The K7RA Solar Update

We've seen average daily sunspot numbers for this reporting week. Since
last Thursday through Wednesday this week, the numbers rose more than 9
points to 28; the average solar flux slipped more than 2 points to 81.9.
Geomagnetic indices were a tiny bit lower. Sunspot numbers for January
21-27 were 17, 30, 40, 32, 34, 28 and 15, with a mean of 28. The 10.7 cm
flux was 82.6, 82.4, 84.6, 84.6, 81.2, 79.8 and 77.8, with a mean of
81.9. The estimated planetary A indices were 4, 2, 4, 4, 3, 3 and 2,
with a mean of 3.1. The estimated mid-latitude A indices were 4, 2, 4,
2, 3, 1 and 0, with a mean of 2.3. The predicted solar flux for January
29-31 is 76, 80 on February 1-2, 82 on February 3-5 and 88-89 for the
following five days. We don't see any geomagnetic upset predicted until
February 16, with the planetary A index only rising to 10, which is
hardly an upset.

On the STEREO image, we can see sunspot 1041 in the Sun's southern
hemisphere, around 30 degrees past the central meridian. The unseen area
(not yet visible to the STEREO mission) of the Sun is exactly at 45
degrees wide today, and shrinking. A sunspot is moving toward the
eastern horizon and looks to be less than 55 degrees away from first
visibility. If it takes roughly 27.5 days for a complete solar rotation
relative to Earth, we can divide 27.5 days by 360 degrees, then multiply
the result by 55 to estimate that the sunspot may begin to emerge in a
little over four days.

This week we received a very interesting e-mail from Richard Grubb,
W0QM, an Associate of the NOAA Space Weather Prediction Center in
Boulder, Colorado. Richard pointed out that the third paragraph of last
week's bulletin may have been confusing. He writes: "The term Sudden
Ionospheric Disturbance (SID) is used today to replace Short Wave
Fadeout (SWF) which was coined many years ago in the 1930s when the
immediate effects of a solar flare on the ionosphere were first observed
and correlated. The flare produces a sudden large increase in the flux
of solar x-ray and far EUV radiation (see here for more information)
that reaches the Earth at the speed of light.

"The radiation is absorbed in the ionosphere at D region heights (70-90
km) and produces an increase in ionization that acts to absorb signals
that would otherwise be propagated via the F and E regions. The effect
can be drastic and very obvious for large flares. These effects are
quite independent of the polarity of the Interplanetary Magnetic Field
(IMF). The IMF comes into play when there is a change in the strength
and density of the solar wind reaching the outer boundary of the Earth's
magnetic field. These changes can be due to solar coronal mass ejections
(CMEs) that are generated at the sun by explosive events often
accompanying a flare. A CME, as a shock wave and accompanying sudden
density enhancement takes hours to reach the Earth from the Sun.

"Other changes in the solar wind at the Earth occur as a boundary of the
co-rotating spiral structure of the solar wind passes the Earth. The
effects that these solar wind changes have on the Earth's magnetic field
and the ionosphere are strongly dependant on the polarity of the
magnetic field embedded in the solar wind plasma. If the north-south
component is such that the fields couple (like attracting magnets) then
the effect can be large, or small in the opposite case. The IMF does not
protect the Earth against solar flares per se, but against the
disturbances in the solar wind that may be solar flare produced.

"SIDs of course only occur in the sunlit hemisphere of the Earth. To
cause an SID, the flare can be anywhere above the visible solar rim;
however, flare or event position is very important in determining
whether an event generated in the solar wind propagates to Earth. Events
occurring on the eastern (left-hand side viewed from Earth) are
generally better coupled for propagation to the Earth because the solar
wind is dragged out into a spiral structure by the solar rotation.

"On January 20, we had both effects going on. There were several M class
flares, the largest at 1755 UTC that would have produced a measurable
SID; however, earlier in the day, a co-rotating stream interacted with
the Earth and produced a disturbance in the geomagnetic field that would
also have created an ionospheric effect via the change in the
distribution of the trapped radiation in the magnetosphere. The entire
process of interaction between the solar wind and the Earth's
magnetosphere/ionosphere system that can produce geomagnetic storms is
complex and still the subject of active research. But the broad outlines
are clear.

