is also the corona phenomenon when the cloud is built by small water droplets (Pic. 26).
Pic. 26 Lunar coronae (wikimedia.org).
These phenomena are the effect of the spectral dependence of the angular distribution of scattered light. The intense scattering, that occurs in clouds can quickly extinguish any beam and create in its place a very diffuse radiation flux. I have described this process previously.
Because clouds include water droplets bigger than light wavelength they can reflect the light from the illumination source depending on their color. When for example white midday sunlight strikes a cloud, white light is scattered and reflected (Pic.11, 12, 15). This is why clouds are white (with some shades of grey mixed in if the cloud is thick. In this case, when you look up at a cloud you see a white cloud (sunlight being scattered by cloud droplets) surrounded by blue sky (sunlight being scattered by air molecules).
Pic. 27 Clouds throughout the day have a white or greyscale appearance due to almost white sunlight scattering and reflecting. Odrzykoń, Poland.
In the evening we will face a similar situation with the reddish light described above. As twilight progresses, the color of clouds, depending on altitude level and location in the sky will change as per the picture below (Pic. 28). This is because Earth (both with the atmosphere) is spherical. Thus is very easy to distinguish the cloud layers near sunrise or sunset conditions.
Pic. 28 Color of clouds around sunrise/sunset and during twilight is dependent on altitude level and position in the sky (angular distance from the solar point) (weather.gov).
Pic. 29 At sunset altocumulus looks (and reflects) orange whereas cirrus is yellow (weather.gov)
Pic. 30 Morning or evening clouds reflect long light wavelengths from the Sun (reddish and orange). Shaded parts remain in greyscale, sometimes slightly mixed with direct sunlight color. Szczawnica, Poland.
Sometimes under the overcast sky, when clouds are not thick enough we can notice the sunrise or sunset moment as clouds are turning yellowish.
Pic. 31 When we see only 1 layer of cloud at sunrise or sunset the important role plays an angular distance from the solar position. See the cirrus clouds just before sunrise, when Sun is around 2 deg below the horizon clouds are yellow near the solar point and become more orange when closer to the zenith point. Zręcin, Poland.
Behind the cloud-level terminator line, only scattered light affects the cloud color, which is mainly grey-reddish (Pic. 32, 33). Clouds being located beyond the terminator will reflect light scattered from sunlit clouds, reflecting long light wavelengths. I will describe it more in the future.
Pic. 32 The clouds after sunset appearance (weather.gov.hk).
Pic. 33 Cirrus clouds, when the Sun is around 8 degrees below the horizon. You can spot, that some of them appear to look reddish due to the reflection of red light scattered by other clouds far far away from the observer. Zręcin, Poland.
Looking at the clouds in the sky we can spot only grey color there. Another situation can occur when watching the mountain shadow. Clouds outside the shadow are sunlit, whereas clouds inside the shadow reflect only the light scattered in the atmosphere, which gives them a grey-bluish appearance (Pic. 34).
Pic. 34 The Pico del Teide shadow is seen near the Teide Observatory. Yellow arrows show the solar direct beam, which makes clouds yellowish appearance. Each cloud shows, that the solar point is located behind the observer. Blue arrows indicate the clouds are in the shadow, whereas only light scattered in the atmosphere is reflected. Unlike illuminated clouds, these clouds are the brightest on the top, because basically from the top light hits them. Moreover, these clouds look grey-bluish reflecting Rayleigh-scattered light in the atmosphere. Tenerife, Spain.
The situation is completely different during the nighttime conditions in light-polluted areas. During the night in light-polluted areas, clouds reflect a yellowish artificial light that originated from street lamps. The phenomena are more obvious when the cloud is lower or denser.
Pic. 35 Illuminated clouds above light-polluted area during the night. Kuala Lumpur, Malysia.
Upper parts of clouds or clouds floated on higher levels appear to be dark grey or black, without any light features unless different conditions occur (moonlight or deep twilight), which I will describe in the future.
Another situation is when even a thin cloud looks grey rather than white. We can explain the perception of our eyes. A light gray cloud on a bright white background will look much darker than the same cloud on a dark or black background, in which case it might look white and bright (Pic. 36). On the other hand, a cloud can look dark or gray because it is partially transparent and the blue sky behind it can be seen through the cloud. This will happen in light wispy clouds with little water content and more often in ice crystal clouds. Then halos and sundogs can be visible.
Pic. 36 A thin wisp of clouds is often seen darker than the sky near the horizon, which is caused by human eye perception. On the right is the same picture with the polarizing filter, which roughly explains this phenomenon (wikiwand.com).
In thunderstorm cases (shelf cloud) when the cloud is much thicker and cloud-based at a much lower altitude observer can spot the light reflection from the adjacent ground being still illuminated by a skylight or light scattered by neighboring tiny clouds (green clouds) (Pic. 37, 38). Basically quite often during thunderstorms, before starts raining a light from another cloud is reflected (Pic. 37, 39 – 42).
