QST de W1AW
Propagation Forecast Bulletin 10 ARLP010
From Tad Cook, K7VVV
Seattle, WA March 9, 2001
To all radio amateurs
SB PROP ARL ARLP010
ARLP010 Propagation de K7VVV
Although the week's sunspot numbers and solar flux began low, they rose steadily, with the average sunspot number up over 8 points and average solar flux up over 10. Last Thursday, the beginning of the reporting week, the sunspot number was a very low 59. December 10, 2000 was the last day with a reported sunspot number as low as this, when it was 58. Prior to that, the previous low was around September 11 and 12, 2000, when it was 27 and 38. To find another date with a sunspot number as low, one would have to look on the other side of the solar cycle peak, way back to October 2, 1999, when it was 47. Current activity is a far cry from last summer, when daily sunspot numbers were routinely 200 or more, or even 300, or on July 20 over 400.
Solar flux rose from a low of 129.7 last Friday, then jumped nearly nineteen points in a single day to 176.6 on Wednesday. The official daily solar flux is always the noon reading, but there is also a 10:00 AM and a 2:00 PM reading (at local time for the observatory in Penticton, British Columbia). On that day the early reading was 164.8 and the late one was 165.5, so the noon reading, over a ten- point difference, seems somewhat an anomaly. Solar flux has not been this high since January 13, when it was 184.3.
Solar flux is predicted at 170 for Friday and Saturday, March 9 and 10, and 165 for Sunday and Monday. Current best projections show flux values hanging around 160 for March 13-23, then dropping to 135 around March 28 or 29.
NASA's Spaceweather.com reports that the flux of solar x-rays has increased several-fold since Monday because hot gasses trapped by magnetic fields above several sunspots are glowing with high-energy radiation. M-class solar flares could erupt from regions 9368 and 9371 over the next day. Currently quiet geomagnetic conditions are forecast, but the planetary A index could rise to 15, indicating unsettled conditions on Sunday. For an explanation of the different classes of solar flares, look at http://spaceweather.com/glossary/flareclasses.html.
While the solar cycle appears to have peaked last year, we are still at a high point in the cycle, and headed toward typical spring HF conditions, when overall propagation is best (like in the fall equinox). These times are when sunlight is maximized in both the northern and southern hemispheres, and propagation between the two is best.
This week we will attempt another path projection, this time from Austin, Texas to the rest of the world.
Sunspot numbers for March 1 through 7 were 59, 77, 138, 157, 143, 131 and 102 with a mean of 115.3. 10.7 cm flux was 131.4, 129.7, 139.6, 141, 155.8, 157.8 and 176.6, with a mean of 147.4, and estimated planetary A indices were 5, 8, 14, 17, 18, 6 and 7 with a mean of 10.7.