Blue Sky, Gray Day: What the Evidence Really Shows

"Yet, as photos show, daily life continued under gloomy skies."

"Wildfires raging in Canada have spread smoke and hazardous air to Chicago, Minneapolis, New York City and beyond."

"Officials are advising sensitive groups, including children and people with asthma, to limit their time outdoors."

"The idea of opponent or antagonistic processes as the basic physiological substrate of our ability to perceive colors was originally developed by E. Hering before the discovery of what was initially called visual purple, and long before anything at all was known about cone receptors or the cone photopigments."

"Estimating individual cone sensitivities on the basis of their corresponding individual color matching functions is a classic problem of color vision."

"It is found that the domain 𝛺 does not contain the chromaticity coordinates of all stimuli, and spectral chromaticity coordinates do not distribute in the wavelength order along the spectrum locus, which results in no way to determine the Helmholtz coordinates for certain stimuli."

"Hering’s antagonistic mechanisms were thought by him to be neural, and to be somehow associated with opposite neurochemical processes."

"In the past it was generally accepted that the chromaticity diagram based on either 1931 or 1964 colour matching functions (CMFs), contains all the chromaticity coordinates of stimuli"

"The experimental results show relatively little variability with age, except as expected increases in lens density with age, and older observers showed more inter-observer variability."

"although he published quantitative studies of metameric color-mixture and was concerned with matters such as intensity invariance of color matches and the influence of macular pigment on such data"

"with the assumption that they have the Stockman and Sharpe 10 degree photo-pigment spectral absorbtance in common."

"The analysis suggests that some of the mean colour matching parameters assumed by the CIE, such as the macular pigment optical density, do not apply for these observers."

"La dispersión de cualquier partícula esférica con un parámetro de tamaño arbitrario se explica por la teoría de Mie ."

"La dispersión de Rayleigh se puede definir como la dispersión en un régimen de parámetros de tamaño pequeño X<<1 ."

"Los efectos de dispersión múltiple de la dispersión de la luz por las partículas se tratan mediante técnicas de transferencia radiativa"

"Above 80%, it becomes rapid, and visibility drops sharply even if the actual number of pollutant particles in the air hasn't changed."

"He invented a rather simple gage that consisted of 52 different hues of blue arranged from light to dark on a gradated circular scale."

"The cyanometer is a simply constructed measuring instrument that enables a determination of skyblue."

"His device, called a cyanometer, helped to confirm that the sky’s colour changed with the elevation."

"Simultaneous measurements gave a whiter shade of 7 at Geneva but a dark blue of 1–2 from the summit."

"It consists of a color-scale that is arranged circularly going in equal steps from white to blue (Prussian blue) and finally into black."

"According to its inventor - Horace-Bénédict de Saussure - the azure is determined by the amount of so called opaque vapors in the atmosphere associated with meteorological phenomena."

"This seems to have been caused by multiple scattering and not by mesospheric dust."

"The presence of haze in the lower troposphere and the occurrence of multiple scattering both have relatively minor influences on the recovery of the stratospheric dust properties, provided that 10< \(\overline h \) <30 km."

"The total near-horizon illumination maximizes when the Sun is highest in the sky owing to the intensity of multiple scattering."

"Shadows below the lander should receive illumination from diffusely scattered light low in the sky near Titan's horizon."

"showsthatsinglescatteringplaysadominantroleintheSZA"

"clouds are distinguished from aerosols using multidimensional probability density functions derived from an extensive training set of CALIOP measurements"

"This arises from overlapping attenuated backscatter color ratios (0.5–0.9)"

"This accounts for cirrus clouds' high depolarization (from non-spherical ice crystals)."

"Sensitivity changes, beginning at the first stages of visual transduction, permit neurons with modest dynamic range to respond to contrast variations across an enormous range of mean illumination."

"Background fields which bleached less than 0.5% rod pigment nevertheless diminished photoreceptor sensitivity."

"We found that signals from probes initiated in the L and M cones were affected by backgrounds that changed the mean absorption rates in the L and M cones, but not by background changes seen only by the S cones."

