ARRL Propagation Bulletin ARLP015 (2006)

ARLP015 Propagation de K7RA

QST de W1AW  
Propagation Forecast Bulletin 15  ARLP015
From Tad Cook, K7RA
Seattle, WA  April 13, 2006
To all radio amateurs 

ARLP015 Propagation de K7RA

League headquarters is closed on April 14 for the Good Friday
holiday, so the propagation bulletin arrives a day early.

Average daily sunspot numbers for the week were up over 12 points to
70.7. What really happened was that for the 7 days of March 30
through April 5, the daily sunspot number at the start of the period
was 35, and it rose to 88 by the seventh day. The next day, April 6,
was the first day of the reporting period for this bulletin, and on
that day the sunspot number rose to 105. The next day it had dropped
way down to 65, then 57, then 46 last Sunday, and by Wednesday,
April 12 it had risen again to 79.

Geomagnetic disturbances accompanied the rising solar activity. A
solar wind stream from a coronal hole met the interplanetary
magnetic field (IMF), which was pointing south, and this leaves
Earth vulnerable. On April 9 the mid-latitude A index was 27 and the
K index rose to 4 and 5. The planetary A index was 39, with the
planetary K index reaching 5 and 6.

At 2:30 AM Seattle time on that day my cell phone received an
automated call from Spaceweather Phone (see, alerting me that "The Planetary
K-index has reached a level of 6. This means that a moderate
geomagnetic storm is in progress. High-latitude sky watchers should
be alert for auroras." With this service, users can set it on a web
interface for certain hours that it won't call (for those who are
interested in a sound sleep). But I just have it set for 24-hour
alerts to my wireless phone, and when the cell phone is off at night
the alert goes to voicemail.

A similar condition to April 9 occurred four days earlier on April
5. But at that time sunspot 865 was still visible. This is the
biggest sunspot seen the year, and it has since rotated out of view.

Byron Stoeser, W7SWC on April 7 wrote, "I am out on 17-meter bicycle
mobile almost every day from my Winter QTH in Southern California.
It has been so unexpected to go out with the high sun spot numbers
the past two days and call CQ for 1/2 an hour with no response and
hear very little activity on the band, while a couple of weeks ago I
had calls from Japan, and worked the Caribbean and Europe with 0 sun
spots. Seems to me there is a lot more to this bottom of the sun
spot cycle than just sun spot count."

Yes, Byron is correct. Around that time he was experiencing rough
conditions from the solar wind. Sunspot numbers were up, but so was
geomagnetic activity on April 5.

There is a nice peppering of sunspots on the side of the Sun facing
us, but they are small. We could see another period of geomagnetic
disturbance this Saturday. Planetary A index predicted for the next
few days, Thursday, April 13 through Sunday, April 16, is 10, 25, 40
and 25. The Australian Space Weather Agency (see sent an alert on Tuesday advising of a high
speed solar wind from a coronal hole and increased geomagnetic
activity on April 15-16.

Sunspot numbers may rise again later in the month, perhaps over 100
again. This is most likely around April 24 through May 4.

You may sign up for their geophysical warning email alerts at, You can
check an archive of their previous warnings at,

Michael Mardit, WA2VQW wrote "I was in Dominica for the week
sandwiched around the SSB-WPX and I operated mostly 30 and 17 meters
CW (as J79VQ), while the rest of my team worked the contest. There
is absolutely no question that operating the Grayline is the place
to be if you want to know if anybody is out there. Sunspots or not,
lots of DX shows up during that 'magical' 20 minutes. At other
times, just calling CQ for a while will shake the bushes!"

Michael continues, "It seems that many Hams wait for someone else to
initiate the call, and as such, nobody is transmitting, hence, a
seemingly dead band. The blame is then put on the low sunspot
activity for an empty band. Call CQ and be patient, you will be
rewarded! VKs were calling me long path in the evening on 30 meters,
and the JAs and UA0s were knocking on my door on 17 meters at about
the same time. I was running 100 Watts to a vertical wire with 4
radials on the ground. YES being DX on an island certainly helps,
but you would never know that I was there if I didn't call CQ."

Ron Zond, K3MIY was one of several who wrote to praise the N0HR
Propfire plug-in for the Firefox browser, which monitors solar flux
and the A and K index when you are on the internet. WA1LOU gave
details in his recent Surfin' column on the ARRL web site 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 and an explanation
of the numbers used in this bulletin see the ARRL Technical
Information Service propagation page at, An archive of past
propagation bulletins is found at,

Sunspot numbers for April 6 through 12 were 105, 65, 57, 46, 70, 73
and 79 with a mean of 70.7. 10.7 cm flux was 98.9, 94.5, 91, 89.2,
88.7, 89.7, and 81.1, with a mean of 90.4. Estimated planetary A
indices were 10, 3, 5, 39, 18, 5 and 2 with a mean of 11.7.
Estimated mid-latitude A indices were 6, 2, 3, 27, 11, 3 and 1, with
a mean of 7.6.