Ionospheric Current and Aurora CSI 662 / ASTR 769 Lect. 12 Spring 2007 April 24, 2007 References:...
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![Page 1: Ionospheric Current and Aurora CSI 662 / ASTR 769 Lect. 12 Spring 2007 April 24, 2007 References: Prolss: Chap. 7.1-7.6, P349-379 (main) Tascione: Chap.](https://reader035.fdocuments.in/reader035/viewer/2022062722/56649f345503460f94c5156f/html5/thumbnails/1.jpg)
Ionospheric Current and Aurora
CSI 662 / ASTR 769 Lect. 12 Spring 2007
April 24, 2007
References:
•Prolss: Chap. 7.1-7.6, P349-379 (main)•Tascione: Chap. 8, P. 99 – 112 (supplement)
![Page 2: Ionospheric Current and Aurora CSI 662 / ASTR 769 Lect. 12 Spring 2007 April 24, 2007 References: Prolss: Chap. 7.1-7.6, P349-379 (main) Tascione: Chap.](https://reader035.fdocuments.in/reader035/viewer/2022062722/56649f345503460f94c5156f/html5/thumbnails/2.jpg)
Topics
• Polar Upper Atmosphere• Ionospheric Currents• Aurorae• Ionosphere and magnetosphere coupling
![Page 3: Ionospheric Current and Aurora CSI 662 / ASTR 769 Lect. 12 Spring 2007 April 24, 2007 References: Prolss: Chap. 7.1-7.6, P349-379 (main) Tascione: Chap.](https://reader035.fdocuments.in/reader035/viewer/2022062722/56649f345503460f94c5156f/html5/thumbnails/3.jpg)
Ionosphere Currents
![Page 4: Ionospheric Current and Aurora CSI 662 / ASTR 769 Lect. 12 Spring 2007 April 24, 2007 References: Prolss: Chap. 7.1-7.6, P349-379 (main) Tascione: Chap.](https://reader035.fdocuments.in/reader035/viewer/2022062722/56649f345503460f94c5156f/html5/thumbnails/4.jpg)
Polar Upper Atmosphere• Polar Cap: ~ 30°• Polar oval: a few degree• Subpolar latitude
![Page 5: Ionospheric Current and Aurora CSI 662 / ASTR 769 Lect. 12 Spring 2007 April 24, 2007 References: Prolss: Chap. 7.1-7.6, P349-379 (main) Tascione: Chap.](https://reader035.fdocuments.in/reader035/viewer/2022062722/56649f345503460f94c5156f/html5/thumbnails/5.jpg)
Polar Upper AtmosphereMagnetic field connection• Polar Cap: magnetotail lobe region, open• Polar oval: plasma sheet, open• Subpolar latitude: conjugate dipole field, closed
![Page 6: Ionospheric Current and Aurora CSI 662 / ASTR 769 Lect. 12 Spring 2007 April 24, 2007 References: Prolss: Chap. 7.1-7.6, P349-379 (main) Tascione: Chap.](https://reader035.fdocuments.in/reader035/viewer/2022062722/56649f345503460f94c5156f/html5/thumbnails/6.jpg)
Convection and Electric Field• Polar cap electric field Epc
• Dawn to dusk direction• Epc = 10 mV/m• Polar cap potential: ~ 30 kV from 6 LT to 18 LT, over
3000 km
![Page 7: Ionospheric Current and Aurora CSI 662 / ASTR 769 Lect. 12 Spring 2007 April 24, 2007 References: Prolss: Chap. 7.1-7.6, P349-379 (main) Tascione: Chap.](https://reader035.fdocuments.in/reader035/viewer/2022062722/56649f345503460f94c5156f/html5/thumbnails/7.jpg)
Convection and Electric Field• 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
Eswsw BUE
![Page 8: Ionospheric Current and Aurora CSI 662 / ASTR 769 Lect. 12 Spring 2007 April 24, 2007 References: Prolss: Chap. 7.1-7.6, P349-379 (main) Tascione: Chap.](https://reader035.fdocuments.in/reader035/viewer/2022062722/56649f345503460f94c5156f/html5/thumbnails/8.jpg)
Convection and Electric Field• Polar cap convection
• Caused by EXB drift• anti-sunward• Drift time scale cross the polar cap ~ 2 hours
BEUD /
Drift velocity = 500 m/s, whenE=10 mV/m, andB=20000 nT