"The degree and rate of recovery of receptor sensitivity after exposure to a background field was a function of the total flux (I x t) of the field."

"show that the quantitative fMRI signals are consistent with a simple model of mean-field adaptation based on Naka-Rushton (Naka and Rushton, 1966) adaptation mechanisms within cone photoreceptor classes."

"Rod saturation, i.e. the abolition of rod voltages, occurred after approximately 12% of rod pigment was bleached."

"The results of experiments reveal that the DOP is a key parameter to indicate the accuracy of AOP measurements, and all the output solar meridian orientations extracted by our method in both clear and cloudy skies can achieve a high accuracy for vehicle orientation."

"1901: Untersuchungen über die Polarisation des Lichtes in trüben Medien und des Himmelslichtes mit Rücksicht auf die Erklärung der blauen Farbe des Himmels"

"Model and prediction of skylight polarization distribution pattern that arises due to scattering of sunlight in the atmosphere plays a vital role in bionic navigation sensor system."

"Durch Streulicht am blauen Himmel entsteht ein für den Menschen nicht sichtbares charakteristisches Muster teilweise polarisierten Lichts, das vom Stand der Sonne abhängig ist."

"Ebenso nahm er Messungen der Polarisation des Himmelslichtes und Szintillationsbeobachtungen vor"

"However, insects e.g. flies, honeybees, desert ants, will be able to see the polarization signature of the sky anduseitfornavigation."

"polarimetric signal is also dependent on the incident angle of the sunlight [3]."

"Darum vermutete er drei getrennte chemische Prozesse in der Netzhaut mit je zwei Gegenfarben , mit je einem hemmenden und einem erregenden Anteil, die nach einem Gleichgewicht streben."

"Initially, the normal trichromat is the type in which three colors are required to equal all the other colors: red, blue, and green (Matlin and Foley 1996)."

"the same photoreceptor repertoire can potentially generate different visual outputs depending on retinal circuitry"

"Drei verschiedene Zapfentypen im Auge, die jeweils ihre höchste Empfindlichkeit für kurz (blau)-, mittel (grün)- und langwelliges (rot) Licht haben, liefern Signale an die nachgeschalteten farbopponenten Ganglienzellen der Netzhaut (neuronale Farbkanäle)."

"Die Ursache liegt in den drei Zapfen des Farbsehens. Diese haben ihre Empfindlichkeiten für Blau (S-Zapfen), Grün (M-Zapfen) und Rot (L-Zapfen)."

"since with color blindness, the deficit of one or more of the three cones makes color perception difficult, which makes color contrast low."

"Horizontal cells contribute substantially to spatial and spectral integration by pooling signals from neighboring photoreceptors and providing feedback to the photoreceptor synaptic terminals"

"Auf der neuronalen Ebene werden die Zapfensignale „verschaltet“: „Rot“ und „Grün“ werden subtrahiert, die Differenz wird im Rot-Grün-Kanal weitergeleitet; die Addition von „Rot“ und „Grün“ dagegen ergibt ein Signal, dem die Empfindung von Gelb entspricht; diese Signale werden vom „Blau“-Signal subtrahiert und im Gelb-Blau-Kanal weitergeleitet."

"Um diesen Konflikt von drei oder vier Grundfarben zu entschärfen, teilte Kries den Vorgang des Farbensehens in eine periphere und eine zentrale Zone."

"Bipolar cells transmit photoreceptor-derived information into the inner retina, where amacrine cells introduce additional temporal and spatial processing"

"Obwohl Herings Vorstellungen stark vereinfachend waren, konnten diese drei Prozesse tatsächlich nachgewiesen werden. Seit 1966 bestätigen neurophysiologische Untersuchungsergebnisse, dass es vier grundlegende Farbempfindungen gibt."

"Dabei nimmt die periphere Zone der Sehzellen drei Signale auf. Diese Signale werden in der zentralen Zone, also im Nervensystem, in einem Prozess zu zwei gegensätzlichen Paaren von Grundfarben geformt."

