[RTTY] Geomagnetic Storms, Aurora, and propagation

[NW7US, Tomas]

NW7US Propagation Bulletin - 25-VII-2004 / 1500Z

We are in the middle of a very strong geomagnetic storm.  The estimated  
planetary K index (Kp) reached a level of 8, with the Bolder, Colorado K  
reading a level 7.  We have been seeing the geomagnetic activity increase  
on a steady climb since yesterday.  As I had predicted in my last NW7US  
Propagation Bulletin, we have been experiencing a geomagnetic storm since  
Thursday.

Right after my last bulletin went out, the Kp rose to the level of 6.  For  
most of Friday, the Kp stayed at or above 5, until the end of the UTC  
day.  As Saturday progressed, the geomagnetic field again became highly  
active and reached storm levels.  It has continued to get more intense and  
we've now reached very high storm levels.

All of this activity is caused by several concurrent influences.  During  
the last week, we have had moderate to high solar activity, with a steady  
occurrence of moderate flares (M-class).  Some of these have had coronal  
mass ejections associated with them.  In addition, there are two coronal  
holes that have enhanced the solar space wind.  The steady elevated wind  
speed and pressure, combined with the Interplanetary Magnetic Field's  
southward orientation in relationship with the Earth's Magnetosphere, has  
caused great disturbances in our geomagnetic fields.

At the time of writing this bulletin, the Solar Wind Speed is 528  
kilometers per second.  That's not as high as during other major  
geomagnetic storms, where we've seen it as high as 800 km/s.  However, the  
IMF has been consistantly southward in its orientation for several days.   
(This is shown in the Bz index, where a negative number indicates the  
southerly orientation. The higher the negative index, the more southward  
the IMF's orientation).  This allows a strengthening of the interaction  
between the two magnetic fields.  And, with that, a "window" opens in our  
Earth's natural sheilds through which solar plasma can "rain" down into  
the Auroral ovals at our poles.  This causes an increase in the Auroral  
activity.  We are seeing an Auroral Activity index maxed out right now at  
a level of 10.

The results of all of this continual geomagnetic storminess is the  
degradation of world-wide ionospheric conditions.  Geomagnetic activity  
causes the ionosphere to "recombine," much like what happens during the  
hours of darkenss.  Geomagnetic activity can cause the ionosphere to  
become "depressed" by ten to thirty percent from normal levels.  This  
lowers the maximum usable frequency over any given path.  We also see the  
increase in Aurora propagation (AU).

I have seen reports already of AU openings.  If you are not on the air,  
don't waste any time!  Check out VHF weak-signal propagation via aurora.   
Check out shortwave -- during aurora some interesting HF propagation can  
be experienced.

I expect to see the geomagnetic storms to continue for a number of days.   
There are two coronal holes still influencing the solar wind, and we are  
seeing a steady series of M-class flares, some of which may cause a  
glancing blow of coronal mass ejections.  However, I do expect the level  
of the storms to slowly decrease.  With that, we'll see the solar activity  
decrease a little until the next sunspot group rotates into view.

Until next time, happy DXing!

-- 

73 de Tomas, NW7US (AARØJA/AAAØWA)

: Propagation Editor for CQ, CQ VHF, and Popular Communications :
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