![Page 9: Ionospheric Current and Aurora CSI 662 / ASTR 769 Lect. 12 Spring 2007 April 24, 2007 References: Prolss: Chap. 7.1-7.6, P349-379 (main) Tascione: Chap.](https://reader035.fdocuments.in/reader035/viewer/2022062722/56649f345503460f94c5156f/html5/thumbnails/9.jpg)
Convection and Electric Field• Polar oval electric field Eo
• Dusk to dawn direction, opposite to polar cap field• E0 = 30 mV/m• Counter-balance the polar cap field
• Polar oval convection• Sunward convection• Form a close loop with the polar cap convection• Two convection cells
![Page 10: Ionospheric Current and Aurora CSI 662 / ASTR 769 Lect. 12 Spring 2007 April 24, 2007 References: Prolss: Chap. 7.1-7.6, P349-379 (main) Tascione: Chap.](https://reader035.fdocuments.in/reader035/viewer/2022062722/56649f345503460f94c5156f/html5/thumbnails/10.jpg)
Convection and Electric Field• Polar oval electric field Eo
• Dusk to dawn direction, opposite to polar cap field• E0 = 30 mV/m• Counter-balance the polar cap field
• Polar oval convection• Sunward convection• Form a close loop with the polar cap convection• Two convection cells
![Page 11: Ionospheric Current and Aurora CSI 662 / ASTR 769 Lect. 12 Spring 2007 April 24, 2007 References: Prolss: Chap. 7.1-7.6, P349-379 (main) Tascione: Chap.](https://reader035.fdocuments.in/reader035/viewer/2022062722/56649f345503460f94c5156f/html5/thumbnails/11.jpg)
Ionosphere Current• Pederson current: perpendicular B, parallel E ; horizontal• Hall current: perpendicular B, perpendicular E ;
horizontal• Burkeland current: parallel to B ; vertical
![Page 12: Ionospheric Current and Aurora CSI 662 / ASTR 769 Lect. 12 Spring 2007 April 24, 2007 References: Prolss: Chap. 7.1-7.6, P349-379 (main) Tascione: Chap.](https://reader035.fdocuments.in/reader035/viewer/2022062722/56649f345503460f94c5156f/html5/thumbnails/12.jpg)
Ionosphere Current• 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
![Page 13: Ionospheric Current and Aurora CSI 662 / ASTR 769 Lect. 12 Spring 2007 April 24, 2007 References: Prolss: Chap. 7.1-7.6, P349-379 (main) Tascione: Chap.](https://reader035.fdocuments.in/reader035/viewer/2022062722/56649f345503460f94c5156f/html5/thumbnails/13.jpg)
Ionosphere Current• Pederson current flows from dawn to dusk in the polar cap• Pederson current flows radially in the polar oval, dusk to dawn• Pederson current forms a closed loop with Burkeland currents
in the two boundary regions: region 1 and 2• Hall current direction is opposite to the convection, because
ions drift slower than the electrons• Westward at the dawn sector• Eastward at the dusk sector
![Page 14: Ionospheric Current and Aurora CSI 662 / ASTR 769 Lect. 12 Spring 2007 April 24, 2007 References: Prolss: Chap. 7.1-7.6, P349-379 (main) Tascione: Chap.](https://reader035.fdocuments.in/reader035/viewer/2022062722/56649f345503460f94c5156f/html5/thumbnails/14.jpg)
Ionosphere Conductivity
Euuen
uuenj
Ej
ei
ei
/)(
)(
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
![Page 15: Ionospheric Current and Aurora CSI 662 / ASTR 769 Lect. 12 Spring 2007 April 24, 2007 References: Prolss: Chap. 7.1-7.6, P349-379 (main) Tascione: Chap.](https://reader035.fdocuments.in/reader035/viewer/2022062722/56649f345503460f94c5156f/html5/thumbnails/15.jpg)
Ionosphere Conductivity
Parallel conductivity BE
//
ieemne
snsss umEq
,
2
//
, 0
For plasmas (without neutral), Coulomb collision
ln/])[(108 2/33// kTe
Force equilibrium:Electric force = frictional forceNo Lorentz force
