The K7RA Solar Update


The solar indicators were up again this week, with the average daily sunspot numbers increasing nearly 21 points to 104.3, while the average daily solar flux rose nearly 12 points to 115.5. Geomagnetic numbers were up as well, with the most active geomagnetic day occurring on September 3. Sunspot numbers for September 1-7 were 119, 103, 139, 114, 102, 93 and 60, with a mean of 104.3. The 10.7 cm flux was 111.8, 115.4, 118.7, 119.4, 118.7, 111.5 and 112.8, with a mean of 115.5. The estimated planetary A indices were 3, 3, 13, 8, 6, 7 and 6, with a mean of 6.6. The estimated mid-latitude A indices were 1, 1, 9, 7, 4, 5 and 5, with a mean of 4.6.

We are just two weeks away from the autumnal equinox in the Northern Hemisphere. Look for increasing enhanced HF conditions as a result, as we move from summer conditions with its associated atmospheric noise and daytime absorption.

The latest prediction from NOAA/USAF has solar flux at 105 for September 9-10, 100 on September 11, 95 on September 12-13, 100 on September 14-15, 105 and 103 on September 16-17, and 105 on September 18-22. The planetary A index is predicted at 5 on September 9, 18, 15, 10 and 8 on September 10-13, 5 on September 14-17, 7 on September 18-19, and 5 on September 20-23. Geophysical Institute Prague predicts minor storm for September 9-10, active conditions September 11, unsettled September 12, quiet to unsettled September 13 and quiet on September 14-15.

Both the NOAA and Prague predictions for September 9-10 are probably based on a series of recent solar flares beginning September 6 from sunspot group 1283. These should deliver minor disruptions to Earth on September 9-11, because the energy isn’t squarely aimed toward Earth. In another few days, 1283 will be over our Sun’s western limb and outside the area of influence for Earth. An eruption from a sunspot squarely in the center of the solar image has the potential for the greatest impact here. 1283 was in the center of the solar disc several days ago, but no longer.

Click here for an interesting article about sunspot group 1283. You can see an eruption from 1283 here. Note you can also select a high resolution image from that page. Check out this YouTube video for an interesting video commentary on 1283. Note that in the lower right, you can select a high definition image. Pay no attention to the comments below the video regarding earthquakes, typhoons and planetary alignment. Anyone can post these, and they are not based on any sound science.

Max White, M0VNG, of Worcester, England, sent in an article about the Solar Dynamics Observatory and how they are using it to study solar flares.

All times listed are UTC, unless otherwise noted.

Amateur solar observer Tad Cook, K7RA, of Seattle, Washington, provides this weekly report on solar conditions and propagation. This report also is available via W1AW every Friday, and an abbreviated version appears each Thursday in The ARRL Letter. You can find a guide to articles and programs concerning propagation here. Check here and here for a detailed explanation of the numbers used in this bulletin. An archive of past propagation bulletins can be found here. You can find monthly propagation charts between four USA regions and 12 overseas locations here. Readers may contact the author via e-mail.