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[RTTY] Geomagnetic Storms, Aurora, and propagation

To: SWL <swl@mailman.qth.net>,"SW - TheBasicsOfShortwave" <thebasicsofshortwave@yahoogroups.com>,SWARL <SWARL@yahoogroups.com>, SWBC <swbc@topica.com>,"SWL and Ham DX Club" <hamradioandshortwavedxclub@yahoogroups.com>,VHF <vhf@w6yx.stanford.edu>,"rtty@contesting.com" <rtty@contesting.com>,CQ_Contesting <CQ-Contest@contesting.com>
Subject: [RTTY] Geomagnetic Storms, Aurora, and propagation
From: "NW7US, Tomas" <nw7us@hfradio.org>
Date: Sun, 25 Jul 2004 09:13:41 -0700
List-post: <mailto:rtty@contesting.com>
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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