Earth's Web sites resourses
http://www.seds.org/nineplanets/nineplanets/earth.html
http://eospso.gsfc.nasa.gov
The Earth is composed of:
-
Solid Crust
-
Semi-Solid Mantle
-
Liquid Iron Outer Core
-
Solid Iron Inner Core
The magnetic field near the Earth is
from a combination of three sources:
-
97 - 99 % Main Field (From electric
currents in the Outer Core)
-
>1 - 2 % Crustal Field (From magnetized
rock in the Crust)
-
1 - 2 % External Field (From ionized
particles above the Earth)
The Main Field is near dipolar
and varies in strength from approximately 30,000 nT near the equator to
60,000 nT at the poles. Its secular variation or amount of change is about
1% per year. The north and south pole undergo a reversal (change in direction)
every 500,000 years, on average.
The External Field varies on time
scales of seconds to days, primarily due to solar interactions. These fields
result from current systems and range in intensity from fractions of a
nT to thousands of nT.
Back to Terrestrial Magnetism Home Page
Responsible NASA official:Dr. Herbert Frey
Web Curator: Katia Nazarova (Raytheon)
Email katianh@geomag.gsfc.nasa.gov with comments or suggestions
Last modified on May 15, 2001