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ARRL Propagation Bulletin ARLP006 (2010)

ARLP006 Propagation de K7RA

QST de W1AW  
Propagation Forecast Bulletin 6  ARLP006
From Tad Cook, K7RA
Seattle, WA  February 12, 2010
To all radio amateurs 

ARLP006 Propagation de K7RA

Increasing sunspot activity continues. A glance at the image from
the STEREO mission ( shows a string of
active regions in the Sun's northern hemisphere, both visible and
over the horizon on the far side.

The high sunspot number for the week was 71 on February 8, and the
average for the week was 43.3.  We haven't reported a weekly average
that high since the week of March 27 through April 4 in 2008, when
it was 43.6.  The daily sunspot number hasn't been as high as 71
since May 28, 2006 when it was 78.  The earlier reading that reached
that level or more was 105 on April 6, 2006.

On February 8 when the daily sunspot number was 71, the total area
covered by sunspot activity was 460 millionths of a solar
hemisphere.  That measure hasn't been that high since the same
earlier week in 2008 that had a high sunspot number average.  The
dates were March 26-27, 2008 when the area of sunspots was 520 and

You can find continuous records of these old indices going back
through 1994 at,

The latest forecast has the solar flux index for today, February 12
at 90, followed by 92 on February 13, 94 on February 14-16, 93 on
February 17-18.  Predicted planetary A index for February 12-18 is
10, 8, 8, 7, 8, 8 and 5.

Geophysical Institute Prague sees unsettled conditions February
12-13, unsettled to active February 14, unsettled February 15, quiet
to unsettled February 16, and quiet February 17-18.

A number of people have inquired about short versus long skip on
75-80 meters, and why short skip is often non-existent but long skip
is enhanced.  Dennis Carlson, K9ZMI of Arlington Heights, Illinois
provides an explanation:

"As I understand it, the effect we are seeing is that the F-layer
ionization is weak because of low sunspot activity. A weakly ionized
layer has a low index of refraction (a term used in optics) which
impacts the amount of bending of the HF radio wave impinging on it.
Low index of refraction equals not much bending."

"So an HF radio wave leaving an antenna is typically headed toward
outer space but is bent back (refracted) towards Earth when it
reaches the ionized layers above Earth. The amount of bending
depends on the index of refraction and, for a given index of
refraction, the angle of impingement determines if the radio wave
will return to Earth or not."

"HF radio signals impinging on the weakly ionized layer at a high
angle (necessary for short skip communications between stations
close to each other) are not refracted enough to be "turned back" to
Earth and they simply radiate into space."

"Signals impinging on the weakly ionized layer at a low angle are
refracted enough to be "turned back" to Earth and they appear at a
large distance from the signal's origin, which is long skip."

Thank you, Dennis.  Look at ionosonde data for Boulder, Colorado on
the web at  A
glance at the foF2 column is instructive.  This is the highest
frequency that bounces back a signal from the ionosphere directly
above, with a signal beaming straight up.  For reliable short-skip
communications on 75 meters, we need the foF2 to be at least 4 MHz.

It may be different by the time you see it, but starting at 0000z on
February 11, I see the foF2 dipping below 4 MHz from 0115-1115z,
1145-1330z, and on February 12 0115-0515z, 0600-0615z, 0700-0715z,
and so on.  On February 12 the approximate sunrise at the ionosonde
is at 1402z and sunset at 0028z. It appears that roughly after
sunset until sunrise, possibly there isn't enough sunlight to
support short skip on 75 meters.

On Thursday, Bob Marston, K6TR sent this:

"Today, Feb 11th, NASA successfully launched the Solar Dynamics
Observatory at 10:23 AM EST from Launch Complex 41 at Cape Canaveral
Air Force Station in Florida. After completing its second burn 90
minutes after liftoff, the Atlas Centaur booster released SDO in a
1900 by 21,000 mile elliptical Geostationary Transfer Orbit. Through
a series of burns over the next three weeks SDO's propulsion system
will circularize the orbit. First light from the observatory can be
expected in 60 Days. Full calibration of the satellite will be
completed in early July. Carried on board SDO is the Extreme
Ultraviolet Variability Experiment which will render data of
importance to ham radio operators interested in HF Propagation. EVE
will sample Solar Radiation in the 304 Angstrom Range which composes
half of all radiation that goes into ionizing the F Layer of the
Ionosphere. The 304A number represents a tighter real-time
correlation to F Layer Ionization that the Smooth Sunspot Number
(SSN) or the 2800 MHz Solar Flux Number."

According to news reports, the scheduled launch on Tuesday was
delayed due to high winds.  For more information on SDO, visit  They have a web video channel at

Paul Graziani, W5ZK of Little Rock, Arkansas sent an article from
NASA about the SDO "Variable Sun Mission."  Read it on the web at,

D. Moore, who regularly sends articles of interest, referred us to for
another article on SDO.

Jon Jones, N0JK of Wichita, Kansas is still sending us 6 meter
reports.  On February 3 he reports a great deal of sporadic-E
activity to Mexico and Central America from the Western U.S.  He
notes that sporadic-E activity is unusual in February, and "The
openings Jan 31 - Feb 2 were intense, long lasting, strong, and
favored northern tier stations such as VE1, VE2, VE3, VE4, W1, W2,
W3 and W8, W9 and W0. More like mid-summer. Usually, February Es
favor stations along the Gulf Coast, Arizona and California to XE,
TI, YN, and KP4, etc."

He sent us a bar chart showing that sporadic-E activity is lowest in
March, and highest in May, June and July, with June at the peak.

On the evening of February 5 (February 6, UTC) he reported a lot of
6 meter E activity from Southern California and Arizona to Central
America and Mexico.  He sent logs showing K7JA, KS7S, K6QXY, AJ4F
and K6LPO all getting in on the fun.

Yesterday, February 11, he sent an email noting more 6 meter E-skip,
and that there have been E openings on 6 meters every day since
January 31.

Juan Carlos, CO8TW of Santiago, Cuba says he has a new web page
which aggregates propagation related data from a number of sources.
You can see it at,  Click on the
"Go back to home page" link to learn interesting things about ham
radio in Cuba.

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 February 4 through 10 were 11, 22, 30, 51, 71,
63, and 55 with a mean of 43.3. 10.7 cm flux was 73.9, 77.8, 87.5,
90.3, 93.7, 91.4, and 91.3 with a mean of 86.6. Estimated planetary
A indices were 2, 3, 4, 3, 3, 3 and 3 with a mean of 3. Estimated
mid-latitude A indices were 2, 0, 2, 2, 3, 1 and 1 with a mean of


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