Note! For those that would like to chat with me about solar, space weather and geomagnetic goings on I'm on Yahoo IM and my ID is thomasgiella.
This website is permanently under
construction as I add new data and research information continuously. If you see
any spelling or sentence structure errors I've overlooked "please" feel free to
advise me, thanks! Also feel free to ask for inclusion on this website of
"legitimate" propagation theory. Remember that the definition of "theory" means
that the concept has not or can not be definitively proven in a laboratory
setting but can be inferred via systematic study.
Note these theory notes are primarily for medium frequencies (300-3000 KC)
only.
I have attempted to keep the
propagation theory explanations in simple to understand layman terms, because
long complicated technical explanations can be boring and make one's eyes glaze
over. Unfortunately though sometimes while trying to keep things simple, certain
definitions, meanings and technical aspects can get watered down or even lost,
which tends to open me up to criticism from certain fellow space weather
scientists that just don't understand the educational and public relations
concept of the keep it simple stupid (KISS) principle.
I choose to use W6SAI's (SK) "KISS" method of writing and
communicating. I have found that this method works best whether it be in
teaching about Space or Atmospheric Weather. I do have an extensive teaching
background in Space and Atmospheric Weather.
Unfortunately I'm not be
able to answer all propagation questions from either the layman or scientific
community at this moment, due to ongoing federal government reasons (one of my
peers found this explanation humorous). I'm the only scientist on the planet
with a command of high and medium frequency radio wave propagation theory as a
Space Plasma Physicist and also of atmospheric weather as a Meteorologist.
However because of the nature of my employment with "Uncle Sam", I'm not well
known within typical civilian government and academic circles involving space
weather forecasting nor within the Amateur Radio community, so have been looked
upon with suspicion and/or indifference. I am however well known within
atmospheric weather consulting circles. I do hold basic and advanced degrees in
Meteorology and Space Plasma Physics courtesy of the cold war era "Uncle Sam
University".
In 2003 I was in the research and data collection mode for
a new book concerning MF and LF wave propagation modes and their interaction
with Stratospheric and Troposphere meteorological effects, including lightning,
Internal Buoyancy/Gravity Waves, temperature and moisture discontinuities (cold
frontal inversions), etc. Unfortunately virtually all in depth research data on
the subject is still bottled up within the federal government and it will stay
there for an indefinite period of time because of government reaction to the
09/11/2001 terrorist attacks. The book was to be based on the research that was
to become available in 2003 through the U.S. FOIA. Actually a good amount of
very valuable research data on MF and LF frequency propagation period is still
in a "not to be released to the general public" form. I was to publish the data
in G & A and also in book form in approximately one year but basically the
book has gone the way of Polar Cap absorption so to speak.
Recently I
also became involved in a propagation research project of sorts on 10, 6 and 2
meters. I have set up a propagation beacon on 10 meters, the frequency is 28131
kc USB +1500 hz using 25 watts. Actually there is a group of hams running the
propagation beacons in the U.S. and around the world. Basically it's a marriage
between digital PSK31 and APRS technology, actually software's run on a computer
that is interfaced to a transceiver. Beacon transmission will commence on 20
meters in the future, with the ultimate aim of all HF bands and even 160 meters.
It's been very interesting so far watching F2 propagation openings on 10 meters,
when conventional propagation wisdom says that the opening should not be
occurring. A knowledgeable observer can also pick out Sporadic-E (Es) openings.
You can learn more about the concept by clicking here
for HF PropNET.
We hams
are a curious lot with inquiring minds. A good number of us have a keen interest
in low, medium, high and very high frequency radio wave propagation mechanisms
and this website conglomeration is directed at this cutting edge group.
We also have a segment in our radio service that is basically
disinterested in radio propagation and don't feel it necessary to understand it
in order to successfully work DX, which is certainly okay.
Then we have
a third and smaller group with gigantic runaway egos that insist that they are
omniscient by virtue of their license class, ARRL DXCC entity totals and
"possible" electrical engineering backgrounds. Anal Retentives? They spend their
time arguing with ignorance (Alchemists) against explanations put forth via this
and other scientists, with solid backgrounds in atmospheric and/or space weather
physics.
Other experts within our great radio
service include our own NM7M, K9LA, N4XX, W3ASK, NW7US and others
unintentionally left out of this list!
While on the subject of distant galactic objects on 12/27/2004 more than a dozen spacecraft recorded the brightest event from outside the solar system ever observed in the history of astronomy. This gamma and X-ray producing super flare was emitted by a Magnetar star named SGR 1806–20. This star is an estimated 50,000 light years distant in the constellation Sagittarius on the far side of the Milky Way galaxy and obscured behind dense interstellar clouds.
