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The K7RA Solar Update


On Wednesday, April 13, the daily sunspot number reached a new high for Solar Cycle 24 when it hit 153. I looked back over this calendar year and saw that the previous high was 137 on March 8, 2011, 16 points lower than Wednesday. That week’s Solar Update said that “the last time the daily sunspot number was higher than this was July 7, 2005, when it was 149.”

I knew I would have to inspect sunspot numbers prior to that date to find something higher, which would be on the after-the-peak down-side of Solar Cycle 23. I went here and only had to look two days earlier to July 5, 2005, when it was 181. In fact, the day prior to that was even higher, 192. If you look at that table, you can see that around the end of June and in early July 2005, the Sun produced a good burst of activity on Solar Cycle 23’s down side. You can read a bulletin from early July 2005 here. At that time, we must have assumed that we were already near a low point in the sunspot cycle, but did not know that five years later, we would still be waiting for a significant increase in sunspot activity. The bulletin mentions this was the most activity seen since November 26, 2003.

Sunspot numbers for April 7-13 were 73, 97, 56, 56, 80, 114 and 153, with a mean of 89.9. The 10.7 cm flux was 112.3, 108.7, 105, 104.8, 105.8, 110.3 and 117.8, with a mean of 109.2. The estimated planetary A indices were 6, 8, 10, 5, 9, 23 and 14, with a mean of 10.7. The estimated mid-latitude A indices were 4, 5, 4, 3, 5, 14 and 10, with a mean of 6.4. The average sunspot number for the past week rose 21.6 points, from 68.3 to 89.9, while the average daily solar flux declined by 2.6 points to 109.2.

Eight new sunspot groups emerged this week. There was one new group on April 7, two more on April 8, another new one on April 11, two more on April 12, another new group on Wednesday, April 13 and yet another on April 14.

The predicted solar flux values from NOAA/USAF for the near term have increased since the forecast in The ARRL Letter on Thursday. The predicted solar flux is 125 and 128 on April 15-16, 130 on April 17-19, 135 on April 20-21 and 115 on April 22-23. The planetary A index for the same period is predicted to be 5 on April 15-17, 7 and 10 on April 18-19 and 5 on April 20-27. Geophysical Institute Prague predicts quiet geomagnetic conditions April 15-17, quiet to unsettled April 18, active conditions April 19 and unsettled conditions April 20-21.

On April 12, a solar wind stream hit Earth, causing aurora to be visible across the northern tier states in the US. The high latitude College A index hit 39 and the planetary A index was 23. The next period of higher geomagnetic activity predicted by NOAA/USAF is April 28-29, with a planetary A index of 12 and 15.

Jon Jones, N0JK, of Wichita, Kansas, reports: “I heard OA4TT (Peru) on 50.135 MHz on April 4 at 2020. KN5O in Louisiana had OA4TT in strong, but it was weak for me, maybe due to direct F2 to the Gulf Coast then weak Es on to Kansas. KN5O is on my great circle bearing to Peru.”

Jeff Hartley, N8II, of Shepherdstown, West Virginia, reports: “There have been plenty of recent propagation surprises. On April 8, K3SWZ near Harrisburg, Pennsylvania, reported to me working DU9RG on 10 meters SSB at 2348. Sunset here was 2343. I didn’t find Robin, but I did work my first VK6 of Solar Cycle 24 on 10 meters, VK6DU on SSB around 2350. There were several other eastern VKs and ZLs with good signals on 10 around the same time. I have worked 5N7M around 2300 on 10 meters CW and he is frequently on 10 and 12 meters very late for him right around the bottom of the band. I heard him as late as 0044 with a good signal on 12 meters last night, then he went down to the bottom of 15 meters CW around 0100. 5M2TT (Liberia) was running a big pile up on 17 meters SSB around 0000 and I worked him on Monday around 2330 on both 10 meters phone and CW. Fifteen has been regularly open to Japan in our evenings this week and was still open at 0110 last night. Earlier in the week, I had a ‘run’ of JAs on 15 CW around 2330 with signals up to S9, not an everyday event for this location with about the poorest prop to Japan in the USA (beam heading is 330).”

Jeff is more than 6800 miles to Japan. From K7RA in Seattle, it is about 4900 miles at 300 degrees.

Dick Grubb, W0QM, of Boulder, Colorado suggested that in addition to the STEREO website, another view can be found here. This image shows the same data that are displayed at the first site, but flattened out instead of the spinning globe.

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.



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