Atmospheric Radiation

1
Atmospheric Radiation

• Jack McConnell
• York University

2
Atmospheric Radiation

• Introduction Sun and other stuff
• Radiative Transfer Equation
• Scattering
• Heating
• J Values
• Remote Sensing

3
Introduction

• The Sun
• Radius about 700,000 km
• 0.5 degree in sky
• Ordinary late type star similar in properties (in
  gross sense) to Planck body
• T of photosphere 5700 K
• Energy flux at 1 AU of E? 1.38 kJ/m2/s1

4
Introduction ctd

• Solar Stability
• Sunspots with 11 year variability
• Total output varies by lt 0.1 (over 20 years)
• Early stellar energy is about 70 of current
• X-rays changes x100s
• EUV 3-4 times solar min-max
• 200 nm lt3

5
Introduction ctd

• Top left Shape of solar spectrum showing
  similarity to Planck spectrum of 5700K.
  Fraunhoffer lines are not shown. Note non-thermal
  nature of spectrum in the sub-UV and supra-IR
  range.
• Right panel - 300 years of sunspot data

6
Radiation ERBE Albedo average and clear sky

• (a) Top panel
• albedo for solar radiation for average January
  conditions
• (b) Bottom Panel
• Clear sky albedo for January conditions
• (b) Low ocean albedo, (a) cloud over ocean (a, b)
  high albedo over desert (a) ITCZ
• Atlas of satellite observations related to global
  change, Edited by R.J.Gurney, J.L. Foster and
  C.L. Parkinson, CUP, 1003.

7
Effective Temperature, Teff and Greenhouse

• If we estimate the temperature of the Earth
  required to balance the incoming radiation we
  find that the energy captured by the Earth is
  that due to a circle which is a projected sphere.
  Of the energy intercepted only (1-A) is absorbed
  so the global heating may be written
• ?R2(1-A)E?
• where A is the albedo and R is the radius of
  the Earth
• while the Earth cools over the surface of a
  sphere
• 4?R2 ?T_eff4
• Thus the effective Temperature, T_eff is given by
  
• T_eff ((1-A)
  E? /4 ?)0.25
• For A 0.3, T_eff 255 K or -18C. Now the
  global average surface temperature is 288 K or
  15C so that we have a 33 C difference which is
  due to the greenhouse effect.
• Also using the global average lapse rate of
  6.5C/km (define) we find that the atmosphere is
  radiating from about 5 km

8
Atmospheric Radiation

• Light Electromagnetic Radiation
• Waves, photons IR, visible (0.4-0.7?m) , UV,
  etc
• c wavelengthfrequency ??
• E h? where h 6.626E-34 Js Plancks
  constant
• Can be polarized
• Characterized by Stokes Parameters
• Interacts with objects for which there is an
  associated cross section determined by quantum
  mechanics (geometrical optics)

9
Atmospheric Radiation

• Sunlight is unpolarized
• Interaction with gases and aerosols often results
  in polarization (Important for instruments as
  skylight is polarized)
• Most work assumes that light is unpolarized
• Deal with spherical body
• Single phase function for scattering as opposed
  to matrix

10
Atmospheric Radiation

• 6000 K Solar radiation enters the Earths
  atmosphere
• Scatters
• absorbed
• Extinction scattering absorption
• Molecules, droplets (cloud, rain, aerosols)
• Transformed to 300 K IR

11
Cross sections

• EM Cross section, Q?, determined by wavelength of
  light, ?, and object dimension, r, and whether or
  not a resonance exists
• For visible light (0.5 µm) ? r
• 1 µm object has Q? approx geometrical ie pr2
• Mie Scattering
• Smaller objects
• Light frequency ? c/? 3e10/0.5e-4 6e14s-1
• Atomic frequency
• ? v/r 2e8/1e-8 cm/s 2e16 s-1
• Atom sees a stationary polarization field and
  classical EM theory predicts a 1/?4 wavelength
  dependence

12
Cross sections ctd

• Rayleigh scattering is 1/?4 wavelength
  dependence
• 0.5 µm Q?(air)6e-27 cm2
• Efficiency Q?(air)/(pr2) 1e-11
• In air column /cm2
• Number of molecules P/mg 2.5e25/cm2
• EM (0.5 µm) area of air molecules/cm2 0.15

