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[Propagation] NW7US Propagation Bulletin: 26-XII-2004 / 1725 UTC(CQ WW C

To: CQ_Contesting <CQ-Contest@contesting.com>
Subject: [Propagation] NW7US Propagation Bulletin: 26-XII-2004 / 1725 UTC(CQ WW CW Contest Outlook)
From: "NW7US, Tomas" <nw7us@hfradio.org>
Date: Fri, 26 Nov 2004 09:59:33 -0800
List-post: <mailto:propagation@contesting.com>
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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