Average daily solar flux weakened over the past seven days, and so did the outlook for the near term, at least until Thursday, April 10. Average daily solar flux declined from 149 to 142.2, while average daily sunspot numbers remained about the same, moving from 130.4 to 129.3

From the NOAA/USAF 45 day forecast, predicted solar flux is 140 on April 11-12, 145 on April 13-15, 150 on April 16-18, 140 on April 19, 135 on April 20-23, 130 on April 24-27, 125 on April 28 through May 3, and 140 on May 4-6.

In yesterday’s ARRL Letter we reported the prediction from Wednesday, April 9 showed an average daily solar flux of 133.3 over April 10-15. But just two days earlier, on Monday April 7 the predicted average for the same period was 142.5, and back on March 30 the prediction for April 10-15 showed an average solar flux of 145.8. The predicted solar flux for April 10 was 150 on March 30, 140 on April 7 and 130 on April 9, which indicated a progressively pessimistic outlook.

However, the April 10 prediction showed higher values. For April 11-18, average solar flux is predicted at 145.6, ten points higher than the prediction for the same eight days on April 9, which was 135.6.

Predicted planetary A index is 5 on April 11, 8 on April 12, then 12 on April 13, 8 on April 14-15, 5 on April 16-18, 8 on April 19, then 5 on April 20 through May 5, and 8 on May 6-7.

OK1HH predicts a quiet geomagnetic field on April 11-13, mostly quiet April 14, quiet to unsettled April 15-16, quiet to active April 17, quiet April 18, mostly quiet April 19-20, quiet to active April 21, quiet to unsettled April 22, mostly quiet April 23, quiet on April 24, mostly quiet April 25-26, quiet April 27, mostly quiet April 28, quiet on April 29, mostly quiet April 30, quiet May 1-2, mostly quiet May 3, quiet to unsettled May 4, quiet May 5, quiet to unsettled May 6, and back to quiet again on May 7-8.

A week ago (but too late for this bulletin) NASA released their monthly Solar Cycle prediction, little changed from the March version:

http://solarscience.msfc.nasa.gov/predict.shtml

The forecast begins, “The current prediction for Sunspot Cycle 24 gives a smoothed sunspot number maximum of about 70 in the late summer of 2013. The smoothed sunspot number reached 73.1 in September 2013) so the official maximum will be at least this high.”

The March forecast said “The current prediction for Sunspot Cycle 24 gives a smoothed sunspot number maximum of about 69 in the late summer of 2013. The smoothed sunspot number reached 68.9 in August 2013) so the official maximum will be at least this high.”

These are smoothed numbers, averaged over a year, so that is why the numbers from the end of last summer changed, because recent higher activity is now averaged in.

Here is an interesting article, “Small Groups, Big Flares” from Belgium’s Solar Influences Data Center:

http://sidc.oma.be/news/245/welcome.html


Wayne Starnes, KU4V, of Cary, North Carolina sent an email concerning the radio blackout mentioned in last week’s bulletin.

“Yes, I also experienced the blackout during the CQ WPX, but do not actually recall the time it happened. I was running on 10 meters as I recall and – boom! –  20 dB+ atmospheric noise on the band! I then checked 10 through 160 meters and it was the same intensity on every band. I have never heard anything like it.

“After a few minutes it stopped and the bands seemed to be in better shape, actually.

“Then, on Sunday, March 30, at 1503 UTC while running on 10 meters, YB2DX calls me – very weak, but we made it. At 1522 UTC YC0IEM calls me, again very weak, but we made it. At 1547 UTC 4Z5ML called.

“After the contest I worked the TX5 guys on 10 and 15. Amazing and interesting propagation this past weekend.”

Chris Wreck, K2HVE, of Bayonne, New Jersey wrote: “Yes! It was the same at my station. I am located in Hudson County, 1.5 miles SW of the Statue of Liberty and 2.5 miles SW of lower Manhattan. I was on 20 meters during the CQ WPX Contest on Saturday 29 March working European and Russian stations one after another when, at around 1750 UTC, the whole band was wiped out. There was nothing but noise at an S3 level. It was like somebody pulled my antenna wire out. I began checking antenna connections on my IC-7600 transceiver and found nothing amiss.

“Shortly afterward I received a NOAA SWPC alert noting the solar flare. The disturbance lasted about 30 to 45 minutes, then slowly the US Stations came back up and finally the Europeans. In an hour it was like nothing had ever happened. In all the years I never had anything so sudden happen at station regarding Ol' Sol.”

Jon Jones, N0JK, sent a correction concerning working long path on 6-meters. “Fred, KH7Y, made the first 6 meter Hawaii to Europe TPL (trans-polar long path) contact of Solar Cycle 24 with IT9 on February 28. But it was TPL going southeast of Hawaii. It took place in the early afternoon HST (Hawaii Standard Time).

“I think I made the first Hawaii to Europe TPL contact of solar cycle 24 going southwest of Hawaii March 30 with S57RR. It was around midnight HST for me.”

Jon also reported, on April 10: “During the last week many contacts were made in the afternoon from the Gulf Coast and southern parts of the Midwest to CX, LU and PY in South America on 6 meters. A few fortunate hams in AR, MO and OK worked the Falkland Islands. The propagation mode is "afternoon TEP." This link has information about this propagation mode: http://home.iprimus.com.au/toddemslie/aTEP-Harrison.htm.

“Not much to report since arriving home (to Kansas) from Hawaii. I heard CE4WJK working CO2QU on April 6 at 2100 UTC on 50.140 MHz. Today April 10 heard the K5AB/b 50.060 MHz on Es at 2350 UTC.”

Thanks, Jon!

Scott Craig’s Solar Data Plot utility has an updated data file, useful if you are just starting out with the program. Otherwise you update it auto-magically weekly with this bulletin. You can find it at http://www.craigcentral.com/sol.asp. This program runs on Microsoft Windows, but I’ve never been able to use it on Windows 7 computers, so I’ve used a virtual XP mode or just my old XP machine. Now I see Microsoft has ended support for XP.

This weekend is the Japan International DX CW Contest. See details at http://jidx.org/.


For more information concerning radio propagation, see the ARRL Technical Information Service at http://arrl.org/propagation-of-rf-signals. For an explanation of the numbers used in this bulletin, see http://arrl.org/the-sun-the-earth-the-ionosphere. An archive of past propagation bulletins is at http://arrl.org/w1aw-bulletins-archive-propagation. More good information and tutorials on propagation are at http://k9la.us/.

Monthly propagation charts between four USA regions and twelve overseas locations are at http://arrl.org/propagation.

Instructions for starting or ending email distribution of ARRL bulletins are at http://arrl.org/bulletins.

Sunspot numbers for April 3 through 9 were 137, 174, 172, 127, 106, 94, and 95, with a mean of 129.3. 10.7 cm flux was 153, 156.9, 142.1, 140.9, 139.9, 132, and 130.6, with a mean of 142.2. Estimated planetary A indices were 6, 6, 14, 5, 11, 5, and 5, with a mean of 7.4. Estimated mid-latitude A indices were 7, 5, 11, 3, 10, 4, and 5, with a mean of 6.4.