NZ4O 160 METER RADIO PROPAGATION THEORY NOTES

Layman Level Explanations Of "Seemingly" Mysterious 160 Meter Propagation Occurrences
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Welcome to the "NZ4O 160 Meter Radio Propagation Theory Notes" weblog styled website. Contained within you will find the most comprehensive explanation of 160 meter and medium frequency (300-3000 kc) radio propagation occurrences on the Internet.

In my personal opinion understanding and taking advantage of low/medium/high frequency radio propagation conditions is an integral part of successful DX operation. Therefore this site exists as an educational tool.

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.

These theory notes are primarily applicable to the 300-529 kc long wave aviation and marine navigation beacon band, 530-1700 kc AM broadcast band, 160 meter amateur band and 120 meter shortwave tropical broadcast band.
However virtually all of the content is also applicable to the 3000-30000 kc HF shortwave spectrum.

A while back I became involved in a propagation research project of sorts on 10, 6 and 2 meters. I have set up a propagation beacon currently 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 other HF bands in the future, with the ultimate aim of all HF bands and even 160 meters. It's been very interesting so far watching Es and 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.

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 or any other subject.

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 forward looking 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. However within this group exists a total lack of understanding concerning the most basic aspects of the subject. Often times I will here them say, "The band is shifting". This lack of basic knowledge can be traced back to the licensing process where very few questions exist in the exam pools.

Then we have a third and smaller group with gigantic runaway egos that insist that they are omniscient by virtue of their Extra Class license, ARRL DXCC entity totals and "possible" electrical engineering backgrounds. Anal Retentive types?! 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. You know who you are and should be ashamed of yourselves.

 

                                                                                                          Table Of Contents

1.) Medium Frequency (MF) Radio Wave Propagation Overview

2.) Aurora Oval Blockage, Absorption And Refraction

3.) Equatorial Ring Current

4.) Coronal Mass Ejection (CME)

5.) Coronal Hole

6.) Solar Filament

7.) Correlation Of Energetic Protons, Solar Flux and Ap & Kp Indices With Medium Frequencies

8.) E Valley-F Layer Propagation Ducting Mechanism/Chordal Hop Propagation

9.) Electron Gyro Frequency Absorption

10.) Medium & High Frequency Radio Signal Propagation Path Skewing

11.) Geomagnetic/Ionospheric Storm

12.) Geological/Meteorological Effects On Medium Frequency Propagation

13.) Polar Cap Absorption (PCA)

14. Sunspot Group

15.) Short Wave Fadeout (SWF)

16.) Solar Flare

17.) Sporadic-D (Ds) Absorption & Wave Guiding

18.) Sporadic-E (Es) Absorption, Blocking & Refraction

19.) Long Delayed Echo (LDE)

20.) Sudden Stratospheric Warming (STRATWARM ALERT)

21.) D Layer Mid Winter Absorption Anomaly

22.) F3 Ionospheric Layer

23.) The Gray line/Gray line Propagation

24.) Plage


Back To The Top

1.) Medium Frequency Radio Wave Propagation Overview-

Popular Myth- We don't understand medium frequency (300-529 kc long wave aviation and marine navigation beacon band, 530-1700 kc AM broadcast band, 160 meter amateur band and 120 meter shortwave tropical broadcast band) radio wave propagation conditions and therefore it can't be forecasted.

Fact- Yes it can and is on a regular basis at NZ4O Daily LF/MF/HF/6M Frequency Radiowave Propagation Forecast http://www.wcflunatall.com/nz4o5.htm .

a.) Medium frequencies encompass 300 to 3000 kc. The simplest way to look at medium frequencies with respect to propagation issues from a layman's point of view, is to accept the fact that propagation is poor the majority of the time (See definition #6. Electron Gyro Frequency Absorption), especially past approximately 1250 miles (one refraction off of the E layer), with occasional short-lived good periods as far as 3200 miles.

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, more often out of phase. The out of phase extra-ordinary ray represents a 50% power loss on the receive end of a path.

b.) Why is medium frequency propagation poor the majority of the time? D layer absorption! At daytime the D layer which is at an approximate height of 30-60 miles in the mesosphere, totally absorbs medium frequency RF signals the majority of the time.
I say the majority of the time because at higher latitudes, during the winter season and especially at the low part of a sunspot cycle, daytime penetration of RF signals through the weakened D layer and then refraction via the E layer and/or Sporadic E (Es) clouds does occur. Another issue is the fact that the D layer does not totally disappear at night. Many books that deal with wave propagation erroneously state that the D and E layer's disappear after sunset, totally incorrect thanks to Galactic X-Rays, Galactic Cosmic Rays and Lightning.

c.) Background electromagnetic radiation in the 1 to 10 Angstrom range (Hard X-Rays) is a major source of ionization of the day time D layer, with our Sun as the source of Cosmic Rays, also playing a role.

