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

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

CSI 662 / PHYS 660 Nov. 12 2009 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

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

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

Atmospheric Layers Horizontal Structure of the Terrestrial Atmosphere

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

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

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 1 2 7 8 Mass Number 1 4 14 16 28 32 f (Degree of freedom) 3 3 3 3 5 5 3 translation + 2 rotation

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

Barospheric Density Distribution Isothermal Scale Heights Hi = kT/(mig) for g(200 km) HN2 = 0.032* T HO2 = 0.028* T HO = 0.0567* T N2 O O2 Altitude interval where density decreases by 10:

SOLAR - TERRESTRIAL ENERGY SOURCES Source Energy Solar Cycle Deposition (Wm-2) Change (Wm-2) Altitude Solar Radiation total 1366 1.2 surface UV 200-300 nm 15.4 0.17 10-80 km VUV 0-200 nm 0.15 0.15 50-500 km Particles electron aurora III 0.06 90-120 km solar protons 0.002 30-90 km galactic cosmic rays 0.0000007 0-90 km Joule hearing rate taken from Roble et al, JGR, 92, 6083, 1987 Peak Joule Heating (strong storm) E=180 mVm-1 0.4 90-200 km Solar Wind 0.0006 above 500 km

TOTAL IRRADIANCE VARIABILITY SPECTRUM VARIABILITY

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

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, …

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+

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

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

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

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

Continued on November 19, 2009

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

Ionization Production Photoionization Primary Secondary Charge Exchange Particle Precipitation

Photoionization Processes Ionization Energies O + h ( 91.0 nm)  O+ + e O2 + h ( 102.8 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

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

Particle Precipitation Play an important role in high latitude

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

Ionization Loss Radiative Recombination of Atomic Ions Charge Exchange

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

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

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

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

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

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

Natural Oscillation in a Plasma: Plasma Frequency

Forced Oscillation in a Plasma:

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

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

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

Radio Wave

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

Ionosphere Currents

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

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

Convection and Electric Field Fast and Slow Wind

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

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

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

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

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

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

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

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

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

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

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

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

The End