SB PROP @ ARL $ARLP037
ARLP037 Propagation de K7RA
QST de W1AW
Propagation Forecast Bulletin 37Â ARLP037
From Tad Cook, K7RA
Seattle, WAÂ September 11, 2015
To all radio amateurs
SB PROP ARL ARLP037
ARLP037 Propagation de K7RA
The Australian Space Forecast Centre issued a GeomagneticÂ Disturbance Warning at 0132 UTC on September 8. They wrote, “TheÂ effect of a high speed solar wind stream from a coronal hole isÂ keeping geomagnetic activity enhanced.
“Geomagnetic activity is expected to remain mostly enhanced toÂ Active levels on 8 September with the possibility of some minorÂ storm periods.”
If you look at ftp://ftp.swpc.noaa.gov/pub/indices/DGD.txt you canÂ see the effect, which is high numbers indicating geomagneticÂ instability. What does this mean for performance on the air? For HFÂ it can mean higher absorption rates (meaning radio waves may beÂ absorbed more than they are reflected) but it can mean someÂ interesting propagation modes may occur on VHF.
The Australian Space Forecast Center issued another geomagneticÂ disturbance warning at 0017 UTC on September 11: “A high speed solarÂ wind stream from a coronal hole is expected to arrive late on 11Â September. This may result in the geomagnetic activity rising toÂ Active to Minor Storm levels. This rise in geomagnetic activity isÂ expected to continue on 12 September.”
Frank Donovan, W3LPL sent a fascinating article about a rejuvenationÂ in solar magnetic strength toward the end of 2014, and an alternateÂ view from the recent news stories about a long term dearth ofÂ sunspots. Instead, they propose that Cycle 25 (the next one) may beÂ similar to Cycle 24 (the one we are now in).
Read it at,Â http://aasnova.org/2015/09/02/witnessing-solar-rejuvenation/ .
Weak solar activity continued this week. The average daily sunspotÂ number for September 3-9 was only 37.3, down 11 points from theÂ previous seven days. Average daily solar flux was 85.3, compare toÂ 97 for the previous week.
Geomagnetic activity was strong, with average planetary A index upÂ from 19.4 to 27.1. The most active day was Wednesday, September 9Â when the planetary A index was 59.
The latest solar flux prediction from USAF/NOAA has readings of 85,Â 90 and 100 on September 10-12, 105 on September 13-14, 110 onÂ September 15-17, 115 on September 18-22, then 110, 105, 100 and 95Â on September 23-26, 90 on September 27 to October 1, and 85 onÂ October 2-7. Flux values then rise to 115 on October 15-19.
Predicted planetary A index is 28, 16 and 27 on September 10-12,Â then 16, 10 and 8 on September 13-15, 5 on September 16-17, then 8,Â 20 and 10 on September 18-20, 5 on September 21-23, then 15 and 10Â on September 24-25, 5 on September 26-29, then 8 and 18 on SeptemberÂ 30 through October 1, 12 on October 2-4, 8 on October 5, then 5 onÂ October 6-7, then 8, 12 and 8 on October 8-10, and 10 on OctoberÂ 11-13.
Both the solar flux and planetary A index predictions are fromÂ September 9. The new forecast appears every day after 2100 UTC, butÂ so far early on September 11 the September 10 forecast is notÂ available. You can catch up by checking,Â ftp://ftp.swpc.noaa.gov/pub/forecasts/45DF/ .
We do have a geomagnetic forecast from OK1MGW who predicts quiet toÂ active conditions September 11-13, (with September 11 conditionsÂ perhaps at active to disturbed levels), quiet to unsettled SeptemberÂ 14, quiet to active September 15-16 (with September 15 conditionsÂ possibly at active to disturbed levels), quiet to unsettledÂ September 17-18, active to disturbed conditions September 19, thenÂ mostly quiet on September 20-21, quiet to active September 22,Â active to disturbed September 23-24, quiet to unsettled SeptemberÂ 25, quiet on September 26-28, mostly quiet September 29, and quietÂ to unsettled September 30. He expects increases of solar wind onÂ September 11-13, 15-16, 19, and 22-24.
Note that the mid-latitude A index for September 8 and 9 listed atÂ the end of this bulletin are wild guesses on my part, based onÂ tracking with the planetary A index. If you look atÂ ftp://ftp.swpc.noaa.gov/pub/indices/DGD.txt you will see there is noÂ data for those dates. This is probably because geomagnetic activityÂ was strong enough to knock the Fredericksburg and College (for theÂ high latitude number) magnetometers out of service.
If you would like to make a comment or have a tip for our readers,Â email the author at, email@example.com.
For more information concerning radio propagation, see the ARRLÂ Technical Information Service web page at,Â http://arrl.org/propagation-of-rf-signals. For an explanation of theÂ numbers used in this bulletin, seeÂ http://arrl.org/the-sun-the-earth-the-ionosphere. An archive of pastÂ propagation bulletins is atÂ http://arrl.org/w1aw-bulletins-archive-propagation. More goodÂ information and tutorials on propagation are at http://k9la.us/.
My own archives of the NOAA/USAF daily 45 day forecast for solarÂ flux and planetary A index are in downloadable spreadsheet format atÂ http://bit.ly/1VOqf9B and http://bit.ly/1DcpaC5 .
Click on “Download this file” to download the archive and ignore theÂ security warning about file format. Pop-up blockers may suppressÂ download. I’ve had better luck with Firefox than Internet Explorer.
Monthly propagation charts between four USA regions and twelveÂ overseas locations are at Â http://arrl.org/propagation.
Instructions for starting or ending email distribution of ARRLÂ bulletins are at http://arrl.org/bulletins.
Sunspot numbers for September 3 through 9 were 27, 36, 24, 38, 47,Â 40, and 49, with a mean of 37.3. 10.7 cm flux was 86.5, 89.9, 85.4,Â 85.6, 83.7, 83.5, and 82.3, with a mean of 85.3. Estimated planetaryÂ A indices were 9, 20, 13, 14, 46, 29, and 59, with a mean of 27.1.Â Estimated mid-latitude A indices were 9, 18, 10, 12, 27, 24, and 31,Â with a mean of 18.7.
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