The K7RA Solar Update
If today is like yesterday and the day before that, it will be the 26th consecutive day with no sunspots. Think this is bad? At the last solar minimum, there were only four days showing any sunspots between September 5 and October 24, 2006.
Last week's bulletin should have reported on the upcoming weekend geomagnetic activity. For this week, geomagnetic conditions should mild in the beginning and increasing later. Predicted planetary A index for July 18-24 is 8, 5, 5, 5, 10, 15 and 12. Geophysical Institute Prague predicts quiet conditions for July 18, quiet to unsettled July 19-20, quiet again on July 21 and unsettled July 22-24. Sunspot numbers for July 10-16 were 0, 0, 0, 0, 0, 0 and 0 with a mean of 0. The 10.7 cm flux was 65.4, 65.7, 64.9, 65.2, 65.6, 65.7 and 64.6 with a mean of 65.3. Estimated planetary A indices were 4, 7, 21, 14, 10, 7 and 7 with a mean of 10. Estimated mid-latitude A indices were 2, 6, 16, 10, 9, 7 and 4 with a mean of 7.7.
Chuck Shinn, W7MAP, of Coppell, Texas sent in an interesting observation comparing the current solar minimum to the one between Solar Cycles 18 and 19. Cycle 19 was the biggest sunspot cycle on record, and peaked around October 1957 to April 1958. Chuck observed that there was a long period of little solar activity in 1953 and 1954. He used a table of smoothed sunspot numbers and noted that from December 1953 through most of 1954, the smoothed sunspot number was fewer than seven.
Each monthly smoothed number in the table represents an average of monthly averages, I believe, for 13 months, six months prior and six months following. That's why December 2007 is the last value shown in this table, since to calculate the January 2008 number, you need to know the average of daily sunspot numbers for all of the current month, July 2008.
Looking at it this way, against the 1954 minimum, the current lack of activity does not seem unusual, and the lack of 1954 sunspots didn't indicate that Cycle 19 would be below average. The minimum during that period was 2.4 in April 1954. Between Solar Cycles 19 and 20, the lowest value was 7.2 in June 1964. From Solar Cycle 20 to 21, March 1976 at 11.1 was lowest, and from Solar Cycle 21 to 22 it was September 1986 at 10. The last minimum was 8 in May and August 1996.
This puts the current minimum in an interesting perspective. The current minimum is quite low, but it hasn't yet lasted as long or gone as low as the minimum preceding the largest sunspot cycle in recorded history. None of this, of course, can predict the size or length of the upcoming Solar Cycle 24.
The August 2008 issue of Scientific American has an interesting article concerning solar and geomagnetic activity titled "Bracing for a Solar Superstorm." It begins with a narrative describing a huge space weather event on August 28, 1859, 100 years prior to 20th century's Solar Cycle 19. This was the fiercest ever recorded; it resulted in shutdown of telegraph traffic, and an aurora was observed in the Caribbean. The article says a storm of this magnitude comes along every 500 years or so, but reconstructs events and imagines the impact on current technology infrastructure. There are wonderful graphics and numerous sidebars. Included are some Web links I wasn't previously aware of. Within one of the sites listed site is a history of great solar events, a short primer and a downloadable PDF of the book, The 23rd Cycle: Learning to Live with a Stormy Star.
Jeff Hartley, N8II, of Shepherdstown, West Virginia sent a report on more multi-hop Sporadic-E activity, this time in the IARU HF World Championship contest last weekend. Jeff wrote, "Conditions would have been dreadful with a high K index (peaked at 5) if not for the multi-hop Sporadic-E during the IARU contest. I made about 20 QSOs on 10 meters running QRP and was late getting there. There were Europeans and North Africans with good signals on 10 meters from around 1530-1900 UTC, and again weaker from 2330 or earlier thru past 2400 UTC."
Jeff continued: "The HQ stations were like beacons (TM0HQ, 9A0HQ, S50HQ, GB7HQ, OL4HQ, EH8U), operating whenever the bands were open. I couldn't get thru to TM0HQ on 10 meter phone despite a loud S7-8 signal, but did get them easily on CW. All together, about 10 European contacts were made, and a couple with South America on 10 meters. Fifteen meters was open to all of Europe, except most of Scandinavia at its best, and RU1A had a good but unworkable signal with my QRP. Best surprise was easily working ZD8Z on 20 meters. Second best was getting thru to OL4HQ on 75 meters SSB thru the static. Fifteen was open well again in the last hour at 1100 UTC. There was some action on 6 meters into Europe from my area into Portugal and Spain, but I was too busy with the contest."
Amateur solar observer Tad Cook, K7RA, of Seattle, Washington, provides this weekly report on solar conditions and propagation. This report also is available via W1AW every Friday, and an abbreviated version appears in The ARRL Letter. Check here for a detailed explanation of the numbers used in this bulletin. An archive of past propagation bulletins can be found here. You can find monthly propagation charts between four USA regions and 12 overseas locations here. Readers may contact the author via e-mail.