Pic. 37 The green cloud effect mechanism is shown with the cloud light reflection process: 1 – direct solar beam, 2 – light scattered and reflected by puffy cumulus or cumulonimbus cloud, 3 – light secondly reflected by another cloud, 4 – light reflected from the ground both from the sun and from the cloud. 5 – green cloud appearance at the bottom of the cumulonimbus cloud.
Pic. 38 Often the green clouds effect is identified with the forthcoming tornado, although in general refers to an extremely low suspended shelf cloud, which is able to reflect light from the ground. This green is not perfect as seen on grass, but clouds are slightly greenish in their greyscale. Adequately to the conditions, we can observe a blue cloud (above sea) or yellow cloud (above desert) effect depending on the surface (Matt Denis, box72.com).
Pic. 39, 40 An example of light reflection before or after a thunderstorm outside the precipitation area, where: 1 – direct sunlight reflection and scattering, 2 – scattered sunlight reflection. From the human eye’s perspective, this part of the cloud looks even darker than indicated in point 3 because this shaded portion of a cumulonimbus cloud is drowned by a much brighter portion from points 1, 3 – scattered sunlight reflection, 4 – secondary scattered light, coming from another cloud or part the cloud being in the vicinity (yellowish edges).
Pic. 41, 42 Another example of secondary scattered light coming from the different clouds, groups of clouds, or the atmosphere. Blue arrows show discernable brighter cloud edges, which reflect the scattered light coming from the brighter section of the sky seen on the left.
Optical effects with haze
Haze is represented by large aerosols with a size similar to light wavelength so it does not scatter a blue color preferentially like small molecules do. Hazy conditions in the atmosphere correspond to Mie scattering. The atmosphere is not clear enough to give a perfect blue sky and clear horizon but is more transparent than a cloudy or foggy medium. Mainly Mie scattering is typical for the lowest part of the troposphere – the atmospheric boundary layer, where the concentration of haze is the biggest. Everywhere above – in the “free atmosphere” zone the haze density is low and the effects are somewhere between Rayleigh and Mie scattering. The haze phenomena will be described in the following article, however here I will list all atmospheric optic phenomena related to hazy conditions. Firstly I would like to say a bit about macroscale phenomena created by haze presence in the atmosphere. They’re crepuscular rays, anticrepuscular rays, dawn’s warm glow (solar and antisolar rays), and mountain shadow. These atmospheric optics are similar to each other and often visible in more or less hazy conditions. Both crepuscular rays and dawn’s warm glow are rays of sunlight, that appear to radiate from the point of the sky, where the Sun is located. The difference between crepuscular rays and dawn’s warm glow is the period of daytime when they are to be observed. Crepuscular rays can be seen throughout the day, whereas a dawn’s warm glow, is to be seen around sunrise and sunset only. The dawn’s warm glow is the kind of both crepuscular and anticrepuscular rays. Anticrepuscular rays are to be seen when looking toward the antisolar direction. All these atmospheric optics are produced by the presence of clouds. Mainly there are cumulus, stratocumulus, or cumulonimbus clouds, with sharp borders. The solar rays stream through the cloud gaps and appear as columns of sunlit air separated by darker cloud-shadow regions (Pic. 43). These rays are in fact near-parallel shafts of sunlight.
Pic. 43 Crepuscular rays produced by stratocumulus clouds above Southampton coast (wikimedia.org).
Anticrepuscular rays are more frequently visible around sunrise and sunset. Anticrepuscular rays are also near parallel, but appear to converge in an antisolar point (Pic. 44). This convergence is actually an optical illusion because their apparent convergence is toward a vanishing point, which is an infinite distance away from the viewer.
Pic. 44 Anticrepuscular rays (wikimedia.org).
Both crepuscular and anticrepuscular rays are similar to dawn’s warm glow, which is often called solar or antisolar rays. This kind of ray occurs when the Sun is about to rise/set and mainly during the civil twilight. These rays are mainly produced in a “free atmosphere” where aerosol concentration is low, thus they are not dependent on Mie scattering only, because Rayleigh Scattering is also important to factor there. Dawn’s warm glow is visible as a group of extended reddish rays or darker elongated shadows from solar points throughout the sky sphere towards an antisolar point or civil wedge. Basically, the dawn’s warm glow can be visible from deep nautical twilight when conditions are favorable (e.g. at the top of high mountains) (Pic. 45).
Pic. 45 Dawn’s warm glow (solar rays) seen from Tenerife at 2400 m.a.s.l near Teide Observatory, when the Sun was 9 degrees below the horizon (middle of nautical dawn). Tenerife, Spain.
Pic. 46 Dawn’s warm glow (antisolar rays) can touch the twilight wedge (the Belt of Venus) (Jeff Dai, atoptics.co.uk).
