Basic magnetic theory
ENVI-MAG Manual B1-9
Overview
Magnetic storms
When the timing and duration of micro-pulsations becomes severe it is then
called a magnetic storm. Typical micro-pulsations last a few hours whereas
magnetic storms can last for days. The next figure (Figure B-10) illustrates a
hypothetical magnetic storm. Needless to say, it is not recommended to
conduct a total-field survey during a magnetic storm, as you may not be able
to remove all of the rapidly changing variations in the magnetic field, giving
rise to perhaps false anomalies.
Figure B-10 Typical magnetic storm (after Breiner, 1973).
You can obtain magnetic activity forecasts (much like weather forecasts)
from several agencies worldwide, through an international network of
centres called the IUWDS, (International Ursigrams and World Days
Services). There exist ten regional warning centres (RWC’s) that provide
geomagnetic activity information to the scientific and user communities
within their own region. Please note that not all of these centres provide the
same services and forecasts. However, all of them have access to all
information provided by the other centres.
The following table gives a list of contact telephone, facsimile and telex
numbers for each of these regions. In Canada, geomagnetic forecasts are
available through the Geophysics Division of the Geological Survey of
Canada, while in the United States this information is available from NOAA.
This information will greatly help you in planning your magnetometer survey.
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