1. Atmospheric Optics/Ice Halos
What is atmospheric optics?
Eric West PH 464
11/15/2018

2. What are ice halos comprised of?
Incoming light
Ice crystals
Light refraction
11/15/2018

3. Ice crystals Hexagonal shape Behave like jewels
Identical interfacial angles
Deep crystalline order at a molecular scale gives symmetry
11/15/2018

4. Crystal environment High atmosphere location Cirrus clouds
Supercooled water droplets
Slow drifting
Alignment
11/15/2018

5. Crystal size .05mm to .1mm Diffraction happens when <.01mm
Larger crystals have weak optical quality
.1mm or greater gives sharp image
11/15/2018

6. 11/15/2018

7. Refraction Crystals act like prisms 2 refractions
Angle of minimum deviation
11/15/2018

8. 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
11/15/2018

9. Sun dogs (parahelia) Position of sun 22 degree Horizontal crystals
Refraction of color by different amount
11/15/2018

10. Tangent arcs Location to halo Column crystals horizontal
Red inner edge
>29 degrees makes circumscribed
11/15/2018

11. Circumzenithal arc Oriented plate crystals Downward sun rays
Refraction of rays parallel to side face
Sun higher than 33 is reflected internally
11/15/2018

12. Parahelic circle Reflection of crystals Vertical position
Many ray paths
No net refraction
11/15/2018

13. Facts Use your hand Shield the sun Cirrostratus Same diameter
Not weather telling
11/15/2018

14. 11/15/2018