Upon arrival at Earth the X-rays were powerful enough to increase absorption in the D layer of our ionosphere and create a dayside Sudden Ionospheric Disturbance (SID) and a blackout of radio signals, amazing!!! To read more about this rare event check out this link at: http://skyandtelescope.com/news/article_1464_1.asp .
d.) Recently I saw a post on the Topband
Reflector E-List, lamenting the seemingly unexplainable differences in 160
propagation on certain paths from night-to-night. A reasonable explanation? Yes,
unfortunately small increases in the density of the night time D-layer over
short periods of time, caused by smaller solar flares and also the general
variability of the solar background X-Ray flux level, can have a profound
negative impact on propagation in the form of increased absorption of high and
even mid-latitude medium-frequency signal paths, both on the MF broadcast band,
160 and 120 meters. Why? It only takes 10 electron volts (ev) of energy to
ionize the atmosphere and 1-10 Angstrom X-ray photons energize the atmosphere at
a factor of 100. This translates into D layer absorption of medium frequency
signals. The lower half of the MF broadcast is always affected first followed by
the upper half of the AM broadcast band, then 160 and 120 meters. If you learn
nothing else on this website, remember this simple explanation and pass the
word.
e.) After much personal observational research over a 30 year
period, I've come to the conclusion that high and mid latitude TA and TP
propagation paths tend to open up only after a significant period of time passes
with an energetic proton event of no greater then (10+0) on 160 meters and no
greater then (10-1) on the medium frequency broadcast band. Openings also occur
when the average solar background X-ray level falls back to or below C1 for 160
meters and B9 for the AM broadcast band, with A9 or less best.
f.)
Remember though that there are daily extremes of the Background X-ray flux
level. So even though the daily average might have been good at say B2.2, the
daily "extreme" maximum could have been C1.5, which would have been bad and have
cause a short period of increased D layer absorption.
g.) Though high
latitude paths on the day light side of the Earth are primarily effected, night
time high latitude paths can also be impacted by higher intensity energetic
proton events. This fact is still stubbornly opposed by some otherwise very
knowledgeable space weather physicists hung up on high latitude threshold
riometer data tied to Polar Cap Absorption (PCA).
h.) Another wrench in
the gears preventing consistent good propagation on medium frequencies is
related to Sporadic-D (Ds) absorption. Sporadic-D (Ds) occurrences have an
inter-relationship with brief but intense Sun based and Galactic Cosmic Rays,
huge positive cloud to ground lightning strokes and interrelated Elves and
Sprites. Very large bursts of Gamma Rays have also been observed to occur in
conjunction with Sprites.
i.) Also there is another unavoidable problem,
Magneto Ionic Power Coupling. Antenna polarization plays a large role in the
success of a long haul DX contact. As a medium frequency RF signal traverses
Earth's magnetic lines of force in a perpendicular manner on high and mid
latitude paths say between W3 land and SM, higher angle horizontally polarized
signals are more readily absorbed then lower angle vertically polarized signals.
On other propagation paths on the globe opposite results can be found, i.e.
horizontally polarized signals suffer less absorption on a propagation path
between VK6 and W6 or S9 and W4.
Magneto Ionic Power Coupling expert Bob Brown NM7M has a good
educational thread on this bugaboo on the May 2002 Topband Reflector. The thread
can read in it's entirety by going to this link Topband Reflector May 2002 Archives Layer
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Earth's Magnetosphere
Click To Enlarge
j.) Geological effects such as
earthquakes and volcanic eruptions, as well as meteorological effects such as
troposphere originating Internal
Buoyancy/Gravity Waves (IBGW), stratospheric level Quasi-Biennial
Oscillations (QBO) and stratospheric warming (See definition #20 on
Stratospheric Warming) have a negative effect on MF RF signals in the form of
small to medium increased absorption variations of MF RF signals via the D layer
caused by traveling ionospheric disturbances (TID's). Also temperature and
moisture discontinuities (frontal inversions) can refract/scatter MF radio
signals in unpredictable ways, most notably on high transmitted RF power levels.
k.) The Quasi-Biennial Oscillation (QBO) is a wind shift in the
equatorial stratosphere, an oscillation from easterly to westerly and back on
the time scale of approximately two years (26 months) and is a source of
Internal Buoyancy/Gravity Waves (IBGW's) which create absorptive perturbations
in the D and E layers and even in the F-1&2 layers.
