Original Message
Subject:[QRP-L] Friday's X2 solar flare (long)
Date: Sat, 28 Jan 2012 00:41:13 -0700
From: Paul Harden NA5N n...@zianet.com
To: qr...@mailman.qth.net
Gang,
I've gotten a few emails wondering why I haven't commented on the recent
solar activity like I did during the last solar maximum. I mean didn't
it take like 10 years to get through the solar minimum? Anyway,
laziness, I guess is my excuse. And I realize we have many new hams who
are learning how propagation works on the HF bands, now that the solar
flux is above like 65 :-( and of course what all this solar flare, CME,
geomagnetic storm stuff is all about.
So here goes.
Friday, there was a fairly large X2 (X1.7 to be exact) solar flare on 27
January at 1837Z. An X-class flare is the highest category and can
cause radiation storms on earth and effect HF propagation - some of it
good.
Go here to see the x-ray emissions from this flare:
http://www.swpc.noaa.gov/today.html
The first chart is the x-ray emissions as detected by two different
sensors on the GOES-15 satellite. The X-class flare is easily seen
towards the end of the UTC day on 27 Jan. X-rays are ionizing
radiation, that is, they can knock electrons away from their host atoms
and molecules. In our upper ionosphere, this ionizing radiation knocks
electrons away from oxygen, nitrogen and hydrogen atoms. These
electrons just roam around in our ionosphere, being knocked around by
the ionizing radiation from the sun. For this reason, they are called
free electrons, not currently being associated with a host atom. The
more free electrons in the ionosphere, the more reflective are the E and
F layers, and the higher the maximum usable frequency (MUF). During a
solar flare, ionizing radiation increases almost immediately, producing
more free electrons in our ionosphere, making the E and F layers even
more reflective, and often raising the MUF. This condition quickly
improves HF propagation.
Therefore, for QRPers, solar flares are often a good thing. From the
time of the flare until local sundown, enhanced HF propagation will be
present. With higher reflectivity, this means QRP signals get reflected
more efficiently for an environment of working longer skip distances
(and new DX) than normal. Once the sun goes down ... that is, when the
ionosphere above our heads is no longer illuminated by the sun and
receiving the solar x-rays, the free electrons recombine with their host
atoms, reflectivity and the MUF drops, and we fall back into normal
night time propagation. The lack of ionizing radiation and free
electrons is why the MUF drops at night, and the higher day time bands
shut down. During the day, this ionizing radiation penetrates deep into
our ionosphere, causing a layer of free electrons we know as the
D-layer. Seldom do our signal bounce off this layer, but penetrates
it. Unfortunately, the electron density of the D-layer does eat up
(attenuates) some of our signal. At night, solar radiation and ionizing
radiation is gone. The E and F layers combine, and with no deep
penetrating radiation, the D-layer disappears. Without the attenuation
of the D-layer, this is why signals appear stronger and less noisy at
night - because they are!
As stated above, a solar flare is often a good thing from the time of
the flare until local sundown ... except in those cases of a very strong
solar flare. Its radiation can be so strong that the D-layer becomes
nearly saturated with free electrons, such that signals can not pass
through at all. Higher above our heads, the E and F layers are also
saturated with free electrons and the MUF drops quickly, sometimes to a
few MHz or less, or below the lowest usable frequency or LUF. This is a
radio blackout. The D-layer consumes virtually all of your signal
power, and the MUF can fall to below 3 MHz. This extreme case of a
total radio blackout is fairly rare.
Friday's X-class flare was associated with a CME - a coronal mass
ejection. As the name implies, a CME is where the flare belched out
copious amounts of solar mass - mostly electrons and protons. This is
usually an explosive event, forming a shock wave as the CME travels
outward from the sun. While the x-rays from the sun travel at the speed
of light, reaching the Earth in about 8 minutes, a CME travels much
slower than light speed, reaching the Earth in about 3 days ... if the
flare and the CME is located near the center of the sun. If the flare
is located near the edges, or limbs, of the sun, the CME will travel
outward into space, but away from the earth.
Today's X-class flare was a doozie. The shock wave was measured at
1,532 km/sec., about 950 miles per second, and about 3.5 million miles
per hour. Anything over about 1,000 km/sec. is considered a strong
shock wave and almost guaranteed to trigger a major geomagnetic storm
about three days later - if it hits the earth.
Friday's X-class flare occurred in region 1402, located
