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ARRL Propagation Bulletin ARLP014 (2010)

ARLP014 Propagation de K7RA

QST de W1AW  
Propagation Forecast Bulletin 14  ARLP014
From Tad Cook, K7RA
Seattle, WA  April 9, 2010
To all radio amateurs 

ARLP014 Propagation de K7RA

A strong geomagnetic storm on Monday and Tuesday, April 5-6, was the
biggest since 2006, at least in terms of high planetary A index.  On
those days the mid-latitude A index was 28 and 22, and the planetary
A index was 49 and 46.  This was caused by a mighty solar wind
stream.  A search for similar numbers over the past few years yields

In 2009 the highest planetary A index was 19 on August 30, and in
2008 it was 37 on October 11.  This is indicative of how quiet space
weather has become in the past few years.  In 2007 the planetary A
index reached 30 on April 1, and we have to go back to 2006 to find
any geomagnetic activity as strong, when the planetary A index
reached 63 and 104 on December 14-15.

It seems counter-intuitive, but average daily sunspot numbers rose
by 3.5 points this week to 32.4, while average daily solar flux
dropped over 7 points to 77.8.

NOAA and USAF predict solar flux at 75 for April 9-15, rising to 78
on April 16.  This is substantially different from Wednesday's
prediction, which had solar flux rising to 80 by April 15.  Now they
don't see a rise to 80 again until April 23.  The same forecast
predicts planetary A index for April 9-15 at 8, 5, 5, 12, 10, 5 and
5.  Geophysical Institute Prague predicts unsettled conditions for
April 9, quiet April 10-12, April 13 unsettled to active, April 14
active, and April 15 unsettled to active.

Looking back to December 14-15, 2006 which was the last time the
planetary A index was as active as it was this week, check out the
propagation bulletins from that time at, and

Note the paper predicting a large sunspot Cycle 24, which now seems
unlikely.  Big geomagnetic activity is often good for VHF
propagation, and this week we heard from Ed Richardson, VE4EAR of
Winnipeg, Manitoba about his experiences on 6 meters.

Ed wrote, "Just to let you know, this week's increase in Geomagnetic
activity was sufficient for several auroral contacts on 6m. On April
6th between 02:30 and 03:30 I enjoyed contacts with stations in
Ontario, Quebec and Minnesota and as well as VE8NSD up in the NWT.
All stations were worked with the beam pointed NNE and strengths
varied from 52 to 57. There were reports of stations in MN working
AK via Auroral E skip."

Go to and click on the antenna image to
see what's on Ed's tower.  Also note the number of lookups listed
below his address.

Carl Zelich, AA4MI of Chuluota, Florida sent images of logbook
pages, showing many worldwide contacts during recent good
conditions.  He comments on changing conditions this week:

"HF band openings have been opening later and closing sooner. This
was true of 40M, 10M and 20M bands. The 15M band has been very
quiet.  My log shows only one Indian Ocean QSO. This is in contrast
to 5-6 Indian Ocean QSOs during the prior week.

"Only one African QSO; as a note, the African Continent has been
generally quiet with a lack of stations.

"Eastern Europe and Caribbean activity had strong signals while
Western Europe had weak signal and a scarcity of stations.

"Overall conditions were very QSB with a wide swing in signal
strength over a short time period.  One point of note: A 6M QSO from
Central FL to MI lasted from 11:36A for 40 minutes! Can Spring be
far behind?"

Last week I was across the lake in Redmond, and stopped in to
Northwest Research Associates to chat with Jim Secan, who produces
an indicator called "Effective Sunspot Numbers."  These numbers are
derived from data produced by ionospheric soundings.  A signal
beamed upward is swept through the HF spectrum, and the reflected
signal is measured to determine the optimum frequencies and signal
strengths bounced from the sky overhead.  The Effective Sunspot
Number is not a count of sunspots, but an indicator of actual HF
radio conditions.  Check the NWRA pages at,, and

We've mentioned in the past that propagation prediction programs
such as W6ELprop are modeled on using the predicted smoothed sunspot
number as the data to drive propagation analysis, but that another
alternative was to use the average of several days of sunspot
numbers for a more up-to-date forecast.

Jim feels that the best results are obtained by averaging the latest
seven days of 10.7 cm solar flux -- available from, or -- for more detailed and timely data
directly from the Penticton observatory.  The local noon reading
(2000z) is the official daily number, and the numbers you want are
from the "fluxobsflux" column.  This is the same solar flux data
presented here at the end of each propagation bulletin.

Jim is not an amateur radio operator, but has done considerable
research on solar indices and propagation for the federal government
and military.  His opinion on using solar flux data instead of
sunspots is not shared by most of the amateur radio operators who I
consider most knowledgeable about propagation.  Jim says his studies
show that recent solar flux numbers give a more realistic view of
actual HF propagation when used with the propagation prediction

Red Haines, WO0W (that third character in his callsign is a zero)
sent along some thoughts and recent observations on April 7:
"Following a couple days of low critical frequencies, during which
the Boulder f0F2 never reached 4.0 MHz, the f0F2 reached 8.9 MHz at
2000z today. A quick scan of my records shows that is a high for the
year for Boulder. A more detailed scan will probably show that is a
high for a long time, possibly a couple years.

"Six of the 15 meter and 3 of the 10 meter DX beacons recorded on
"BeaconSee" between 2130z and 2200z, compared to none yesterday.

"The major difference in solar activity appears in the hard X-ray
flux detected by GOES 14.  It increased by an order of magnitude,
from around 2 x 10-9 watts per square meter for a few days to 2 x
10-8 watts per square meter.

"Other solar activity indicators show little change.  Soft X-ray
remains unchanged at about 4 x 10-8 for most of that time and the
sunspot number, April 4-7 was 40, 41, 41, and 41. The number for
today is not yet available, but the MDI Magnetogram image shown on
the SOHO site shows the same groups, moved slightly. Geomagnetic
activity is decreasing, from G2 to G1 in that period."

The foF2 data that Red mentioned is available from,, and
for Boulder Colorado, Wallops Island Virginia and Millstone Hill in
Westford, Massachusetts.

Note there is data going back a bit further at  For Millstone
Hill, from this list you can go to,
for February data, and you can change the 201002 in the URL to
201003 for March or 201004 for April.

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 a detailed
explanation of the numbers used in this bulletin, see An archive of past
propagation bulletins is at

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

Instructions for starting or ending email distribution of this
bulletin are at

Sunspot numbers for April 1 through 7 were 25, 28, 27, 40, 41, 41,
and 25 with a mean of 32.4.  10.7 cm flux was 79.2, 76.2, 77.4,
78.7, 79.3, 77.5 and 76.3 with a mean of 77.8. Estimated planetary A
indices were 12, 12, 8, 13, 49, 46 and 21 with a mean of 23.
Estimated mid-latitude A indices were 9, 10, 5, 11, 28, 22 and 15
with a mean of 14.3.


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