l.) A note, the
E-valley/Flayer ducting propagation mechanism does not exist only during gray
line periods. Internal Buoyancy/Gravity Waves (IBGW's) are a source of the
ducting mechanism and allow for occurrences of ducting along any propagation
path in total darkness. Measurement of the timing of arrival of propagated MF RF
signals demonstrates the existence of the ducting mechanism, versus conventional
numerous E layer land/ocean surface hops.
m.) Yet another mechanism to deal with that impacts medium frequency radio
wave propagation in a negative fashion is the D-Region Mid Winter Anomaly. It is
a period of increased MF radio wave absorption at high and mid latitudes
occurring in mid winter and is associated with sudden stratospheric warming and
the Quasi Biennial Oscillation (QBO).
n.) The HAARP ionospheric program,
earthquakes, volcanic eruptions, thunderstorms, lightning (especially positive
cloud to ground strokes), elves, sprites, tornadoes, hurricanes and even man
made activities such as rocket launches including the space shuttle, are all
sources of (IBGW's). Many times I've heard ham's lament that propagation was
going to go to crap due to another space shuttle launch, in a sense they are
correct. Much more research is needed on MF and LF radio wave propagation.
o.) Another issue facing MF AM broadcast Band DXers and 160 meter operators
is lower latitude propagation path absorption due to the Equatorial Ring
Current. This phenomenon acts as a repository for precipitated electrons and the
end result is unpredictable MF RF signal blockage absorption and refraction.
Absorption is similar to higher latitude Auroral absorption.
p.) Here
are some interesting website links concerning LF and VLF radio propagation
theory.
A reliable gauge for measuring the up to three day lingering post geomagnetic storming medium frequency transmitted RF absorption is the Dst index, measured in nT's. It is an estimated value from Kyoto Japan and is based on a formula. Large negative values after a major geomagnetic storm indicates a high Equatorial Ring Current level. (See definition #2. Aurora Oval Blockage, Absorption And Refraction). Here is a website link to the Kyoto, Japan Dst Index http://swdcdb.kugi.kyoto-u.ac.jp/dstdir/ and the U.C. Berkeley website link http://sprg.ssl.berkeley.edu/dst_index and a NASA GSFC website link http://image.gsfc.nasa.gov/poetry/ask/a10021.html . (See definition #2. Aurora Oval Blockage, Absorption And Refraction).
Coronal mass ejections are not random meaningless
eruptions but instead a process by which the Sun expels complex magnetic
signatures enroute to changing it's magnetic polarity or said a different way
the swapping of the Sun's magnetic poles. Basically the Sun swapped it magnetic
polarity at the peak of present solar cycle 23 somewhere between July 2000 and
December 2001. The next polarity swap will occur during solar cycle 24 somewhere
around 2010-2011.
Coronal holes occur most often on the downside of a solar cycle and their absence at the bottom of a solar cycle and at the beginning of the next, allow for the best LF and MF radio propagation conditions. Many think it's the lower solar flux values seen at the bottom of a solar cycle that accounts for improved propagation conditions but it's actually pretty much a lack of coronal holes and geomagnetic storming. (See definition #11. Geomagnetic/Ionospheric Storm).
One thing to keep in mind is that the high
velocity solar wind stream emanating from a coronal hole is a neutral phenomena
with respect to the Bz (magnetic component) of the interplanetary magnetic field
(IMF). If the Bz component is negative (southward) prior to arrival of the solar
stream, there will exist a tendency to see a larger swing negative after the
disturbance arrives. If the Bz component is positive (northward) prior to
arrival of the solar stream, there will exist a tendency to see a larger swing
positive after the disturbance arrives.
2.) For medium frequencies a solar flux under 150, under 100 better, 70 is best for E layer multi hop.
Keep in mind though that the 10.7 cm (2800 mhz) solar flux index is not a "reliable" gauge of ionization in our atmosphere for F layer MF frequency refractions, as the energy of photons at this frequency is to low on the order of one million times. However most are used to solar flux and sunspot number and it's a hard habit to break. A better indicator is the background x-ray flux. See #7 below.
3.) Solar flux of at least 100 for E valley-F
layer ducting mechanism.
4.) Previous 24 hour Ap index under 10, under 7
for several days consecutively is best.
5.) Previous 3 hour Kp index
under 3 for mid latitude paths, under 2 for high latitude paths, 0-1 for several
days consecutively is best.
6.) Energetic protons no greater then 10 MeV
(10+0) for 160/120 meters and no greater then (10-1) on MF broadcast band.
7.) Background x-ray flux levels less than C1 for several days
consecutively for 160/120 meters and less then B9 for MF broadcast band, A9 or
less is best.
8.) No current STRATWARM alert.
