Toni atmosphere L7 Flashcards
(21 cards)
What is Csca and what does this tell us
the scattering cross section - Csca tells us how much light a particle scatters
how do we calculate the scattering cross section
Csca = Wsca/ Ii
W - scattered intensity
Ii -incident light intensity (W/m2)
What is Cabs and what does this tell us
Cabs is the absorption cross section - tells you how much light a particle absorbes
How do we calculate absorption cross section
Cabs = Wabs/ Ii
Wabs - absorbed intensity
Ii - incident light intensity
What is Cext and what does this tell us
extinction cross section/total extinction tells you how much light is lost overall by both scattering and absorption
How do we calculate Cext
total extinction is the sum of the scattering and the absorption
Cext = Cabs + Csca
What is the optical cross section
the optical cross section can be thought as the cross section of the shadow cast by the object when illuminated.
What do efficiencies tell us
Tells us how good the particle is at blocking light
Define extinction efficiency
Extinction efficiency is a measure of how effectively a particle blocks or reduces the intensity of light through both scattering and absorption.
How do we calculate the extinction efficiency
Qext = Cext/σgeom
Cext - extinction cross section
σ Geom - geometric cross section
What do we expect the extinction efficiency to be
to be equal to 1
What does it mean if Qext = 1
If Qext = 1, the particle blocks exactly as much light as its size suggests.
What does it mean if Qext>1
the particle is more effective at removing light than expected – this is part of the extinction paradox.
What is the extinction paradox
The value of 2 is the maximum limiting value of extinction efficiency, the particle is able to absorb/scatter more light than is geometrically incident upon it
Describe how we get values of Qext above 1
due to diffraction effects even if light doesn’t hit a particle it can still be affected by the particle’s presence. The diffracted light is redirected away from the beams direction removing it from the path.Diffraction contributes to light be redirected, increasing extinction
Define diffraction
diffraction is when light bends around the edges of object instead of going straight
What do the broad oscillations in Qext arise from
arise from interference with light passing around the edges of the particle out of phase with light passing through the particle
What are finer modulations in Qext referred to
ripple structures
What are ripple structures and when do they occur
Ripple structure occurs at discrete
size parameters, where combination of wavelength and radius lead to a standing wave within the droplet.
How do rainbows form
Light enters the raindrop and bends because it slows down.This bending separates the light into different colors like a prism. Inside the Drop
The light bounces off the back of the raindrop. Leaving the
The light bends again as it leaves the drop, spreading out even more.
What is the difference between geometric size and optical size
geometric size, the actual radius or area of the particle.
Optical size, how much light the particle appears to interact with, can be larger than geometric size due to wave effects
