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

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

Atmospheric Classifications Turbopause Mixing ~ Diffusion

Diffusion v ni+ z z ni- v

Diffusion (Continued)

Diffusion (Continued)

Diffusion(cont)

Diffusive Equilibrium

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

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

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

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

Dominant Ions Observed Ions Produced Earth : O + hn ® O+ + e   N2 + hn ® N2+ + e O2 + hn ® O2+ + 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.

Earth’s Ionosphere (D-region)

E-region ~ 110 km

E Region (cont)

F1 Region (~180km)

TIME CONSTANTS: F1 Region

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

Ambipolar Diffusion(F2)

RADIO WAVES Spacecraft Observations of Ionosphere s c E F

Earth’s Ionospheric Layers Day Time

Mars and Venus Ionospheric Layers dePL

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

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