[South Florida DX Association] Solar Wind Loses Power.....

[Bill Marx]

Thomas F. Giella KN4LF writes:

For those that have not seen this article yet.
Solar Wind Loses Power, Hits 50-year Low:
 http://science.nasa.gov/headlines/y2008/23sep_solarwind.htm?list1057721


Gang,
I really do encourage you to read the above NASA press release if you
haven't already.  It explains quite a few of the electro-magnetic aspects of
our sun-earth interconnect and our solar system in very understandable
terms.

I would like to add a few comments.  After all, with the solar minimum
lasting longer than the presidential campaign, there's nothing else to do
except yack about it :-(

We all grew up hearing about "cosmic waves."  As the article pointed out, it
was not until the 1960s Viking and Voyager missions that cosmic rays from
the sun were first measured and proven to really exist.  That wasn't that
long ago.  And, it wasn't until the 1972 Skylab mission that solar flares
were first photographed and measured for which the flare, coronal mass
ejection (CME) and the shock wave were scientifically verified.  Prior to
that, a solar flare, effecting propagation on earth from hours to days
later, was only a guess.

Today, we as radio amateurs, can turn to the internet and see the solar
x-ray, electron and earth's magnetic field effects in real time, such as at
http://www.swpc.noaa.gov/today.html, or see those cosmic rays in the form of
the solar wind velocity, density, temperature and direction in real time at
http://umtof.umd.edu/pm/

The point is, it wasn't that long ago that professional astronomers and
astrophysicists would have killed to have the data available to us today.
Even as late as the late 1990s, most solar flares were captured by high
altitude balloons launched from White Sands in New Mexico, coordinated with
observations with the Very Large Array (VLA) radio telescope.  That method
proved a dismal less than 3% chance of catching a solar flare.  Now with
GEOS, SOHO, etc. satellites, we have this data in real time on our laptop
screens.

 --- 

The article discusses the drop in solar wind.  Actually, it is not the solar
wind SPEED (km/sec) that is dropping, but the DENSITY of the solar wind
(particles per cubic centimeter).

If you look at the present, solar minimum solar wind
(http://umtof.umd.edu/pm/), you will notice it is hovering around 300 km/sec
(a mere million miles per hour).  With the sun 93 million miles from Earth,
at this rate, it takes the solar wind about 90 hours, or nearly 4 days, to
reach the Earth.  Compare this to a fairly large solar flare that can hurl a
shock wave at Earth at well over 1000 km/sec., and if Earth bound, can
trigger a geomagnetic storm in about two days after the flare.

The solar wind speed never falls much below 300 km/sec, even during the
solar minimum -- simply because this is the escape velocity of the sun.
Particles traveling slower than this are simply pulled back to the sun's
surface by the sun's gravity.  Those just barely reaching the sun's escape
velocity will, well, escape at 300 km/sec.  This is what sets the minimum
solar wind speed at around 300 km/sec.

NASA scientists (and others) have noticed the solar wind density has been
apparently declining "over the past 50 years," or since the first Pioneer
and Voyager spacecraft mission measurements.  Then in the 1970s, some
instruments on Space Lab until satellites with solar wind instruments came
into use in the 1990s.

The drop in solar wind is certainly a curiosity, but not necessarily an
indication that things are going very, very wrong on the sun.  In light of
the above discussion about Pioneer, Voyager, etc., recall that the solar
wind has only been instrumented a bit more than a decade, and sporadically
for 30 years before that.  We only have a fairly spotty short-term record to
play with.

 --- 

The solar wind pushes outward until it stops, forming the heliopause, as the
article explains.  This is where the outward solar wind pressure becomes
equal to the incoming pressure from our galaxy.  It forms a fairly defined
wall of solar particles (we think).  However, scientists have absolutely no
idea how far away from the sun the heliopause is located.  Various
mathematical models give a guess, but the errors are in the tens of millions
of miles.

This is a very exciting final role of the Voyager spacecrafts (V_GER to you
Star Trek fans).  Most instruments are shut down to conserve energy except
for a couple of plasma physics sensors to detect when the spacecrafts pass
through the heliopause.  The article is a bit misleading in that since we
don't know where the heliopause is located, how will we know if it's
shrinking?  Regardless, when Voyager punches through the heliopause, this
will answer one of the last huge, unanswered questions we have about the
physics of our sun.  How far does the influence of our sun extend?  Guesses
as to when Voyager will find the heliopause  range from several years ago to
another 5-10 years.  That's a fairly large error window!

 --- 

Lastly, us hams know the poor ole HF spectrum has been largely ignored since
the early 1970s (when everything seemed to move to the microwave region).
While we have all these cool, nifty and neat sensors monitoring the sun from
Earth and space, instruments at HF frequencies, where propagation and
ionospheric effects are the most pronounced, are sadly lacking.  That is
changing.

I have been slightly involved with the design stages of the Long Wavelength
Array (LWA).  This will be an array of numerous antennas and receivers,
covering 8-88 MHz, forming a huge interferometer.  This will be capable of
making detailed maps, including 3D real time images of our ionosphere!  Most
of the antennas will be located in southwest New Mexico.  Initial tests of
the receivers and the "big blade" antennas are very encouraging.  And, all
the huge spikes of RFI from 50-88 MHz, called television, will go away early
next year!

Remember that HAARP test a few months ago?  The real purpose of that test
was to illuminate the LWA prototype array.  (There are a couple upcoming
similar tests that likely won't be announced via the ARRL.  I will try to
post their occurance when I learn of them).

A brief description of LWA is at: http://www.phys.unm.edu/~lwa/about.shtml

And, a brief description of the science goals are at:
http://www.phys.unm.edu/~lwa/s_drivers_key.shtml

The LWA website is a bit out of date.  It states some of the LWA "may" be
built around the VLA.  Since then, it has been decided the first four arrays
will be built at the VLA (center of the array, already there), at the end of
the VLA north arm, the 3rd station near Magdalena, NM, and the 4th near
Horse Springs, NM.

This is a project many years in the making.  However, when completed, this
will be an amazing tool available to amateurs for real-time HF propagation.
A 3D model of the ionosphere, including the exact positions and shape of the
D, E and F layers, should allow fairly accurate predictors of where your
signals will land at any given frequency and other related information.
Just think, you could watch a 3D display of the ionosphere above your head
on your laptop, and watch it compress in real time when the shockwave of a
solar flare arrives.  Or watch the electron density of each layer to
determine the MUF every ten minutes or so.

Since the LWA is in it's infancy stage of development and prototyping, not
much has been reported on it yet.  Thought you'd like a heads up on this
exciting new instrument, with elements of it hopefully online as we approach
the next solar maximum.  Remember, you heard about it here first :-)

 --- 

I was hoping the length of this post might extend past the solar minimum -
but no such luck :-(  Hopefully some of you found the above information
interesting and makes some of this solar physics stuff a little more
understandable.

73, Paul Harden, NA5N
Socorro, NM

(Speaking for myself, not representing the LWA or VLA observatory)