The following paragraph was contributed by Carl Luetzelschwab K9LA, a scientist with a very good understanding of radiowave propagation.

.....A couple years ago I was playing with Proplab Pro on a one-hop 936km path on 160m during daylight. I plotted absorption versus sunspot number. I expected a nice monotonic increase as the sunspot number increased. But the plot showed that absorption started at about 60dB at zero sunspots and was constant out to a sunspot number of about 50. Then it started climbing, reaching 100dB at a sunspot number of 150. This suggested that there was something other than hard X-rays and Galactic Cosmic Rays as the source of daytime D region absorption. So I dug into Davies 1990 (page 61), Hunsucker and Hargreaves (page 31), and Brekke (page 233). They all seem to point to the Lyman-alpha line of the solar spectrum at 1215 Angstroms ionizing NO as the main source of the quiet daytime D region. So in terms of my absorption versus sunspot number plot, the flat portion up to a sunspot number of 50 is probably due to the Lyman-alpha line ionizing NO. Then above a sunspot number of 50 the hard X-rays start contributing as the Sun becomes more active.....

Carl has produced two really good .pdf files on 160 meter propagation in 2003 and 2004. Read them here:
160 Meter Propagation Disturbances To Propagation .
He also has a propagation website with allot of good information on it at K9LA's Amateur Radio Propagation. In 2009 Carl produced yet another excellent article on 160 meter operation at Is This Solar Minimum Better or Worse Than the Last Solar Minimum on 160m?


Ionosphere Ion Types



Ionosphere Profile
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Also speaking of the ionosphere at and near solar minimum the mid and high latitude D layer of the ionosphere at mesosphere altitude cools approximately 2 degrees C, contracts in thickness and signal absorption in the layer increases.

While I'm visiting the subject of electromagnetic radiation, our Sun emits electromagnetic radiation and matter, as a result of the nuclear fusion process. Electromagnetic radiation at wavelengths of 100 to 1000 Angstroms (Ultraviolet) ionizes the F layer, radiation at 10 to 100 Angstroms (Soft X-rays), as well as Galactic Cosmic Rays ionize the E layer. Galactic X-rays, Galactic Cosmic Rays and Lightning are the reason that the E layer is "always" present at night time, the D layer also. Background electromagnetic radiation in the 1 to 10 Angstrom range (Hard X-Rays) is a major source of ionization of the day time D layer,

Via K7RA's weekly ARRL Propagation Forecast Bulletin #46 published on November 9, 2007:

In last week's bulletin, Carl Luetzelschwab K9LA said the closest measurement we have to radiation that ionizes the F2 region is the GOES X-ray data at 0.1 to 0.8 nm.  K9LA says that is not correct- he received an e-mail from Michael Keane, K1MK, with the following information:

"There does exist an instrument that measures solar EUV flux directly.  That is the SOHO Solar EUV Monitor (SEM) at
http://umtof.umd.edu/semflux. One SEM channel covers solar EUV in the 17-70 nm range. The other channel monitors just the 30.4 nm resonance line of singly ionized helium. In most models, this 30.4 nm line by itself represents 25-50% of the energy input to the thermosphere/ionosphere."


Galactic Cosmic Rays are not rays at all, but particles. They are ionized atoms, atoms with missing electrons ranging from a single proton up to an iron nucleus and beyond but typically protons and alpha particles, which have 2 protons and 2 neutrons. They originate from deep space, being produced by a number of different sources, such as other stars, and more exotic objects, such as supernova, which are exploding stars and their remnants, neutron stars, black holes, and distant galaxies. Cosmic Ray particles travel very close to the speed of light, and are highly energetic.

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. A similar event also occurred in 1998.

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 and http://www.sciencedaily.com/releases/2006/02/060221084628.htm .

d.) Recently I saw a post on the Topband Reflector lamenting the seemingly unexplainable differences in 160 propagation on certain paths from night-to-night. is there 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 of greater than A0, 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 medium frequency AM 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 medium frequency broadcast is always affected first followed by the upper half of the medium frequency 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 35 year period, I've come to the conclusion that high and mid latitude TA and TP propagation paths tend to open up only after an approximate three day period of time passes with an energetic proton event of no greater then (10+0) on the medium frequency AM broadcast band, 160 and 120 meters.

f.) Also there are daily extremes of the background x-ray flux level. So even though the daily average might have been pretty good at say A1.1, the daily "extreme" maximum could have been C1.5, which would have been bad and would have caused 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, extremely large positive cloud to ground lightning strokes and interrelated Elves. 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 than 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 NM7M Robert Brown, PhD. has a good educational thread on this bugaboo on the May 2002 Topband Reflector. The thread can read in its entirety by going to this link
Topband Reflector May 2002 Archives Layer .

