The Aurora: A Look from Above

1. The Aurora: A Look from Above 1.Ground-based observations 2. Plasma: the fourth state of matter 3. The sun and interplanetary space 4. The magnetosphere 5. Auroral acceleration

2. An example of discrete aurora

3. Auroral striations aligned with the geomagnetic field

4. High altitudered auroraproduced by low energy electrons

5. Pink lower borders produced by high energy electrons

6. Aurora seen from the SpaceShuttle

7. Types of aurora • Discrete: produced by active acceleration • Auroral patches: Precipitation caused by wave-particle interaction • Diffuse: Caused by inward convection and wave-particle interaction

8. Aurora is magnetically conjugate

9. The Auroral Substorm

10. Seen from the all-sky camera

11. Seen from a polar-orbiting satellite

12. The Substorm • Growth Phase – convection and equatorward moving diffuse arc • Expansive Phase – Bright, rapidly moving aurora, magnetic disturbances • Recovery Phase – Patchy, diffuse aurora

13. Other things that happen • Magnetic bays caused by auroral electrojet current. Transmission grid outages • Magnetic pulsations • Radio emissions - chorus and hiss • Ionospheric radio absorption

14. Storm vs Substorm

15. Plasma: The fourth state of matter • A gas made up of electrically charged particles, ions and electrons • Density differences between ions and electrons -> space charges -> electric fields • Differential motion between ions and electrons -> electric currents -> magnetic fields • Charged particle motion is affected by electric and magnetic fields • A plasma is distinguished by long-range collectiveinteraction

16. Waves in Plasmas • Plasma Oscillation • Alfven waves: • Compressional mode: magnetic field has pressure • Shear mode: magnetic field has tension • Electron cyclotron waves • Electrostatic waves

17. The Plasma Oscillation

19. Effect of Collisions on Particle Motion

21. Particle Trapping

23. The Sun and InterplanetarySpace

24. The Sun

25. Poloidal and Toroidal Fields

26. Chromosphere and Corona

27. Corona and Solar Wind

28. Rocket Motor Analogy of Solar Wind Expansion

29. Properties of the Solar Wind at Earth’s Orbit • It blows by the Earth at speeds of about 400 km/sec • Consists primarily of protons, but carries multiply charged ions of other species, primarily O+++++++ and He++ • Typical densities of 5 cm-3 • Carries a highly variable magnetic field the order of 10 nT.

30. The Earth’s Magnetosphere

33. Substorm growth phase • Begins with southward turning of the interplanetary magnetic field • Enhanced convection • Stretching of the magnetotail • Expansion of the auroral oval and equatorward movement of diffuse aurora

34. Ionospheric convection

35. Reconnection event

36. Action of magnetotail field lines during substorm expansion

37. Numerical Simulation Of Substorm Expansive Phase

38. Magnetic Field

39. Plasma Flow

40. Turbulent generation and propagation of Alfven waves

41. Field-aligned currents

42. Other parameters

43. Polar Satellite Observations

44. Substorm expansive phase • Decrease or reorientation of interplanetary magnetic field (not always) • Extended tail magnetic field snaps back carrying plasma earthward • Turbulence in inner edge of plasma sheet and Pi2 magnetic pulsations • Auroral expansion • Auroral electrojet • Ring current injection

45. Auroral Acceleration • We have presented circumstantial evidence linking shear Alfven waves and the aurora. • We now examine mechanisms for accelerating auroral electrons.

46. First Satellite Observation

47. The simulation domain

48. Simulation Parametersdi

49. Parallel Electric Fields

50. Energy Spectra Run #1