The average daily sunspot numbers declined seven points over the past week to 110.3, while the average daily solar flux dropped 3.3 points to 131. Sunspot numbers for May 17-23 were 114, 118, 110, 124, 120, 95 and 91, with a mean of 110.3. The 10.7 cm flux was 136.3, 132.2, 130.9, 130.8, 125.1, 121.3 and 117.2, with a mean of 127.7. The estimated planetary A indices were 6, 8, 5, 13, 7, 16 and 18, with a mean of 10.4. The estimated mid-latitude A indices were 5, 8, 5, 12, 7, 15 and 13, with a mean of 9.3.

The unsettled geomagnetic conditions over the past few days most likely resulted from an interplanetary shock wave that originated from a solar flare on May 20. The predicted planetary A index is 8, 5 and 8 on May 25-27, then 5 on May 28-June 4, then 8, 12, 15, 10 and 8 on June 5-9, then 5 on June 10-11, 8 on June 12-13, 5 on June 14-16, then 8, 15, 10 and 8 on June 17-20, and 5 on June 21-25. The predicted solar flux is 115 on May 25, 110 on May 26 through June 1, 125 on June 2-3, 130 on June 4, 135 on June 5-9, 130 on June 10, 125 on June 11-12, and 120 on June 13-15. Six new sunspot groups arose since May 15, one each on May 15, 18, 20, 22, 23 and 24. Until June 4, the predicted solar flux values are below the average for the past week, 127.7.

We are again receiving geomagnetic forecasts from the Czech Republic, this from Frantisek K. Janda, OK1HH, of Ondrejov, from the Czech Propagation Interest Group. He predicts quiet to unsettled conditions on May 25-26, quiet on May 27-28, mostly quiet May 29, quiet to active May 30, quiet May 31-June 1, mostly quiet on June 2, quiet to unsettled June 3, quiet to active June 4, active on June 5, quiet to active June 6, active on June 7, quiet to active June 8, quiet to unsettled June 9, quiet June 10-11, quiet to active June 12, mostly quiet June 13, and quiet to unsettled on June 14-15. Janda said that on May 30-31, and again on June 5, there is a high probability of changes in the solar wind, which may cause changes in the magnetosphere and ionosphere.

Bill Lauterbach, WA8MEA, of Hanover, Michigan, had a question about MUF (Maximum Usable Frequency) and LUF (Lowest Usable Frequency). He says the LUF seems to have changed, so that it is sometimes close to the MUF in the current cycle. He wonders if LUF should be lower when MUF is higher.

I passed this on to Carl Luetzelschwab, K9LA. Carl commented: “The MUF is determined by the amount of ionization -- most of the time it’s the amount of ionization in the F2 region that sets the MUF. And you can’t do anything to your station to change the MUF. The LUF is essentially determined by absorption in the D region. You can lower the LUF on a given path by increasing transmit power, or increasing your antenna gain or somehow reducing your man-made noise. In essence, your LUF is the frequency at which the received signal is at your noise level. Since a higher MUF means more ionization, it seems to me that generally there would be more absorption, too, which would increase the LUF.” Thanks, Carl!

Another Carl -- Carl Hickman, N5XE, of Sulphur, Oklahoma – wrote: “On Thursday evening, (0330 UTC Friday, May 25), I called CQ on 15 meters. TA2KN answered my call with a 599+ signal. He was so strong, I was hearing an echo on his signal (both short and long paths), which made copy somewhat tough. Both paths were strong -- he was LOUD! I had to use my attenuator to lessen the effects of his long path signals. Less than 10 minutes later, I worked N5RB on the same band (short skip for me). After more than 33 years as a ham, I am still amazed at propagation conditions that crop up from time to time. It’s always fun to participate in rare openings on the bands.”

Thanks, Carl. TA2KN is at a scout camp in Turkey, where they have quite a nice antenna system. Carl worked them at what is probably the best time of the day on 15 meters over that path at this time of year. I see that the short skip distance that Carl mentioned between N5RB (Ecru, Mississippi) and N5XE in Oklahoma is 452 miles. I calculated that by looking up their licensed addresses on a map, then using the latitude and longitude for each station to calculate distance on W6ELprop. Carl heard the station in Turkey on both long and short paths, and those distances are 18,680 miles and 6194 miles, respectively. This was calculated using the location for the scout camp shown here, which is 41.07 degrees north latitude, 29.117 degrees east longitude.

Don Kalinowski, NJ2E, of Cary, North Carolina, alerted me to the National Air and Space Lecture Series, specifically one about the Solar Dynamics Observatory. See it here and click on the “View Archived Recording” link to watch the 71 minute video, titled The Solar Dynamics Observatory: The Sun Up Close and Personal.

Jon Jones, N0JK, of Lawrence, Kansas, fills us in on 6 meter activity with a station in Argentina. He wrote: “I encountered some interesting propagation on 6 meters the afternoon of May 19. K0HA in EN10 reported working LU1DMA around 2010 UTC. I went out portable with a 2 element Yagi. Initially, I heard no signals, other than the WB0RMO/b EN10 on groundwave. Then at 2105, LU8YD appeared on 50.110 on an otherwise dead band. He was weak, then he built up to a reasonable signal. I called him, and he replied, giving me 5×5 report and copied EM28 fine. His grid is FF51 and he logged at 2108 UTC. I see Alex was spotted by K2ZD and a W3. This was probably an ‘Es link’ to afternoon TEP. There were single hop Es before to Florida and afterwards to W3, W4 and W7. This was the first LU on 6 meters in Solar Cycle 24 for me.” Thank you, Jon.

Jeff Hartley, N8II, of Shepherdstown, West Virginia, wrote on May 19: “I haven’t been on the air much, but I did manage to work the 7O6T guys on 40-15 meters, one QRP contact near the end on 15 meters SSB. Signals were loud on 20, 17, 12 and 15 most of the time in our evening. The big operation stimulated quite a round of how to work a rare one, with big pile ups on the PVRC reflector. Some DXers are obviously masters of the art. One tip I found very useful in spotting the listening frequency on CW is to listen with a wide filter (more than 2 kilohertz); it makes finding the DX station caller much easier. Then try to figure out which way they are tuning and follow along a bit higher or lower depending on what direction they are tuning. I operated in the CQ M contest May 12, just about 2-1/2 hours and found 20 meters to be very poor from 1200-1300, but 15 meters sounded good with one of the loudest signals from UP0L. On 20 meters in the evening around 0200, there were loud signals from Western Europe across to Zone 18, but virtually all except the Spanish stations, had heavy flutter, making copying at high speeds difficult.”

This weekend is the CQ World Wide WPX Contest. Conditions should be fair, with unsettled but not terribly active geomagnetic conditions, and low sunspot activity.

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.