![Page 16: Ionospheric Current and Aurora CSI 662 / ASTR 769 Lect. 12 Spring 2007 April 24, 2007 References: Prolss: Chap. 7.1-7.6, P349-379 (main) Tascione: Chap.](https://reader035.fdocuments.in/reader035/viewer/2022062722/56649f345503460f94c5156f/html5/thumbnails/16.jpg)
Ionosphere Conductivity
Transverse conductivity BE
0)( , snssss umBuEq
Force equilibrium:Electric force + magnetic force= frictional force
![Page 17: Ionospheric Current and Aurora CSI 662 / ASTR 769 Lect. 12 Spring 2007 April 24, 2007 References: Prolss: Chap. 7.1-7.6, P349-379 (main) Tascione: Chap.](https://reader035.fdocuments.in/reader035/viewer/2022062722/56649f345503460f94c5156f/html5/thumbnails/17.jpg)
Ionosphere Conductivity
Transverse conductivity BE
}{
}{
22,
2
22,
2
22,
,
22,
,
)()(
)(
)()(
)(
)()()()(
iBni
iB
eBne
eB
iBni
iBni
eBne
eBne
Ben
H
Ben
P
Maximum conductivity: Transverse conductivity, especially Hall, confines to a rather narrow range of height (~ 125 km), the so called dynamo layer
iBni ,
![Page 18: Ionospheric Current and Aurora CSI 662 / ASTR 769 Lect. 12 Spring 2007 April 24, 2007 References: Prolss: Chap. 7.1-7.6, P349-379 (main) Tascione: Chap.](https://reader035.fdocuments.in/reader035/viewer/2022062722/56649f345503460f94c5156f/html5/thumbnails/18.jpg)
Aurora
Image taken near Richmond VA, Oct 29, 2003
![Page 19: Ionospheric Current and Aurora CSI 662 / ASTR 769 Lect. 12 Spring 2007 April 24, 2007 References: Prolss: Chap. 7.1-7.6, P349-379 (main) Tascione: Chap.](https://reader035.fdocuments.in/reader035/viewer/2022062722/56649f345503460f94c5156f/html5/thumbnails/19.jpg)
![Page 20: Ionospheric Current and Aurora CSI 662 / ASTR 769 Lect. 12 Spring 2007 April 24, 2007 References: Prolss: Chap. 7.1-7.6, P349-379 (main) Tascione: Chap.](https://reader035.fdocuments.in/reader035/viewer/2022062722/56649f345503460f94c5156f/html5/thumbnails/20.jpg)
Akasofu, Secrets of the Aurora
![Page 21: Ionospheric Current and Aurora CSI 662 / ASTR 769 Lect. 12 Spring 2007 April 24, 2007 References: Prolss: Chap. 7.1-7.6, P349-379 (main) Tascione: Chap.](https://reader035.fdocuments.in/reader035/viewer/2022062722/56649f345503460f94c5156f/html5/thumbnails/21.jpg)
Patches and Bands
Akasofu, Secrets of the Aurora
![Page 22: Ionospheric Current and Aurora CSI 662 / ASTR 769 Lect. 12 Spring 2007 April 24, 2007 References: Prolss: Chap. 7.1-7.6, P349-379 (main) Tascione: Chap.](https://reader035.fdocuments.in/reader035/viewer/2022062722/56649f345503460f94c5156f/html5/thumbnails/22.jpg)
Aurora• Form
• Discrete: arcs, bands, rays, patches• Diffuse
• Height: > 100 km• Orientation
• Vertical: along the magnetic field line• Horizontal: primarily east-west direction
• Colors and emitting elements• O: red (630.0 nm, 630.4 nm), yellow-green (557.7 nm)• N2
+: blue-violet (391.4 nm – 470 nm)• N2: dark red (650 nm – 680 nm)
• Intensity: up to a few 100 kR (kilo Rayleigh)
![Page 23: Ionospheric Current and Aurora CSI 662 / ASTR 769 Lect. 12 Spring 2007 April 24, 2007 References: Prolss: Chap. 7.1-7.6, P349-379 (main) Tascione: Chap.](https://reader035.fdocuments.in/reader035/viewer/2022062722/56649f345503460f94c5156f/html5/thumbnails/23.jpg)
Aurora• Aurorae are caused by the incidence of energetic particles onto
the upper atmosphere• Particles move-in along the open polar magnetic fields• The particles are mostly electrons in the energy range of ~100
ev to 10 kev. • Ions are also observed
![Page 24: Ionospheric Current and Aurora CSI 662 / ASTR 769 Lect. 12 Spring 2007 April 24, 2007 References: Prolss: Chap. 7.1-7.6, P349-379 (main) Tascione: Chap.](https://reader035.fdocuments.in/reader035/viewer/2022062722/56649f345503460f94c5156f/html5/thumbnails/24.jpg)
