A coronal mass ejection (CME) hit the Earth on September 30, triggering a jump in geomagnetic indices. The planetary A index on October 1 was 31, and the K index jumped to 7, making aurora visible across the northern tier of the United States. The northern latitude college A index was 23 (near Fairbanks, Alaska), about the same as the mid-latitude index -- which was 21 -- in Fredericksburg, Virginia. It is common during a geomagnetic disturbance to see indices go much higher in the far-northern latitudes.

The average daily sunspot numbers declined 8.3 points to 73, while the average daily solar flux was off exactly 1 point, to 128.7. Sunspot numbers for September 27-October 3 were 97, 77, 70, 95, 59, 55 and 58, with a mean of 73. The 10.7 cm flux was 133.2, 137.8, 136, 135.6, 128.1, 118.2 and 111.7, with a mean of 128.7. The estimated planetary A indices were 5, 2, 4, 10, 31, 5 and 5, with a mean of 8.9. The estimated mid-latitude A indices were 3, 2, 4, 9, 21, 5 and 5, with a mean of 7.

The latest prediction from NOAA/USAF has the solar flux on October 5-6 at 110, 105 on October 7, 100 on October 8-11, 115 on October 12-13, 120 on October 14-15, 130 on October 16, 140 on October 17-18, and then peaking at 145 and 150 on October 19-20. The same forecast has solar flux rebounding to 150 on November 16 after reaching a minimum of 110 on November 4-5. The predicted planetary A index is 5 on October 5-8, 10 and 8 on October 9-10, 5 on October 11-14, then 8, 12 and 10 on October 15-17, 5 on October 18-25, 10 on October 26, 5 on October 27-28, and reaching a peak of 15 on October 29.

In September, we saw a slight decline in the sunspot averages: The monthly averages of daily sunspot numbers for April-September 2012 were 84.5, 99.4, 90.1, 99.6, 85.8 and 84. Three-month moving averages of daily sunspot numbers -- for three-month periods ending February-September 2012 -- were 83.3, 73.7, 71.2, 87.3, 91.5, 96.5, 91.9 and 89.9. So the last number, 89.9, was an average of the daily sunspot numbers for all of July, August and September, and the number prior to that, 91.9, was for the months of June, July and August.

In 6 meter news, Floyd Chowning, K5LA, of El Paso, Texas wrote: “I have been seeing many spots on the DX cluster where stations are working from Africa to Europe earlier in the day our time. So I decided to start listening and finally heard a DX station.” He copied the beacon CE3AA/B in Santiago at 2122 on October 4 on 50.0293 MHz, a distance of nearly 5100 miles.

Jon Jones, N0JK, of Wichita, Kansas, said there was “a fairly impressive aurora” on October 1, and Dan Kaeo, KF6A, in Alma, Michigan, copied the N0LL 6-meter beacon in Smith Center, Kansas at 0442 on that day on 50.0776 MHz. The distance was 770 miles, and the direction from the beacon toward the receiving station was 66.6 degrees, or roughly east-northeast.

“The next day (or later the same day, UTC) conditions were good on 24 MHz to 3D2C Conway Reef,” Jon wrote. “They were very loud to Kansas around 2030 on October 1. I was able to work them with my mobile set up. With the good -- but not high -- solar flux, 24 MHz has often been a good band for DXing, better than 10 or 15 meters. Signals from 3D2C were not nearly as loud on 10 meters when I listened.”

The NASA solar cycle prediction was revised slightly since last month. You may recall that the predicted peak was moved recently from spring to fall 2013, and now the predicted peak has gone down 1 point, from a smoothed sunspot number of 76 to 75.

Larry Godek, W0OGH, in Gilbert, Arizona reported this on October 1: “On Saturday and Sunday, both the RTTY portions were overloaded with activity. I Couldn’t believe the number and signal strength of stations. On Saturday night, 40 meters was something I’ve not heard in many years. On SSB -- 10 meters in particular -- it sounded like the days of AM when stations were overlapping. Amazingly, there were very few, maybe a half-dozen that I heard ragchewing between 28.6 and 29.0 MHz; almost everything else was below 28.6. I even had good AM activity above 29.0 MHz, as some of the locals were talking about the QSOs they had in that segment of the band.

“On 10 meters FM, the KQ2H repeater had European stations until after lunch time here in the west. I only heard one or two other station from the US, all of it was foreign. Even 29.640 MHz had lots of traffic, although nothing like 29.620. I didn't check anything on the WSPR modes, but it would have been interesting to see how the high solar flux and the A indices affected them as well. You could tell that by late Sunday afternoon, things had changed, as the noise level came way up -- almost like the summer afternoons. Previous to this, the band noise has been almost nil the past three days. I had to turn the gain way up on 10 meters, as I thought no noise meant weak signals, but that wasn't the case at all. I suspect the stations who were active this past weekend will be talking about this opening, as it truly brought back memories of the good times when the bands were full of activity with great signals.”

The day before, on September 30, Larry wrote: “WOW! The RTTY ops must have thought they died and went to heaven! RTTY signals on 15 meters alone occupied 70 kilohertz of the band, and a lot of excellent quality DX signals as well. 10 meters was really nice, too, but I didn’t spend much time there as I was busy down on the lower part of the band. I worked five new countries on 10 meters FM, and even more on the CW and SSB modes. Let’s hope that this is an indication of what’s left of this solar cycle. I could certainly use some extra oxygen on days like this, when my heart gets a cardiac workout from the excitement of hot bands! Whoever is responsible, keep up the good work! It makes being retired a lot more fun, as I may only get one more of these cycles to play in.”

Herb Lacey, W3HL, of Cary, North Carolina noted that there seem to be more sunspots south of the Sun’s equator than in the north. I responded that this seems to be true lately, but when I looked in the spaceweather.com archives over the past year, there didn’t seem to be more sunspots in the southern hemisphere. I consulted with Carl Luetzelschwab, K9LA, and he said that asymmetry in the north-south distribution of sunspots is common. He referred to butterfly diagrams of solar cycles, and you can see them here.

As each solar cycle progresses, sunspots emerge closer to the equator. Carl drew our attention to Solar Cycle 20, around 1970. You can see a weighting toward the northern hemisphere. The previous cycle, around 1960, Solar Cycle 19, also seems to favor northern spots, and Solar Cycle 22 around 1990 seems to favor southern sunspots. Carl said that he doesn’t know of any explanation for the asymmetry, but noted that it is probably tied to plasma flow in the Sun.

All times listed are UTC, unless otherwise noted.

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 each Thursday in The ARRL Letter. You can find a guide to articles and programs concerning propagation here. Check here and 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.