The Sun just finished an extended period (16 days) of zero sunspots. There were none on March 4, one visible on March 5, then none on March 6-20. Finally, one sunspot group appeared on March 21-23, with a sunspot number of 12 on all three days.

A sunspot number of 12 does not mean there were 12 sunspots. Every group of sunspots counts as 10 points, and every sunspot within those groups counts for one point. Therefore, the minimum non-zero sunspot number is 11. So, for the past three days, there were two sunspots in one group.

The average daily sunspot number this week (March 16-22) was 3.4, compared to zero during the previous seven days. Average daily solar flux increased from 70.3 to 71.2.

Average daily planetary A index increased from 8.1 to 10 and average mid-latitude A index increased from 6.4 to 7.1.

The mid-latitude A index is measured at one magnetometer at Wallops Island, Virginia while the planetary A index is calculated based on a number of magnetic observatories, most in the northern hemisphere.

Predicted solar flux is 75 on March 24-26, 78 on March 27-30, 72 on March 31 through April 4, 71 on April 5, 70 on April 6-17, 71 on April 18, 72 on April 19 until May 1 and 71 again on May 2.

Predicted planetary A index is 14 on March 24, 8 on March 25-26, then 20, 40, 35, 20 and 18 on March 27-31, then 15, 20 and 15 on April 1-3, 12 on April 4-5, 10 on April 6, 5 on April 7-16, then 8, 12, 20, 8, 5 and 8 on April 17-22 then 8, 35, 30, 20, 18, 15, 20 and 15 on April 23-30, and 12 on May 1-2.

The Australian Space Forecast Centre issued a geomagnetic disturbance warning at 2336 UTC on March 23: “Due to the continued effect of the high speed solar wind stream from a recurrent coronal hole, solar wind speed is still high. IF Bz shows sufficiently southward values for long enough intervals of time, there is some possibility for some minor storm periods to occur on 24 March.”

From F.K. Janda, OK1HH, geomagnetic activity forecast for the period March 24-April 19, 2017

Geomagnetic field will be:
Quiet on March 25, April 8-9, 14-15
Mostly quiet on April 13, 19
Quiet to unsettled March 26-28, April 10, 12, 18
Quiet to active on March 24, 31, April 1-4, 6, 11, 17
Active to disturbed on March 29-30, April 5, 7, 16

Amplifications of the solar wind from coronal holes are expected on March 24, 30-31, April 1-4, (5-8,) 12-13. (14,) 16-20, Dates in parenthesis are less likely to have enhanced solar wind.


This weekend is the CQ Worldwide SSB WPX Contest. The CW portion is on May 27-28. See http://www.cqwpx.com/rules.htm for details. One cool aspect of this contest is that unique prefixes count for multipliers. So, instead of counting states worked or countries worked and using those totals to multiply your final score, you total up the number of unique prefixes worked.

Right now, as K7RA, I am not in much demand for this contest, because the K7 prefix is quite common. But starting in the 1980s, I was KT7H, and this made my call sought after as a desirable multiplier, depending on how many other stations in the contest had a call sign starting with KT7.


The Washington Post comments on the naked Sun. Note there is a comment at the bottom from N3JLY. http://wapo.st/2nKw6nd


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 March 16 through 22, 2017 were 0, 0, 0, 0, 0, 12, and 12, with a mean of 3.4. 10.7 cm flux was 70.5, 70.5, 70.2, 71.2, 72.7, 71, and 72.5, with a mean of 71.2. Estimated planetary A indices were 6, 4, 2, 2, 3, 26, and 27, with a mean of 10. Estimated mid-latitude A indices were 5, 3, 1, 2, 2, 18, and 19, with a mean of 7.1.