Space Weather

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. (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.

K Index 0 1 2 3 4 5 6 7 8 9
A Index 0 3 7 15 27 48 80 140 240 400

The plot below contains the estimated 3-hour planetary K-index. The chart below is created with data using ground-based magnetometers throughout Canada and the United States. K-indices of 5 or greater indicate storm-level geomagnetic activity. (Courtesy

The following information is provided by the Solar Terrestrial Dispatch and is used with permission.  The image below is a recent high-resolution map of Maximum Usable Frequencies (MUF) for 3,000 kilometer radio signal paths. It is also a map showing the current location of the auroral ovals, the sunrise/sunset terminator and the regions of the world where the sun is 12 degrees below the horizon (which estimates the gray-line corridor where HF propagation is usually enhanced).

The MUF map above can be used by radio communicators to determine maximum usable frequencies for any world-wide path at the indicated time (UTC). RED lines will appear on the MUF map if x-rays reach levels capable of producing high frequency (HF) fadeouts on daytime paths. The red contour ines represent the highest frequency (MHz) that may be absorbed by the enhanced solar flare x-rays.

The MUF for any 3,000 kilometer path can be determined by finding the midpoint (half-way point) of the path and examining the MUF at that midpoint on the map by finding the labelled MUF contour value. All contours are given in MHz. For 4,000 kilometer paths, multiply the given contoured MUF values by 1.1. The MUF for the given 4,000 km path is then determined at the midpoint of the desired path. For longer path lengths, divide the path into equal 3,000 or 4,000 km segments and compute the MUFs corresponding to the two midpoints that are 1,500 or 2,000 km from each end of the path. Then select the lower of these two MUFs.