Aurora Processes• Primary collision
• Scattering (elastic collision)• Collisional ionization• Collisional dissociation• Collisional excitation
• Secondary process• Secondary ionization• Secondary dissociation• Secondary scattering• Charge exchange• Dissociation exchange• Excitation exchange• Dissociative recombination• Radiative recombination• Collisional quenching
Energy conversion:•1% radiation•50% heating•30% chemical energy•Other: scatter back to magnetosphere
![Page 25: Ionospheric Current and Aurora CSI 662 / ASTR 769 Lect. 12 Spring 2007 April 24, 2007 References: Prolss: Chap. 7.1-7.6, P349-379 (main) Tascione: Chap.](https://reader035.fdocuments.in/reader035/viewer/2022062722/56649f345503460f94c5156f/html5/thumbnails/25.jpg)
The Rayleigh (R): A Basic Unit for measuring Aurora-Airglow Emissions
0
dzI(θ,φ, ) = ε(z,θ,φ, )
cosθ
• One R corresponds to the emission rate of 106 photons per second radiated isotropically from an atmospheric column with a base area of 1 cm2
• Brightness of the Milky Way Galaxy: 1 kR
![Page 26: Ionospheric Current and Aurora CSI 662 / ASTR 769 Lect. 12 Spring 2007 April 24, 2007 References: Prolss: Chap. 7.1-7.6, P349-379 (main) Tascione: Chap.](https://reader035.fdocuments.in/reader035/viewer/2022062722/56649f345503460f94c5156f/html5/thumbnails/26.jpg)
Auroral Particles• Not solar wind particles• Particles are from magnetotail plasma sheet, with which the
polar oval is magnetically connected• Diffuse aurora
• convection and subsequent pitch angle diffusion of plasma sheet particles
• Discrete aurora• Produced by higher energy electrons (Ee > 1 keV) • Plasma sheet electron (Ee < 1 keV)• Additional acceleration is needed • Acceleration along magnetic field-aligned electric fields
• Double layer• Plasma instability produces localized potential
differences
![Page 27: Ionospheric Current and Aurora CSI 662 / ASTR 769 Lect. 12 Spring 2007 April 24, 2007 References: Prolss: Chap. 7.1-7.6, P349-379 (main) Tascione: Chap.](https://reader035.fdocuments.in/reader035/viewer/2022062722/56649f345503460f94c5156f/html5/thumbnails/27.jpg)
Ionosphere-Magnetosphere Coupling• Region 1 current
• Magnetotail current is re-directed to the ionosphere
• Also produce auroral oval electrojet
• Energy is from solar wind dynamo
• Energy is dissipated in the ionosphere through Joule heating
![Page 28: Ionospheric Current and Aurora CSI 662 / ASTR 769 Lect. 12 Spring 2007 April 24, 2007 References: Prolss: Chap. 7.1-7.6, P349-379 (main) Tascione: Chap.](https://reader035.fdocuments.in/reader035/viewer/2022062722/56649f345503460f94c5156f/html5/thumbnails/28.jpg)
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
![Page 29: Ionospheric Current and Aurora CSI 662 / ASTR 769 Lect. 12 Spring 2007 April 24, 2007 References: Prolss: Chap. 7.1-7.6, P349-379 (main) Tascione: Chap.](https://reader035.fdocuments.in/reader035/viewer/2022062722/56649f345503460f94c5156f/html5/thumbnails/29.jpg)
Ionosphere-Magnetosphere Coupling• Drift of particles from
the plasma sheet
Lu
u
D
BEE
D
ED
grD
gr Lu
Lu
1
2
3
• 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
![Page 30: Ionospheric Current and Aurora CSI 662 / ASTR 769 Lect. 12 Spring 2007 April 24, 2007 References: Prolss: Chap. 7.1-7.6, P349-379 (main) Tascione: Chap.](https://reader035.fdocuments.in/reader035/viewer/2022062722/56649f345503460f94c5156f/html5/thumbnails/30.jpg)
The End