| 词条 | 46° halo |
| 释义 |
A 46° halo is a rare member of the family of ice crystal halos, appearing as a large ring centred on the Sun at roughly twice the distance as the much more common 22° halo. At solar elevations between 15–27°, the 46° halo is often confused with the less rare and more colourful supralateral and infralateral arcs, which cross the parhelic circle at about 46° to the left and right of the sun.[1] The 46° halo is similar to, but much larger and fainter than the more common 22° halo. It forms when sunlight enters randomly oriented hexagonal ice crystals through a prism face and exits through a hexagonal base.[2] The 90° inclination between the two faces of the crystals causes the colours of the 46° halo to be more widely dispersed than those of the 22° halo. In addition, as a lot of rays are deflected at larger angles than the angle of minimum deviation, the outer edge of the halo is more diffuse.[3] To tell the difference between a 46° halo and the infra-/supralateral arcs, one should carefully observe sun elevation and the fluctuating shapes and orientations of the arcs. The supralateral arc always touches the circumzenithal arc, while the 46° halo only achieves this when the sun is located 15–27° over the horizon, leaving a gap between the two at other elevations. In contrast, supralateral arcs cannot form when the Sun is over 32°, so a halo in the 46°-region is always a 46° halo at higher elevations. If the Sun is near the zenith, however, circumhorizontal or infralateral arcs are located 46° under the Sun and can be confused with the 46° halo. [4][5]References1. ^The 46° halo was first explained as being caused by refractions through ice crystals in 1679 by the French physicist Edmé Mariotte (1620–1684). See: Mariotte, Quatrieme Essay. De la Nature des Couleur (Paris, France: Estienne Michallet, 1681). Sun dogs as well as the 22° and 46° halos are explained in terms of refractions from ice crystals on [https://books.google.com/books?id=y10O12JjHskC&pg=PA466#v=onepage&q&f=false pages 466 - 524]. 2. ^{{cite web | url = http://www.meteoros.de/arten/ee12e.htm | title = 46°-halo | publisher = Arbeitskreis Meteore e.V. | accessdate = 2007-04-16 | archiveurl= https://web.archive.org/web/20070331081342/http://www.meteoros.de/arten/ee12e.htm| archivedate= 31 March 2007 | deadurl= no}} 3. ^{{cite web | url = http://www.atoptics.co.uk/halo/46form.htm | title = 46° Halo Formation | publisher = Atmospheric Optics | accessdate = 2007-04-16 | author = Les Cowley (?)}} (including an illustration and an animation) 4. ^{{cite web | url = http://www.atoptics.co.uk/halo/46orsup.htm | title = Is it a 46° halo or a supra/infralateral arc? | publisher = Atmospheric Optics | accessdate = 2007-04-16 | author = Les Cowley (?)}} 5. ^{{cite web | url = http://www.meteoros.de/arten/ee21e.htm | title = Supralateral arc | publisher = Arbeitskreis Meteore e.V. | accessdate = 2007-04-16 }} External links
1 : Atmospheric optical phenomena |
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