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A Long Overdue Review of Gray Line Propagation on the Low Bands. Carl Luetzelschwab K9LA e-mail: k9la@arrl.net web site: http://k9la.us. Thanks to WWROF. http://wwrof.org World Wide Radio Operators Foundation

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a long overdue review of gray line propagation on the low bands

A Long Overdue Review of Gray Line Propagation on the Low Bands

Carl Luetzelschwab K9LA

e-mail: k9la@arrl.net

web site: http://k9la.us

WWROF Webinar - Sept 2014 - K9LA

thanks to wwrof
Thanks to WWROF

http://wwrof.org

World Wide Radio Operators Foundation

“Dedicated to improving the skills pf amateur radio operators around the world, utilizing education, competition, advancement of technology and scientific research, promoting international friendship and goodwill, and preparing them to better serve society in times of communication need.”

WWROF Webinar - Sept 2014 - K9LA

topics
Topics
  • Quick status of Cycle 24
  • Origin of ‘gray line’ propagation
  • Some confusion with gray line
  • Common explanation for gray line propagation
  • Doubts about the explanation
    • YB1A QSO on 40m vs IONCAP
    • Topband reflector comment
    • 3Y0X DXpedition QSOs to JA on 160m
    • Ray tracing software
  • The ionization process
  • What I think is really happening

This presentation challenges some long-held beliefs

And it gets into physics deeper than usual

WWROF Webinar - Sept 2014 - K9LA

cycle 24 where we are
Cycle 24 - Where We Are
  • We’re in the second peak of Cycle 24
  • Contesting on the higher bands should be good this fall

WWROF Webinar - Sept 2014 - K9LA

disappearing sunspots
Disappearing Sunspots
  • This is what I presented in my “Maunder Minimum” webinar in April 2014
  • Updated data at that time was only through end of 2013

original data

updated data: end of 2013

WWROF Webinar - Sept 2014 - K9LA

latest data
Latest Data
  • Latest data shows the magnetic field strength has leveled off
  • This suggests we aren’t headed for a Maunder-type Minimum
  • It may just be a period of small cycles as seen before

WWROF Webinar - Sept 2014 - K9LA

first known mention of gray line
First Known Mention of Gray line
  • Article by K6UA and W6NLZ, with editing by K6SSS
  • CQ magazine, Sept 1975
  • Worked mostly EU, AF and Mideast via long path on 80m SSB
  • At morning sunrise and evening sunset

from article: gray line is “long path opening that exists between two points on the Earth which are experiencing simultaneous sunrise and sunset”

WWROF Webinar - Sept 2014 - K9LA

example from cq article
Example from CQ Article

thanks W6ELProp

  • W6NLZ to OJ0AM
  • January 28, 1974
  • 1457 UTC
    • W6 sunrise
    • OJ0 sunset
  • Long path over Antarctica and up across eastern Africa and the Mideast

from article: “signals travel along the edge of the band or ring of twilight encircling the Earth”

this may be a problem

WWROF Webinar - Sept 2014 - K9LA

some confusion
Some Confusion

thanks W6ELProp

  • Sometimes the term ‘gray line’ has been used for a sunrise/sunset enhancement path
  • I subscribe to gray line = follows the terminator
  • Sunrise/sunset enhancement is on a path going away from the terminator
    • perpendicular is best

K9LA to STØRY, March 28 (2003), 0330 UTC, 160m, signal well out of noise from 0320-0340

WWROF Webinar - Sept 2014 - K9LA

sunrise sunset enhancement
Sunrise/Sunset Enhancement
  • Believed to be due to ducting in the electron density valley above the E region peak in the dark ionosphere
  • Valley not well developed along the terminator
  • Pretty much non-existent in the daytime ionosphere

valley in the dark ionosphere

ray trace in the dark ionosphere showing ducting

WWROF Webinar - Sept 2014 - K9LA

comparison
Comparison

thanks W6ELProp

thanks W6ELProp

this is gray line

this is NOT gray line

WWROF Webinar - Sept 2014 - K9LA

explanation of gray line
Explanation of Gray Line
  • The explanation is rooted in the concept that before sunrise the F2 region is formed prior to the D region
  • Similarly, after sunset the D region goes away prior to the F2 region going away
  • Thus there’s a band along the terminator of F region ionization without D region ionization (low or no absorption)

WWROF Webinar - Sept 2014 - K9LA

how does this happen
How Does This Happen?