9.) IMF Bz with a
(positive number) sign, indicates a lesser chance of high latitude path auroral
absorption/unpredictable refraction or scattering of MF RF signals, when the Kp
is above 3.
10.) A -50 or better towards a positive number Dst index
during the recovery time after a geomagnetic storm, as related to the Equatorial
Ring Current.
-----
8.) E
Valley-F Layer Propagation Ducting Mechanism/Chordal Hop Propagation-
Antenna polarization plays a large role in the success of a long haul DX
contact. As a medium frequency RF signal traverses our planets magnetic lines of
force in a perpendicular manner on high and mid latitude paths say between W3
land and SM, higher angle horizontally polarized signals are more readily
absorbed then lower angle vertically polarized signals. On other paths on the
globe opposite results can be found, i.e. horizontally polarized signals suffer
less absorption on a propagation path between VK6 and W4.
You would
expect a true long path QSO on 160 to be theoretically possible but improbable
on most paths during any season. However a G to VK long path might be possible
if the E-valley/F-layer ducting propagation mechanism or the Chordal Hop
propagation mechanism is involved. A 160 meter signal can traverse a daylight
path via these propagation modes if the transmitted signal enters/exits at each
end of the path at or near sunrise/sunset when the D layer ionization is weak
(ionospheric tilting).
The downward tilt of ionospheric layers is
eastward at sunrise. As a result, signals coming from the west are refracted
downward at steeper angles and are therefore heard better on higher angle
antennas. The opposite is true at local sunset.
A note though, the
E-valley/Flayer ducting propagation mechanism does not exist only during gray
line periods. Internal Buoyancy/Gravity Waves (IBGW's) are a source of the
ducting mechanism and allow for occurrences of ducting along any propagation
path in total darkness. Measurement of the timing of arrival of propagated MF RF
signals demonstrates the existence of the ducting mechanism, versus conventional
numerous E layer land/ocean surface hops.
The majority of the time
medium frequency RF signals in excess of approximately 3200 miles propagate via
the E-valley/F-layer propagation mechanism or via the Chordal Hop (mostly on HF)
propagation mechanism. High solar flux values can aid in long haul medium
frequency propagation, as high solar flux values ensure a strong F-layer half of
the E-Valley/F-layer duct mechanism. Typically the majority of transmit
antenna's radiation must be focused between 40-60 deg. to enter the
E-Valley/F-layer duct.
If one is lucky enough to be on the receive end
of a ducted medium frequency signal due to an IBGW or two, a change in the
vertical and/or horizontal electron gradient will allow the RF to drop out of
the duct at your QTH.
A note, high solar activity in the form of
increased ionization created by ultraviolet and X-ray radiation, can fill in the
E-Valley/F-layer ducting region with medium frequency absorptive ionization and
interfere with the E- Valley/F-layer ducting mechanism. In a sense the E/F layer
duct is shut down and the medium frequency RF signal can only propagate between
the E-layer and land/ocean surface, at a higher angle and with more signal loss.
This closing of the duct can be reciprocal on each end of the propagation path
or one way only. (((((When closing of the duct occurs the advantage of a low
angle vertical radiator is lost, with a higher takeoff angle horizontal dipole
making the contact still possible, albeit maybe weaker.)))))
Medium
frequency radio waves possess elliptical polarization, with the signal splitting
into ordinary and extra-ordinary rays. These rays can propagate in or out of
phase, mainly out of phase. The out of phase extra-ordinary ray represents a 50%
power loss on the receive end of a propagation path.
-----
9.)
Electron Gyro Frequency Absorption-
Unfortunately medium frequencies
fall within or very near the electron gyro-frequency which is in the approximate
range of 630 to 1630 kHz and of course the AM broadcast band and 160 meter band
is very close to these electron gyro-frequencies. There is a direct correlation
between the strength Earth's magnetic field lines and electron gyro frequencies.
Basically, the electron gyro-frequency is a measure of the interaction
between an electron in the Earth's atmosphere and the Earth's magnetic field.
The closer a transmitted a medium frequency carrier or sideband wave frequency
is to the electron gyro-frequency, the more energy that is absorbed by the gyro
electrons from that carrier wave frequency. This is especially true for medium
frequency signals traveling perpendicular to the Earth's magnetic field, meaning
high latitude NW and NE propagation paths. Unfortunately this form of medium
frequency signal absorption is ALWAYS present.
