Greg,
The A-index is a measure of magnetic activity at a particular magnetic
bservatory. There is a global A-index too, averaged over a dozen
observatories around the world. The K-index is given eight times a day
and represents current conditions, not averaged over more than 3 hours.
In any event, magnetic activity starts to get interesting when the
A-index gets above 25, with magnetic storming for A above 40-50. Those
conditions involve energy input to the atmosphere, from collision ionization
by energetic auroral electrons and the ohmic-heating of ionospheric current
systems. That input has been observed to propagate to lower latitudes
from the auroral zones and can perturb the lower atmosphere by generating
travelling ionospheric disturbances (TID) and acoustic/gravity waves.
Those conditions can also affect propagation on Top Band but are not
well-documented as observations by the scientific community have become
sporadic now that the main features of the events have been established.
But it is of interest to log Top Band conditions with various levels of
magnetic activity, for your information as well as possible recurrences.
Have fun, another season is about to start with the equinox.
73,
Bob, NM7M
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