The K7RA Solar Update
ARRL Headquarters is closed for Good Friday on April 18, so the bulletin comes to you a day early.
After a few days in the doldrums on April 8-13 with sunspot numbers in the double digits, solar activity made a strong recovery over the following three days, with daily sunspot numbers of 105, 149 and 245. Sunspot numbers have reached this level several times in the past 12 months. On February 28, 2014 the daily sunspot number reached 279, it was 245 on January 6, and back on November 15-17, 2013 it was 272, 213 and 282.
The average daily sunspot number was actually down this week compared to last, dropping from 129.3 to 118.4. Average daily solar flux was higher, rising from 142.2 to 149.1. There was one geomagnetically active day, when the planetary A index reached 25 on April 12. This was caused by a solar wind stream.
Predictions for solar flux made a big leap yesterday, when it was predicted to be 190 on April 17-19, 185, 180 and 175 on April 20-22, 170 on April 23-24, 140 on April 25-27, 130 on April 28-29, 125 on April 30, 120 on May 1-2, 125 on May 3-5 then peaking at just 145 on May 12-19.
Predicted planetary A index is 8 on April 17-18, 5 on April 19 to May 10, 8 on May 11-12, then 5 for the remaining days of the 45-day forecast period.
On April 12, OK1HH predicted the geomagnetic field to be quiet to active on 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 April 24, mostly quiet April 25-26, quiet April 27, mostly quiet April 28, quiet 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 quiet on May 7-8.
For the first time in many years, WWV again is transmitting on 25 MHz, on an experimental basis. A week ago David Crawford, KF4VXJ of Raleigh, North Carolina reported hearing the 25 MHz signal on April 10 at 2118 UTC with some fading, with signal strength varying from S5-S8. He included this in a reception report to WWV, along with readings at 10, 15 and 20 MHz (2.5 and 5 MHz signals were inaudible).
He got this reply: “Thanks for your email, and your reception report of the WWV experimental broadcast at 25 MHz.
“WWV first began broadcasting on 25 MHz in 1946, but the broadcast was suspended in 1977. Due to listener interest and changes in broadcasting technology, NIST is pleased to be able to provide this service on a limited basis once again. At present, the broadcast is carried on a base-fed broadband monopole antenna. All normal WWV frequencies operate on a center-fed half-wave dipole antenna, with a dedicated backup transmitter that will come online automatically should the main transmitter fail. The 25 MHz broadcast does not have this capability at this time. Please note that the experimental 25 MHz broadcast may be interrupted without notice at any time.
For the latest status in the 25 MHz broadcast, refer to the NIST Radio Station WWV web site: http://www.nist.gov/pml/div688/grp40/wwv.cfm .”
Well that’s it for this week. There were no other reports from readers.
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 10 through 16 were 78, 83, 74, 95, 105, 149, and 245, with a mean of 118.4. 10.7 cm flux was 136.7, 137.6, 135.9, 137.1, 150.3, 161.9, and 183.9, with a mean of 149.1. Estimated planetary A indices were 3, 8, 25, 16, 8, 6, and 5, with a mean of 10.1. Estimated mid-latitude A indices were 4, 7, 16, 13, 7, 5, and 5, with a mean of 8.1.