Description of geomagnetic activity

Short Term Hourly Range Activity Levels (nT)
Zone Quiet Unsettled Active Stormy Major Storm
Polar Cap 0 - 50 50 - 100 100 - 180 180 - 600 600+
Auroral Zone 0 - 90 90 - 170 170 - 300 300 - 1000 1000+
Sub-Auroral Zone 0 - 30 30 - 50 50 - 90 90 - 300 300+
Map showing the location of magnetic activity zones in Canada.  The auroral zone is a band across the Hudson Bay and the Yukon.  North of that is the polar cap.  South of the auroral zone is the sub-auroral zone.

The levels of geomagnetic field activity, or disturbance, currently used in the short-term forecasts are labelled qualitatively for general usage. For each of the three major zones (subauroral, auroral, polar cap), the range of activity typically experienced in the zone is subdivided into five classifications: quiet, unsettled, active, stormy, major storm. The actual boundaries in terms of field intensity vary from zone to zone. This is because, for a given global state of the magnetic field, the auroral zone activity tends to be more intense than that in the polar cap and the subauroral zone. There are many measures of magnetic activity, but we use a simple one that can be determined extremely quickly and that is quite sufficient for this purpose. We consider how much the intensity changes during an hour (ie maximum value - minimum value), known as the hourly range. During an interval of several hours, we consider the median and maximum hourly ranges. The observed (forecast) median range provides the main review (forecast) message, while the maximum observed (forecast) range provides the supplementary review (forecast) message. The intensities are based on measurements derived from representative magnetic observatories in each zone (units are nanoteslas, nT)

For the benefit of those users who need to relate to the Kp index, we provide the following equivalences, which apply to all three of the zones used in our forecasts. In the diagram, the top layer indicates our forecast levels, the second and third layers indicate the Kp index and its subdivisions. It should be noted that the Kp index is defined for 3-hour intervals.

Kp Diagram.  Description follows.

Some information on the Kp index can be found at the following external links:

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