Topband: this past weekend

[N1BUG]

> Are there any guide lines so we can define the severity
> of Auroras?

A book could be written on that subject!   :-)

To define the overall intensity of a geomagnetic disturbance 
on a global basis, the Kp and Ap indices  (planetary K and 
A) would be a good starting point.  The K (Kp) index ranges 
from 0 to 9.  Last night Kp was running 4 to 6 (active to 
major storm).  Previous disturbances this season have 
produced periods of Kp 8 and 9 (very severe to extremely 
severe storm).  The K index is a measure of geomagnetic 
activity over a 3 hour period; A index covers a 24 hour 
period and is derived from the eight 3-hour K indices for 
the 24 hours in question.  Kp (and Ap) is derived from a 
large network of magnetometers around the world to provide 
an overall global representation of storm intensity.

Kp/Ap provide a good means of defining the overall global 
intensity of a disturbance, but are not well suited to 
defining the intensity of aurora for a particular region at 
a particular time, which might be more appropriate to our 
purposes if we are interested in a particular propagation 
path.  There are many variables involved there: local 
substorming, time of day, geomagnetic latitude, etc.  
Indices derived from one or more local or regional 
magnetometers would be more revealing there.  I haven't 
looked up last night's data for specific regions of 
interest. There are other useful indices and measurements 
in addition to K and A.  I'm not writing the book so I 
won't get into that at the moment.

Generally speaking, Kp of 4 to 6 results in very intense 
aurora at high geomagnetic latitudes, but far less 
impressive aurora here in the northeast US.

The descriptions of storm levels vary somewhat depending on 
just where you look up the information, but generally the K 
index correlations are as follows:

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

Paul  N1BUG