[SFDXA] Explanation of Solar Flux A&K index

[Irwin Wallace]

This information is for those of us (myself included) who need a good 
short remainder.    

*The Earth's magnetic field is continuously monitored by a network of 
magnetometers. These readings are converted into the A and K index values.

The K index is computed once every three hours (eight times a day) and the 
values can range from 0 to 9, with 0 being inactive, and 9 representing an 
extreme severe storm condition. The values are quadi-logarithmic.

    * K = 0 Inactive
    * K = 1 Very quiet
    * K = 2 Quiet
    * K = 3 Unsettled
    * K = 4 Active
    * K = 5 Minor storm
    * K = 6 Major storm
    * K = 7 Severe storm
    * K = 8 Very severe storm
    * K = 9 Extremely severe storm 

The A index is linear, and is computed from the eight previous K index values. 
It ranges from 0 (quiet) to 400 (severe storm).

    * A = 0 - 7 Quiet
    * A = 8 - 15 Unsettled
    * A= 8 - 15 Unsettled
    * A = 16 - 29 Active
    * A = 30 - 49 Minor storm
    * A = 50 - 99 Major storm
    * A = 100 - 400 Severe storm 

Generally, propagation conditions are best when the A index is 15 or lower, and 
the K index is 3 or lower.

Besides causing auroral activity, high geomagnetic field conditions can affect 
the electrons in the ionosphere, reducing the maximum usable frequency (MUF).
-- *