QST de W1AW
Propagation Forecast Bulletin 36 ARLP036
From Tad Cook, K7RA
Seattle, WA September 5, 2003
To all radio amateurs
SB PROP ARL ARLP036
ARLP036 Propagation de K7RA
Daily sunspot numbers were lower this week than last, and solar flux remained about the same. But the average daily planetary A index dropped by more than half to 14.3. That's the lowest it's been since the reporting week of July 3-9, 2003. The best day this week--in terms of stable geomagnetic conditions--was Sunday, August 31, when the planetary A index was only 7, and the mid-latitude A index was 5. The eight mid-latitude K indices for that day, reported every three hours, were 1, 2, 1, 1, 2, 1, 2 and 1. This is rather remarkable compared to recent conditions.
The forecast for the next few days is for unsettled to active geomagnetic conditions, with the predicted planetary A index for Friday through Monday, September 5-8, at 20, 12, 12 and 15. Predicted solar flux for Friday and Saturday is 115 and 120, then 125 for Sunday through Friday, September 12.
On August 29 a solar wind passed Earth around 1500 UTC, but this and subsequent wind from a coronal hole did not cause major disturbances. There were predictions last weekend of possible aurora for September 1 or 2, but the interplanetary magnetic field pointed north, and this protects Earth from disturbances. It is when the field points south that we are vulnerable, and despite a continued solar wind, any geomagnetic upset over the next few days is expected to be minor because of the north-pointing field. Participants in this weekend's All Asian DX Phone Contest or the North American CW Sprint have nothing to fear.
August has ended, and statistics show the average daily sunspot number dropped from 132.8 to 114.3 from July to August. The average daily solar flux declined by a smaller margin, from 127.7 to 122.1.
How does August compare with recent history, considering the solar cycle is declining? The average daily sunspot number for August is identical to April's value, 114.3, and only February and March had lower sunspot averages for 2003. Average daily sunspot numbers by month, from August 2002 through August 2003, were 191.0, 206.4, 153.9, 159.8, 144.8, 150.0, 87.9, 119.7, 114.3, 89.6, 118.4, 132.8 and 114.3. Average daily solar flux by month, from August 2002 through August 2003, was 183.9, 175.8, 167.0, 168.7, 157.2, 144, 124.5, 133.5, 126.8, 116.6, 129.4, 127.7 and 122.1. This looks like a steady decline in numbers. Especially dramatic are comparisons between August 2002 and August 2003.
Perhaps we're coming to the phase in the cycle following the peak when geomagnetic disturbances subside. This would be good for HF operators. Although we want plentiful sunspots, we also need stable geomagnetic conditions, especially in latitudes toward the poles and for propagation over polar paths.
Currently the prediction for the bottom of the sunspot cycle is for September 2006 to May 2007. The forecast for solar flux is about the same. Looking further out, a rough estimate shows the flux and sunspot values on the other side of the minimum for December 2007 at about the same level as December of next year, 2004. Between those dates are very low levels of activity, a good time to explore 160, 80, 60 and 40 meters.
The cycle prediction is from the August 12 edition of the NOAA Space Environment Center's Weekly Preliminary Report and Forecast of Solar Geophysical Data and the guide to the Report and Forecast.
Sunspot numbers for August 28 through September 3 were 146, 132, 120, 101, 59, 90 and 74, with a mean of 103.1. The 10.7-cm flux was 118.7, 116.3, 114, 109.7, 108.1, 105.7 and 110.5, with a mean of 118.9. Estimated planetary A indices were 18, 15, 17, 7, 14, 12 and 17, with a mean of 14.3.