Using spherical geometry, we can work out how long before sunrise an ionospheric height becomes illuminated by the Sun

WWROF Webinar - Sept 2014 - K9LA

and the results are
And the Results Are . . .
  • Top image: Earth-ionosphere system 69 minutes before K9LA sunrise
  • Middle image: Earth-ionosphere system 35 minutes before K9LA sunrise
  • Bottom image: Earth-ionosphere system at K9LA sunrise
  • Thus the F2 region of the ionosphere is illuminated 34 minutes before the D region is illuminated

WWROF Webinar - Sept 2014 - K9LA

the present explanation
The Present Explanation
  • Gray line propagation allegedly happens because:
    • Before sunrise there’s an F2 region but no D region
    • After sunset there’s an F2 region but no D region
  • This occurs all along the terminator
  • In my mind, several doubts have crept in over the years . . . .

WWROF Webinar - Sept 2014 - K9LA

doubt 1 yb1a on 40m cw
Doubt #1 - YB1A on 40m CW

thanks W6ELProp

  • December 3, 2002 at 2231 UTC (my sunset)
    • YB1A was S8 = -78 dBm on my calibrated S-meter
  • My inv-vee can’t tell if it was short path or long path
  • Most experienced DXers would say it was long path
  • Long path
    • 153 degrees, 24,467 km
    • -180 dBm predicted by IONCAP assuming YB1A at 1 kW and +3 dBi antennas
  • Short path
    • 333 degrees, 15,565 km
    • -130 dBm predicted
  • Even assuming short path, is IONCAP off by 52 dB?

WWROF Webinar - Sept 2014 - K9LA

doubt 2 topband reflector
Doubt #2 - Topband Reflector
  • I posted a message to the topband reflector in early April 2005
  • It commented on the F2 region forming before the D region as sunrise approached
  • Mike K1MK responded personally with an interesting comment:

“While illumination by visible light to which the atmosphere is transparent will start prior to ground-level sunrise and continue after ground-level sunset, direct solar ionizing flux would be expected to appear and disappear at all altitudes simultaneously with ground-level sunrise/sunset.”

WWROF Webinar - Sept 2014 - K9LA

doubt 3 3y0x
Doubt #3 – 3Y0X

thanks W6ELProp

0210 UTC

thanks W6ELProp

0901 UTC

  • February 2006 DXpedition to Peter I
  • On 160-Meters they worked 764 US stations between 0210 UTC and 0901 UTC
    • Note that the paths get away from the terminator

WWROF Webinar - Sept 2014 - K9LA

doubt 3 continued 3y0x
Doubt #3 continued – 3Y0X

thanks W6ELProp

  • Nice gray line to JA via short path at 15,263 km
  • IONCAP says MUF okay but absorption prohibitive on 160m
  • QSOs – 1 JA during the entire DXpedition
  • If gray line via long path is so efficient, why isn’t short path?
  • I’ve never seen a report of fantastic short path gray line
    • G0KYA monitored VP8NO in November 2002 on 40m
      • 3-6 dB average enhancement 30 minutes before mutual sunrise – why not the entire gray line period?

Is propagation along the terminator efficient as is commonly believed?

WWROF Webinar - Sept 2014 - K9LA

comments about absorption
Comments About Absorption
  • At HF, absorption is proportional to electron density times collision frequency (Davies, 1990)
    • Electron density increases as altitude increases
    • Collision frequency decreases as altitude increases
    • Expect a maximum in absorption where they intersect
  • Absorption occurs in the D region during the day
  • Absorption occurs in the lower E region at night

electron density

collision frequency

altitude ->

WWROF Webinar - Sept 2014 - K9LA

comments about absorption1
Comments About Absorption
  • Absorption does not go to zero in the dark ionosphere on 160m
  • On 160m at night, there’s still about 10 dB of absorption per hop
    • This limits multi-hop to about 10,000 km with 1000 W into +0 dBi antennas assuming external noise limits sensitivity (not your receiver)
    • This is why ducting is likely for the longer paths on 160m
  • Ionospheric text books give an equation for absorption that is tied to the solar zenith angle
    • Nice smooth function, but probably doesn’t represent the real-world around sunrise and sunset

WWROF Webinar - Sept 2014 - K9LA

the problem
The Problem
  • Is the explanation of gray line propagation correct?
    • RF follows the terminator where there’s an advantageous band of ionization
  • Or is our model of the ionosphere correct?
    • Propagation along the terminator is not efficient
    • Something else is going on

WWROF Webinar - Sept 2014 - K9LA

who s right and who s wrong

atmosphere here

and here

Who’s Right and Who’s Wrong?