Geomagnetic Storm Levels
|
Planetary K
Indices |
Geomagnetic Storm
Level |
|
K = 5 |
G1 Minor |
|
K = 6 |
G2 Moderate |
|
K = 7 |
G3 Strong |
|
K = 8 |
G4 Severe |
|
K= 9 |
G5 Extreme |
|
Active K =
4 A= 100-400
Severe |
K- 0=
A- 0 |
Solar
Radiation Storm Levels
|
Flux
Level of > 10 MeV Particles |
Solar Radiation Storm
Level |
|
10 |
S1 Minor |
|
102 |
S2 Moderate |
|
103 |
S3 Strong |
|
104 |
S4 Severe |
|
105 |
S5
Extreme |
MF Radio Blackout Levels
|
Peak
X-Ray Level And Flux |
Radio Blackout
Level |
|
M1 and
(10-5) |
R1 Minor |
|
M5 and (5 x
10-5) |
R2 Moderate |
|
X1 and
(10-4) |
R3 Strong |
|
X10 and
(10-3) |
R4 Severe |
|
X20 and (2 x
10-3) |
R5
Extreme |
((((Note! Unfortunately elevated Kp indices of as little as a 3
will create absorptive conditions for medium frequency signal propagation on
higher propagation paths)))).
Initial phase of a geomagnetic storm is
that period when there may be an increase of the middle latitude horizontal
intensity.
Main phase of a geomagnetic storm is that period when the
horizontal magnetic field at middle latitudes is generally decreasing.
Recovery phase of a geomagnetic storm is that period when the depressed
northward field component returns to normal levels.
By the way effects
of the solar wind on the magnetosphere decreases as we approach the
Summer/Winter solstice and increase at the Fall/Spring Equinox. Why? Basically
it's the orientation of Earth's magnetic field with respect to the
Interplanetary Magnetic Field within the Solar Wind. When solar material and
shock waves reach Earth their effects may be enhanced or dampened depending on
the angle at which they arrive. READ
ABOUT IT HERE.
The Wang-Sheeley Interplanetary Magnetic Field (IMF)
Model is used to predict Sun's IMF polarity. When the polarity of the IMF is
negative a visible mid latitude Aurora display is likely as a Coronal Mass
Ejection (CME) strikes the Earth's magnetic field.
-----
12.)
Geological/Meteorological Effects On MF Propagation-
Geological effects
such as earthquakes and volcanic eruptions, as well as meteorological effects such as
troposphere originating Internal Buoyancy/Gravity Waves (IBGW's), stratospheric
level Quasi Biennial Oscillations (QBO) and warming (STRATWARM) have a negative
effect on MF RF signals in the form of small to medium increased absorption
variations of MF RF signals via the D layer, due to traveling ionospheric
disturbances (TID's).
Also temperature and moisture discontinuities
involved with cold frontal inversions and air mass triple points involved with
extra-tropical low pressure systems can refract, diffract or scatter MF radio
signals in unpredictable ways, most notably on high transmitted RF power levels.
This is another concept that a fellow Physicist and expert in optics took me to
task over.
As far as MF refraction it's more significant at say 3000 kc,
then 1850 kc or 1500 kc. But it's also more noticeable with higher transmitted
RF powers, i.e. WSAI 1530 50 KW and even more so with BSKA 1521 KC 1000 KW and
now defunct 2000 kc region 100 KW marine stations.
We know that the MF
spectrum is defined as 300-3000 kc but the differences in refractive properties
between 300 and 3000 is very significant significant. At 3000 kc refraction is a
good description, on 160 scattering, at 300 kc diffraction.
Using the
strictest definition of RF refraction, it's effect on 160 meters is small but it
has been measured by government researchers as significant enough to impact 160
but near the air mass triple point. In my opinion scattering is actually the
more consistent propagation medium for 160 meters along a cold front, away from
the extra-tropical cyclone center.
However the temperature and moisture
discontinuities in the vicinity of a triple point air mass structure such as
seen with a mature extra-tropical cyclone is very complex and fluid. The NW
quadrant of the extra-tropical cyclone is the location that the original
government researchers identified as the region of existence for the complex
temperature/moisture discontinuity structure that allows for refraction of RF
signals as low as 1500 kc. I have not been successful at garnering data from the
federal government that can be released to the general public. NOAA has been
similarly stymied and therefore is now conducting similar research.
The
QBO is a wind shift in the equatorial stratosphere, an oscillation from easterly
to westerly and back on the time scale of approximately two years (26 months)
and is a source of Internal
Buoyancy/Gravity Waves (IBGW) which create absorptive perturbations in the D
and E-layers and even possibly the F 1/2 layer. A note, the E-valley/Flayer
ducting propagation mechanism does not exist only during gray line periods.
