Australia’s Space Weather Services issued a Geomagnetic Disturbance Warning at 0022 UTC on August 16. "Geomagnetic activity is expected to be at Quiet to Active levels due to coronal hole effects. A period of significant southward Bz component could produce isolated Minor Storm levels."

What is the Bz component? It is a component of the interplanetary magnetic field, or IMF. http://pluto.space.swri.edu/IMAGE/glossary/IMF.html explains:

"The IMF is a vector quantity with three directional components, two of which (Bx and By) are oriented parallel to the ecliptic. The third component--Bz--is perpendicular to the ecliptic and is created by waves and other disturbances in the solar wind. When the IMF and geomagnetic field lines are oriented opposite or "antiparallel" to each other, they can "merge" or "reconnect," resulting in the transfer of energy, mass, and momentum from the solar wind flow to magnetosphere. The strongest coupling --with the most dramatic magnetospheric effects-- occurs when the Bz component is oriented southward."

A high-speed solar wind stream is expected to emerge from the coronal hole.

Solar activity is still very weak. The previous bulletin (ARLP032) reported two days with a sunspot number of 11, on each day, for August 2-8, yielding the average daily sunspot number for the week at 1.6. This week’s average was 3.4, based on a sunspot number of 12 on both August 14 and 15. That activity continued Thursday, August 16, also with a daily sunspot number of 12.

Average solar flux went in the other direction, changing to 68.7 from 69.7 in the previous week. Geomagnetic indicators were higher, with average daily planetary A index shifting from 5.7 to 6.9, and mid-latitude A index from 6.9 to 7.3.

Activity is weak and should get weaker, at least until two years from now in 2020 when we will probably reach the bottom of solar cycle 24.

Predicted solar flux (August 16 forecast from USAF via NOAA) is 69 on August 17-23, 70 on August 24 through September 5, 68 on September 6-18, and 70 on September 19-30.

Predicted planetary A index from the same forecast is 10 on August 17, 5 on August 18-20, 15 on August 21-22, 10 on August 23, 5 on August 24 through September 2, then 12, 8, 5, 5, 10, 8 and 8 on September 3-9, then 5 on September 10-11, then 12, 15, 8, 5, 15 and 12 on September 12-17, 5 on September 18-28, 8 on September 29 and 12 on September 30.

F.K. Janda, OK1HH sends us his Geomagnetic Activity Forecast for the period August 17 to September 12, 2018.

Geomagnetic field will be:

Quiet on August 22-24, 31, September 5, 9

Quiet to unsettled on August 18, 25, 30, September 1-2, 4, 6

Quiet to active on August 17, 19, 26-29, September 3, 8

Unsettled to active on August 21, September 7, 10, 12

Active to disturbed on August 20, September 11

Solar wind will intensify on August (16-19), 20-22, 28 -30, September 10-12

Remarks:

- Parenthesis means lower probability of activity enhancement.

- Reliability of predictions remains low.

Here is an interesting article about cosmic rays: https://bit.ly/2KTiMcH. The article was written by Dr. Tony Phillips of Spaceweather.com.

On Tuesday, August 14, Dr. Tamitha Skov sent this message and video: "Another quick note to let you know my latest ‘forecast shorty’ is up for viewing on You Tube. However, I can report some good news since I shot the forecast. A new, albeit tiny active region is emerging on the Earth-facing Sun and is growing fast! This means both solar flux and amateur radio propagation might be getting a much-needed boost over the next couple of days. I will be sure to keep you updated on how this new region is progressing when I shoot my full length forecast in the next couple of days. Again, a huge thank you to the Patreon members during this pre-launch phase, who are making these ‘forecast shorty’s possible!"

See Dr. Skov’s latest video: https://youtu.be/fl325AOjItM

Dr. Skov mentioned the Parker Solar Probe, which launched August 12: https://youtu.be/AzDa9bJykBY

Also, https://www.nasa.gov/content/goddard/parker-solar-probe

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 August 9 through 15, 2018 were 0, 0, 0, 0, 0, 12, and 12, with a mean of 3.4. 10.7 cm flux was 70.3, 69.5, 67.4, 68.1, 67.8, 68.7, and 68.8, with a mean of 68.7. Estimated planetary A indices were 5, 4, 11, 5, 5, 4, and 14, with a mean of 6.9. Estimated mid-latitude A indices were 6, 4, 11, 6, 6, 6, and 12, with a mean of 7.3.