ZCZC AP31
QST de W1AW
Propagation Forecast Bulletin 31 ARLP031
From Tad Cook, K7RA
Seattle, WA July 30, 2004
To all radio amateurs
SB PROP ARL ARLP031
ARLP031 Propagation de K7RA
Sunspot 652 has rotated out of view, but it was the source of major excitement this week. Coronal mass ejections caused big geomagnetic storms on Sunday and Tuesday, July 25 and 27. The planetary A index was 122 on Sunday, 31 the next day and 162 on Tuesday. This caused radio blackouts on the HF bands, but it provided some excitement for 6-meter operators who reported great openings. The activity was enhanced by a south-pointing interplanetary magnetic field, leaving the Earth vulnerable to blasts of energy from the sun.
Auroral displays accompany periods of high geomagnetic activity, but they tend to predominate at higher latitudes. The stronger the activity, the higher the K and A index and the further south that northern lights can be seen. We're used to seeing photos of aurora from Alaska, especially above the Arctic Circle, but the Science@NASA site displays a photo taken July 27 at Borrego Springs, California--just 20 miles north of the 33rd parallel in Southern California.
Marc Weinberg, K9PET, sent a note about being maritime mobile in Svalbard as JW/K9PET last week. He was north of the 79th parallel, and when geomagnetic disturbances hit, he said he "thought the world had disappeared." The Lindblad Expeditions site includes a photo--taken from a distance--of his Amateur Radio operation on land from Raudfjorden Spitsbergen on July 20. In a few weeks, K9PET expects to post additional photos on his own Web site.
ARRL Lab Test Engineer Mike Tracy, KC1SX, let me know about an interesting link for a Macromedia Flash movie, HF Propagation Primer, by AE4RV.
Over the next few days expect unsettled to active geomagnetic conditions, and declining sunspot and solar flux numbers. Predicted planetary A index for Friday through Monday, July 30 through August 2, is 30, 20, 20 and 8. Predicted solar flux for the same period is 95, 90, 85 and 90. Solar flux is expected to peak again at about 125 around August 14-18. More sunspot activity is ahead, at least for the near term.
For more information concerning propagation and an explanation of the numbers used in this bulletin see the ARRL Technical Information Service Propagation page.
Sunspot numbers for July 22 through 28 were 117, 86, 109, 130, 113, 66 and 66, with a mean of 98.1. The 10.7 cm flux was 172.9, 165.1, 147.2, 156.2, 128, 118.1 and 100.7, with a mean of 141.2. Estimated planetary A indices were 19, 47, 27, 122, 31, 162 and 14, with a mean of 60.3. Estimated mid- latitude A indices were 13, 21, 29, 64, 26, 119 and 11, with a mean of 40.4.
