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Atmospheric Optics/Ice Halos

Atmospheric Optics/Ice Halos. What is atmospheric optics?. Eric West PH 464. What are ice halos comprised of?. Incoming light Ice crystals Light refraction. Ice crystals. Hexagonal shape Behave like jewels Identical interfacial angles

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Atmospheric Optics/Ice Halos

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  1. Atmospheric Optics/Ice Halos • What is atmospheric optics? Eric West PH 464

  2. What are ice halos comprised of? • Incoming light • Ice crystals • Light refraction

  3. Ice crystals • Hexagonal shape • Behave like jewels • Identical interfacial angles • Deep crystalline order at a molecular scale gives symmetry

  4. Crystal environment • High atmosphere location • Cirrus clouds • Supercooled water droplets • Slow drifting • Alignment

  5. Crystal size • .05mm to .1mm • Diffraction happens when <.01mm • Larger crystals have weak optical quality • .1mm or greater gives sharp image

  6. Refraction • Crystals act like prisms • 2 refractions • Angle of minimum deviation

  7. 22 degree halo • 22 to 50 degrees • Most are close to 22 and bright • Approximate alignment • Strong deviation produces outer edge • Hole in the sky • Red refracts less • Halo image is unique

  8. Sun dogs (parahelia) • Position of sun • 22 degree • Horizontal crystals • Refraction of color by different amount

  9. Tangent arcs • Location to halo • Column crystals horizontal • Red inner edge • >29 degrees makes circumscribed

  10. Circumzenithal arc • Oriented plate crystals • Downward sun rays • Refraction of rays parallel to side face • Sun higher than 33 is reflected internally

  11. Parahelic circle • Reflection of crystals • Vertical position • Many ray paths • No net refraction

  12. Facts • Use your hand • Shield the sun • Cirrostratus • Same diameter • Not weather telling

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