"Ganglion cells represent a major output stage of the retina, transforming local retinal activity into action potentials that are transmitted through the optic nerve to higher visual centers"

"So entstehen, wie auch Hering postulierte, drei Empfindungsdimensionen: 1. Helligkeit, 2. Gelb-Blau-Komponente, 3. Rot-Grün-Komponente, aus denen dann mehrere tausend Farbarten unterschieden werden können."

"Da keine Farbe zugleich rötlich und grünlich oder gleichzeitig Gelb und Blau ist, nahm er komplementäre Wahrnehmungen an, in denen die Farbwahrnehmung aus einem Rot-Grün-, einem Gelb-Blau- und einem Schwarz-Weiß-Ablauf besteht."

"the colour of the blue sky under clear conditions"

"Scattering is given a wavelength (λ) dependence of λ −4 for air molecules (Rayleigh scattering), λ −1 for tropospheric aerosols, and λ +1 for volcanic aerosol particles."

"En el campo de la óptica realizó una serie de trabajos sobre la polarización de la luz, contribuyó a la teoría de la radiación del cuerpo negro y logró dar una explicación del color azul del cielo."

"λ −1 for tropospheric aerosols"

"にヘイズが濃くなるとB/R比は1.0に接近し，空は青"

"Fine particles are particularly important in total optical extinction because of their high mass scattering efficiency and absorption cross-sections."

"Atmospheric aerosols influence the global radiation balance by directly scattering and absorbing solar radiation."

"The results show that fine particles played important roles in controlling visibility in Tianjin."

"When the mass concentration of PM2.5 is constant, the larger the geometric mean of the particle diameter is, the larger the visibility is."

"The result shows that the higher PM2.5 concentration is，the more obvious the multiple scattering effect is."

"The average extinction coefficient and scattering coefficient of atmospheric aerosols were 0.253 1/km and 0.213 1/km in non-haze days, while 0.767 1/km and 0.665 1/km in haze days."

"Als Mie-Streuung oder auch Lorenz-Mie-Streuung (nach den Physikern Gustav Mie und Ludvig Lorenz ) bezeichnet man die elastische Streuung elektromagnetischer Wellen an sphärischen Objekten, deren Durchmesser in etwa der Wellenlänge der Strahlung entspricht."

"das Medium weißlich trüb erscheinen lassen, wenn sie größer sind."

"Near the horizon, light travels through more air and more particle‑filled layers, so additional Mie scattering from dust and pollution adds white light and makes the blue look paler and less saturated."

"Der Effekt ist allerdings selbst nicht für die blaue Farbe des Himmels verantwortlich."

"Above your head is roughly 8 miles of atmosphere, but when looking at the horizon, the light must travel through 100 miles or more of the atmosphere before reaching your eye."

"Looking toward the horizon means viewing through a longer path of air and more particle‑filled layers that contain dust, pollution, and droplets. These larger particles enhance Mie scattering, adding a whitish component that dilutes the intense blue sky."

"John William Strutt, 3. Baron Rayleigh , postulierte 1899 als erster, dass keine kolloiden Teilchen für das Blau des Himmels benötigt werden, dass vielmehr auch reine Luft die entsprechende Streuung, die nach ihm genannte Rayleigh-Streuung , verursacht."

"Mie scattering, by contrast, happens when the particles are similar in size to the wavelength of light, such as water droplets or particles from dust and pollution. These larger particles scatter all visible wavelengths more evenly, creating a whiter, more washed‑out appearance."

"Looking out at the horizon, that same sightline runs through many times more air and through the dustier, more humid layers near the ground, so Mie scattering and repeated Rayleigh scattering wash the blue out toward white."

"For fine-mode aerosol, on the other hand, the change of pattern is not sensitive to the absorbing property of aerosol."

"When coarse-mode aerosol changes from scattering to absorbing, the decreasing trend in the sky downward degree-of-linear-polarization largely slows down when aerosol optical depth increases."