Also an excellent but more technically oriented website covering 160 meter propagation and more is the "HF Propagation Tutorial" by NM7M Bob Brown, Ph.D. and hosted by ON4SKY Thierry Lombry and can be found at: http://www.astrosurf.com/luxorion/qsl-hf-tutorial-nm7m.htm .



Horizontal & Vertical Components Of Earths Geomagnetic Field
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Earth's Geomagnetic Field
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Earth's Magnetosphere
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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 medium frequency RF signals in the form of small to medium increased absorption variations of medium frequency RF signals via the D layer caused by traveling ionospheric disturbances (TID's). Also temperature and moisture discontinuities (frontal inversions) can refract/scatter medium frequency 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.

l.) A note, the E-valley/F layer 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 medium frequency RF signals demonstrates the existence of the ducting mechanism, versus conventional numerous E layer land/ocean surface hops which, would allow for approximately 40 db of attenuation on a North America to Europe propagation path. 

Another note! When it comes to 160 meter vertical antenna's you can get a lower take off angle (TOA) from a full 1/4 wave vertical or electrical 1/4 wave tee vertical of 10-20 deg., versus ~30 deg. with the inverted L. However it's a moot point as the night time E layer MUF blocks 160 meter low angle transmitted radio signals from ever reaching the F layer to be propagated. So unlike with high frequency propagation, medium frequency propagation success does not require the lowest of take off angles.

Also higher take off angles of 30-40 deg. via the inverted L are better able to take advantage of the low signal loss E valley-F layer propagation duct mechanism, a form of Chordal Hop propagation.

A solar flux of at least 150 is necessary for routine stable formation of the E Valley/F Layer ducting mechanism. Therefore formation of the duct is less prevalent at the bottom of solar cycle and long haul propagation poorer at solar minimum.

m.) Yet another mechanism to deal with that impacts medium frequency radio wave propagation in a negative fashion is the D Layer Mid Winter Anomaly. It is a period of increased medium frequency 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 research program, earthquakes, volcanic eruptions, thunderstorms, lightning (especially positive cloud to ground strokes), elves, 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.

o.) Another issue facing medium frequency 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 medium frequency RF signal blockage absorption and refraction. Absorption is similar to higher latitude Auroral absorption.

p.) LF propagation theory is out of my realm from a standpoint of formal education. Alan Melia G3YNK is studying LF propagation and has made some very interesting observations and put forth some fascinating theories.

Here are some interesting website links concerning LF and ELF radio propagation theory.

LF PROPAGATION THEORY INFO BY ALAN MELIA G3YNK

PROPAGATION OF LONG RADIO WAVES BY J.A. ADCOCK VK3ACA

RADIO WAVES BELOW 22 KC


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2.) Aurora Oval Blockage, Absorption And Refraction-

The aurora ovals "generally" have a negative impact on medium frequency propagation. If the path over which you are communicating lies along or inside one of the Aurora Ovals, you will experience degraded propagation in one of several forms; strong signal absorption, brief periods of strong signal enhancement, which is mainly caused by tilts in the ionosphere that allow signals to become focused at your location or very erratic signal behavior in the form of strong and rapid fading, etc., caused by a variety of effects such as multi-pathing, anomalous and rapid variations in absorption, non-great-circle propagation, horizontal or side refraction and/or scatter (skewing) due to changes in electron density and polarization changes. (See definition #7. Propagation Path Skewing).

When the Aurora Oval zones are contracted and latitudinally-thin coinciding with low geomagnetic activity, it is possible for a medium-frequency transmitted signal to propagate through the Aurora Oval zone without being heavily absorbed by skirting underneath it.

During periods of very low geomagnetic activity, areas of the Aurora Oval zones may only have a latitudinal thickness of approximately 300 miles. But radio signals reflected from the E layer can travel over distances of as much as 300 to 1250 miles at heights below the ionosphere for low take-off angles of between 10 and 25 degrees. When the geometry is just right, the medium-frequency transmitted signal can literally propagate underneath and through the Aurora Oval zones into the polar ionosphere which is less disturbed and from the polar ionosphere back into the middle latitude ionosphere, without ever coming in contact with the highly absorptive Aurora Ionosphere. This type of propagation is not as rare as you might think and it can provide unusually stable polar region path openings to (TA) Transatlantic and (TP) Transpacific regions. But because the Aurora Oval zone expands and contracts constantly, such conditions often do not last very long. (See definition #3. Equatorial Ring Current).



