Register Account

Login Help

ARRL Propagation Bulletin ARLP016 (2021)

ARLP016 Propagation de K7RA

QST de W1AW  
Propagation Forecast Bulletin 16  ARLP016
From Tad Cook, K7RA
Seattle, WA  April 16, 2021
To all radio amateurs 

ARLP016 Propagation de K7RA

On April 12 new sunspot group AR2814 appeared following five days of
no sunspots at all. Daily sunspot numbers on the following four days
were 16, 16, 17 and 22 bringing the average daily sunspot number for
this reporting week (April 8-14) to 7, from 6.4 last week. The April
15 sunspot number of 22 was not included in this average. So far in
2021, 39% of the days had no sunspots.

Geomagnetic indicators were quiet, with average daily planetary A
index declining slightly from 6.6 to 5.1. Likewise, middle latitude
A index changed from 5.6 to 4.1.

On April 14 reported a high speed stream of solar
wind from a hole in the Sun's southern hemisphere. This could
produce a minor geomagnetic storm on April 17.

At 2338 UTC on April 14 and again at 0239 UTC on April 16, the
Australian Space Forecast Centre issued a Geomagnetic Disturbance
Warning: Geomagnetic activity is expected to increase to Active
levels with a chance of an isolated minor storm period from late 16
April due to coronal hole effects. The April 16 warning said to
expect the effects to continue through Sunday, April 18.

Predicted solar flux is 74 on April 16-19, 72 on April 20-21, 70 on
April 22-23, 75 on April 24 through May 8, and 72 on May 9-17, and
75 on May 18 through the end of the month.

Predicted planetary A index is 18, 20 and 16 on April 16-18, then
12, 8, 5 and 10 on April 19-22, 8 on April 23-24, 5 on April 25-26,
then 10 and 8 on April 27-28, 5 on April 29 through May 3, 15 on May
4, 5 on May 5-7, 8 on May 8, 5 on May 9-10, 8 on May 11-12, 5 on May
13, 20 on May 14, 8 on May 15-16 and 5 on May 17-18.

Geomagnetic activity forecast for the period April 16 to May 11,
2021 from F.K. Janda, OK1HH, who has compiled this weekly bulletin
since January 1978.

"Geomagnetic field will be
quiet on: April 25, May 1-3, 5
quiet to unsettled on: April 26, 28-30, May 6-11
quiet to active on: April 19-20, 23-24
unsettled to active: April 21-22, 27
active to disturbed: April 16-17, (18,) May 4
"Solar wind will intensify on: April (16-17,) 18-19, (21-22, then
irregularly between April 23-May 1,) May 3-5, (6-7, 10-11).
"Parenthesis means lower probability of activity enhancement."

Jon Jones, N0JK reported on April 15: "Stations in New England
spotted CE2SV and CE3SX FF46 on 50.313 MHz FT8 ~ 2200z April 13.
Likely a sporadic-E link to TEP.

"AC4TO EM70 Florida reported 18 DX contacts in 10 DXCC countries
April 13. Solar flux was up at 83."

Steve Sacco, NN4X reported:

"Here in Florida, we saw late-afternoon opening into Europe on both
10M and 12M.

"Looking west on 10M FT8, I noticed ZL3IO completing a QSO with
CT1ENI, and then calling EA5RW.  Note that it's the middle of the
night in EU at 2034Z!"

Don't miss this truly remarkable presentation by Frank Donovan,
W3LPL to the Central Arizona DX Association on "HF Ionospheric

"Universe Today" has an article on Galileo sunspot drawings and an
application of artificial intelligence:

Here is the April 14 report and forecast from Dr. Tamitha Skov,

If you would like to make a comment or have a tip for our readers,
please email the author at, .

For more information concerning shortwave radio propagation, see and the ARRL Technical Information
Service at For an
explanation of numbers used in this bulletin, see

An archive of past propagation bulletins is at More good
information and tutorials on propagation are at

Instructions for starting or ending email distribution of ARRL
bulletins are at .

Sunspot numbers for April 8 through 14, 2021 were 0, 0, 0, 0, 16,
16, and 17, with a mean of 7. 10.7 cm flux was 74, 77.8, 70.4, 72.9,
82.8, 72.8, and 74.4, with a mean of 75. Estimated planetary A
indices were 5, 3, 5, 6, 5, 5, and 7, with a mean of 5.1. Middle
latitude A index was 3, 2, 3, 5, 4, 5, and 7, with a mean of 4.1.


Instragram     Facebook     Twitter     YouTube     LinkedIn