"As hams, we probably want to have a simple picture of the solar effects
on the propagation we observe. But the distinction between the prompt
(SID) and the delayed solar wind carried disturbances is important and
needs to be kept clear. It is the right hand (western) side of the Sun
as viewed from Earth that is most strongly coupled to the Earth for
events propagating through the interplanetary medium. Small events tend
to follow the spiral magnetic field to the Earth. Large events can
effectively force their way to the Earth from center or eastward
locations on the Sun.

"The Stanford site shows how to monitor SIDs using simple VLF receiver
monitors. One of the reasons that the term SWF was largely dropped in
favor of SID was because -- apart from the HF absorption -- the prompt
effects of the x-ray radiation from the Sun is a the change in
propagation of VLF signals via the D region that can be readily
monitored by the changes in amplitude and phase at a remote receiver. We
used to use VLF monitors for solar flare detection at the SWPC (SESC) in
the '50s and early '60s before we had the x-ray monitors on the GOES.
See also here and here."

Thanks to Dick for a very enlightening message.

Steven Hammer, K6SGH, of Santa Barbara, California, has a very gripping
and suspenseful account of battling the Santa Barbara Jesusita Fire in
May 2009 as it raced toward his rural home and ham station perched on a
canyon rim. Check it out here.

Someone named D. Moore has sent us many interesting articles over the
years, and this week he posted an article on the new Solar Dynamics
Observatory that you can read here. Several months ago, he sent an
article on NASA's MESSENGER spacecraft that we neglected until now, and
you can see it here. Yes, being in all caps, MESSENGER is an acronym,
although a tortured one: It is derived from MErcury Surface, Space
ENvironment, GEochemistry and Ranging probe. The name has a connection
to Greek mythology, because Mercury was the messenger of the gods.

Don't miss the CQ World Wide 160 Meter CW Contest this weekend; low
solar activity and weak solar wind generally mean good conditions for
this event.

Take a break from the contest tonight and observe the biggest full moon
of the year as it reaches perigee, the point of closest approach to
Earth. It is full at 0618 UTC January 30, which is 10:18 PM PST January
29 here on the West Coast. You can check local moonrise time with the
calculator here. Try to catch it low in the sky early on so you can see
it through foreground objects, maximizing the moon illusion. It should
be huge.

Finally, this edition of the bulletin is dedicated to Howard S. Pyle,
"YB of W7OE," born 112 years ago yesterday, January 28, 1898 (he became
a Silent Key on November 29, 1972). When I was a kid, he was a
well-known author of Amateur Radio books and magazine articles, mostly
in 73 or CQ. I met him one day on HF CW when I was 14, and he was local
to me in Seattle, on Mercer Island. He only used CW, never used
directional antennas and always operated barefoot. YB told many great
stories about working as the radio operator at a mine in Alaska (I think
the call sign there was YB), later on board ship and as an inspector for
the FCC. He encouraged me to write, and sent a letter of introduction to
Jim Fisk, W1DTY, at that time (1968) the editor of 73 Magazine, who
later founded Ham Radio magazine. To my surprise, they published my
article and the next one I sent them as well. YB had been on the air
since he was 9 years old in 1907 when he first operated a spark gap
transmitter. He also inducted me into the low power operator's
organization, QRP Amateur Radio Club International, which is still going
strong. At that time, the club had very modest goals and encouraged
members to run 100 W or less! YB said that Novice class licensees were
all qualified, because we were restricted to 75 W, crystal controlled CW
on HF.

Amateur solar observer Tad Cook, K7RA, of Seattle, Washington, provides
this weekly report on solar conditions and propagation. This report also
is available via W1AW every Friday, and an abbreviated version appears
each Thursday in The ARRL Letter. Check here for a detailed explanation
of the numbers used in this bulletin. An archive of past propagation
bulletins can be found here. You can find monthly propagation charts
between four USA regions and 12 overseas locations here. Readers may
contact the author via e-mail.