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Back To The Top


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3.) Equatorial Ring Current- 

A phenomenon that acts as a repository for precipitated electrons in the vicinity of the magnetic equator. The electrons travel by spiraling around north south magnetic field lines at a frequency called the 'gyro frequency. The end result is lower latitude propagation path medium frequency transmitted RF signal blockage and absorption via the D layer. Absorption is similar to higher latitude Aurora Oval absorption and is inter-related with same.

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://swdcwww.kugi.kyoto-u.ac.jp/dst_realtime/presentmonth/index.html and the U.C. Berkeley website link http://sprg.ssl.berkeley.edu/dst_index and a NASA GSFC website link http://sprg.ssl.berkeley.edu/dst_index . (See definition #2. Aurora Oval Blockage, Absorption And Refraction). Another excellent source of a daily Dst figure is at http://www.alan.melia.btinternet.co.uk/latest.htm .


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4.) Coronal Mass Ejection (CME)-

A Coronal Mass Ejection is the name given to an ejection of a large amount of matter from the Sun's outer atmosphere or corona. These ejections typically comprise millions of tons of material in the form of charged particles and can be seen because the material reflects sunlight. When one of these ejections is directed towards the Earth (or conversely, directly away from the Earth), it looks like a roughly circular "halo" surrounding the blanked out Sun.

The "Halo CME's" are those CME's which are more likely to impact the Earth than those which are shot out at right angles to the Earth-Sun line. Energetic protons emitted during CME's play a major role in increased day time and night-time D layer absorption of medium frequencies.

Coronal Mass Ejections were once thought to be completely initiated by solar flares. However it is now known that many (CME's) are not associated with Solar Flares but instead with collapsing Solar Filaments. If a (CME) collides with the Earth, it can excite a Geomagnetic Storm if the polarity of the Interplanetary Magnetic Field (IMF) has a negative sign. We must be vigilant in watching for geo-effective (CME's), in order to not be caught by surprise with a seemingly sudden and unexpected Geomagnetic Storm. (See definition #6. Solar Filament). (See definition #11. Geomagnetic/Ionospheric Storm). (See definition #16. Solar Flare).

Coronal Mass Ejections are not random meaningless eruptions but instead a process by which the Sun expels complex magnetic signatures enroute to changing its magnetic polarity or said a different way the swapping of the Sun's magnetic poles. Basically the Sun swapped its 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 2012.


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5.) Coronal Hole-

The Corona is not part of the Sun's surface. It is instead part of the Sun's atmosphere, much like Earth's troposphere. Coronal Holes are low density areas associated with open magnetic field lines and are found near the Sun's poles at the bottom of a sunspot cycle and everywhere during a cycle maximum. A Coronal Hole is a dark region where a breakdown in the magnetic field structure in the solar corona has occurred. From these regions stream the high velocity solar wind that is a source of geomagnetic storming on Earth.

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 medium frequency 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 phenomenon 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.



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6.) Solar Filament-

A relatively cool and dense ribbon of gas held together by solar magnetic fields. From Earth they usually appear as relatively dark lines across the face of the Sun. At times the magnetic lines holding the filament open up creating a tremendous eruption similar in size and impact of a Coronal Mass Ejection (CME). (See definition #4. Coronal Mass Ejection). (See definition #11. Geomagnetic/Ionospheric Storm).



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7.) Correlation Of Energetic Protons, Solar Flux and Ap & Kp Indices With Medium Frequencies-

I've been observing energetic proton levels, as well as the Ap & Kp indices for 35 years and see a direct correlation between high energetic proton levels above 10 MeV (10+0) and poor propagation on high and at times mid latitude medium frequency paths at day AND night, where as the A & K indices don't as readily correlate. (See paragraph three of definition #2. Aurora Oval Blockage, Absorption And Refraction) and (definition #7. High Latitude Path Skewing) for a further explanation on the lack of correlation of Ap & Kp indices with medium frequency propagation conditions.

High solar flux values are "incorrectly" considered to be detrimental to medium frequency signals both domestic and TA/TP, as more absorption can be present as the transmitted signal makes two trips through the D layer, near sunrise and sunset. However most medium wave frequency RF signals in excess of 3100 miles are propagated via the E valley/F layer ducting and/or Chordal Hop/Pederson Ray propagation mechanism and a high solar flux value ensures a strong E valley/F layer duct mechanism. Actually a solar flux of at least 150 is needed for a consistent E valley/F layer ducting mode.

