1. Introduction to Space Weather
Ionosphere
Nov. 12, 2009
CSI 662 / PHYS 660
Fall, 2009
Jie Zhang
Copyright ©

2. Roadmap Part 1: The Sun Part 2: The Heliosphere
Part 3: The Magnetosphere
Part 4: The Ionsophere
Part 5: Space Weather Effects
Part 4: The Ionosphere

3. CSI 662 / PHYS Nov
The Ionosphere Height profile and layers Ionization production Ionization loss Radio wave Ionosphere Currents
References:
Kallenrode: Chap. 8.3
Prolss: Chap. 2, Chap. 4, Chap. 7

4. Plasma Physics Reference: Kallenrode, Chap. 8.3.2
Anisotropic Conductivity: field-aligned, Pederson, and Hall

5. Brief History Fast and Slow Wind
Fluctuation of geomagnetic field by atmospheric current (Kelvin, 1860)
First transmitting radio waves across Atlantic (Marconi, 1901)
Solar UV radiation responsible for the charge carriers (Kennelly, Heaviside and Lodge 1902)
Radio wave experiment on ionosphere (Appleton 1924)
Appleton was awarded the Nobel prize for the work of ionospheric physics.
Fast and Slow Wind

6. Atmospheric Layers
Horizontal Structure of the Terrestrial Atmosphere

7. Atmospheric Layers Classified by temperature Troposphere Stratosphere
0  10 km
~300 K  200 K
Stratosphere
10 50 km
~200 K 250 K
Mesosphere
50 km  80 km
~250 K  160 K
Thermosphere
> 80 km (~10000)
160 K  ~1000 K

8. Atmos. Layers Fast and Slow Wind Classified by Gravitational binding
Barosphere
0 km 600 km
binding
Exosphere
> 600 km
Escaping or evaporation
Classified by Composition
Homosphere
0 km 100 km
Homogeneous
Heterosphere
100 km  ~2000 km
Inhomogeneous
Hydrogensphere (Geocorona)
> ~2000 km
Dominated by hydrogen
Fast and Slow Wind

9. Basic Parameters Chemical composition (ni/n): Pressure: H He N O N2 O2
Height = 0 km, 78% N2, 21% O2, 1% others (trace gases)
Height = 300 km, 78% O, 21% N2, 1% O2
Pressure:
Height = 0 km, P = 105 pa
Height = 300 km, P=10-5 pa
H He N O N2 O2
Atomic Number
Mass Number
f (Degree of freedom)
3 translation rotation

10. Barospheric Density Distribution
Hydrostatic equilibrium or aerostatic equations
Pressure Scale Height
Barometric Law
isothermal

11. Barospheric Density Distribution
Isothermal Scale Heights
Hi = kT/(mig)
for g(200 km)
HN2 = 0.032* T
HO2 = 0.028* T
HO = * T N2 O O2
Altitude interval where density decreases by 10:

12. SOLAR - TERRESTRIAL ENERGY SOURCES
Source Energy Solar Cycle Deposition
(Wm-2) Change (Wm-2) Altitude
Solar Radiation
total surface
UV nm km
VUV nm km
Particles
electron aurora III km
solar protons km
galactic cosmic rays km
Joule hearing rate taken from Roble et al, JGR, 92, 6083, 1987
Peak Joule Heating (strong storm)
E=180 mVm km
Solar Wind above 500 km

13. TOTAL IRRADIANCE VARIABILITY
SPECTRUM VARIABILITY

14. Solar Energy Deposition Atmospheric Structure
SPACE WEATHER
GLOBAL CHANGE
EUV FUV MUV
RADIATION

15. Atmospheric Absorption Processes
Ionization
O2 + h  O2+ + e*, …
Dissociation
N2 + h  N + N, …
Excitation
O + h  O*
O* O + h ’ radiation
O* + X  O + X quenching or deactivation
Dissociative ionization – excitation
N2 + h  N+* + N + e, …

16. Ionosphere Structure Classified by Composition D region h < 90 km
Negative ions, e.g., NO3-
E region
90 km < h < 170 km
O2+, NO+
F region
170 km < h < 1000 km O+
F1 region, F2 region
Plasmasphere
h > 1000 km H+

17. Ionosphere Structure Height of maximum density: 200 – 400 km
Maximum Ionization Density:
1 – 30 X 1011 m-3
Column Density:
1 – 10 X 1017 m-3 F2 F1
Total ne E

18. Chapman Layer
The Chapman profile of an ionospheric layer results from the superposition of the height dependence of the particle density and the flux of the ionizing electromagnetic radiation
Chapman Profile

19. Chapman Layer Neutral particle density: barometric height formula
Radiation Intensity: Bougert-Lambert-Beer’s Law

20. Optical Depth Definition For several species
i = N2, O2, O
Altitude of unit optical depth: F(z)= F() e-1
Solve (z) = 1 for z
Where solar radiation is effectively extinct

21. Continued on
November 19, 2009

22. Ionosphere Structure Ionosphere: Weak ionization
Electrons and ions represent trace gases
Ion/neutral ratio (n/nn)
10-8 at 100 km
10-3 at 300 km
10-2 at 1000 km

23. Ionization Production
Photoionization
Primary
Secondary
Charge Exchange
Particle Precipitation

24. Photoionization Processes Ionization Energies
O + h ( 91.0 nm)  O+ + e
O2 + h ( nm)  O2+ + e
N2 + h ( 79.6 nm)  N2+ + e
Ionization Energies
Species
Dissociation
(Å)
(eV)
Ionization O O2 N2
2423.7
1270.4
5.11
9.76
910.44
1027.8
796
13.62
12.06
15.57

