1. Magnetosphere: Structure and Properties
CSI 662 / ASTR Lect Spring 2007
March 27, 2007
Magnetosphere: Structure and Properties
References:
Prolss: Chap. 5.4 – 5.6, P ; Chap. 6.4, P (main reference)
Tascione: Chap. 5.0 – 5.6, P. 57 – 68 (supplement)
Gombosi: Chap – 14.3, P278 – P291 (supplement)

2. Magnetosphere Fast and Slow Wind Inner Magnetosphere Radiation Belt
Ring Current
Plasmasphere
Outer Magnetosphere
Magnetopause
Cusp
Magnetotail neutral sheet
Magnetotail Lobe
Magnetotail Plasma sheet
Magnetospheric Boundary Layer
Fast and Slow Wind

3. Magnetosphere
Fast and Slow Wind

4. Inner Magnesphere Fast and Slow Wind
Particles are trapped in the inner magnetosphere, subject to
Gyration
Bounce motion
Drift motion
Fast and Slow Wind

5. Radiation Belt Fast and Slow Wind
Populated by high energetic particles
Energy: proton 1 – 100 Mev
e.g, 20 Mev: gyro = 5 ms, bounce = 0.5 s, drift = 2 min
L shell of inner belt: 1.2 – 2.5
Source: cosmic ray
Loss: deceleration; pitch angle diffusion into loss cone
Particle life: 1 year at 20 Mev
Also called Van Allen Radiation Belt
South Atlantic Anomoly
Fast and Slow Wind

6. Ring Current Fast and Slow Wind Populated by medium energy particles
Energy: proton 1 – 200 Kev
e.g, 20 Kev: gyro = 0.1 s, bounce = 1 min, drift = 9 hour
L shell: 3 – 6
Source: ionosphere and plasma sheet
Loss: charge exchange, pitch angle diffusion
Life time: 2 hours at 20 Kev
Concentrate in low latitude
Charge Exchange: gain an electron from cold hydrogen, become a hot neutral then escape; life time ~ 2 hours at 20 Kev, L=3
Coulomb Collision: interaction between charged particles, small angle interaction
Fast and Slow Wind

7. Plasmasphere Populated by low energy particles Energy: proton 1ev
e.g, 0.6 ev: gyro = 0.1 s, bounce = 2 hour, drift = 45 year
L shell: 1.2 – 5
Source: ionosphere
Loss: transport, charge exchange, convection
Collision time: only 0.5 hour because of low speed
Corotation
Corotation Electric Field: pointing toward the Earth

8. Outer Magnetosphere Fast and Slow Wind
Solar wind interaction fundamentally modifies the Earth’s magnetic field in large distances
The Earth magnetic field is confined by magnetopause
Dayside: ellipsoidal shape, subsolar point at 10 RE
Nightside: greatly extended, magnetotail ~ 200 RE
Fast and Slow Wind

9. Neutral Sheet and Tail Lobe
Neutral sheet: in the magneto-equatorial plane of night-side magnetotail, a polarity reversal across this sheet and BX vanish
Magnetotail lobe: regions between neutral sheet and magnetopause
Polar cap: footpoint region of the tail lobe field lines
Polar cap boundary: 75°
Fast and Slow Wind

10. Magnetotail Plasma Sheet
Plasma sheet is a slab-like particle population centered on the mid-plane of the magnetotail
It separates the tail lobes
Populated by medium energetic particles (5 kev)
Reservoir of particles which precipitate and produce aurora
Plasma sheet is highlighted in yellow
Fast and Slow Wind

11. Auroral Oval Fast and Slow Wind Auroral oval
A ring-like region around each polar cap
Auraral oval is actually formed by the footpoints of the field lines in the plasma sheet
68°-72°
Fast and Slow Wind

12. Cusp or Cleft Fast and Slow Wind
Cusp: dayside region separating field lines that close on the frontside of the magnetosphere from those extend into magnetotail
Minimum in magnetic intensity
Polar Cusp
Fast and Slow Wind

13. On Magnetosphere Current Systems
CSI 662 / ASTR Lect Spring 2007
April 03, 2007
On Magnetosphere Current Systems

14. Magnetopause Current: Dayside
Also called Chapman-Ferraro current
Separating Earth’s magnetic field and plasma from the solar wind
Current is induced when charged particles are deflected by the magnetopause magnetic field
Stagnation point: at the nose, SW speed becomes zero
Location: ~ 10 RE
Fast and Slow Wind

15. Tail Currents Fast and Slow Wind
Cross-tail current in the magnetopause
Neutral sheet current on the equatorial plane
These two currents form a closed circuit in the magneto-tail
Partially closed with ionosphere during storm time
Fast and Slow Wind

16. The End