The main reason that medium frequency radio propagation "seems to be better" at the bottom of a sunspot cycle is not so much due to lower solar flux levels BUT due to much less geomagnetic activity.

Keep in mind though that the 10.7 cm (2800 mhz) solar flux index is not a "reliable" gauge of ionization in our atmosphere, 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 inter-related background X-ray flux. (See definition #1 paragraphs e & f).

An elevated energetic proton flux level greater then (10+0) creates noticeably increased winter time day and year round night time D layer absorption of medium wave frequencies, especially on high latitude propagation paths but it can also negatively impact mid latitudes, depending on the intensity of the event.

Elevated energetic proton events too small to be categorized as a Polar Cap Absorption event (PCA) can still impact high and at times mid latitude medium frequency propagation paths in the form of excessive D layer absorption.

((((Note, high latitude medium frequency radio propagation paths can still be disturbed for days and up to weeks, following the end of an official >10 MeV (10+0) proton event.))))

GENERAL GUIDELINES CONCERNING CORRELATION OF PROPAGATION INDICES TO ACTUAL MF/HF PROPAGATION CONDITIONS.

NOTE!!!
 The propagation indices "interpretations" are my personal intellectual property. Therefore the propagation indices interpretations contained herein is copyrighted � 1988-2008 by Thomas F. Giella, NZ4O, all rights reserved. Reproduction of information herein is allowed without permission in advance as long as proper credit is given.

1.) Dropping indices numbers are better.

2.) A solar flux of 150 or higher, 200+ best, for medium frequencies under 100, under 70 best.

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 medium 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.) A solar flux in the mid 100's for routine stable formation of the 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).

7.) Background X-Ray flux levels less than A1 for several days consecutively.

8.) No current STRATWARM alert.

9.) Interplanetary Magnetic Field (IMF) Bz with a (positive number) sign, indicates a lesser chance of high latitude path Auroral absorption/unpredictable refraction or scattering of medium frequency RF signals, when the Kp is above 3.

10.) A -20 or better towards a positive number Dst index during the recovery time after a Geomagnetic Storm, as related to the Equatorial Ring Current. A positive number best.

11.) Rising Positive T Index number. The T Index tracks with the F2 layer critical frequency (foF2) and sunspot number (SSN) and indicates the capability of the F2 layer to refract RF signals.

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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/F layer 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 medium frequency 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 near local sunrise and sunset) propagation mechanism.

Typically the majority of transmit antenna's radiation must be focused between 40-60 deg. to enter the E Valley/F Layer duct. (See definition #23.) The Gray line/Gray line Propagation).

A solar flux of at least 150 is necessary for routine stable formation of the E Valley/F Layer ducting mechanism. Therefore formation of the duct is less prevalent at the bottom of solar cycle and long haul propagation poorer at solar minimum.

Well Known Chordal Hop LP Routes Courtesy Of Larry Duncan K4WLS

Here are some well known Chordal Hop LP routes from the East Coast and Mid-West:

Late Afternoon, Mid-February to Mid-March - Western Australia and beyond, and Southern Malaysia: Predominately 20M.

0700-1000 Local, Early to Late Summer - Eastern and Southern Africa, and Indian Ocean: 20, 15, 17, 12, and 10M (17 through 10M depending on Solar Flux).

0800-1000 Local, Early Fall - Western Australia and S.E. Indian Ocean: 20M

0500-0700 Local, * December - Malaysia, Indonesia, and S.E. Asia: 40M

Sunset to 1 Hour Before, Fall to Mid-December - Middle and Eastern Asia: 40M

0700-0800 Local, Mid-December - Middle East: Predominately 20M

Sunset to 1 Hour Before, Mid-December - Northern Middle and Eastern Asia: 20 and 40M (20M depending on Solar Flux).

* Sporadically as late as early March

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. Galactic Cosmic Rays also play a role in where an RF signal drops out of the duct.

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, more often out of phase. The out of phase extra-ordinary ray represents a 50% power loss on the receive end of a propagation path.

As follows is a recent experience I had in Florida with this propagation mode on 160 meters.

I began listening for DX on 160 meters at 5:00 pm EST this evening February 05-06, 2006. I was watching the OH2AQ spot and the stations in ME to VA were working stations in Europe and Africa. I could hear the stateside stations real well but not a peep out of any DX.
 
Then right at my local sunset which was at 6:15 pm EST it was like flipping a switch as all the DX stations just showed up. It was a classic example of the E Valley-F Layer ducting mechanism propagation mode with the duct opening up right over Florida as the ionized layers changed height with the arrival of the gray line terminator.

