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Continuous Refraction

Atmo II 116. Continuous Refraction.

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Continuous Refraction

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  1. Atmo II 116 Continuous Refraction Under favorable conditions (here cold air over the Mediterranean in winter) continuous refraction allows to see objects, which are way too far to bee seen geometrically – here Mt. Canigou in the Pyrenees in ~250 km distance from Marseille (credit: J.-F. Coliac).

  2. Atmo II 117 Mock Mirage An observer right above an inversion layer may see a mock mirage (illustration: Les Cowley) resulting in a “mushroom sunset” (photos: Oscar Blanco).

  3. Atmo II 118 Earth Shadow If we turn around after a beautiful sunset, we may see the Earth shadow rising. The characteristic blue tone is caused by absorption in the ozone layer. Above we san see the pink anti-twilight arch(„Gegendämmerung“) – also known as “Belt of Venus”. The pink color is a result of mixing back-scattered red sunlight (sunset) with blue skylight (photo: Marko Riikonen, illustration: Les Cowley).

  4. Atmo II 119 Anti-Twilight Arch The „Belt of Venus“ above Dachstein (UF).

  5. Atmo II 120 Shadow Games “Sun rays” or crepuscular rays are nicely visible when there are gaps in the cloud cover. The (almost) parallel sun rays just appear to diverge because of the perspective – just like rail tracks – or trees (UF).

  6. Atmo II 121 Cloud Shadows It seems credible the crepuscular ray gave our ancestors the inspiration to build pyramids (credit: Greg Parker). If we turn around …

  7. Atmo II 122 Cloud Shadows … we will likely see anti-crepuscular rays, which seem to converge at the horizon (credit: John Britton).

  8. Atmo II 123 Mountain Shadows Mountain shadows appear always triangular – even more if the mountain is cone-shaped – like the volcano Nevado Sajama (credit: George Steinmetz).

  9. Atmo II 124 Mountain Shadows David Harrington Michael Onnelly Mauna Kea on Hawaii is a good (and easy to reach) observation point for mountain shadows. If the moon is visible it has to be full moon. If this does not seem to be the case (left) this is caused by a lunar eclipse. Alex Mukensnable

  10. Atmo II 125 Mountain Shadows Mt. Rainier casts a shadow on the bottom side of altocumulus clouds (credit: Sally Budack).

  11. Atmo II 126 Rainbows Rainbows are caused by (double) refraction at the surface and reflection. On the backside of spherical raindrops. This can happen under different angles, but there is a maximum angle of 42° (Caspar David Friedrich, C. D. Ahrens).

  12. Atmo II 127 Rainbows Snell's Law (nAir = 1) G.H. Liljequist Minimum Angle

  13. Atmo II 128 Rainbows Les Cowley

  14. Atmo II 129 The Colors of the Rainbow The refraction of violet light (n = 1.3435) is stronger than that of red light (n = 1.3318), leading to a color separation (photo: Steve Crowe, illustrations: wikimedia, C.D. Ahrens).

  15. Atmo II 130 Double Rainbow A second rainbow appears (at an angle of ~ 51°), when the light is reflected twice inside the raindrop. Note the reversedorder of the colors and Alexander’s dark band in between (credit: Kimberly Perez, wikimedia).

  16. Atmo II 131 Supernumerary Rainbows There seem to be too many bows – “Supernumerary Rainbows”. They are caused by interference– an they provided a first hint that light can act like a wave (credit: Verena Tiessen) (small, same-sized raindrops).

  17. Atmo II 132 Rainbows for Advanced Students Additional rainbows caused by reflection (Terje O. Nordvik, Les Cowley).

  18. Atmo II 133 Rainbows for Advanced Students Twinned rainbows are (most likely) caused by non-spherical, large raindrops (photo: Benjamin Kühne, simulation: Les Cowley).

  19. Atmo II 134 Complete Rainbows From the right (elevated) observation point you may see a complete rainbow (credit: S.S. Matthiasson (l.), I. Parker, T. Gamache (inset)). But where is the treasure?

  20. Atmo II 135 Fogbows Fogbows are formed in a similar way – but at (much smaller) fog (cloud) droplets. They are lacking the brilliant colors, but in the center we see a new phenomenon (credit: Mila Zinkova).

