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ARRL Propagation Bulletin ARLP022 (2007)

ARLP022 Propagation de K7RA

QST de W1AW  
Propagation Forecast Bulletin 22  ARLP022
From Tad Cook, K7RA
Seattle, WA  May 25, 2007
To all radio amateurs 

ARLP022 Propagation de K7RA

This week saw a return to active geomagnetic conditions after a
period of relative quiet.  The planetary A index reached a high of
42 on Wednesday, May 23, and the mid-latitude A index on that day
was 28.  At the same time, sunspot numbers are dropping, from a high
of 56 on May 16 to 44, 23, 15, 14, 12 and 0 on May 19-24.  Currently
the interplanetary magnetic field points south, making Earth
susceptible to geomagnetic upsets from solar wind.

We could see a blank sun through the end of May.  On Thursday, May
24 at 2134z the USAF and NOAA released a second daily 45 day outlook
(revised from the initial forecast 35 minutes earlier), calling for
solar flux values through the end of the month of 70, 70, 65, 65,
65, 70 and 70 for May 25-31.  When the sun is devoid of spots for
extended periods, we often see solar flux values below 70, so
predicting a solar flux of 65 implies no sunspots.

The three lowest solar flux values I am aware of were between July
19-22, 1996 when they were 64.9, 66.1, 65.4 and 65.1.  There you
have it, the lowest, second lowest and third lowest solar flux
values, all during those four days.  The fourth lowest value I am
aware of was 65.8 the year before, on May 27, 1995.  During the
current sunspot minimum and the previous one around 1996, I am not
aware of any other solar flux values below 66, but my records only
go back to January 1, 1989.  My records of solar flux resolved to
one tenth of a point don't begin until May 27, 1992.  Prior to that,
they are all recorded as whole numbers.

Geomagnetic indices should remain active for the next few days, with
predicted planetary A index for May 25-29 at 25, 25, 20, 10 and 5.
Geophysical Institute Prague predicts active conditions for May
25-26, unsettled May 27, quiet to unsettled May 28, and quiet May
29-31.  During the CQ World Wide WPX CW Contest this weekend, expect
no sunspots and declining but still active or unsettled geomagnetic

Several readers this week reported recent six-meter openings.  Mark
Bell, K3MSB of Airville, Pennsylvania (about 40 miles southeast of
Harrisburg in grid square FM19) worked NP4A (FK68) and WP4N (FK78)
around 0000z on May 13.  Don't miss Mark's photos of old classic ham
radio gear at

Mike Williams, W4DL of Pompano Beach, Florida sent a message from
the Dayton Hamvention about an opening on six meters on May 14.
''After work, I dutifully turned on the 6 meter gear and by 8 PM
that evening, I had worked a page full of stateside stations on CW,
(my favorite), SSB, FM and AM.  What a pleasant early evening!
There is much more activity on 52.525 and above and numerous CW
stations as compared to last year''.

Kenneth Tata, K1KT of Warwick, Rhode Island (FN41) wrote on May 22
that a strong six meter opening began at 2030z toward ''4-land'',
the southeast of the United States.  A few days earlier, he sent his
favorite links for spotting VHF openings.  For two meters, there is
a map based on APRS networks at  A
description of the network lives at

Ken also likes the tropo ducting maps at  He checks the two and six
meter loggings at and  Ken writes, ''A much more ambitious
website is .  Gabriel has done a truly amazing
job with this site!  He collects VHF/UHF contacts BY BAND and
presents them on a map TO USER SPECIFICATIONS!  It can also
automatically email propagation warnings to subscribers.  And
there's a lot more there, too.''

Ralph Burgess, VE3BSJ asked, ''Very simply, what figures should I
hope for?  Right now, I see on the top of my DX monitor: SF=70 A=37
K=3.  What would show an improvement for me?''  My response follows.

An A index of 37 is generally undesirable, although K of 3 means
conditions have settled down a bit.  The exception is if you want to
use auroral propagation on six meters, in which case a higher number
is desirable.  Aurora appears at lower and lower latitudes as the A
and K index rise.

We want the solar flux (70) to be as high as possible.  It generally
tracks with sunspot numbers.  Minimum solar flux is below 70, when
there are no sunspots.  For good HF conditions, we want many
sunspots with less geomagnetic activity.

Here is the relationship between A and K index:

The A index is calculated every 24 hours, and is based on the eight
K index readings done every 3 hours throughout the day.

From the nomograph at the URL above we can see that if we had 24
hours of K=1, A would be 4, A would be 7 if all the previous K index
readings were 2, 15 if they were 3, and 27 if they were 4.  So your
A index of 37 probably means that most of the day's K index readings
were around 4 or 5.

The latitude of your address in Parry Sound is 45.344 degrees north,
which is actually 2.3 degrees south of my latitude in Seattle.  The
farther north we are, the more we are negatively affected by high A
and K index.  In fact, these geomagnetic indices can be measured
anywhere, and when there is geomagnetic activity you will see higher
numbers at higher latitudes.

Look at this:

The A index you are seeing may be from Boulder, Colorado and is the
number derived at the end of the day (in UTC) for yesterday, while
the K index is the most recent reading:

Or perhaps it is from some European source.

My general rule is that HF conditions are better when the K index is
below 3, and worse when they are above 3.  We have seen very quiet
conditions most recently, but when we have more sunspots in a few
years a Boulder A index of 3 will be about average.

You can see from that table of A and K index that the College
(Fairbanks, Alaska, at 64.9 deg N) index (both K and A) yesterday
(May 23) was much higher than the mid-latitude index, which is from
Fredericksburg, Virginia at 38.3 deg N latitude.  The planetary
indices are derived from a combination of magnetometers around the
world.  The Boulder numbers on WWV are from 40 degrees north

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 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

Sunspot numbers for May 17 through 23 were 30, 45, 44, 23, 15, 14
and 12 with a mean of 26.1. 10.7 cm flux was 76.5, 75.8, 74.8, 74.1,
73.2, 72, and 70.1, with a mean of 73.8. Estimated planetary A
indices were 6, 18, 12, 6, 6, 11 and 42 with a mean of 14.4.
Estimated mid-latitude A indices were 4, 15, 10, 6, 6, 10 and 28,
with a mean of 11.3 


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