The K7RA Solar Update


The daily sunspot number went all the way to 74 this week (on Tuesday, October 26), but the average sunspot number was down more than 5 points from the previous week, to 50.3. Sunspot numbers for October 21-27 were 34, 34, 43, 57, 57, 74 and 53, with a mean of 50.3. The 10.7 cm flux was 83.5, 82.2, 84.3, 82.1, 86.2, 86.1 and 87.6, with a mean of 84.6. The estimated planetary A indices were 3, 6, 23, 14, 6, 8 and 4, with a mean of 9.1. The estimated mid-latitude A indices were 1, 4, 16, 10, 4, 6 and 3, with a mean of 6.3.

Several sunspot groups contributed this week. Group 1113 first appeared October 13 and was visible through October 26. Group 1115 emerged on October 15 and ran through October 27, its last day. Group 1117 emerged October 19 and was still growing yesterday, October 28. But 1117 is now approaching the western horizon, and is less and less geoeffective.

The latest prediction is for solar flux of 85 through October 31, 82 on November 1, 78 on November 2-5 and then 80 on November 6-11 and rising after that. The predicted planetary A index for October 29-November 1 is 5, 8, 5 and 7, then back to 5 on November 2-17. Geophysical Institute Prague sees quiet to unsettled conditions October 29-30, quiet October 31 through November 1, November 2-3 unsettled and November 4 quiet to unsettled.

Conditions shouldn’t be bad this weekend for the CQ World Wide SSB DX Contest. Geomagnetic conditions should be relatively quiet, and we’ve had a little sunspot activity of late. But with sunspot group 1117 disappearing, unless a new one emerges, the sunspot number could drop back to 0.

A look at the STEREO mission shows some possible activity just over the Sun’s eastern horizon. There is also a very bright area, indicating magnetic activity straddling the unseen sector, which keeps getting smaller. Coverage should reach 96 percent around 1014 UTC on November 1, 97 percent at 0014 UTC on November 22, 98 percent coverage at 0014 UTC on December 14 and 99 percent at 1700 UTC on January 7, 2011.

Look here for a dramatic sun photo taken on October 20 by amateur astronomer Alan Friedman with a small telescope. Thanks to Phil Plait’s Bad Astronomy Blog at for this.

Rich Dowty, W7EET, reminds us of the DX Sherlock maps for propagation on 28 MHz and higher.  Go here and dial in your favorite band and region.

Stu Phillips, K6TU, had some comments regarding remarks I had in last week’s bulletin regarding WSPR real time data and how it might be used for evaluating propagation paths for other modes, such as SSB and CW: “For every WSPR spot (which you can see in the database at the WSPR Web site), there is a power level in dBm and a signal to noise ratio reported by the receiving station. Although the antenna used by the transmitting station isn’t known, you can get a pretty good idea of the path and what it would take in terms of increased ERP to successfully conclude either a CW or a SSB contact. I’ve also found pretty good correlation between propagation predictions using VOACAP that when adjusted for bandwidth (WSPR calculates SNR assuming a 2.5 kHz effective bandwidth) and power levels, correspond pretty closely with the SNR levels reported by WSPR. So pick you reference point -- for example, if you need 12 dB SNR in a 200 Hz bandwidth to complete a CW contact, you can scale the WSPR report by adding 10 dB for the bandwidth delta and then scale appropriately for power/ERP delta. Most WSPR transmissions on the HF bands are 5 W or fewer -- so even a ‘standard’ ham transmitter at the 100 W level is a further uplift of 13 dB even without ERP boost from a decent antenna.”

We’ll have more information next week from K6TU regarding WSPR and propagation.

All times, unless otherwise noted, are UTC.

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 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.