13
Cross sections

• Absorption and Emission (gases and solids)
• The absorption cross sections of gases and solids
  determined by their electronic structure which
  is, in turn, constrained by quantum mechanics.
  There are 3 major types of emission and
  absorption lines
• electronic - energies of order a few eV - UV
• vibrational - energies of order 0.1 eV- mid-IR
• rotational - energies of order 0.01 eV - far-IR
• Continuum
• We will return to this

14
(No Transcript)
15
(No Transcript)
16
(No Transcript)
17
(No Transcript)
18
(No Transcript)
19
(No Transcript)
20
(No Transcript)
21
Changing atmospheric composition
22
Radiative Transfer Equation

• Preliminaries
• Solid angle
• Extinction scattering absorption
• Phase function
• Cross sections
• Emission

23
dOdS/r2 solid angle
24
Radiance, L (photons cm-2/s/v/st) wrt normal
surface
25
(No Transcript)
26
(No Transcript)
27
Phase functions
28
Phase functions
29
Phase functions
30
Scattering efficiency Q(?)/pr2
31
in LTE with no scattering
emission
extinction
scattering
Components of radiative transfer equation
32
kv av sv Q?/m
Single scattering albedo

Fraction absorbed per scattering
Radiative Transfer equation
33
(No Transcript)
34
Upward and downward fluxes
Net Flux of energy
Optical depth EM area/unit area
35
Up/downward fluxes
Band transmission
Heating Rate
36
Solution Methods
37
Methods for scattering

• Solve for radiance or flux
• Discrete ordinate method (several types)
• Radiance field is approximated as stream
• 2 stream, 4 stream etc
• Delta-Eddington approximation for particles
• Doubling and adding
• Montecarlo
• Treatments
• Plane parallel, spherical, pseudo-spherical

38
Single scattering to calculate transmission and
reflection operators
39
Layer adding to form new operators
40
(No Transcript)
41
(No Transcript)
42
Atmospheric Transmissionsolar and IR
43
Transmission of solar and IR radiation

• Left top panel uppermost section shows the
  relative distribution of solar and terrestrial
  radiation bottom section shows transmission
  throughout this region at the surface Middle
  section shows transmission at 11 km where there
  is much less water.
• Bottom left panel height where solar radiation
  if reduced by a factor of 2.718 by absorption of
  molecules of N2, O2, O and ozone. Note that the
  flux of high energy radiation is reduced for
  wavelengths shorter than 0.3 micrometres.

44
(No Transcript)
45
(No Transcript)
46
(No Transcript)
47
Molecular Cross-sections and Transmission
48
(No Transcript)
49
(No Transcript)
50
(No Transcript)
51
O2 O.2 µm
52
CH4 3.4 µm
53
N2O 7.8 µm
54
CO 4.67 µm
55
CO2 12.64 µm
56
H2O 14.9 µm
57
O3 9.61µm
58
(No Transcript)
59
(No Transcript)
60
(No Transcript)
61
(No Transcript)
62
(No Transcript)
63
(No Transcript)
64
Solution Methods

• LBL line by line
• Band models
• Goody, Elasser, random, etc
• Correlation-K
• Problems
• Accuracy with speed
• Computational overhead for 3D models
• Overlapping lines
• Line shapes not well determined

65
(No Transcript)
66
(No Transcript)
67
(No Transcript)
68
(No Transcript)
69
(No Transcript)
70
(No Transcript)
71
Non-LTE
Level 1 collisions Level 0
Spontaneous Emission, A (s-1)
Absorption
KqM A(sec-1)
72
(No Transcript)
73
Non-LTE source Function/B
74
(No Transcript)
75
Global Heating Rates
76
(No Transcript)
77
Globally Averaged Solar and Terrestrial Radiation
Budget (ctd)

• This figure (PO) shows the solar (SW) and mid-IR
  heating (LW) of the troposphere and stratosphere.
• In the stratosphere ozone solar heating is
  balanced by mid-IR CO2 cooling.
• In the troposphere the net effect is cooling
  everywhere (mostly) by H2O.
• What heating process balances the IR cooling?

