Introduction to Space Weather Jie Zhang CSI 662 / PHYS 660 Spring, 2012 Copyright © Ionosphere II: Radio Waves April 12, 2012

Roadmap Part 1: Sun Part 2: Heliosphere Part 3: Magnetosphere Part 4: Ionosphere Part 5: Space Weather Effects CH10: Ionosphere I CH11: Ionosphere II

CH10: Ionosphere I CSI 662 / PHYS 660 Apr. 12, Atmospheric Layers 10.2 Density Profiles of Ionosphere Ionization Production and Loss Plasma-14: Chapman Layers

CH10: Ionosphere I References and Reading Assignment: KAL CH (on Atmospheric Layers) KAL CH (on Chapman Layers) PRO CH4.1 (On Atmospheric Layers) PRO CH4.2 (On Ionization Production and Loss) PRO CH4.3, CH4.4 and CH4.6 (on the Density profile)

Fast and Slow Wind Introduction Fluctuation of geomagnetic field by atmospheric current (Kelvin, 1860) First transmitting radio waves across Atlantic Ocean (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.

CH 10.1 Atmospheric Layers Horizontal Structure of the Terrestrial Atmosphere

Atmospheric Layers Classified by temperatures Troposphere 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

Fast and Slow Wind Atmos. Layers 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

Basic Parameters Chemical composition (n i /n): Height = 0 km, 78% N 2, 21% O 2, 1% others (trace gases) Height = 300 km, 78% O, 21% N 2, 1% O 2 (O 2 is much easier to dissociate than N 2 ) Pressure: Height = 0 km, P = 10 5 pa Height = 300 km, P=10 -5 pa H He N O N 2 O 2 Atomic Number Mass Number f (Degree of freedom) translation + 2 rotation

Barospheric Density Profile Hydrostatic equilibrium or aerostatic equations The Scale Height Barometric Law isothermal

Continued on April 19, 2012

Isothermal Scale Heights –H = kT/(mg) for g(200 km) H O2 = 0.028* T H N2 = 0.032* T H O = * T Atomic O relative abundance increases quickly with height <~100 km, homosphere: same abundance >~100 km, hetereosphere: abundance changes with height O N2N2 O2O2 Barospheric Density Distribution

SOLAR - TERRESTRIAL ENERGY SOURCES Source Energy Solar Cycle Deposition (Wm -2 ) Change (Wm -2 ) Altitude Solar Radiation total surface UV nm km FUV nm km Particles electron aurora III km solar protons km galactic cosmic rays km Peak Joule Heating (strong storm) E=180 mVm km Solar Wind Solar Wind above 500 km

SPECTRUM VARIABILITY TOTAL IRRADIANCE VARIABILITY

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

Energy Absorption Processes Three basic processes 1.Ionization 1.O 2 + h  O e *, … 2.Dissociation 1.N 2 + h  N + N, … 3.Excitation 1.O + h  O * –The basic processes can be combined, e.g., ionization excitation Each basic process has a corresponding reverse process 1.Ionization Recombination 2.Dissociation Association 3.Excitation Radiation

CH10.2. Density Profiles of Ionosphere

CH10.2 Electron Density Profile Height of maximum density: 200 – 400 km Maximum Ionization Density: 1 – 30 x m -3 Column Density: 1 – 10 x m -3 Total n e E F1 F2

Density Profiles Ionosphere: Weak ionization Electrons and ions represent trace gases Ion/neutral ratio (n/n n ) at 100 km at 300 km at 1000 km

Ionosphere Layers Classified by Composition of charge carriers: D region h < 90 km Only day time Charge H 3 O + : cluster ions E region 90 km < h < 170 km Peak at ~120 km Charge O 2 + :ionization of O 2 F region 170 km < h < 1000 km Peak at ~ 250 km Charge O + : ionization of O Fragment into F1 (mixture of O 2 +, O +,NO + ) and F2 (O + ) during the day time

Plasma 14- 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

Chapman Layer

CH10.3. Ionization Production and Loss The density of charged particles is determined through the dynamic balance of the continuous ionization production rate and the loss rate

Ionization Production Photoionization Charge Exchange Particle Precipitation

Photoionization Processes –O + h (  91.0 nm)  O + + e –O 2 + h (  nm)  O e –N 2 + h (  79.6 nm)  N e Photon Energy Threshold SpeciesDissociation (nm) Dissociation (eV) Ionization (nm) Ionization (eV) OO2N2OO2N

Charge Exchange Does not change the total ionization density Important source for NO + and O 2 + in the lower ionosphere Important source for H + for the plasmasphere Charge Exchange Process Charge Exchange Rate (q) Charge Exchange constant (k, from lab experiment)

Particle Precipitation Play an important role in high latitude

Ionization Loss Dissociative Recombination Radiative Recombination Dissociative recommendation is more efficient than radiative recombination Charge Exchange

Ionization Loss Dissociative Recombination of Molecular Ions Ion loss Rate Dissociation Recombination k: Reaction constants Largest reaction constant for O 2 +,N 2 +, and NO +

Ionization Loss Radiative Recombination of Atomic Ions

Ionization Loss Charge Exchange Charge exchange is efficient due to the presence of large amount of neutrals

Ionization Loss E region ( O 2 + ) 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: approximated by production-loss equilibrium Night time: production is negligible. A good approximation:

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 TEC (Total Electron Content, 1 TEC=10 16 electrons/m 2 ) diurnal variation After sunrise

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

The End