Again this week sunspot numbers and solar flux were higher than the
week before.

Average daily sunspot numbers 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.

Three new sunspot groups emerged on April 13, one more on April 16,
and another on April 17.

Predicted solar flux over the next few weeks is 145, 140 and 135 on
April 21-23, 130 on April 24-25, 125 on April 26-27, 160 on April
28-29, 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, then 172 on May 19-21, then
168 and 162 on May 22-23, 160 on May 24-26, 165 on May 27, and 172
on May 28-30.

Predicted planetary A index is 20, 16, 12 and 8 on April 21-24, 5 on
April 25-27, 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, 15 and 18 on May
23-24, 15 on May 25-27, then 12 and 10 on May 28-29.

Weekly Commentary on the Sun, the Magnetosphere, and the Earth's
Ionosphere - April 20, 2023 from OK1HH.

"Of the fifteen sunspot groups observed over the past week, AR3272
and AR3282 were the source of most of the flares. Both had a
beta-gamma magnitude configuration. 61 C-class flares and 4 M-class
flares were observed.

"The partial halo CMEs on 15 and 16 April were the source of
particles that reached Earth on 18 April, when the solar wind speed
increased abruptly at 1308 UTC and a geomagnetic disturbance
developed.

"A positive phase of the ionospheric disturbance was recorded on the
afternoon of 18 April, followed by a negative phase on 19 April.
This was followed on 20 April with a significant increase in f0F2
and improved shortwave propagation conditions before noon UTC.

"The outlook looks promising for the first half of May, when solar
activity should increase further."

Dan Handa, W7WA commented on the news last week about the current
solar cycle reaching a peak earlier than predicted, perhaps by the
end of this year.

I told him I hoped it would not peak early, because I wanted to see
several more years of increasing activity.

Dan sent a very detailed graph of Solar Cycle 19 from 1954 to 1966,
and wrote: "I have read, and more than once, a slow rise means a low
sunspot max. The previous Solar Cycle 24 took five 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 did not know this.

In a subsequent message, Dan further commented:

"There was a lot of short term variation in the Solar Cycle 19
sunspot number, just like we're seeing now. From the graph the
timing of the Solar Cycle 19 peak can be defined three different
ways: the daily peak, the smoothed monthly peak or the smoothed
yearly peak, take your pick."

Another Solar Cycle 19? Many hams have dreamed of this for the past
six decades.

Dale, WB6MMQ reported that the solar images in the ARRL Letter with
a preview of our Friday bulletin show a blank Sun. I wasn't sure
what he was talking about, but now I realize this must be a stock
image (not from me!) used in the Letter.

I sent Dale links to some recent images from Spaceweather.com:

https://www.spaceweather.com/images2023/20apr23/hmi1898.gif

https://www.spaceweather.com/images2023/19apr23/hmi1898.gif

https://www.spaceweather.com/images2023/18apr23/hmi1898.gif

https://www.spaceweather.com/images2023/17apr23/hmi1898.gif

I hope this clears up the confusion.

An odd correlation between an ancient epidemic and solar activity:

https://bit.ly/3Lsqfxf

A story about a possible early Solar peak:

https://www.space.com/sun-solar-maximum-may-arrive-early

A story about possible M-class solar flares:

https://bit.ly/3KVc1n1

Send your tips, reports, observations, questions and comments to
k7ra@arrl.net. When reporting observations, don't forget to tell us
which mode you were operating.

For more information concerning shortwave radio propagation, see
http://www.arrl.org/propagation and 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/ .

Instructions for starting or ending email distribution of ARRL
bulletins are at http://arrl.org/bulletins .

Sunspot numbers for April 13 through 19, 2023 were 154, 153, 151,
155, 162, 140, and 113, with a mean of 146.9. 10.7 cm 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.