Glory- Phsics 32.1 Report

8/2/2019 Glory- Phsics 32.1 Report

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GloryAn optical phenomenon

Physics 32.1 Group Report



What are ‗glories‘?



















Glory from the Airplane View–Houston, Texas

Taken by Jonathan Lansey



Glory from the Airplane View 2

Taken by Nik Szymanek



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



Brocken Spectre

• The shadow grotesquely distorted by perspective.



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



Simulation of Glory caused by r=10µmdroplet

Left – Mie Theory, Right – Debeye Series



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



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



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



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.



V-shaped trajectory



However…

• As a light ray entered and exited, it would bend via

refraction



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.



Surface Wave



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



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



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



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.



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



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



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



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?



END.

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Glory- Phsics 32.1 Report