QST de W1AW
Propagation Forecast Bulletin 10 ARLP010
From Tad Cook, K7VVV
Seattle, WA March 7, 2003
To all radio amateurs
SB PROP ARL ARLP010
ARLP010 Propagation de K7VVV
Thanks to Carl Luetzelschwab, K9LA for filling in and writing last week's Propagation bulletin.
Carl mentioned the decline of the current solar cycle. During the early years of the decline (which is where we are now) we see quite a variation in the solar flux and sunspot numbers from week to week, although the trend is definitely downward. At the bottom of the cycle there is very little variation. Just week after week of hardly any sunspots or none at all.
Check this Propagation bulletin from July 1996 at http://www.arrl.org/w1aw/prop/1996-arlp031.html. "No sunspots visible for 11 days in a row," back in the very quiet summer of '96.
This week we saw the average daily sunspot number increase nearly 50 points over the previous week, and average daily solar flux up 30 points. The geomagnetic indices were active after a robust solar wind arrived on March 3. The most active period was late on March 3 into March 4 when the planetary K index reached 4 and Alaska's College K index reached 6.
Currently on Thursday evening we are affected by a high-speed solar wind stream from a coronal hole causing minor geomagnetic storms in high latitudes. This would result in absorption of HF signals over polar paths. Geomagnetic indices are expected to be unsettled to active over the next few days, and solar flux should decline again. Solar flux is expected to go below 145 by March 10 and then reach a short-term minimum below 110 around March 22-23.
Since February is over, now we can look at monthly average sunspot and solar flux numbers to spot a trend. Average daily sunspot numbers for September 2002 through February 2003 were 206.4, 153.9, 159.8, 144.8, 150.0 and 87.9. Average daily solar flux for those same months was 175.8, 167.0, 168.7, 157.2, 144.0 and 124.5. This is quite a decline. The average sunspot number for February of last year was nearly 107 points higher at 194.5, and average solar flux was 205, more than 80 points higher than February 2003.
For more information about propagation and an explanation of the numbers used in this bulletin, see the Propagation page on the ARRL Web site at, http://www.arrl.org/tis/info/propagation.html and especially the article "The Sun, the Earth, the Ionosphere," by Carl Luetzelschwab, K9LA.
Sunspot numbers for February 27 through March 5 were 82, 77, 73, 67, 136, 160, and 138, with a mean of 104.7. 10.7 cm flux was 117.6, 124.9, 138.1, 147.3, 149.1, 146, and 148.5, with a mean of 138.8. Estimated planetary A indices were 22, 17, 14, 14, 15, 26, and 16, with a mean of 17.7.