THE IMPORTANCE OF REAL-TIME DATA IN SOLAR-TERRESTRAIL PHYSICS

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Geomagnetic Storms
Y. Kamide Kyoto University
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Outline

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• Geomagnetic disturbances
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Storms
Substorms
Inner magnetosphere
Magnetotail
Low latitudes
High latitudes
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Chapman 1961

• A magnetic storm consists of sporadic and
  intermittent usually polar disturbances, lifetime
  being one or two hours. These I call polar
  substorms.
• Although substorms occur most often during
  magnetic storms, they appear also during quiet
  periods.

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The beginning of solar-terrestrial
physics (1) The discovery of geomagnetic storms
(later term) by Graham in 1724 (2) The discovery
by Oersted in 1820 that electric currents produce
magnetic forces (3) The law of Ampères force in
1821 (4) Electromagnetic induction by Faraday in
1831 which were to lead subsequently to
Maxwells equations of electromagnetism.
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Who, and when, introduced the geomagnetic storm
into the scientific community? Alexander von
Humboldt (1769-1859) used magnetisches
Ungewitter (magnetic thunderstorms) to describe
the variability of geomagnetic needles, which
were associated with the occurrence of light
meteor, (auroras). He thought that magnetic
disturbances and auroras are two manifestations
of the same phenomenon. It was found that
the storm-time disturbance generally reduces the
daily mean value of the horizontal intensity.
During the First Polar Year (1882-1883),
scientists defined geomagnetic storms as
intense, irregular variabilities of geomagnetic
field which occur as a consequence of solar
disturbances.
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• Energy Balance Equation
• dE/dt Q - L
• Q - E/t

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• Magnetospheric storm
• ? (Magnetospheric substorm) i

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• Magnetospheric storm
• ? (Magnetospheric substorm) i
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• Magnetospheric storm
• ? ai (Magnetospheric substorm) i

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• Magnetospheric storm
• ? (Magnetospheric substorm) i
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• Magnetospheric storm
• ? ai (Magnetospheric substorm) i

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• Summary
• A geomagnetic storm is identified by the
  development of the ring current in the
  magnetosphere, which is carried by energetic (10
  - 200 keV) ions in L 2 - 7. The growth and
  decay of geomagnetic storms can be monitored by
  the Dst index.
• Studies of geomagnetic records with the help from
  solar and auroral observations were conducted in
  parallel with discoveries of the important laws
  of electromagnetism.
• 3. Most of the Dst variance during intense
  geomagnetic storms can be reproduced by knowledge
  about changes in large-scale electric fields in
  the solar wind. A continuing controversy exists,
  however, as to whether the successive occurrence
  of substorms plays a direct role in the
  energization of storm-time ring current particles.

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• CMEs and CIRs are the primary sources leading to
  major geomagnetic storms. These are dominant
  near the maximum phase and during the declining
  phase of the solar cycle, respectively.
• The increase in the ring current of about 50 of
  the largest geomagnetic storms goes through two
  steps at the main phase.
• Not only the ring current but also the
  magnetotail current is the main sources to
  produce storm-time changes in Dst.
• 7. The abundance of ionosphere-origin ions is
  high and is correlated well with substorm
  activity during the main phase of geomagnetic
  storms.