Introduction to Space Weather Jie Zhang CSI 662 / PHYS 660 Spring, 2012 Copyright © Ionosphere II: Radio Waves April 19, 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

CSI 662 / PHYS 660 Apr. 19, Radio Waves in the Ionosphere 11.2 Ionosphere Currents Plasma-15: Radio Waves in the Ionosphere

CH11: Ionosphere II References and Reading Assignment: PRO CH 4.7 (on radio waves) KAL CH (on currents)

CH11.1 Radio Waves in the Ionosphere Radio wave is altered during its passage through the ionosphere –Propagation direction changes: Refraction Reflection –Intensity changes: Attenuation Absorption

Radio Wave

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

Plasma Frequency: Natural Oscillation in a Plasma:

Forced Oscillation in a Plasma:

Ionosphere as a Dielectric Interaction depends on frequency N ref Θ 1

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

Reflection: Ionosphere as a Conductor 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

(Continued on April 26, 2012)

CH11.2. Ionosphere Currents

Fast and Slow Wind Polar Upper Atmosphere Polar Cap: ~ 30° Polar oval: ~5° (noon) to ~10° (night) Subpolar latitude: < 65°

Fast and Slow Wind Polar Upper Atmosphere Magnetic field connection Polar Cap: open field connecting to magnetotail lobe region Polar oval: night side: quasi-closed field connecting to plasma sheet day side: open field connecting to solar wind – the cusp Subpolar latitude: closed dipole field

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 Polar Upper Atmosphere

Fast and Slow Wind Convection and Electric Field Dawn Dusk The circular cells are for the pattern of the dynamo velocity

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

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

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

Fast and Slow Wind Ionosphere Current Birkeland current: Field-aligned current Region 1 current: on the poleward side of the polar oval, connecting to the magnetopause curret Region 2 current: on the equatorward side of the polar oval, connecting to the plasma sheet current

Ionosphere-Magnetosphere Coupling Region 1 current Plasma sheet 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 magnetopause at a geocentric distance of L ≈ 7-10

Fast and Slow Wind Ionosphere Conductivity (optional) 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, perpendicular to B Hall σ: perpendicular to both E and B

Fast and Slow Wind Ionosphere Conductivity Parallel conductivity For plasmas, Coulomb collision Force equilibrium: Electric force = frictional force No Lorentz force

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 End