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8/2/2019 Glory- Phsics 32.1 Report
http://slidepdf.com/reader/full/glory-phsics-321-report 1/33
GloryAn optical phenomenon
Physics 32.1 Group Report
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What are ‗glories‘?
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Glory from the Airplane View–Houston, Texas
Taken by Jonathan Lansey
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Glory from the Airplane View 2
Taken by Nik Szymanek
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GloryoAn optical phenomenon which resembles an
iconic saint‘s halo
oA multicolored-light halo surrounding the
shadow (Nussenzveig, 2012)
oCan only be seen when the observer is directlyopposite between the sun and cloud of
refracting water droplets
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Brocken Spectre
• The shadow grotesquely distorted by perspective.
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Simulation of a Glory
oMie Scaterring Theory
Mathematical Theory of Diffraction by a Sphere (2 droplet)
Calculates the solution of infinite sum of terms called partial
waves
Not until 1990s this theory gives realistic results
Says Only what happens but not how
oPeter Debye
Reformulated Mie Theory To separate the contributions made by various scattering
processes
Goes far beyond the limitations of geometric optics
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Simulation of Glory caused by r=10µmdroplet
Left – Mie Theory, Right – Debeye Series
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How are glories formed?
oThe science of glories is still subject of
debates and researches.
oOver the centuries, physicists have offered
several explanations for glories that proved to
be incorrect
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In the beginning of 19th Century
oGerman Physicist Joseph von Fraunhofer
Sunlight is scattered – that is, reflected back – from
droplets deep within a cloud would be diffracted bydroplets at the outer layers
Double scattering colored diffraction rings
Like a corona
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In 1923…
oIndian Physicist B. B. Ray
Refuted Fraunhofer‘s proposal
After experimenting with artificial clouds
Glory rings have a distribution of brightness and colors
very different from those of coronas
They arise directly from the outer layers of a cloud, fromsingle backscattering by individual 2 droplets
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In the middle of 20th Century
• Hendrik C. van de Hulst
• A pioneer of modern radio astronomy
• Provided the 1st significant insight into the physicalexplanation of glories
• Pointed out that a light ray that entered a droplet
very close to the droplet‘s edge might follow a V -shaped trajectory inside the droplet, bouncing off at
the back, and return almost exactly in the same
direction that it came from.
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V-shaped trajectory
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However…
• As a light ray entered and exited, it would bend via
refraction
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Surface Wave
• Surface waves attached to an interface between two
different media arise in a variety of situations.
• The idea was that a tangentially incident ray would graze
the droplet, travel along its surface a short distance, thenpropagate through the droplet to its rear.
• There it would again travel along the surface and reflect
back through the droplet. A final passage along the surface
would send it on its way.
• The overall effect would be to scatter the ray back in the
same direction that it came from.
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Surface Wave
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But still…
o Surface waves lose energy by shedding radiation
tangentially
At the time when he propsed, no quantitative procedure to
evaluate the surface-wave contributions was available
o All the information about glories had to be implicitly
contained within the Mie partial-wave series
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A Different Perspective
oIn 1987, Warren Wiscombe and Herch Moysés
Nussenzveig
That light rays passing outside the sphere couldmake a significant contribution
HOW?
Light waves in particular — have the uncanny
ability of ―tunneling,‖ or jumping through a
barrier
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Tunneling
• Total Internal Reflection
• electric and magnetic fields that make up the light
waves do not drop completely to zero at the
interface
• Forming Evanescent Waves
• Makes the electromagnetic field near the surface vibrate in
place, like strings of guitar
• If, however, a third medium is placed within a short
distance of the boundary so that it overlaps with theevanescent waves, the waves can resume their outward
propagation in the third medium and thus siphon energy
away. TUNNELING
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Newton on Tunneling
• As far back as 1675
• He was investigating patterns of interference now known
as Newton‘s Rings
• By laying a convex lens on a flat glass plate
• He found out that even when an extremely narrow air gap
separated the surface of the lens from the plate, some light
that should have undergone total internal reflection jumped
across the gap instead.
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Quantum Mechanics
• Russian-born Physicist George Gamow
• explained how certain radioactive isotopes can emit
alpha particles
• Alpha particles should not have enough energy to
detach from a larger nucleus
•
But, he was able to demonstrate that alphaparticles can still tunnel through this energy gap
and escape.
• Because of their wavelike nature
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Mie Resonance
• Also called ‗Whispering Gallery Modes‘
• Dome of St. Paul‘s Cathedral in London
• a person who whispers facing the wall at one side can be heard
far away at the other side because the sound undergoes multiplereflections, bouncing around the curved walls.
• A tiny change in wavelength suffices to detune the
resonance so that Mie resonances are extremely sharp and
concentrated and yield large intensity enhancement
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Based on Nussenzveig…
• There are three potential effects contend for
primary contributors to the glory phenomenon:
I. Rays that hit the sphere
Ray‘s geometric -optic axial backscattering
II. Edge Rays
van de Hulst‘s Surface Waves
III. Mie Resonance
Tunneling of Light
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Lastly, Glories and Climate
• Study of Glories
• necessary for estimating the role of clouds will have
in climate change
• Will it —
• help keep the planet cool by reflecting more sunlight back
into space, or
• will it contribute to heating by acting as an additional
blanket to trap infrared radiation?
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