Atmospheric Optics - DrPhysics · Atmospheric Optics Gabriel Lombardi presented at CPS-AAPT Meeting...
Transcript of Atmospheric Optics - DrPhysics · Atmospheric Optics Gabriel Lombardi presented at CPS-AAPT Meeting...
Atmospheric Optics
Gabriel Lombardi
presented atCPS-AAPT Meeting
Spring 2003
A selection of phenomena
• rainbows• halos• sunsets• sun pillars• the green flash• noctilucent & iridescent clouds• contrails / rocket trails
Causes
• refraction (rainbows, halos, green flash)• diffraction (iridescent clouds)• Rayleigh scattering (sunsets)• Mie scattering (noctilucent clouds)• reflection (sun pillars)
What color is the Sun?
yellow... orange?
Chromaticity
• CIE chromaticity diagram
• 5000-6000Kblackbody is white
http://casa.colorado.edu/~ajsh/colour/Tspectrum.html
The color of stars
http://www.physics.sfasu.edu/astro/color.html
http://casa.colorado.edu/~ajsh/colour/Tspectrum.html
A real picture
The Sun is white!
Sunset colors
B:G:R
0.16 : 0.90 : 1.0 0.16 : 0.62 : 1.0 0.16 : 0.37: 1.0 0 : 0.28: 1.0
Rayleigh scattering
k
E
• polarized• spectrally weighted to the blue• scattering from density fluctuations
I ~ !"4
0.2 0.4 1.0R:G:B
0.0 0.0 1.0R:G:B
Rainbows
• secondary bow (colors reversed)• brighter inside the primary• polarization
Rainbow theory
Isaac Newton, Opticks
primary
secondary
from Sun
Rainbow geometry
10
15
20
25
30
35
40
45
0.2 0.4 0.6 0.8 1
distance from axis
angle
distance
220 Halos
http://hyperphysics.phy-astr.gsu.edu/hbase/atmos/halo.htmlFred Kinley, personal communication
Hexagonal ice crystals
n=1.31
600
Deviation by a prism
20
25
30
35
40
45
0 20 40 60 80 100
incident angle
apex: 600
index: 1.31
220
Sun pillars
• reflection from planar ice crystals
Iridescent clouds
• uniform drop size (Mie scattering)• thin cloud (single scattering)
http://antwrp.gsfc.nasa.gov/apod/ap030311.html
Rocket trails
• altitude/reddening• shear
http://www.freqofnature.com/photos/mmiii/
Noctilucent geometry
! =D
R= 2
2h
R
D = 2Rh h
Pinatubo sunset
http://www.liathach.supanet.com/volcansun.html
• still glowing one hour after sunset• h~20 km
Green flash
http://www.intersoft.it/galaxlux/GreenFlashGallery.htm http://www.isc.tamu.edu/~astro/research/sandiego.html
Green flash geometry
http://hyperphysics.phy-astr.gsu.edu/hbase/atmos/redsun.html
Chinese lantern
Ed Ruf, personal communication