Once the DX showed up I heard oodles of CW DX stations including VQ9LA and 6W/G4WFQ who were 55 on the receive loop. MM0SJH, G3FPQ and I7RIZ showed up on phone between 1841 and 1849 kc and they were 57. I didn't bother to work anything this time as the only countries I heard that I've never worked were VQ9LA and 6W/G4WFQ and I couldn't break the pileups with 100 watts.

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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 of 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 medium frequency carrier or sideband wave frequency is to the electron gyro frequency, the more energy that is absorbed by the gyro (spinning) 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.


Electron Gyro-frequency Map From Prop lab Pro Software
Click To Enlarge

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10.) Medium & High Frequency Radio Signal Propagation Path Skewing-

Medium & High frequency radio signal propagation path skewing occurs due to changes in the "horizontal" electron gradient. Put in simple layman's terms the transmitted RF signal will "always" seek to propagate along the path with least absorption, which almost always means via a darkness path.

As an example a medium frequency signal (say 1830 kc) transmitted from Norway to New England, which is via a polar great circle path, will be directly absorbed most of the time by the Aurora Oval, with the remaining signal skirting south and then west on the darkness path via the E layer, arriving in New England from say the SE rather then the expected NE path.

Another example is a high frequency (say 28400 kc) signal transmitted from Florida that arrives from the SE at Clipperton Island (FO/TX5), which is located in the Eastern North Pacific Ocean near 11 degrees north latitude and 110 degrees west longitude. This relatively short path contact gives the appearance of the double hop Sporadic E (Es) propagation mode, which frequently occurs during a low point in a solar cycle, when actually it is a skewed F2 layer propagation mode.

A general east-west band of high (25000-35000 kc) maximum usable frequencies (MUF's) exist north and south of the geomagnetic equator http://www.spacew.com/www/realtime.gif . These bands allow for the existence of the north-south propagation mode called Trans Equatorial Propagation (TEP). In any event the contact between Florida and Clipperton Island was made via the horizontal gradients that existed in the band of high MUF's north of the geomagnetic equator.


Side View Of High MUF Bands North & South Of The Geomagnetic Equator

By the way skewed propagation paths are the norm rather than the exception on medium frequencies, especially past approximately 3200 miles.

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11.) Geomagnetic/Ionospheric Storm-

A worldwide disturbance of the Earth's magnetosphere and or ionosphere, induced by direct connection to the Sun's Interplanetary Magnetic Field (IMF), distinct from regular diurnal variations. Basically it's a precipitation of electrons trapped within our magnetosphere, as the electrons collide. The end result is a reduction of the MUF of the F2 layer. (See definition #3. Equatorial Ring Current). (See definition #4. Coronal Mass Ejection). (See definition #5. Coronal Hole). (See definition #6. Solar Filament).


                                                                                                 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
Unsettled K = 3
Quiet K= 0, 1, 2

A= 100-400 Severe
A= 50-99 Major
A= 30-49 Minor
A= 16-29 Active
A= 8-15 Unsettled
A= 0-7 Quiet

K- 0= A- 0
K- 1= A- 3
K- 2= A- 7
K- 3= A- 15
K- 4= A- 27
K- 5= A- 48
K- 6= A- 80
K- 7= A- 140
K- 8= A- 240
K- 9= A- 400

                                                

                                                                                                  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

                                                              

                                                                                               Medium Frequency 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. http://science.nasa.gov/headlines/y2001/ast26oct_1.htm?list101234.

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.

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12.) Geological/Meteorological Effects On Medium Frequency Propagation-

Geological effects such as earthquakes and volcanic eruptions, as well as
meteorological effects such as Troposphere originating Internal Buoyancy/Gravity Waves (IBGW's), Stratosphere level Quasi Biennial Oscillations (QBO) and warming (STRATWARM) have a negative effect on medium frequency RF signals in the form of small to medium increased absorption variations of medium frequency 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 medium frequency 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 medium frequency 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 medium frequency spectrum is defined as 300-3000 kc but the differences in refractive properties between 300 and 3000 is very significant At 3000 kc refraction is a good description, on 160 scattering, at 300 kc diffraction.

Using the strictest definition of RF refraction, its 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 medium frequency 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, 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 NASA Space Shuttle launch, in a sense they are correct.


Troposphere Height Jet Streams And Lightning/Thunderstorms And Their Interaction With The Ionosphere
Click To Enlarge

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13.) Polar Cap Absorption (PCA)-

An anomalous condition of the polar Ionosphere whereby medium frequency (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.

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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.

