1. Upper Atmosphere + Ionosphere Part-4
Diffusion : Molecular + Eddy: turbopause
Photo-ionization
Ionosphere : D, E, F1, F2 Regions
Ambipolar Diffusion: F2 Region
Radio Waves + the Ionosphere
Ionosphere of Other Planets

2. Copied from Goody and Walker p25
Oxygen Densities
Solid lines: mixing and diffusion: Dashed lines:photochemical equilibrium (I.e. no mixing and diffusion) z
Log10 density in cm3
Copied from Goody and Walker p25
NEED DIFFUSION

3. Atmospheric Classifications
Turbopause
Mixing ~ Diffusion

4. Diffusion v
ni+ z z
ni- v

5. Diffusion (Continued)

6. Diffusion (Continued)

7. Diffusion(cont)

8. Diffusive Equilibrium

9. AB + hn ® AB+ + e Ji Photochemistry and the Ionosphere
Simple Model
AB + hn ® AB+ + e Ji
AB++ e ® A + B a
A + B + M ® AB + M k
dnAB+ /dt = Ji nAB - a ne nAB+
dne /dt = 0, ne = nAB charge neutrality
nAB+ » [ Ji nAB / a ]1/2
nAB µ exp[-z/HAB] ; Ji µ exp[-ti(z)]
Chapman Layer for Ion AB+ is Formed

10. Ionospheres (continued)
exp[-z/2HAB] z
NAB sabs » 1
nAB+ » [ Ji nAB / a ]1/2
At top: ion scale height twice neutral H

11. Earth’s Ionospheric Layers
Day and Night
Principal Species
Favored ions have lowest ionization energies
N2 --> N2+ + e (15.5eV)
O --> O+ + e (13.6eV)
O2 --> O2+ + e (12.1eV)
NO --> NO+ + e (9.3eV)
Therefore, if made NO+ is favored

12. Nitrogen Photochemistry
Light absorption begins at 120 nm
Dissociation:
N2+hn(80<l<91nm)  N(4S) + N(2D)
Ionization:
N2+hn (l<80nm)  N2+ + e-
At 91nm s=4x10-20 cm2
atmospheric absorption by a 1km layer:
Beer-Lambert law: I = I0exp(-n s z); n ~const
ln(I0/I) = n s z =(9x1012)(4x10-20)(1x105) = 0.036
I/I0 = 0.92; T = 0.92; A=1-T = 0.08
T: transmission; A: absorption
Result: 8% of the light is absorbed by the 1km layer at 100km

13. Dominant Ions Observed
Ions Produced
Earth : O + hn ® O+ + e
  N2 + hn ® N e
O2 + hn ® O e
But ionosphere has a large, sometimes dominant, amount of NO+
Similarly:Mars : CO2 + h --> CO2+ + e    But ionosphere is predominantly O2
Dominant Ions Observed
Ion-molecule reactions are fast and tend toward species with lowest ionization state: IA > IB,
A++ B --> A + B+ exothermic
B++ A --> B + A+ endothermic;need energy
Metal ions, if available, dominate: Na, Mg, etc.

14. Earth’s Ionosphere (D-region)

15. E-region ~ km

16. E Region (cont)

17. F1 Region (~180km)

19. TIME CONSTANTS: F1 Region

20. F2 – region > 250 km O+ + e ambipolar diffusion of O+ and e
Thermal diffusion
O Forms by (2)
ambipolar diffusion of O+ and e

21. Ambipolar Diffusion(F2)

22. RADIO WAVES
Spacecraft Observations of Ionosphere
s c E F

23. Earth’s Ionospheric Layers
Day Time

24. Mars and Venus Ionospheric Layers
dePL

25. Giant Planet Ionospheres
dePL
H2+h --> H2+ (or H + H +) + e
H H2 -> H3+ + H
Ingress and Egress apply to Voyager
radio wave results

26. Uniform and Non-uniform Turbopause (Homopause) Diffusive Equilibrium
#4 Summary
Things you should know
Diffusion Equations
Uniform and Non-uniform
Turbopause (Homopause)
Diffusive Equilibrium
Photo-ionization
Photochemistry of Ionosphere
Layered Ionosphere
Ambi-polar Diffusion
Refraction of SC Radio Signal
Ionospheres of Other Planets