Internal Buoyancy/Gravity Waves (IBGW's) are a source of the ducting mechanism
and allow for occurrences of ducting along any propagation path in total
darkness. Measurement of the timing of arrival of propagated MF RF signals
demonstrates the existence of the ducting mechanism, versus conventional
numerous E layer land/ocean surface hops.
The HAARP ionospheric program,
earthquakes, volcanic eruptions, thunderstorms, lightning (especially positive
cloud to ground strokes), elves, sprites, tornadoes and hurricanes and even man
made activities such as rocket launches including the space shuttle, are all
sources of (IBGW's).
Many times I've heard ham's lament that propagation
was going to go to crap due to another space shuttle launch, in a sense they are
correct. Much more research is needed on the subject.
 |
 |
-----
13.) Polar Cap Absorption (PCA)-
An anomalous condition of the polar ionosphere whereby MF (300-3000 kc)
radio waves are absorbed, and LF and VLF (3-300 kHz) Radio waves are wave guided
at lower altitudes than normal. In practice, the absorption is inferred from the
proton flux at energies greater than 10 MeV (10+0), so that PCA's, Polar Radio
Blackouts and Proton Events are interrelated and often simultaneous.
((((NOTE!!! high latitude radio propagation paths may still be disturbed
for days, up to weeks, following the end of an official proton event.)))) This
fact is still stubbornly opposed by some otherwise very knowledgeable space
weather physicists, hung up on threshold Riometer readings.
-----
14. Sunspot Group-
Sunspot groups are bipolar magnetic
concentration regions on the photosphere of the Sun where magnetic field
strengths many thousands of times stronger than the Earth's magnetic field
reside. Sunspots appear as dark spots on the surface of the Sun because
temperatures in the dark centers of sunspots drop to approximately 3700 K
compared to 5700 K for the surrounding photosphere. The difference in
temperature makes the spots appear darker than elsewhere. Sunspots typically
last for several days to several weeks. They are seen to rotate around the sun,
since they are on the surface, and the sun rotates fully every 27.5 days.
Sunspots usually come in groups with two sets of spots. One set will
have a positive or north magnetic field while the other set will have a negative
or south magnetic field. The magnetic field is strongest in the darker parts of
the sunspots called the umbra and weaker and more horizontal in the lighter part
called the penumbra.
The twisted magnetic fields associated with sunspot
groups are one source of the solar flares, coronal mass ejections and
geomagnetic storms that wreak havoc with the ionosphere here on Earth.
-----
15.) Short Wave Fadeout (SWF)-
During a Solar
Flare event or Sudden Ionospheric Disturbance (SID), abrupt increased ionization
of the D-layer results in reduced to total absorption of MF circuits which are
reflected by the ionosphere on the sunlit hemisphere of the earth. This is known
as a Shortwave Fadeout (SWF).
Solar flares produce copious amounts of
electromagnetic radiation including energetic protons which increase the
ionization of the daytime D-layer. MF communication depends on the reflection of
signals from the higher E and F2 layers and these signals must travel through
the D layer at least twice.
Lower frequencies are affected first and
higher frequencies last. The stronger the event, the stronger the ionization of
the D layer, the higher the frequency effected via absorption.
Daytime
E-layer propagation of the AM broadcast band and 160 meters (See definition #1.
Overview) usually only occurs during the winter season and especially at higher
latitudes with a lower sun angle and at the low part of a sunspot cycle,
therefore SWF's rarely are rarely noticed. The 80/75 meter and 40 meter bands
are most noticeably affected, with the higher bands least affected.
An
SWF can last from several hours on the lower frequencies to minutes on the
higher frequencies. (See definition #16. Solar Flare).
-----
16.)
Solar Flare-
A day side earthward bound solar filament and/or
approximate C5 class or higher solar flare can move the proton flux >10 MeV
(10+0) and initiate large scale high latitude propagation path absorption but
even smaller C4 class flares and weaker are the culprit behind hour-to-hour and
night-to-night variations in signal strength on the AM broadcast band and 160
meters, both stateside and DX. This transfer of increased density and RF signal
absorption from the day-side D-layer to night-side of the ionosphere occurs
through high level neutral winds.
X-Ray Class Solar Flare. The rank of a
solar flare based on its X-ray energy output. Flares are classified by the order
of magnitude of the peak burst intensity (I) measured at the earth in the 1 to
10 angstrom band as follows:
Class (in Watt/sq. Meter)
B- I less than
(l.t.) 10.0E-06
C- 10.0E-06 l.e.= I l.t.= 10.0E-05
M- 10.0E-05 l.e.= I
l.t.= 10.0E-04
X- I g.e.= 10.0E-04
Background radiation in the 1 to
10 Angstrom range (Hard X-Rays), as well as Solar and Galactic Cosmic Rays is
the source of ionization of the D-layer.