25. Charge Exchange Charge Exchange Process Charge Exchange Rate
Does not change the total ionization density
Important source for NO+ and O2+ in the lower ionosphere
Important source for H+ for the plasmasphere

26. Particle Precipitation
Play an important role in high latitude

27. Ionization Loss Dissociative Recombination of Molecular Ions
Ion loss Rate
Dissociation Recombination Reaction constants for O2+,N2+, and NO+
Largest reaction constant

28. Ionization Loss
Radiative Recombination of Atomic Ions
Charge Exchange

29. Ionization Loss E region (O2+)
Dissociative recombination is the quickest way of removing ions and elections

30. Ionization Loss F region (O+)
Charge exchange is the quickest way of removing O+ ions

31. Density Balance Equation
Density is determined by the ion production term, ion loss term and ion diffusion term, for species s
Day time: production-loss equilibrium
Night time: production is negligible

32. Variation of Ion Density
The ionization production depends on the solar radiation intensity and the zenith angle
The ion density shows daily, seasonal variation as well solar rotation and solar cycle effects
After sunrise
TEC (Total Electron Content) diurnal variation

33. Variation of Ion Density
D and F1-layers may disappear at night

34. Radio Waves in the Ionosphere
Radio wave is altered during its passage through the ionosphere
Propagation direction changes: refracted, reflected
Intensity changes: attenuated, absorbed

35. Natural Oscillation in a Plasma: Plasma Frequency

36. Forced Oscillation in a Plasma:

37. Ionosphere as a Dielectric
Interaction depends on frequency
Nref < 1, radio wave will be refracted according to the familiar Snell’s law. Θ2 > Θ1

38. Ionosphere as a Dielectric
Wave damping due to electron interaction with neutral particles
Radio wave (e.g., 5 Mhz) refraction and damping usually occur in the upper D region and lower E region

39. Ionosphere as a Conducting Reflection
Wave interacts strongly with plasma, inducing a large current. Ionosphere acts like a conductor
Radio wave is reflected
This often occurs in the F-region

40. Radio Wave

41. Ionosonde A special radar to examine ionosphere from ionogram:
Elapsed time  height
Frequency  electron density
ionosonde

42. Ionosphere Currents

43. Polar Upper Atmosphere
Polar Cap: ~ 30°
Polar oval: a few degree
Subpolar latitude
Fast and Slow Wind

44. Polar Upper Atmosphere
Magnetic field connection
Polar Cap: magnetotail lobe region, open field
Polar oval:
(1) night side: connect to plasma sheet
(2) day side: connect to cusp region
Subpolar latitude: conjugate dipole field, closed
Fast and Slow Wind

45. Convection and Electric Field
Fast and Slow Wind

46. Convection and Electric Field
Polar cap electric field Epc (from measurement)
Dawn to dusk direction
Epc = 10 mV/m
Polar cap potential: ~ 30 kV from 6 LT to 18 LT, over 3000 km
Polar oval electric field
Dawn sector: equatorward
Dusk sector: poleward
Epc=30 mV/m
Potential drop: ~ 30 kV, counterbalance of the polar cap E
Subpolar region electric field
< 5 mV/m
Fast and Slow Wind

47. Convection and Electric Field
Polar cap convection
Caused by E X B drift
anti-sunward
Drift time scale cross the polar cap ~ 2 hours
Polar oval convection
Sunward convection
Form a close loop with the polar cap convection
Two convection cells
Drift velocity = 500 m/s, when
E=10 mV/m, and
B=20000 nT

48. Solar Wind Dynamo Fast and Slow Wind
Polar cap electric field originates from solar wind dynamo electric field
Same direction
Same overall electric potential drop
Electric field is ~ 40 times as strong as in solar wind
Fast and Slow Wind

49. Ionosphere Current Fast and Slow Wind
Pederson current: perpendicular B, parallel E ; horizontal
Hall current: perpendicular B, perpendicular E ; horizontal
Burkeland current: parallel to B ; vertical
Fast and Slow Wind

50. Ionosphere Current Fast and Slow Wind
Birkeland current: Field-aligned current
Region 1 current: on the poleward side of the polar oval
Region 2 current: on the equatorward side of the polar oval
Fast and Slow Wind

51. Ionosphere-Magnetosphere Coupling
Region 1 current
Magnetotail current is re-directed to the ionosphere
Current flows into the ionosphere in the dawn sector
Current flows out the ionosphere in the dusk section

52. Ionosphere-Magnetosphere Coupling
Region 2 current
Associated magnetic field lines end in the equatorial plane of the dawn and dusk magnetosphere at a geocentric distance of L ≈ 7-10
Driven by excess charge in the dawn and dusk sectors of the dipole field, caused by different particle paths of electrons and ions

53. Ionosphere-Magnetosphere Coupling
Drift of particles from the plasma sheet
At small L, curvature-gradient drift dominates
Particles can only drift to within a certain distance of the dipole
Ions and electrons drifts in different direction along the dipole
There is a forbidden zone for ions (electrons)
Excess charges accumulate

54. Ionosphere Conductivity
Deriving conductivity σ is to find the drift velocity under the E in the three components:
Birkeland σ: parallel to B
Pederson σ: parallel to E, E per B
Hall σ: per E and B
Fast and Slow Wind

55. Ionosphere Conductivity
Parallel conductivity
Force equilibrium:
Electric force = frictional force
No Lorentz force
For plasmas (without neutral), Coulomb collision
Fast and Slow Wind

56. Ionosphere Conductivity
Transverse conductivity
Force equilibrium:
Electric force + magnetic force= frictional force
Fast and Slow Wind

57. Ionosphere Conductivity
Transverse conductivity
Maximum conductivity:
Transverse conductivity, especially Hall, confines to a rather narrow range of height (~ 125 km), the so called dynamo layer
Fast and Slow Wind

58. The End