[HCDX] NW7US Propagation Update: 18-XI-2003

[Tomas NW7US <nw7us@xxxxxxxxxxx>]

Old solar sunspot region 486 (now numbered 506?) is rotating back
into view on the solar disk.  At 1011Z 18-XI-2003, it produced an 
M4.5 flare, showing that it will play a significant role in space 
weather over the next week.  Region 486 was the origin of the 
historic X28 flare of 4-XI-2003.

The other giant sunspot groups 493, 487 and 488 are also coming 
into view as they rotate from around the far side of the sun.  
Remember, these groups were the origin of many M- and X-class 
flares during the end of October and the beginning of November 
2003.  Do they hold enough punch to continue the strong flare 
activity we saw before?  It does appear that they are complex 
enough to continue producting moderate flares, as we are seeing 
quite strong activity on the eastern solar limb.

Region 501 continues to have a structure that is capable of 
additional M-class flares.  Already, today, this group produced 3 
M-class flares, and the forth seems to be associated with the old, 
returning region 486.  Sunspot region 501 will remain with us for 
the rest of the week.

At the same time, the large coronal hole that has continued to 
influence the geomagnetic activity is moving toward the edge of 
the sun, and will rotate out of view soon.  The solar wind speed 
is slightly decreasing as a result.  The orientation of the 
Interplanetary Magnetic Field is now mostly northward in its 
orientation (Bz is positive), so this has helped quite the 
geomagnetic activity, but not by much.

Speaking of coronal holes and coronal mass ejections: A CME was 
detected from a flare from region 501.  This CME will at least 
partially impact Earth in the next 24 to 36 hours.  This will 
elevate the already disturbed geomagnetic activity.

High Frequency propagation is expected to be fair to good for the 
next 12 hours or so.  The slight lull in the geomagnetic activity 
has helped overall conditions, and there is an increase in the 
10.7-cm flux level.  This is causing a slight improvement over 
most low- to mid-latitude paths.  But, conditions will become 
rough as we see an increase in X-ray flare activity as well as 
the arrival of new CMEs.  HF propagation will be poor over the 
high-latitude regions (there is a chance of returning proton-
event causing X-ray flares from the old regions now rotating into 
view), and poor to fair over the mid- and low-latitude paths.

The highest frequencies will have short and weak openings, with 
the strongest being on paths between north and south stations.  
The middle frequencies will be strong and reliable for the next 
12 to 24 hours, but will experience degradation with the return 
of the flaring and geomagnetic activity.  Low frequency 
propagation will be fair for the next 12 hours, then degrading 
with increased geomagnetic activity and flares.

X-ray flares cause short-term radio blackouts on the sunlit side 
of the Earth that can last mere minutes (with weaker flares) to 
several hours (with major flares).  CMEs can cause geomagnetic 
storms, which cause the ionosphere to recombine (causing the 
ionosphere to lose its ionization).  This causes the maxiumum 
usable frequencies to fall as much as 50% of normal.  Having 
both X-ray flares along with geomagnetic storms can close HF 
down completely.

I will continue to monitor solar weather, and will post updates 
as events warrent.  A full discussion is on-going at 
http://hfradio.org/forums/ - and live data is organized for 
your browsing at http://prop.hfradio.org/


73 de Tomas, NW7US (AAR0JA/AAM0EWA)
--
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