At 0549 UTC on August 3 the Australian Space Forecast Centre issued this warning:
“During UT days 4-5 August expect an increase in geomagnetic activity up to active to minor storm levels due to influence of the recurrent coronal hole.
INCREASED GEOMAGNETIC ACTIVITY EXPECTED DUE TO CORONAL HOLE HIGH SPEED WIND STREAM FROM 04-05 AUGUST 2017.
GEOMAGNETIC ACTIVITY FORECAST
04 Aug: Active
05 Aug: Active”
Spaceweather.com issued this warning later on the same day:
“GEOMAGNETIC STORM WATCH: NOAA forecasters say there is an 80 percent chance of polar geomagnetic storms on Aug. 4th when a solar wind stream is expected to buffet Earth’s magnetic field. The wind is flowing from a canyon-shaped hole in the sun’s atmosphere, so wide that it is almost bisecting the solar disk. Storm levels could reach G2-category (moderately strong) during the late hours of Aug. 4th, subsiding to G1-category (minor) on Aug. 5th. Visit Spaceweather.com for more information and updates.”
More zero-sunspot days appeared over the past week, but less than the previous week, in fact the average daily sunspot number increased from 1.7 to 5, and average daily solar flux went from 69.7 to 71.
Both are very low numbers, and below the minimum non-zero sunspot number (11) for any single day.
We saw average daily planetary A index go from 11.9 to 5, and the average dally mid-latitude A index (measured in Virginia) decline from 12.9 to 6.
These numbers are generally good for HF propagation, being lower, but for the best HF propagation we like sunspot numbers and solar flux as high as possible.
Predicted solar flux is 77 on August 4-11, 75 on August 12-13, 73 on August 14, 70 on August 15-26, 78 on August 27-29, 75 on August 30 through September 9, 73 on September 10, and 70 on September 11-17.
Predicted planetary A index is 25 on August 4-5, 12 and 8 on August 6-7, 5 on August 8-16, 15 on August 17-18, 12 on August 19, 10 on August 20-22, 5 on August 23-26, then 12, 10, 8 and 5 on August 27-30, then 25, 18, 12 and 8 on August 31 through September 3, then 5 from September 4 through 12, and 15 from September 13-14, 12 on September 15 and 10 on September 16-17.
F. K. Janda, OK1HH of the Czech Propagation Interested Group passes on his geomagnetic activity forecast for the period August 4-30, 2017.
“Geomagnetic field will be:
Quiet on August 8-10, 15, 25-26, 29-30
Mostly quiet on August 11, 16, 27
Quiet to unsettled August 7, 14, 21, 23-24, 28
Quiet to active on August 6, 12-13, 17-20, 22
Active to disturbed on August 4-5
Amplifications of the solar wind from coronal holes are expected on August 5-9, 14-23, (28).
– Parenthesis means lower probability of activity enhancement and/or lower reliability of prediction.
– A further Geomagnetic activity forecast will be issued on a regular basis August 10th, but the next will be compiled on August 31, because of the author’s participation in the expedition.
Contrary to the ancient times when our publishing began, there are other relatively reliable and usable resources today.”
OK1HH refers to an upcoming DXpedition, but I don’t have any info on it yet. I checked some of the usual sources, but came up with nothing, and will check with OK1HH.
W7WKR sent this: http://nyti.ms/2f4mpNH
Max White sent this: http://bit.ly/2uUxsNm
Note the Perseid meteor shower is on for this week, with the peak occurring August 11-13.
N0AX and others reminded me that the upcoming HamSCI experiment this month in conjunction with the solar eclipse is not actually sponsored by the ARRL, but is a creation of HamSCI, Ham Radio Science Investigation. Check them out at http://www.hamsci.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 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 July 27 through August 2, 2017 were 0, 0, 12, 11, 0, 0, and 12, with a mean of 5. 10.7 cm flux was 68.3, 69.5, 69.9, 69.5, 72.2, 73.5, and 74.4, with a mean of 71. Estimated planetary A indices were 6, 7, 4, 4, 3, 6, and 5, with a mean of 5. Estimated mid-latitude A indices were 8, 7, 4, 3, 2, 10, and 8, with a mean of 6.