The last phenomenon caused by Mie scattering is a mountain shadow. It is produced analogically to dawn’s warm glow, but in this case, solar beams are covered by mountains rather than clouds. Likewise in the case of solar and antisolar rays, Mie scattering is not the main factor here, because also Rayleigh scattering is important due to “free atmosphere” conditions. This view is typical for the area with freestanding high mountains above much lower terrain or sea surface. The mountain shadow is perfectly visible when standing at the top (Pic. 47). However, an observer can notice it is next to the mountain (Pic. 45, 46). When the freestanding mountain is very high (a few km above ground level) then its shadow can even merge with a twilight wedge (the Belt of Venus) (Pic. 46).
Pic. 47 A typical example of mountain shadow seen from the top of the Mauna Kea (Greg Chavdarian, apod.nasa.gov)
Pic. 48, 49 – Pico del Teide mountain shadow seen from the position, when an observer is located somewhere next to the mountain (near Teide Observatory). Aside from shadow, there are two other things to spot: 1 – glory seen on clouds, which shows a roughly current antisolar point. 2 – the shadow column is seen in the air, which becomes more visible as goes closer to the clouds. It is related to the increasing thickness of the shadow when closer to its end. Tenerife, Spain.
Pic. 50 The Pico del Teide shadow merging with a rising twilight wedge (the Belt of Venus). Tenerife, Spain.
Other interesting phenomena, which occur mainly in the lowest part of the troposphere are aerial perspective, Bishop’s ring, and pollen corona.
Aerial perspective is a very common phenomenon present in the Earth’s atmosphere and refers to every weather condition ranging from very fair days with near-Rayleigh scattering conditions down to foggy weather. Atmosphere behavior affects the object’s appearance seen by the observer from a distance. As the distance between the object and the observer increases, the contrast between the object and background decreases (Pic. 51). More about it I will develop in further writing.
Pic. 51 The aerial perspective seen in Bieszczady Mts. Every subsequent range from the observer looks fainter and fainter due to intensive light scattering on haze particles. Wołosate, Bieszczady, Poland. Wołosate, Bieszczady, Poland.
Bishop’s ring is produced by the scattering of sunlight by ash and hydrate sulfate droplets. This phenomenon is often present after volcano eruptions.
Pollen corona is caused by high pollen concentration in the lowest part of the atmosphere when stable high-pressure conditions. The pollen aerosols are quite big and produce small coronae around the Sun or Moon (Pic. 53).
Pic. 52 The Bishop’s ring phenomena (Bob Harrington, bobgat.com, atoptics.co.uk).
Pic. 53 Pollen corona around Moon (skyandtelescope.com)
In the finish is worth mentioning about morning/evening sky color is affected by haze concentration. As I have shown in the previous article the color of the zenith sky varies throughout the day. The sky color near sunrise/sunset depends on the haze concentration likewise throughout the day (Pic. 5). As haze presence increases sky looks reddish because longer wavelengths are scattered on aerosol particles. Nevertheless, even in the worst-case scenario, the main color of the evening zenith sky remains blue (Pic. 54).
Pic. 54 The Evening zenith sky is blue with some greenish, orange, and reddish tint, which appears to be more significant when the haze concentration is bigger (on the right).
Well, it’s time to finish this extremely long writing. Light scattering in the atmosphere is a very wide topic, that goes far beyond this article. Many of the things included here need to be described separately as I want to describe much more about them. Anyway, you can treat this whole article as a good indicator of places, where you can find more on the web. Hopefully, I have encouraged you to observe these phenomena and broaden your knowledge about them
Mariusz Krukar
References:
- Ahrens C.D., 2003, Meteorology Today: An Introduction to Weather, Climate, and the Environment, vol. 1, Nature, London.
- Bohren, C.F., 1987, Clouds in a glass of beer, Dover Publications Inc., New York
- Flammer J., Mozzafarieh M., Bebie H., 2013, The interaction between light and matter (in:) Basic sciences in Opthamology; Physics and Chemistry, Oxford University Press, Oxford
- Kassinov E., et all, 2011, Shortwave spectral radiative forcing of cumulus clouds from surface observations (in:) Geophysical Research Letters, vol. 38.
- Van de Hulst H. C., 1957, Light scattering by small particles, Dover Publications Inc., New York.
Links:
- Mie plot – Mie scattering computer simulation.
- Gsp.humboldt.edu: Atmospheric scattering
- Corpuscular rays in St. Peter Basilica
- Cowley: Antisolar rays above Tibet
- Antisolar rays
- Antisolar rays – explanation mechanism
- Mountain shadow
- Perspective effect – mountain shadow formation
- Sciencedaily.com: Effect of cloud-scattered sunlight on Earth’s energy balance depends on the wavelength of light
- Green_clouds.shtml
- Why does the sky turn green before a tornado?
- Bishop’s ring.htm
- Pollen corona
Wiki:
- Mie_scattering
- Tyndall_effect
- Colloid
- Crepuscular_rays
- Vanishing_point
- Anticrepuscular_rays
- Antisolar_point
- Multicellular_thunderstorm
- Diffuse_sky_radiation
- Halo_(optical_phenomenon)
- Aerial_perspective
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