Storms :: essays research papers

If you know where and when to look, you cantreat yourself to a colourful display of atmospherichaloes, spots and pillars. These images can tell yousomething about the clouds crash and possiblechanges in the weather. All of these images arecreated by light shining through cirrostratus clouds.These clouds occur at an altitude of 6,000-12,000metres. They appear as a thin sheet or layer(strata) that is pure white. The layer of cloud is sothin (only 100-450 metres) that is doesnt obscurethe sunlight or moon, so you should be suitable to seeyour shadow. Cirrostratus is made of many typesof ice crystals. However, four crystal shapes areresponsible for producing most of the commonlysee haloes-plate crystals, columns, cappedcolumns and bullets. The most open-and-shut halo isfound around the sun. If the layer of cirrostratus isextensive, youll see an entire ring. Within the layerof cloud, sunlight is striking and passing throughthe sides of randomly-oriented ice crystals. As thesunlight passes through each crystal, the lightchanges direction, or refracts. The radius of thehale depends on the amount of change in thedirection of the suns light. Usually this is 22degrees. Since the sun is 1/2 of a degree across,the radius of the halo is 44 sun-widths.Occasionally you may see a second halo at 46degrees from the sun (that is, with a radius of 92sun-widths). This is produced by sunlight passingthrough both the side and bottom of each crystal.Moonlight will likewise produce a halo, around themoon, with the proper layer of cirrostatus.Another common optical effect is known as "mocksuns" or "sun dogs" or "parhelia" (Greek for "withthe sun"). These bright spots on either side of thesun, outside of the halo, occur when sunlightpasses through the sides of capped columns,bullets and plate crystals, when these crystals arearranged with their sides vertical. The crystalswobble, distribute and smearing the colours of themock sun. You can see haloe s and mock sunsmore clearly if you block out your view of the realsun by holding your hired hand in front of it at armslength. Another spectactular optical effect is thesolar pillar. This is a vertical shaft of light the samecolour as the sun stretching upwards from the sunand is most often seen at sunset or sunrise. Itsproduced by sunlight reflecting of the base of plateand capped column crystals in the clouds.