Week 38
Lecture 9:
• Internal magnetic field
• Magnetic elements
• Dipole description
• Spherical harmonic
analysis of B-field
Lecture 10:
• Magnteosphere
shape/modified by
external currents
• Stand-off distance
• L-shell mapping
• Chapmann Ferraro
current
• Tail currents
History
221-206 BC : Probably first compass made in China
(during Qin dynasty)
800-1050 AD: Compass seems to have become a usual
tool for navigation
1596 :
Barentz makes the first measurements of
declination in Norway after it became clear
that compass does not point exactly north
1600 :
Gilbert suggested that the source of the
Earth’s magnetic field lies inside the Earth &
published ”De magnete”
1838 :
Gauss introduced spherical harmonic
analysis.
History cont.
~1820 :
Hans Christian Ørsted discovered the
relationship between electric currents and Bfields
1896-1903 : Kristian Birkeland organized major
campaigns to map the impact of solar activity
on the Northern Light & Earth magnetic field
) William Gilbert (1544-1603)
1600 – The Earth is a Big Magnet
Drift of the Magnetic North Pole
from 1831 to 2006
Will the MNP be in Sibir in 40 years?
B- Vector Field
Which Pole is Which?
• Field line
perpendicular at Dip
Pole (Dip=90°)
• Dipole Axis (Dip<90°)
Mathematical fit to
observations is dipole
with quadropole,
octopole components
• Eccentric Dipole Axis
(Dip<90°) minimizes
higher order poles by
moving away from
Earth’s center.
Dip-polen (N1)-Dipol-polen (N2)
omkring 1980