Magnetosphere: Structure and Properties CSI 662 / ASTR 769 Lect. 08 Spring 2007 March 27, 2007 Magnetosphere: Structure and Properties References: Prolss: Chap. 5.4 – 5.6, P. 241-271; Chap. 6.4, P325 -- 335 (main reference) Tascione: Chap. 5.0 – 5.6, P. 57 – 68 (supplement) Gombosi: Chap. 14.1 – 14.3, P278 – P291 (supplement)

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

Magnetosphere Fast and Slow Wind

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

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

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

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

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

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

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

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

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

On Magnetosphere Current Systems CSI 662 / ASTR 769 Lect. 09 Spring 2007 April 03, 2007 On Magnetosphere Current Systems

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

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

The End