from slide 5

I believe this is a problem

  • The figure assumes that ionizing radiation can go thru the atmosphere TWICE to ionize the F2 region in the dark ionosphere
  • Let’s look at the ionization process

from article: “signals travel along the edge of the band or ring of twilight encircling the Earth”

WWROF Webinar - Sept 2014 - K9LA

it s all about energy
It’s All About Energy
  • More than 50% of the F2 region is due to EUV (extreme ultraviolet) radiation at wavelengths between 26 and 34 nm
    • Ionizes atomic oxygen
    • We’ll use 30 nm for the following analysis
  • From Planck’s Law, the energy of one photon at 30 nm is 41 eV
  • The ionization potential of atomic oxygen is 13.6 eV, but an ionization efficiency issue results in needing about 34 eV to create an electron-ion pair
  • Important - One photon at 30 nm creates one free electron for the F2 region
  • After that its energy is too low to do any more ionization
  • Thus the F2 region ionizing radiation can’t even get thru the atmosphere ONCE
    • This is why we can’t measure EUV at ground level

WWROF Webinar - Sept 2014 - K9LA

what about the d region
What About the D Region?
  • There are two sources of ionizing radiation for the D region
    • 0.1-1.0 nm that ionizes all atmospheric species at D region altitudes
    • 121.5 nm that ionizes nitric oxide (NO) at D region altitudes
  • The same conclusion results as for the F2 region
  • The energy of the ionizing radiation is used up before it gets to ground level
  • Just like the F2 region, the D region ionizing radiation can’t get thru the atmosphere ONCE
    • This is why we can’t measure D region ionizing radiation at ground level

WWROF Webinar - Sept 2014 - K9LA

measuring ionizing radiation
Measuring Ionizing Radiation
  • Prior to World War II, we couldn’t measure ionizing radiation
    • It does not get through the atmosphere to the ground
  • We had to wait for rocket flights and eventually satellites

WWROF Webinar - Sept 2014 - K9LA

illumination
“Illumination”
  • Yes, before sunrise the F2 region and D region are illuminated by the Sun
  • This illumination is by visible light
  • Visible light has nothing to do with the ionization process
  • Photons of visible light (400-700 nm) have an energy of around 2 to 3 eV
    • Visible light couldn’t ionize its way out of a paper bag 
  • That’s why visible light gets thru the atmosphere unimpeded – it does not do any ionization
    • Just like 10.7 cm solar flux

WWROF Webinar - Sept 2014 - K9LA

when does the f2 region ionize
When Does the F2 Region Ionize?

Around sunrise - just like K1MK said

WWROF Webinar - Sept 2014 - K9LA

when does the d region ionize
When Does the D Region Ionize?
  • Electron density over Arecibo from incoherent scatter radar
  • Local sunrise at 0602 (AST)
  • Look at D region altitude of 80 km

sunrise at 0602 local

Around sunrise - just like K1MK said

WWROF Webinar - Sept 2014 - K9LA

why sunrise
Why Sunrise?

Sunrise is when photons can get to the ionospheric regions without having to plow through the atmosphere twice

WWROF Webinar - Sept 2014 - K9LA

another interim summary
Another Interim Summary
  • I’m very confident that the explanation of gray line on the low bands is incorrect
  • This conclusion is based on an understanding of the ionization process and absorption
  • The ionospheric regions begin ionizing around sunrise, not way earlier
  • “Around” sunrise = variability

propagation along the terminator is efficient

  • Ozone layer can block ionizing radiation
  • Ionosondes do not have pencil-thin beams - can receive off-zenith reflections
  • Dayside E region plasma can move horizontally into the dark ionosphere via advection
  • Photons can scatter into the dark atmosphere

WWROF Webinar - Sept 2014 - K9LA

what s really happening
What’s Really Happening?
  • Just saying the current explanation is incorrect isn’t enough
  • An alternative explanation needs to be presented
    • It has to mesh observations and physics
  • The clue is in the quote from the CQ article that was cited on slide 4

from article: gray line is “long path opening that exists between two points on the Earth which are experiencing simultaneous sunrise and sunset”

WWROF Webinar - Sept 2014 - K9LA

w6nlz to oj0am map again

thanks W6ELProp

OJ0AM

W6NLZ

W6NLZ to OJ0AM Map - Again
  • What else happens when W6NLZ and OJ0AM experience simultaneous sunrise and sunset?
  • There is a dark ionosphere in between W6NLZ and OJ0AM

Gray line is “long path opening that exists between two points on the Earth which are experiencing simultaneous sunrise and sunset”

