atmospheric radiative transfer phys 721 “the ocean sunglint in a dusty/polluted day” picture by...
TRANSCRIPT
Atmospheric Radiative Transfer
PHYS 721
“The ocean sunglint in a dusty/polluted day”Picture by Yoram J. Kaufman
http://userpages.umbc.edu/~martins/PHYS721/
- Motivation, applications and issues
- Definitions and Radiation Quantities
- Thermal Emission/Absorption Basics
- Solar and Terrestrial Spectra
- From Single to Multiple Scattering
- The Radiative Transfer Equations – Theory and Solution Methods
- Absorption and Emission by Gas Molecules
- Radiation and Climate Issues
Frequency (=/2)Wavelength (=c/)
The EM spectrum
Our domain of interest
Two important BB lawsWien’s law: Wavelength (frequency, etc.) of maximum emission:
max(µm)≈3000/T
Location of maximun depends on representation (see solved problem at end of notes). Equal wavelength intervals do not correspond to equal frequency intervals:
Stefan-Boltzmann law: Total (wavelength-integrated) emitted flux: FBB=BT4
2 1 c1 2
12
You’ll often see normalized plots of the Planck function (see also last solved problem of the notes)
Normalization of Planck functions
Results from the TSI instrument on Sorce
1357
W/m
2
1362
2003 2007
2007
TSISORCE
Special Note on TIM TSI Data• The TIM's measured value of TSI at 1 AU is lower than that reported by other TSI-
measuring instruments; an upcoming solar minimum value of 1361 W/m2 is estimated from the current TIM data. This is due to unresolved differences between TSI instruments. The TIM measures TSI values 4.7 W/m2 lower than the VIRGO and 5.1 W/m2 lower than ACRIM III.
• This difference exceeds the ~0.1% stated uncertainties on both the ACRIM and VIRGO instruments. Differences between the various data sets are solely instrumental and will only be resolved by careful and detailed analyses of each instrument's uncertainty budget. We report only the TSI measurements from the TIM, and make no attempt to adjust these to other TSI data records.
• The TIM TSI data available are based on fundamental ground calibrations done at CU/LASP, NIST, and NASA. On-orbit calibrations measure the effects of background thermal emission, instrument sensitivity changes, and electronic gain. The TIM TSI data products have been corrected for instrument sensitivity and degradation, background thermal emission, instrument position and velocity, and electronic gain. The TIM relies on several component-level calibrations, as no calibration source or detector is available with the level of accuracy desired for this instrument -- a level of accuracy nearly 10 times better than that previously attempted for space-based radiometry.
Solar Spectrum at different levels:
http://lasp.colorado.edu/sorce/instruments/sim/sim_science.htm
Interactions between Aerosols and Molecules with Radiation:
(a) Black Body
Curves
(m)
Aerosol Extinction Coef.
(m-1)
5780 K 255 K
N O R M A LI
Z A D F L u X
A B S O R P
T
I O N
%Large Aerosols
Small Aerosols
Absorption spectra of atmospheric gases
CH4
CO2
N2O
H2O
O2 & O3
atmosphere
AB
SO
RPTIV
ITY
WAVELENGTH (micrometers)IR Windows
InfraredVisible
UV
H2O dominates >15 µm
Average Solar Radiation intercepted by Earth and Distributed over its Surface
Surf
ace
Are
a 4
R2
Sola
r Con
stan
tSo
RA
rea
Inte
rcep
ting
Sola
r
Rad
iatio
n =
R
2
R2So = 4R2<So>
<So> = So/4
Simple Climate Model: Earth as a Black Body and no Atmosphere
<So>In equilibrium·Te
4 = <So>
Te = +5.8oC
All the solar radiation is absorbed and re-emitted by the surface
So = 1370W/m2
<So> = So/4 = 342.5W/m2
= 5.669x10-4Wm-2deg-4
<So>
A·<So>
In equilibrium·Te4 = (1-A) ·<So>
(1-A)<So>
(1-A)<So>
A=0.3
Simple Climate Model: Earth with Albedo = 0.3 and no Atmosphere
Te = -17oC
Simple Climate Model: Earth with Atmosphere and Albedo = 0.3
So
A·<So>
In equilibrium·Te4 = 2·(1-A) ·<So>
Absorption and emission in the atmosphere: greenhouse gases, clouds, aerosols…
Atmospheric Scattering: Molecules, aerosols, clouds, and surface.
(1-A)<So>
(1-A)<So>
(1-A)<So>
A=0.3
Te = +30oC
ATOA < ASUP
Warming
AEROSOL plus Surface Albedo Effect
ATOA = ASUP
Balance
ATOA > ASUP
CoolingLarge contrast in radiative forcing due to the combination of surface
and aerosol properties
Smoke – Instantaneous Direct Radiative Forcing over Varying Surface Albedo (Cuiaba – Brazil) for = 1
Rparticles = RSUP
Balance between
Absorption and Scattering
Rparticles << RSUP
Surface Darkening or
Warming
Rparticles > RSUP
Surface Brightening or Cooling
Large contrast in radiative forcing due to the combination of surface
and aerosol properties
Smoke – Instantaneous Direct Radiative Forcing over Varying Surface Albedo (Cuiaba – Brazil) for = 1
AEROSOL plus Surface Albedo Effect
AEROSOL DIRECT RADIATIVE FORCING
Rparticles = RSUP
Balance between
Absorption and Scattering
Rparticles << RSUP
Surface Darkening or
Warming
Rparticles > RSUP
Surface Brightening or Cooling
Large contrast in radiative forcing due to the combination of surface
and aerosol properties
Smoke – Instantaneous Direct Radiative Forcing over Varying Surface Albedo (Cuiaba – Brazil) for = 1
+10
-95
W/m
2
• Hansen, 2000: Separation of the BC forcing from other aerosol types
• Jacobson, 2001 - Radiative Forcing:
BC = +0.55 Wm2
CH4 = +0.47 Wm2
CO2 = +1.56 Wm2
Andreae, 2001: 1/3 of carbon-cycle resources should go to Black Carbon studies
“The Dark Side of Aerosols”
(Andreae, A. 2001)
or The Dark Side of the Aerosol Forcing
Aerosols containing black carbon
Aerosols not containing black
carbon
Hansen et al. [2000]
50 yrs climate change scenario