78
(No Transcript)
79
(No Transcript)
80
(No Transcript)
81
(No Transcript)
82
Basic Radiative Balance
SW

• LW

Net
83
Different Models

• Fig 4

84
Longwave Cooling
O3 9.6mm
Rotation
Continuum
Pressure (hPa)
CO2 15mm
Wavenumber

• Brindley Harries 1998 (SPARC 2000)

85
IR Gas Contributions

• Fig 3C

86
Globally Averaged Solar and Terrestrial Radiation
Budget (ctd)

• The top panel (from PO) gives the net heating
  due to several processes as a function of height
  and latitude - note that there is heating in the
  tropics and cooling at higher latitudes
• The 3 panels below give the details
• (b) mid-IR cooling which is fairly uniform as a
  function of latitude
• (c ) heating due to latent heat release, ie due
  to condensation of the water vapour evaporated
  from the surface.
• (d) heating extracted from the surface by winds

87
(No Transcript)
88
(No Transcript)
89
(No Transcript)
90
(No Transcript)
91
(No Transcript)
92
Photolysis Rates

• J values

93
in LTE no scattering
emission
extinction
scattering
Components of radiative transfer equation
94
Convolution of flux and cross sections
modulated by the optical depth
No surface albedo
95
J values ctd

• Scattering enhances the photon density
• Main absorbers in clear sky are O2 and O3
• Cloudiness is very important
• Enhances scattering and absorption
• Potentially up to a factor of three enhancement
  due to clouds.
• Multiple scattering off and in clouds can enhance
  J values by up to a factor of 5
• With surface visible J J(0)(1 2Aµ)
• Incoherent scatter of resonance lines with
  optical depths of 1E6 (OI(1304)) can have much
  larger enhancements

96
J values ctd

• In Chemistry continuity equation, species, n
  satisfies
• dn/dt - Jn (cm-3 s-1)
• and
• n(t) n(o)exp(-t/tchem)
• Thus
• tchem 1/J
• gives a characteristic time constant for
  destruction

97
Radiation ERBE Albedo average and clear sky

• (a) Top panel
• albedo for solar radiation for average January
  conditions
• (b) Bottom Panel
• Clear sky albedo for January conditions
• (b) Low ocean albedo, (a) cloud over ocean (a, b)
  high albedo over desert (a) ITCZ
• Atlas of satellite observations related to global
  change, Edited by R.J.Gurney, J.L. Foster and
  C.L. Parkinson, CUP, 1003.

98
(No Transcript)
99
(No Transcript)
100
O1D quantum Yield
101
(No Transcript)
102
(No Transcript)
103
(No Transcript)
104
(No Transcript)
105
(No Transcript)
106
(No Transcript)
107
(No Transcript)
108
(No Transcript)
109
For Schumann-Runge (1,0) band compare Monte
Carlo (solid lines) with UCI standard J-code
(dashed) (pseudo-spherical plane parallel)
direct sunlight
scattered only
110
Also inferred J-Cl2O2 Avallone LM, Toohey DW,
Tests of halogen photochemistry using in situ
measurements of ClO and BrO in the lower polar
stratosphere, JGR 106 (D10) 10411-10421 MAY 27
2001
111
(No Transcript)
112
Applications to remote Sensing
113
Remote sensing

• Passive and active
• Passive
• Nadir viewing (MOPITT), GOME, etc
• Limb viewing, HIRDLS,
• Light source as probe
• Occultation (sun or star or car headlight etc)
  HALOE, ATMOS, ACE
• Emission of atmosphere, MOPITT
• Scattering from atmosphere (OSIRIS)

114
(No Transcript)
115
in LTE no scattering
emission
extinction
scattering
Components of radiative transfer equation
116

occultation
117
Emission
Nadir viewing in frequency band, ??, o_ means
surface emission is included

W is weighting function or Kernal I is the
instrument function
T is the transmission function
118
Spectral complexity
119
Nadir Viewing Kernals
120
(No Transcript)
121
(No Transcript)
122
NLTE impacts
Limb viewing emission
123
Solar scattering limb observation
124
Solar occultation
125
Limb kernals
126
Thank You?
127
Acknowledgements