WWROF Webinar - Sept 2014 - K9LA

possible path with a problem

thanks W6ELProp

OJ0AM

W6NLZ

Possible Path – With a Problem
  • Absorption is least in the dark ionosphere
  • The RF must take a short cut across the dark ionosphere – the white path
  • But RF follows a great circle path unless refracted, reflected or scattered
  • The path in white that I drew isn’t a great circle path – it’s just a sketch to show the idea
    • There are only two great circle paths between W6NLZ and OJ0AM

WWROF Webinar - Sept 2014 - K9LA

the solution a skewed path
The Solution – A Skewed Path
  • Observations by those with directional antennas have resulted in the following two axioms
    • Listen south-southwest at your sunrise
    • Listen south-southeast at your sunset
  • Thus the path is more “along the terminator” than “at right angles to the terminator”
  • It has to be far enough away from the terminator when it encounters the ionosphere on the first hop so that
    • Absorption is minimum
    • The ducting mechanism is available
  • Need to look at great circle paths out of both W6NLZ and OJ0AM

WWROF Webinar - Sept 2014 - K9LA

great circle paths from w6nlz
Great Circle Paths from W6NLZ

Great circle paths out of W6NLZ in 10 degree increments

WWROF Webinar - Sept 2014 - K9LA

great circle paths from oj0am
Great Circle Paths from OJ0AM

Great circle paths out of OJ0AM in 10 degree increments

What we’re looking for:

1. Great circle paths out of W6NLZ and OJ0AM that get away

from the terminator – use 3Y0X as a guideline

2. Where these great circle path intersect

WWROF Webinar - Sept 2014 - K9LA

putting it all together
Putting It All Together

terminator (black)

great circle path (red)

night

day

night

skew area

alternative paths (green)

WWROF Webinar - Sept 2014 - K9LA

possibilities for the skew
Possibilities for the Skew
  • Ionospheric origin
    • Normal ionosphere – E region or F2 region
      • Example: FT5ZM on 10-Meters
        • Practical Propagation column in CQ Plus for July 2014
    • Electron precipitation in the auroral oval
      • Example: W4ZV to SM4CAN on 160-Meters
        • “Skewed Paths to Europe on the Low bands”; K9LA; CQ August 1999
    • F2 region trough
      • Example: “Time of flight and direction of arrival of HF radio signals received over a path along the midlatitude trough: Observations”; Siddle, Stocker, Warrington; Radio Science, Vol 39, 2004
  • Sea scatter
    • “Great-Circle and Deviated-Path Observations on CW Signals Using a Simple Technique”; Silberstein and Dickson; IEEE Trans A&P; January 1965

WWROF Webinar - Sept 2014 - K9LA

lack of data
Lack of Data
  • For the W6-to-OJ0 path, we don’t have a lot of data in the skew area to ascertain which of the four possibilities is most likely
    • Probably never will
  • But physics says it is possible
  • And most of us have experienced a similar phenomenon

WWROF Webinar - Sept 2014 - K9LA

thanks
Thanks

Many have contributed to this presentation – whether they know it or not!

  • Bob NM7M (SK) – My mentor who insisted on applying physics to propagation
  • Bill W4ZV (then WØZV) – Wrote about long path and skewed path on the low bands in the SWL publication Fine Tunings
  • Mike K1MK – Personal discussions of the physics of the ionosphere
  • Ed N4II – Personal discussions of QSOs between Florida and VK9CZ (Cocos-Keeling) on 80m – likely these are also skewed path QSOs
  • JC N4IS – Personal discussions of his 160m QSOs to SE Asia and discussions of polarization on 160m at low latitudes
  • And the many others that I missed

WWROF Webinar - Sept 2014 - K9LA

let s wrap this up
Let’s Wrap This Up
  • Propagation along the terminator on the low bands does not appear to be efficient
    • Physics says there’s no magic before sunrise
    • Our model of the ionosphere (thru IONCAP, VOACAP, W6ELProp, etc) agrees
  • Low band RF takes a short cut across the dark ionosphere
    • Far enough away from the terminator to minimize absorption
    • Need a skew point to kick RF off one great circle path to another great circle path - mechanisms are out there to do this
  • You don’t have to change your operating habits
    • South-southwest at your sunrise and south-southeast at your sunset still applies
  • Civil twilight, nautical twilight and astronomical twilight have nothing to do with propagation - all that matters is sunrise and sunset which ties into the ionization process
  • On the higher bands, gray line is simply a MUF issue
    • Absorption is inversely proportional to the square of the frequency

WWROF Webinar - Sept 2014 - K9LA