Basically a C-class solar flare
possesses energy 1/10 the level of an M- class solar flare and an M-class solar
flare possesses energy 1/10 the level on an X-class solar flare. (See definition
#15. Shortwave Fadeout).
Solar flares are not random meaningless explosions but
instead a process interelated with coronal mass ejections (CME's) by which the
Sun expels complex magnetic signatures enroute to changing it's magnetic
polarity or said a different way the swapping of the Sun's magnetic poles.
Basically the Sun swapped it magnetic polarity at the peak of present solar
cycle 23 somewhere between July 2000 and December 2001. The next polarity swap
will occur during solar cycle 24 somewhere around 2010-2011.
Like stratospheric level warming and troposphere level temperature and moisture discontinuities, Sporadic-E can depending on the circumstances absorb, block and refract medium, high and very high frequency RF signals in an unpredictable manner.
The main source for high latitude Sporadic E is radio aurora activity.
The main sources for mid latitude Sporadic-E include wind shear, internal buoyancy/gravity waves (IBGW's), and traveling ionosphere disturbances (TID's), most of which are produced by severe thunderstorm cell complexes. The tie in between Sporadic-E and a severe thunderstorm is the sprite and elve.
The main sources for low latitude Sporadic-E include wind shear, internal buoyancy/gravity waves (IBGW's), and traveling ionosphere disturbances, most of which are produced by severe thunderstorm cell complexes tied to tropical cyclones.
The forecasting of Sporadic-E has long been considered to be impossible. However it is possible to identify certain troposphere level meteorological conditions that can lead to the formation of Sporadic-E. One is as mentioned above the severe thunderstorm cell complex.
Sporadic-E have been observed to occur within approximately 150 km/90 mi to the left of a severe thunderstorm cell complex in the northern hemisphere, with the opposite being observed in the southern hemisphere. To complicate matters is the fact that Sporadic-E clouds not only have been observed to move from west to east but at times also east to west. So one has to look for Sporadic-E on either side of a severe thunderstorm cell complex.
Not all thunderstorm cell complexes reach severe levels and not all severe thunderstorm cell complexes produce Sporadic-E. This is where knowledge in tropospheric physics and weather forecasting is necessary. Coincidentally I have a B.S. in Meteorology and an M.S. in Space Plasma Physics and am qualified to identify which severe thunderstorm complexes are most likely to produce Sporadic-E.
Some but not all key elements in identifying which severe thunderstorm cell complexes have the potential to produce Sporadic-E via wind shear, internal buoyancy/gravity waves, traveling ionosphere disturbances, sprites and elves include:
1.) Negative tilted mid level long wave troughs.
2.) Approximate 150 knot/170 mph jet stream jet maxes that produce divergence and therefore create a sucking vacuum effect above thunderstorm cells, that assist thunderstorm cells in reaching and penetrating the tropopause into the stratosphere.
3.) 500 mb temperatures of -20 deg. C or colder, which produce numerous positive and negative lightning bolts and inter-related sprites and elves.
4.) Approximate 150-175 knot/172-200 mph updrafts within thunderstorm cells that create overshooting tops that penetrate the tropopause into the stratosphere (See definition #20 on Stratospheric Warming), launching upwardly propagating internal buoyancy/gravity waves, traveling ionosphere disturbances and wind shear.
More to come.
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19.) Long Delayed Echo (LDE)-
A fairly common propagation mechanism by which an RF transmitted signal returns to the sender within 1.25-5 seconds and in rare cases of up to 30 seconds. Research in the 1980's with HF OTHR discovered one propagation mechanism which involves ducting of the transmitted signal in the E-valley-F layer region of the ionosphere. A signal traveling along a magnetic field line much like a lightning induced whistler is another possibility.
The best time to observe an LDE is during the Fall/Spring equinox period when conditions are more balanced in the ionosphere. LDE's are very noticeable on amateur and SW broadcast signals between 17-28 mc with a peak near the maximum usable frequency (MUF). As recently as fall 2003 I did my own brief experiments using Morse code (CW) on the 15 meters band. I personally observed LDE's of my own transmitted signal of approximately 1.5-3 seconds and I could hear a mushy kind of doppler shift on my returned signal frequency.
Claims of very long delayed echo's (VLDE) on the order of
hours and even days have been reported since the beginning of radio. Time
periods of this magnitude would point to the "seeming possibility" of a
refracting ionospheric type medium outside of Earth's own ionosphere, possibly
somewhere past Pluto in the Oort Cloud. However no evidence so far has been
found of such a medium and 99% of reported VLDE's are "probably"
hoaxes.
