|Magnetic Field -
Secular Variation of the Inclination Component for the Epoch 2010.0
What this map layer shows:
Lines of equal change in the inclination of the Earth's magnetic field in arc-minutes per year.
is a force produced between electric currents. Electric currents within
the core of the Earth create a magnetic field which surrounds the
Earth. This field is what causes a compass needle to point north,
and it can be seen in the aurora
that is sometimes visible at high latitudes. The magnetism of the
Earth is referred to as geomagnetism.
For thousands of years, people have tried to solve the mysteries of
the Earth's magnetic field, making the study of geomagnetism one of
the oldest of the geophysical sciences. As early as the 1600s, scientists
recognized the need for accurate and continuous measurements of the
Earth's magnetic field. The first permanent magnetic observatories
were established 150 years ago. Today, a global network of more than
200 magnetic observatories, supported by individual national agencies,
provides the data that form the foundation for the modern science
of geomagnetism. The U.S.
Geological Survey (USGS) operates 14 magnetic
observatories as part of this global network.
As our society becomes progressively dependent upon advanced technological
systems, our need for geomagnetic data increases. Information collected
on the Earth's magnetic field is used to meet the growing needs of
Federal, State, and local governments, industry, academia, and the
public. We use geomagnetic data for mineral exploration, military
and commercial navigation, and geologic dating. Geomagnetic
storms (rapid variations in the magnetic field) pose significant
hazards to satellites, electrical power distribution systems, radio
communications, and geophysical surveys. The collection of geomagnetic
data allows scientists to provide advanced warning of geomagnetic
storms. An advanced warning of even a few minutes can save millions
of dollars in losses by permitting satellite and power system operators
to take mitigating actions.
Scientists at the USGS and at other agencies around the world compile
data on the magnetic field in five year increments, which is then
used to produce a model of the magnetic field called the International
Geomagnetic Reference Field (IGRF). Each IGRF model is based on data
collected in the recent past, preceding the model's construction,
and is intended to represent the field in the near future, following
the model's construction. Therefore the model for Epoch 2010.0 is
designed to reflect the magnetic field from 2010 to 2015. When referring
to a specific model, IGRF is followed by the epoch, as in IGRF 2010.
There are five basic elements that describe the direction and intensity
of the forces within the magnetic field. Direction is described by
declination and inclination; intensity is described by three components:
horizontal, vertical, and total field intensity. Five additional elements
describe the change over time, or secular variation, of the basic
elements. Inclination measures the angle between the force lines of
the magnetic field and a plane horizontal to the Earth's surface.
At the magnetic
poles the inclination is perpendicular to the Earth's surface.
The secular variation of the inclination shows how the inclination
is changing over time. This map layer was produced by the U.S. Geological
The Magnetic Field - Secular Variation of the Inclination Component
for the Epoch 2010.0 map layer shows lines of equal annual change
in the inclination of the Earth's magnetic field, derived from the
International Geomagnetic Reference Field (IGRF) for the epoch 2010.0.
Values are provided in arc-minutes per year. The inclination component
and the secular variation of the inclination component change smoothly
over most of the Earth. Also available in the National Atlas are nine
additional map layers describing components of the magnetic field.
More detailed information on geomagnetism is available from the USGS
Program and from the National
Geophysical Data Center Earth Magnetics page.