[CQ-Contest] NW7US Propagation Bulletin: 26-XII-2004 / 1725 UTC (CQ WW CW Contest Outlook)

[NW7US, Tomas]

The contest starts on 27-XII-2004 UTC, during a period of unsettled  
geomagnetic activity.  Several official forecasting centers (i.e., SEC  
NOAA, US Air Force, and SIDC) predict a continued downward trend in the  
planetary A (Ap) index, with the consensus being an Ap index of 10 on the  
27th, and 5 on the 28th.  Another put it at 15 on the 27th, and 10 on the  
28th, while SIDC says the Ap will be 12 on both days.  They all concur  
that the Ap trend is downward.  Does this follow what's on the Sun?

A large and well-defined coronal hole which spans the surface of the  
visible side of the Sun, from the Northern Hemisphere to the Southern  
Hemisphere, is rotating to the very center of the Sun.  This is known as  
the "geoeffective position" since a coronal hole so positioned as to spew  
its plasma out into the solar wind in such a way as to impact the Earth.   
This coronal hole, numbered by Jan Alvestad as CH129, will be in full  
geoeffective position during the weekend of November 27 and 28.  With the  
solar wind speed already over 400, we're going to see the solar wind pick  
up speed, and increase in pressure.  Therefore, sometime during the  
contest period, we're going to see the geomagnetic field increase  
activity.  If the magnetic component of the solar wind turns southward,  
we're going to see minor storm levels later in the contest period.

The 27-day rotation method does show that the Ap should continue in a  
downward trend, with the 27th being High Normal, and the 28th being Above  
Normal (for those of you using the CQ Magazine Last Minute Forecast and  
associated tables).  However, I am taking into consideration the coronal  
hole and estimate that we'll have High Normal on the 27th, and either High  
Normal or Low Normal conditions on the 28th.

The returning sunspot region region NOAA 0696, which has produced several  
X-flares and halo-CMEs during the previous rotation could bring about some  
increased flaring activity over the weekend.  Will we see large flares?   
If so, there will be short periods of radio blackout on the higher HF  
frequencies.  The probability for this is still considered slight, though.

The flux, however, looks promising.  The forecasts all point to a 10.7-cm  
flux of at least 115 for both days, with some forecasting 130 to 135.   
This level of solar activity will provide good propagation over most paths  
during this contest weekend.  Using a digital mode, i.e., CW, you will get  
more bang for the buck.

Good luck to all of you in the contest!

73 de Tomas, NW7US (AAR0JA/AAA0WA)

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