Sunspot groups have a magnetic classification as follows:

A - Alpha (a single polarity spot)
B - Beta (a bipolar spot configuration)
G - Gamma (an atypical mixture of polarities)
B-G - Beta-Gamma (a mixture of polarities in a dominantly bipolar configuration)
D - Delta (an opposite polarity umbrae within single penumbra)
B-D - Beta with a Delta configuration
B-G-D - Beta-Gamma with a Delta configuration

Sunspots usually come in groups with two opposing sets of spots. Whether two or twenty sunspots exist in a particular group they are counted as one sunspot group and numbered, such as 10500. That number would signify sunspot group number 10500, with the number counting system beginning in 1972 if my memory serves me correctly.

One set of sunspots will have a positive or north magnetic field while the other set will have a negative or south magnetic field. See image below. Also check out this website link.

SIDC WELCOME TO SOLAR CYCLE 24

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.


Magnetogram Image
Click To Enlarge

The current system of counting sun spots hails from a previous era when direct observation of sun spots was inherently inaccurate. The sunspot number is derived by counting 10 points for each sunspot group and then adding one point for each spot. So if a sunspot group contains 1 individual sunspot the official count becomes 11. 4 individual sunspots in a sunspot group equals 44 sunspots. (See definition #24. Plage).


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15.) Short Wave Fadeout (SWF)-

During a Sudden Ionospheric Disturbance (SID), which is tied to a Solar Flare and Coronal Mass Ejection, abrupt increased ionization of the D layer results in reduced to total absorption of medium frequency circuits which are refracted by the Ionosphere on the sun lit 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. Medium frequency communication depends on the refraction 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 medium frequency 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, also at the bottom 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).

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16.) Solar Flare-

A day side Earth 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-Ray's), as well as Solar and Galactic Cosmic Rays and ionization of Nitric Oxide (NO) in our atmosphere 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 inter-related with Coronal Mass Ejections (CME's), by which the Sun expels complex magnetic signatures enroute to changing its 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.


Image Of An X45 Class Solar Flare Click To Enlarge



Click for X45 Super Solar Flare Movie

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17.) Sporadic-D (Ds) Absorption & Wave Guiding-

Sporadic-D (Ds) occurrences have an inter-relationship with brief but intense Sun based and Galactic X-rays 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.

Sporadic-D (Ds) absorption occurs both at day and night. Much of the night time occurrence of Sporadic-D (Ds) absorption is often masked by lightning QRN, as well as a lack of radio operation during thunderstorm events, due to the lightning strike hazard and also due to the operator not being able to recognize the mode due to unfamiliarity with it. It's doubtful that you will read about the Sporadic-D (Ds) phenomena anywhere else other then on this website.

While on the topic of lightning and propagation, an ionized lightning channel which normally has a maximum diameter of approximately a silver dollar, can reflect RF much like meteor trails do. I've personally noticed it on the 70 cm band, as a single propagation burst lasting 1/4 to 1/2 second. (See definition #20. D Layer Mid Winter Absorption Anomaly).

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18.) Sporadic-E (Es) Absorption, Blocking & Refraction-

Just as the E layer is the main refraction medium for medium frequency (300-3000 kc) signal propagation within approximately 5000 km/3100 mi, so is a Sporadic-E (Es) cloud. Sporadic-E (Es) clouds occur at approximately 100 km/60 miles in altitude and generally move from ESE to WNW.

Like Stratosphere level warming and Troposphere level temperature and moisture discontinuities, Sporadic-E  (Es) clouds can depending on the circumstances absorb, block or refract medium, high and very high frequency RF signals in an unpredictable manner.

The main source for "high latitude" Sporadic E (Es) clouds is geomagnetic storming induced radio aurora activity.

The main source for "mid latitude" Sporadic-E  (Es) clouds is wind shear produced by internal buoyancy/gravity waves (IBGW's), that create traveling ionosphere disturbances (TID's), most of which are produced by severe thunderstorm cell complexes with overshooting tops that penetrate into the Stratosphere. Another tie in between Sporadic-E (Es) and a severe thunderstorm is the Elve.

The main sources for "low latitude" Sporadic-E  (Es) clouds is wind shear produced by internal buoyancy/gravity waves (IBGW's), that create traveling ionosphere disturbances, most of which are produced by severe thunderstorm cell complexes tied to tropical cyclones. High electron content in the Equatorial Ring Current also plays a role.

The forecasting of Sporadic-E (Es) clouds 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 (Es) clouds. One is as mentioned above the severe thunderstorm cell complex.

