For this week’s ARRL Propagation Bulletin ARLP016:
This week’s sunspot numbers and solar flux were higher than the week before.
Average daily sunspot numbers were more than doubled, from 70.6 to 146.9, and average daily solar flux increased from 141 to 164.5. Both figures represent a substantial increase in solar activity.
Planetary A index averages went from 7.6 to 8.1, while middle latitude A index advanced from 6.4 to 7.3.
Predicted solar flux over the next few weeks is 145, 140, and 135 on April 20 – 22; 130 on April 23 – 24; 125 on April 25 – 26; 160 on April 27 – 29; 165 on April 30; 172 on May 1 – 3; 170 on May 4; 172 on May 5 – 7; 178 on May 8; 182 on May 9 – 12, then 175, 178, and 170 on May 13 – 15; 168 on May 16 – 17; 175 on May 18, and 172 on May 19 – 21.
Predicted planetary A index is 20, 16, 12, and 10 on April 20 – 23, then 8, 5, 15, and 18 on April 24 – 27; 15 on April 28 – 30, then 12 and 10 on May 1 – 2; 8 on May 3 – 4; 5 on May 5 – 6; 12 on May 7; 5 on May 8 – 10, then 8 on May 11 – 12; 5 on May 13 – 18, then 10, 8, 5, and 5 on May 19 – 22.
Dan Handa, W7WA, commented on the news item last week about the current solar cycle reaching a peak earlier than predicted, perhaps by the end of this year.
I told him I hope it will not peak early because I want to see several more years of increasing activity.
Dan sent a detailed graph of Solar Cycle 19, from 1954 to 1966, and wrote, “I have read more than once [that] a slow rise means a low sunspot max. The previous [Solar] Cycle 24 took 5 years to reach a relatively low maximum. A rapid increase can mean a high sunspot maximum. The granddaddy of our lifetime, [Solar] Cycle 19, peaked in three years!” I was unaware of this.
Sunspot numbers for April 13 – 19, 2023, were 154, 153, 151, 155, 162, 140, and 113, with a mean of 146.9. 10.7-centimeter flux was 159.5, 171.3, 175.8, 177.8, 166.6, 153.2, and 147, with a mean of 164.5. Estimated planetary A indices were 6, 7, 9, 4, 6, 13, and 12, with a mean of 8.1. Middle latitude A index was 5, 10, 8, 4, 6, 9, and 9, with a mean of 7.3.