  21. Atmo II 136 Brocken Spectre From above a cloud you may see your own shadow (at the anti-solar point) as “Brocken Spectre“, surrounded by a glory (credit: Hannes Pichler). For the explanation we (would) need Mie scattering and wave optics (diffraction and interference).

  22. Atmo II 137 Brocken Spectre and Glory The phenomenon is named after Brocken, the highest elevation in the Harz mountain range, where it can be frequently observed. Glories and “Brocken Spectre“ are often observed from aircrafts (credit: Rick Stanciewicz, Franz Kerschbaum). [These are not rainbows (google 360° rainbow images)]

  23. Atmo II 138 Glory Each observer will see a glory around its own head – and no glories around those of others (photo: Neil Adams). The formation of glories is still not entirely understood. 180° retro-reclection can only be explained with surface waves (Les Cowley).

  24. Atmo II 139 Ice Halos Halos (here with the sun almost in zenith) are caused by refraction in hexagonal ice crystals, where the ice crystals act like prisms (UF).

  25. Atmo II 140 Ice Halos The 22° Halo can be frequently observed (in the presences of cirrostratus clouds) (photo: UF, illustration: C. Donald Ahrens).

  26. Atmo II 141 Halos and Parhelia Hexagonal plate shaped ice crystals tend to be horizontally oriented, they produce parhelia(„Nebensonnen“), which are aslo known as sundogs (photo: Andrea Steiner, illustration: C. Donald Ahrens).

  27. Atmo II 142 Halos and Parhelia Horizontally oriented hexagons produce parhelia,poorly oriented hexagons the rest of the 22° halo. 22° is the minimum deviation angle (credit: Les Cowley).

  28. Atmo II 143 Parhelia Jerry Walter

  29. Atmo II 144 Halos and more Here we can see many phenomena, which can be caused by refraction and reflection at/in ice crystals (credit: Jay Brazell).

  30. Atmo II 145 Frequent Halos Les Cowley

  31. Atmo II 146 Parhelic Circle Parhelic circles are caused by (multiple) internal reflection on (near) vertical faces of ice crystals (credit: Koby Harati).

  32. Atmo II 147 Moondogs While sun dogs can be quite often observed (left, David Wigglesworth), moondogs (paraselenae) are very elusive (David Cartier).

  33. Atmo II 148 Moondogs Halo, moondogs and tangent arcs during the polar night by Fridtjof Nansen (thanks to Georg Buchner).

  34. Atmo II 149 Pillars Sun pillars are created by reflection on tilted ice crystals (photos: J. Kirkpatrick, P. Sears, illustr.: Les Cowley) (see also right photo on slide 144).

  35. Antihelic Point Atmo II 150 Multiple Halos Diamond dust (here at the South Pole) creates particularly beautiful halos – even in anti-solar direction (photos: Marko Riikonen).

  36. Atmo II 151 Multiple Halos Halos produced by poorly oriented crystals (left) and by oriented plates crystals (right, photos: Marko Riikonen, illustration: Les Cowley).

  37. Atmo II 152 Multiple Halos Halos produced by oriented columnarcrystals (left) and by (even) parry-oriented ones – upper and lower prism sides are horizontal (right, photos: Marko Riikonen, illustrations: Les Cowley).

  38. Atmo II 153 Seven Suns? Around noon on January 24, 1630, seven suns seemed to shine over Rome (of course being regarded as celestial omen). The record by the Jesuit scholar Christoph Scheiner helped to inspire Christiaan Huygens to develop the first theories of how such 'halo effects' are formed (credit: Herzog August Bibliothek Wolfenbüttel).

  39. Atmo II 154 Haloson other Worlds Les Cowley On Mars, Jupiter and Saturn we could observe other phenomena. Octahedral crystals can cause four sundogs (simulations: Les Cowley).

  40. Atmo II 155 Corona A corona is caused through diffraction by small particles– usually by cloud droplets (above, credit: Martin Dietzel), but some-times by (opaque !) pollen grains (right, P.-M. Heden) – “reflecting” even their shape.

  41. Atmo II 156 Aurorae Northern (southern) lights are certainly beyond the realm of meteorology www.northern-lights.no

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