Sporadic-E (Es) clouds have been observed to initially occur within approximately 150 km/90 mi to the right 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 (Es) clouds that initially form to the right of a severe thunderstorm complex in the northern hemisphere, then move from ESE-WNW and end up to the left of the severe thunderstorm complex in the northern hemisphere. So one has to look for Sporadic-E (Es) clouds on either side of a severe thunderstorm cell complex. Things get even more complicated when two severe thunderstorm cell complexes exist approximately 1000- 2000 miles apart.

Not all thunderstorm cell complexes reach severe levels and not all severe thunderstorm cell complexes produce Sporadic-E (Es). This is where knowledge in tropospheric physics and weather analyses/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 cell complexes are most likely to produce Sporadic-E (Es) clouds.

Some of the key elements in identifying which severe thunderstorm cell complexes have the potential to produce Sporadic-E (Es) via wind shear, from internal buoyancy/gravity waves, that produce traveling ionosphere disturbances include:

1.) Negative tilted mid and upper 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.


Overshooting Top Is The Puffy Blister Just
To The Right Of Center Of Flat Ice Anvil Top
Click To Enlarge

4.) Approximate 150-175 knot/172-200 mph updrafts within thunderstorm cells complexes that create overshooting tops (see photograph above) that penetrate the Tropopause into the Stratosphere (See definition #20 on Stratospheric Warming), launching upwardly propagating internal buoyancy/gravity waves, which create traveling ionosphere disturbances and then wind shear.

Lightning And Thunderstorms And Their Interaction With The Ionosphere
Click To Enlarge

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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 duct 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.

http://heim.ifi.uio.no:80/~sverre/LDE and http://www.qslnet.de/member/la3za/prop

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20.) Sudden Stratospheric Warming (STRATWARM ALERT)-

Sudden Stratosphere 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, which is at Mesosphere level. The warming lasts for many days at a time and is characterized by a warming of the Stratosphere temperature by some tens of degrees (temperature inversion), in unison with adjacent Troposphere cooling.

Another way to explain Stratosphere Warming is a major disturbance of the Winter time Polar middle atmosphere from the lower Stratosphere to the Mesosphere, resulting from a breakdown of the single Arctic Circumpolar 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 (NO) gasses, resulting in an increase in electron density and producing strong medium frequency signal absorption at D layer height.

A little related Troposphere level 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 Stratosphere Warming effect medium frequency propagation in any way BUT medium frequency signals do propagate off of Troposphere temperature inversions and moisture discontinuities and a temperature inversion is involved with Stratosphere 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 signal 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 Layer Mid Winter Absorption Anomaly-

A period of increased medium frequency 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 Layer Mid Winter Absorption Anomaly. (See definition #17. Sporadic-D (Ds) Absorption & Wave Guiding). (See definition #19. Sudden Stratospheric Warming (STRATWARM ALERT).

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

The F3 layer primarily exists only in the vicinity of the Earth's magnetic equator. This may represent part of an explanation for (TEP) Trans Equatorial� Propagation.

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23.) The Gray line/Gray line Propagation-

A general east-west transition between daytime and nighttime (twilight)  where enhanced propagation conditions "may" occur. Near local sunrise the absorptive D layer has yet to become illuminated by the Sun, though the higher in altitude F/F2 layer has. Inversely near local sunset the absorptive D layer is losing illumination by the Sun, though the higher in altitude F/F2 layer still is. There is also a strengthening and weakening process in the E layer, as well as angle tilts and altitude changes in the D, E and F layers.

This process can allow for enhanced propagation conditions within the general north-south gray line corridor. It is most pronounced on 30,  40 and 60 meters and less so on 80 and 160 meters. Actually most gray line propagation on 160 meters and to a lesser extent on 80 meters is perpendicular (right angles) to the corridor. In my professional observation the gray line propagation enhancement process is still not totally understood and it's benefit exaggerated to almost mythical proportion. (See definition #8.) E Valley/F Layer Propagation Ducting Mechanism/Chordal Hop Propagation).

24.) Plage-

A patchy H-alpha brightening on the solar disk commonly found in or near active regions of which can last for several days or so. A Plage is irregular in shape and variable in brightness and marks areas of nearly vertical emerging or reconnecting magnetic field lines. Often times a sunspot group will emerge from a Plage. (See definition #14. Sunspot Group).

 

Note! I make no claim of ownership of the images displayed on this website. Also 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. Therefore use these definitions at your own risk with no guarantee or warranty implied. The explanations contained herein is my intellectual property and copyrighted � 1988-2009 by Thomas F. Giella, NZ4O, all rights reserved. Reproduction of information herein is allowed without advanced permission as long as proper credit is given.

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Contact Info:
Thomas F. Giella NZ4O
Lakeland, FL, USA

nz4o at arrl dot net



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