Register Account

Login Help

ARRL Propagation Bulletin ARLP033 (2012)

ARLP033 Propagation de K7RA

QST de W1AW  
Propagation Forecast Bulletin 33  ARLP033
From Tad Cook, K7RA
Seattle, WA  August 17, 2012
To all radio amateurs 

ARLP033 Propagation de K7RA

There was a big drop in solar activity over the past week, with the
average daily sunspot numbers declining nearly 42 points to 77.6,
and average daily solar flux down 20 points to 114.7.

Solar flux has dropped below 100, where it is expected to remain
through August 22. NOAA/USAF predicted solar flux on August 16 and
17 at 100, but it was actually 98.3 on August 16. The prediction for
August 18 is 95, then 90 on August 19-22, then 100, 120 and 130 on
August 23-25, then 135 on August 26-29. It is expected to drop below
100 again on September 12-15. This is almost exactly the forecast
that was in the ARRL Letter on Thursday, with the August 23-24
sunspot numbers dropped by five points on each day.

Predicted planetary A index is 10 on August 17, 14 on August 18, 12
on August 19-20, then 8 on August 21, 5 on August 22-23, 8 on August
24-25, 12 on August 26, followed by 5 on August 27 through September
7, then 8 on September 8-10, and 5 on September 11-14. This is
identical to the forecast in Thursday's ARRL Letter.

The weekly prediction of geomagnetic indicators from OK1HH says to
watch for quiet to unsettled conditions August 17-20, mostly quiet
August 21, quiet on August 22-24, quiet to active August 25-26,
mostly quiet August 27-28, active to disturbed August 29-30, and
quiet again on August 31 through September 1.

Many readers have commented that the short term view of the solar
cycle has a recent peak around Fall 2011, yet predictions still
focus on Spring 2013 for the peak of Cycle 24.

It is interesting to look back over the past two solar rotations,
which is 55 days, and see an average compared with the same 55 days
last year, June 23 through August 16.  The average daily sunspot
numbers for those dates in 2009-2012 are 3.3, 26.5, 61.2, and 91.6.
If we want to look at last Fall's peak we can cherry pick the data,
and chose the 55 day period of November 7 through December 31, 2011.
The average daily sunspot number then was 119.3, about 30% higher
than current values.

This week N7QR, Russ Mickiewicz, of Portland, Oregon (and later
reader David Moore, and others) sent information on a new method for
predicting solar flares, by tracking decay rates in gamma radiation
from radioactive elements. Read about it at

Randy Crews, W7TJ of Spokane, Washington offered some opinions on
future solar activity and propagation.  He writes, "Reading K9LA's
excellent article in QST this past July, the graph on the cover
pretty well confirms the good HF propagation bestowed on DXers for
now, and if one 'connects the dots' the HF propagation following the
years after the peak (sometime in 2013) will be considerably
different from what we all have experienced in the past 30+ years.
Cycles 21, 22 and 23 were good strong normal sunspot cycles. As we
all can conclude from the numerous forecasts, Cycle 24 will be a
very low one. There will be much lower highs to drop from once the
decline begins, and the low point of Cycle 24 will occur much
sooner, unlike the many years of previous cycles where solar
activity declined from solar flux values of 200+. Carl is right.
Enjoy and make the most of propagation now. Once the cycle turns,
everyone will be surprised at the swiftness of the decline of high
band propagation."

George Kutcher, K3GWK of Jenkinsburg, Georgia mentioned that "There
is a simple sunspot data app for the iPhone, iPad and iPod Touch.
The app is called 'Sunspot' by AMI Mobile.  There is a cost for the
app.  'Sunspot' is a simple application to display 3-hour WWV space
weather and NOAA sunspot data on your iPhone, etc. Data is
updateable on demand, as well as current trending from the previous
data set."

Brendan Wahl, WA7HL of Bisbee, Arizona likes the N0HR Propfire
program for the Firefox web browser. It displays the geophysical and
solar data that WWV transmits at 18 minutes after each hour, and can
also display sunspot number. You can get it for free at,

N0AX reports that DX Sherlock has a new URL at,

Turns out our Sun is not perfectly round. Check it out at

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

For more information concerning radio propagation, see the ARRL
Technical Information Service web page at, For an explanation of the
numbers used in this bulletin, see An archive of past
propagation bulletins is at Find more good
information and tutorials on propagation at

Monthly propagation charts between four USA regions and twelve
overseas locations are at

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

Sunspot numbers for August 9 through 15 were 124, 105, 98, 76, 62,
46, and 32, with a mean of 77.6. 10.7 cm flux was 131.2, 125.4,
119.7, 112.3, 108.1, 105.8, and 100.7, with a mean of 114.7.
Estimated planetary A indices were 6, 4, 4, 7, 9, 7, and 6, with a
mean of 6.1. Estimated mid-latitude A indices were 7, 4, 5, 7, 8, 7,
and 7 with a mean of 6.4.


Instragram     Facebook     Twitter     YouTube     LinkedIn