Each of the average solar and geomagnetic indices rose last week (April 20-26) over the previous seven days.

Average daily sunspot number rose from 8.6 to 35.7, and solar flux rose from 76.5 to 81.4.

Average daily planetary A index went from 8 to 26.4, and average daily mid-latitude A index from 6.3 to 18.4.

The day with the most geomagnetic activity was April 22 when the planetary A index was 54. One the same date, Alaska’s College A index (near Fairbanks) was 86.

Predicted planetary A index is 8, 5 and 5 on April 28-30, then 14, 10, 8 and 10 on May 1-4, 15 on May 5-6, 8 on May 7-8, 5 on May 9-14, 8 and 15 on May 15-16, and then into a more active period at 30, 25, 45, 50 and 30 on May 17-21. Then 20 on May 22-24, then 15, 8, 5 and 20 on May 25-28, 10 on May 29-31, 15 on June 1-2, 8 on June 3-4, and 5 on June 5-9.

Predicted solar flux values are 79 on April 28-29, 78 on April 30 and May 1, 77 on May 2-4, 75 on May 5-14, 80 on May 15-18, 85 on May 19-24, 80 on May 25-28 and 75 on May 29 to June 10.


OK1HH sent us this geomagnetic activity forecast for the period April 28 til May 24, 2017.

Geomagnetic field will be:
Quiet on May 9-10, 12-13
Mostly quiet on April 30, May 7
Quiet to unsettled April 29, May 2, 4, 14, 21-24
Quiet to active on April 28, May 1, 3, 8, 11, 15-16, 19
Active to disturbed on May (5-6,) 17-18, 20

Amplifications of the solar wind from coronal holes are expected on April 28, May (1-5,) 6-8, (9-11,) 18-22

Remark:
- Parenthesis means lower probability of activity enhancement and/or lower reliability of prediction.

I thought I ran this last week, but apparently not: https://www.youtube.com/watch?v=JR7D9zTygao

These always seem to come out after the bulletin is posted.

You might want to check this for more up to date videos from Tamitha Skov: https://www.youtube.com/user/SpWxfx/videos

Thanks to Don, N5DM for that tip.


For more information concerning radio propagation, see the ARRL Technical Information Service at http://arrl.org/propagation-of-rf-signals. For an explanation of 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 20 through 26, 2017 were 26, 39, 29, 43, 41, 36, and 36, with a mean of 35.7. 10.7 cm flux was 80.7, 82.2, 83.6, 82.5, 80.2, 81.3, and 79.6, with a mean of 81.4. Estimated planetary A indices were 30, 19, 54, 41, 20, 12, and 9, with a mean of 26.4. Estimated mid-latitude A indices were 20, 11, 37, 24, 19, 10, and 8, with a mean of 18.4.