QST de W1AW
Propagation Forecast Bulletin 45 ARLP045
From Tad Cook, K7RA
Seattle, WA November 7, 2003
To all radio amateurs
SB PROP ARL ARLP045
ARLP045 Propagation de K7RA
The opening line to last week's propagation bulletin read, ''Solar excitement continued this week''. Last week's events caused excitement, but this week was positively historic. The largest explosion ever recorded in our solar system occurred Tuesday, November 4 when an X28 class flare exploded from sunspot 486. See data for this on http://sohowww.nascom.nasa.gov/hotshots/2003_11_04/, from the Solar and Heliospheric Observatory.
The flare erupted as the giant sunspot 486 was about to rotate from the visible disk. This means the blast wasn't aimed at earth, but was in a great position for taking images. The eruption saturated X-ray detectors on NOAA's GOES (Geostationary Operational Environmental Satellites, see http://goes.gsfc.nasa.gov/ ), and was so strong that the X28 measurement had to be estimated, as did the solar flux for November 4. The solar flux for that day (taken from the daily 2000 UTC reading) was measured at the observatory in British Columbia at 560.9, which is way off the scale. It was adjusted downward to an estimated 168 by NOAA's Space Environment Center.
The flare saturated observing satellites for about 13 minutes during the peak of the event, according to Christopher Balch of NOAA SEC, who spoke with Tomas Hood, NW7US (Tomas' web site is http://prop.hfradio.org/ ). The measurements stopped at X17.4. The level of the flare was estimated by analyzing data from HESSI, the High Energy Solar Spectroscopic Imager (see http://hessi.ssl.berkeley.edu/ ). An explanation of the X classes for rating solar flares is at http://spaceweather.com/glossary/flareclasses.html. Also, see http://hesperia.gsfc.nasa.gov/sftheory/flare.htm. The last time a huge flare saturated X-ray detectors was in April, 2001, and that one was X-20, the biggest recorded at that time. Keep in mind that there aren't any accurate records of flare intensity before about 30 years ago.
Roger Bonuchi, WB9JXE of Plainfield, Illinois wrote to say that his astronomy calendar for November 5 noted that on that day in 2001 there was a ''huge red aurora visible for hours over North America''. Looking back to our bulletin that covered that time at http://www.arrl.org/w1aw/prop/2001-arlp046.html we see that indeed there was a large geomagnetic storm. The bulletin reported that frightened Midwest residents, unfamiliar with aurora borealis, called 9-1-1 to report a ''nuclear death cloud''. Roger also said he picked up the N9RET CW beacon, which runs 2 watts on 28.2335 MHz. He found it odd that N9RET is about 25-30 miles from him and he was copying it for the first time at around S6. He called Tim Lanners, N9RET who told him he rarely gets reports from Illinois. Tim is in Broadview, Illinois in the Chicagoland area.
This bulletin is running late past deadline on Friday, so it is time to end it. Today the solar disk is completely blank with no visible spots. Mark Downing, WM7D of Reno, reported another notable event. He wrote that 298.3 was a new solar flux high for cycle 23. The previous high was 282.6 set on September 26, 2001. The Japan International DX Phone Contest is this weekend, as well as the Worked All Europe DX RTTY Contest. We can hope for lower geomagnetic activity, and the planetary A index for Saturday through Wednesday, November 12 is predicted at 15, 15, 20, 30 and 35. Sunspot numbers and solar flux are way down, and the predicted solar flux for the same days is 90, 90, 95, 100 and 115.
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.
Sunspot numbers for October 30 through November 5 were 293, 266, 277, 174, 76, 79 and 32, with a mean of 171. 10.7 cm flux was 271.4, 248.9, 210.4, 190.4, 166.9, 168 and 114, with a mean of 195.7. Estimated planetary A indices were 162, 93, 21, 18, 10, 31 and 9, with a mean of 49.1.