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Space Science Lecture 3, June 11, 2013 Solar Wind–Magnetosphere –Ionosphere Coupling

Space Science Lecture 3, June 11, 2013 Solar Wind–Magnetosphere –Ionosphere Coupling. Hyomin Kim Center for Space Science and Engineering Research Virginia Tech. Terminology. Solar wind-magnetosphere Coupling Magnetosphere-ionosphere coupling Sun-Earth connection

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Space Science Lecture 3, June 11, 2013 Solar Wind–Magnetosphere –Ionosphere Coupling

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  1. Space Science Lecture 3, June 11, 2013Solar Wind–Magnetosphere –Ionosphere Coupling Hyomin Kim Center for Space Science and Engineering Research Virginia Tech

  2. Terminology • Solar wind-magnetosphere Coupling • Magnetosphere-ionosphere coupling • Sun-Earth connection • Solar-terrestrial environment • Space weather

  3. An ideal Earth’s Magnetic Dipole w/o External Forces • North pole is magnetic south pole and vice versa, right?

  4. (Slightly) More Realistic Earth’s Magnetic Dipole • What makes the field lines look like this?

  5. Formation of Magnetosphere • Why do the solar wind particles deflect around the magnetosphere? • Again, what makes the field lines look like this?

  6. Solar Wind–Magnetosphere Coupling The boundary between the magnetosphere and the solar wind, at which Pdyn SW = PB earth • IMF and the earth’s magnetic fields are coupled by magnetic reconnection. The boundary at which the speed of the solar wind abruptly drops from supersonic to subsonic as a result of its approach to the magnetopause.

  7. Plasma Particle-Magnetic Field Interaction • Charged particles are deflected by the Lorentz Force (F = q(E + v x B)). • Under certain conditions a plasma is bound to the magnetic lines of flux that pass through it  “Frozen-in Flux Condition” •  These are the quick-and-dirty answers to the questions “why do the solar wind particles deflect around the magnetosphere?” and “what makes the field lines look like this?”.

  8. Magnetic Reconnection • A physical process in highly conducting plasmas in which the magnetic topology is rearranged and magnetic energy is converted to kinetic energy, thermal energy and particle acceleration. When two oppositely directed magnetic fields (red and blue arrows) get pushed close together, they merge (reconnect) and snap to a new shape. This releases energy and can accelerate electrically charged particles nearby. Image Credit: European Space Agency (cited from www.nasa.gov)

  9. This movie (reconnection) has been removed due to the file size (90 MB!).Please ask me if you want this file.

  10. Magnetosphere-Ionosphere Coupling • Dynamo due to the solar wind • Field-aligned currents (FAC) play an important role in transporting energy from the magnetosphere to the ionosphere and vice versa.

  11. Magnetosphere-Ionosphere Coupling • What we measure on the ground is only from the Hall currents. Why?  Fukushima’s theorem.

  12. E x B Drift • Lorentz Force, F = q(E + v x B) • F = 0 as this term gives only the circular motion at fc . • Therefore, E + v x B = 0. • x B on both sides and get: • v = (E x B)/B2 • This is called E x B drift and v is independent of  the mass and sign of the charge.

  13. Fukushima’s Theorem • Therefore, B measured on the ground is only from the Hall currents.

  14. Fukushima’s Theorem • Fukushima's Theorem holds that for all points beneath the ionosphere the magnetic fields from field-aligned currents and their corresponding Pedersen currents exactly cancel. By superposition the total magnetic field at the ground is then equal to the magnetic field from just the ionospheric Hall currents. • Fukushima's Theorem holds in any planar or spherical geometry, provided that the field-aligned currents are perpendicular to the ground, and that the ionospheric conductance is spatially constant. Neither of these conditions holds strongly in the auroral region of the Earth's ionosphere.

  15. Magnetic Field Measurement on the Ground • How do we measure magnetic field from current?

  16. Ampere’s Circuital Law Electric currents produce magnetic fields around the loop that carries the currents.

  17. SW-M-I Coupling and Space Weather • Note: This is not the only process happening in space! The actual sun-earth connection is much more complex. • Q: What is the most popular manifestation of the sun-earth connection we can possibly see (with the naked eye) on the ground?

  18. Ground Effect of Space Weather • One of the ground effect of space weather is geomagnetically induced current (GIC). • Faraday’s law of induction.

  19. Observations of Magnetic Field • Besides auroral observations, magnetic field measurements are one of the traditional way of observing the space weather phenomena. • “The compass is always in motion” (George Graham, 1722). • Magnetic field sensor - “magnetometer”. • Induction type magnetometers are widely used for space applications.

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