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20.) Sudden
Stratospheric Warming (STRATWARM ALERT)-
Sudden stratospheric warming is
a major temperature change of the winter time polar and middle atmosphere from
the Tropopause (where the troposphere transitions into the stratosphere) to the
base (D-layer) of the ionosphere, lasting for many days at a time and
characterized by a warming of the stratospheric temperature by some tens of
degrees (temperature inversion), in unison with adjacent tropospheric cooling.
Another way to explain stratospheric warming is a major disturbance of
the winter polar middle atmosphere from the Tropopause to D-region which is at
the base of the Mesosphere resulting from a breakdown of the polar vortex into
two circulation cells. Air trapped in the vortexes is mixed by the new
meridional flow and is exposed to sunlight. Solar lyman alpha ionizes the nitric
oxide gasses resulting in an increase in electron density and producing strong
MF absorption.
A little related Troposphere Meteorology:
Interrelated with the splitting and shifting of the Arctic Circumpolar
Vortex, is a Troposphere level negative North Atlantic Oscillation (NAO) and
Pacific-North America Anomaly (PNA), mid and upper air height anomaly pattern.
This equates to a large high pressure ridge in Western North America extending
northward all the way into the Yukon region of Canada and a deep trough in the
Eastern North America, from the eastern U.S. extending down into the Yucatan
region of Mexico, with a second ridge in the western North Atlantic Ocean. This
pattern is also called a dual blocking ridge and taps Siberian Arctic air,
sending it across the North Pole into the eastern 2/3's of Canada and the U.S.
providing for very cold surface temperatures.
As the stratosphere lies
below the ionosphere, which is at mesosphere and thermosphere height, you would
not expect to see stratospheric warming effect medium frequency propagation in
any way BUT medium frequency signals do propagate off of temperature inversions
and moisture discontinuities and a temperature inversion is involved with
stratospheric warming. So it's probable that a medium frequency signal could do
any number of things when scattering off of a temperature inversion, at any
height. Unfortunately though some otherwise very knowledgeable Physicists
stubbornly resist this concept.
You can almost always correlate the
coldest weather occurrences with poor medium frequency propagation conditions.
Also Stratospheric Warming (STRATWARM) has a negative effect on medium
frequency propagation, due to increasing medium frequency radio wave absorption
by the D layer, via upward propagating Internal Buoyancy/Gravity Waves (IBGW's).
This phenomenon also occurs in southern hemisphere winter but is less
pronounced.
Click Here For The U. Of Berlin Germany Stratospheric
Research Group Layer
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21.) D Region Mid Winter
Absorption Anomaly-
A period of increased MF radio wave absorption at
high and mid latitudes occurring in mid winter and is associated with sudden
stratospheric warming and the Quasi Biennial Oscillation (QBO). If you look in
your radio logs for 160 meters you will notice that most of your good DX
contacts are in the fall and spring. This is due to the D Region Mid Winter
Absorption Anomaly. (See definition #17. Sporadic-D (Ds) Absorption & Wave
Guiding). (See definition #19. Sudden Stratospheric Warming (STRATWARM ALERT).
Click Here For A Abstract By Gian-Carlo Rumi Concerning the Mid
Winter Anomaly
And Click Here For "Weather In The Upper Atmosphere"
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22.) F3 Ionospheric Layer-
Click Here For A PDF Article Via IPS Australia About
The Long Suspected But Only Recently Verified F3 Ionospheric Layer
Click Here For PDF Article #2 Via IPS Australia About The Long
Suspected But Only Recently Verified F3 Ionospheric Layer
The
F3 layer primarily seems to exist only in the vicinity of the Earth's magnetic
equator. This may be an explanation for (TEP) Trans Equatorial
Propagation.
Also I use "RAW" and error prone public domain data from the NOAA Space
Environment Center, as well as other U.S. Government organizations, to produce
my "not for profit" propagation forecast outlooks. This data is gathered and
made public by the U.S. Government using taxpayer $$$. However the forecast
outlooks that I produce from the "RAW" public domain data, is my personal
intellectual property. Therefore the propagation outlooks contained herein is
copyrighted © 1988-2005 by Thomas F. Giella, KN4LF, all rights reserved.
Reproduction of information herein is allowed as long as proper credit is given.
Space weather forecasting is still an inexact science. The discussions,
forecasts and outlooks are not official but for educational purposes only and
are subject to human error and acts of God, therefore no guarantee or warranty
implied.