• Michael Prather
• Andrew Gettleman
• Nilesh Goupal
• Piers Forster

128
Tropospheric J-value Observations, incl. Aerosols
Clouds
PAUR EU project Photochemical Activity and
Solar Ultraviolet Radiation, Apr-Sep 1996 Jonson
JE, Kylling A, Berntsen TK, Isaksen ISA, Zerefos
CS, Kourtidis K, Chemical effects of UV
fluctuations inferred from total ozone and
tropospheric aerosol variations, JGR 105 (D11)
14561-14574 JUN 16 2000 Zanis P, Kourtidis K,
Rappenglueck B, Zerefos C, Melas D, Balis D,
Schmitt R, Rapsomanikis S, Fabian P, A case study
on the possible link between surface ozone
photochemistry and total ozone column during the
PAUR II experiment at Crete Comparison of
observations with box model calculations, JGR 107
(D18) Art. No. 8136 SEP 2002 Balis DS, Zerefos
CS, Kourtidis K, Bais AF, Hofzumahaus A, Kraus A,
Schmitt R, Blumthaler M, Gobbi GP, Measurements
and modeling of photolysis rates during the
Photochemical Activity and Ultraviolet Radiation
(PAUR) II campaign, JGR 107 (D18) Art. No. 8138
SEP 2002 Hofzumahaus A, Kraus A, Kylling A,
Zerefos CS, Solar actinic radiation (280-420 nm)
in the cloud-free troposphere between ground and
12 km altitude Measurements and model results,
JGR 107 (D18) Art. No. 8139 SEP 2002
129
Tropospheric J-value Observations, incl. Aerosols
Clouds
Boundary Layer and Air Quality Meloni D, di
Sarra A, Fiocco G, Junkermann W, Tropospheric
aerosols in the Mediterranean 3. Measurements
and modeling of actinic radiation profiles, JGR
108 (D10) Art. No. 4323 MAY 31 2003 Kanaya Y,
Kajii Y, Akimoto H, Solar actinic flux and
photolysis frequency determinations by
radiometers and a radiative transfer model at
Rishiri Island comparisons, cloud effects, and
detection of an aerosol plume from Russian forest
fires, Atm Env 37 (18) 2463-2475 JUN
2003 Castro T, Madronich S, Rivale S, Muhlia A,
Mar B, The influence of aerosols on photochemical
smog in Mexico City, Atm Env 35 (10) 1765-1772
2001 Vuilleumier L, Bamer JT, Harley RA, Brown
NJ, Evaluation of nitrogen dioxide photolysis
rates in an urban area using data from the 1997
Southern California Ozone Study, Atm Env 35 (36)
6525-6537 DEC 2001
130
Tropospheric J-value Observations, incl. Aerosols
Clouds
de Roode SR, Duynkerke PG, Boot W, Van der Hage
JCH, Surface and tethered-balloon observations of
actinic flux Effects of arctic stratus, surface
albedo, and solar zenith angle (FIRE III), JGR
106 (D21) 27497-27507 NOV 16 2001 Shetter RE,
Cinquini L, Lefer BL, Hall SR, Madronich S,
Comparison of airborne measured and calculated
spectral actinic flux and derived photolysis
frequencies during the PEM Tropics B mission, JGR
108 (D2) Art. No. 8234 DEC 5 2002 Crawford J,
Shetter RE, Lefer B, Cantrell C, Junkermann W,
Madronich S, Calvert J, Cloud impacts on UV
spectral actinic flux observed during the
International Photolysis Frequency Measurement
and Model Intercomparison (IPMMI), JGR 108 (D14)
Art. No. 8545 JUL 29 2003 Fruh B, Trautmann T,
Wendisch M, Keil A, Comparison of observed and
simulated NO2 photodissociation frequencies in a
cloudless atmosphere and in continental boundary
layer clouds, JGR 105 (D8) 9843-9857 APR 27
2000 Pfister G, Baumgartner D, Maderbacher R,
Putz E, Aircraft measurements of photolysis rate
coefficients for ozone and nitrogen dioxide under
cloudy conditions (STAAARTE), Atm Env 34 (23)
4019-4029 2000 Junkermann W, An ultralight
aircraft as platform for research in the lower
troposphere System performance and first results
from radiation transfer studies in stratiform
aerosol layers and broken cloud conditions, J
Atmos Ocn Tech 18 (6) 934-946 2001