Post on 04-Jan-2016
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Pat Arnott, ATMS 749, UNR
HOW DO WE TALK ABOUT RADIATION IN THE
ATMOSPHERE?
Pat Arnott, ATMS 749, UNR
Relationship between Spherical and Cartesian Coordinates
Pat Arnott, ATMS 749, UNR
Solid Angle Definition
Pat Arnott, ATMS 749, UNR
Irradiance Definition
F = Irradiance, (also called flux or flux density), is the electromagnetic energy per unit time, per unit area, transported through dA, or deposited on dA. SI units are Watts/m2 when integrated over a distribution function F. (Example: solar flux at the TOA is 1360 W/m2.)
FMonochromatic Irradiance, SI units are W/m3.
Pat Arnott, ATMS 749, UNR
Monochromatic Radiance Definition
I = Monochromatic radiance, is the monochromatic irradiance (measured on a surface normal to the beam) per unit solid angle traveling in a particular direction.
This is the most fundamental measure we can use for radiation in the atmosphere.
Pat Arnott, ATMS 749, UNR
Irradiance - Radiance Relations
Upward irradiance.Note ESPECIALLY the cos term (that gets the normal component of radiance) and the sin term (that helps define the solid angle.)
Pat Arnott, ATMS 749, UNR
Irradiance - Radiance Relations
Special case: I isotropic, same in all directions, like black body radiation from a surface.
Pat Arnott, ATMS 749, UNR
BLACK BODY RADIATION AGAIN: RADIANCE
Note especially the units of radiance on the left.
Pat Arnott, ATMS 749, UNR
ASIDE: EMISSIVITY OF VARIOUS SUBSTANCES
Pat Arnott, ATMS 749, UNR
Irradiance - Radiance Relations
Downward irradiance
Pat Arnott, ATMS 749, UNR
THE BIG PICTURE: Radiation Heating of the Atmosphere
From Oort and Peixoto
Pat Arnott, ATMS 749, UNR
ATMOSPHERE HEATING BY RADIATION: The heating rate is the divergence of the net irradiance (or net flux if you prefer).
From Oort and Peixoto
Pat Arnott, ATMS 749, UNR
ATMOSPHERE HEATING BY RADIATION: The heating rate is the divergence of the net irradiance (or net flux if you prefer).
From Oort and Peixoto
Pat Arnott, ATMS 749, UNR
ATMOSPHERE HEATING BY RADIATION: The heating rate is the divergence of the net irradiance (or net flux if you prefer). This is
the figure caption for the heating rate calculation, and the reference.
2 problems:
1. Is the assumption of stratosphere radiative equilibrium good?
2. Is it correct to separate out the LW emission from components?
From Oort and Peixoto
Pat Arnott, ATMS 749, UNR
Sun and Satellite Perspective: How do the properties of the surface affect what we see?
Pat Arnott, ATMS 749, UNR
Radiance and Irradiance: How do we define radiation?
Types of reflection: Can also think of the reflected light as emitted light from different types of surfaces.
Pat Arnott, ATMS 749, UNR
Geometry for the BDRF (bidirectional reflection function)
ρ(θi,φi;θ f ,φ f ) ≡ BDRF =S0 cos(θi )
I ↑ (θr ,φr )for a clear day.
I ↑ (Ωru ruu) = ρ(
2π∫ Ωi
u ruu,Ωru ruu) I ↓ (Ωr
u ruu)n∑• Ωi dωi for a cloudy day.
S is solar irradiance coming in.
I is the reflected radiance.
Pat Arnott, ATMS 749, UNR
ENERGY BUDGET: 100% in, 100% out. What does it do along the way?
Pat Arnott, ATMS 749, UNR
ASIDE:COMPLEX
REFRACTIVE INDICES OF WATER AND
ICE.
Note that the author DID
NOT show that the real part of the refractive
index for ice at 2.85 microns is
less than 1!
n =c / vphase
vphase =c / n
c=light speed