ZCZC AP31
QST de W1AW
Propagation Forecast Bulletin 31 ARLP031
From Tad Cook, K7VVV
Seattle, WA July 31, 1998
To all radio amateurs
SB PROP ARL ARLP031
ARLP031 Propagation de K7VVV
Solar activity was a bit higher this week, with average solar flux up nearly 14 points and sunspot numbers higher by about six points. Last Thursday, July 23 had a planetary A index of 37, exactly like the previous Thursday. A few days later geomagnetic indices had settled down, and after Saturday conditions were quite stable. Solar activity is still lower than most forecasters predicted for this point in the solar cycle, but perhaps we can take some cheer by comparing current conditions with a year ago. Average solar flux this week is about 45 points higher than the average solar flux for the same week last year. You can peruse last year's propagation bulletins if you look on the ARRL web site at http://www.arrl.org/w1aw/prop/1997-index.html
Over this weekend, Friday through Sunday, predicted solar flux should decline to 112, 110 and 108, and planetary A index should be around 10 each day. Solar flux is expected to bottom out just above 100 around August 9-13, then rise above 110 after mid-month and back around 120 after August 20. Look for disturbed conditions around August 17-21, with the highest A and K indices around August 19 and 20. This is due to a recurring coronal hole rotating back into a position which should affect earth.
A good way to visualize the rotation of the sun with sunspots and coronal holes drifting across the visible solar disk is to look at the Marshall Space Weather bureau 10 day solar animation site on the web at http://spaceweather.com/java/solar-anim.html
Radio telescopes have finally located the SOHO spacecraft rotating slowly near its original position. It is not far off course, and it still may be possible to establish contact and get it working again. If not, it might be feasible to put similar instruments in another proposed orbital craft called Triana, the proposed craft that is supposed to beam a live picture of the earth back to a web page on the internet.
The loss of SOHO has been a big disappointment for solar observers. Things went awry when ground control turned off a gyroscope, hoping to extend the life of the instrument. When a previously unknown software error caused the craft to spin out of control, craft computers looked to the gyroscope for emergency guidance and due to the lack of signal misjudged the position in relation to the sun. When this happened, solar panels turned away from the sun and SOHO lost power.
In August, particularly later in the month, we may start to see some Fall conditions on HF with higher usable frequencies during daylight. 20 meters should be the most reliable band for long range communications, but look for occasional openings on 15 meters and trans-equatorial conditions on 10 and 12 meters.
Interesting events continued on VHF this week, with six and two meter openings from Hawaii to the West Coast. There was a report of six meter propagation from South America to Israel from PY5CC, and N5JHV worked Japan after 0030Z on six.
Sunspot Numbers for July 23 through 29 were 129, 110, 85, 80, 109, 116 and 115 with a mean of 106.3. 10.7 cm flux was 115.4, 125.2, 121.7, 119.1, 119.5, 121.3 and 119.5, with a mean of 120.2, and estimated planetary A indices were 37, 22, 16, 6, 6, 6, and 6, with a mean of 14.1.