Topband: greyline prop forecast

[Thomas F. Giella W4HM]

True grey line radio wave propagation rarely occurs on 160 meters and true 
long path propagation even less. When it does the opening is usually only a 
few minutes long. Instead it's usually a skewed path that includes RF signal 
ducting in the E Valley/F layer propagation region.

I had a web page on the interweb for 20 years concerning MF radio wave 
propagation (300-3000 kHz).

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 grey line 
propagation on 160 meters and to a lesser extent on 80 meters is 
perpendicular (right angles) to the corridor. In my personal observation the 
grey 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).


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 (ionosphere tilting).

There is an upward tilt of ionosphere layers towards the east at sunrise. As 
a result, signals coming from the west are refracted upward 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 Grey line/Grey 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.

And

GENERAL GUIDELINES CONCERNING CORRELATION OF PROPAGATION INDICES TO ACTUAL 
MF PROPAGATION CONDITIONS-

NOTE!!!  The propagation indices "interpretations" are my personal 
intellectual property. Therefore the propagation indices interpretations 
contained herein is copyrighted © 1988-2017 by Thomas F. Giella, W4HM, all 
rights reserved. Reproduction of information herein is allowed without 
permission in advance as long as proper credit is given.

All 13 of the following indices have to occur as described below in order to 
see the best global medium frequency (MF) radio wave propagation possible.

1.) Dropping geomagnetic field indices numbers are better, Kp of 0 best.

2.) A daily sunspot number under 100, under 70 best.

3.) A daily sunspot number no higher then the 100 for routine stable 
formation of the E Valley/F Layer ducting mechanism.

4.) Previous 24 hour Ap index under 10, fewer than 7 for several days 
consecutively are best.

5.) Previous 3 hours Kp index fewer than 3 for mid latitude paths, fewer 
than 2 for high latitude paths, 0 for several days consecutively is best.

6.) Energetic proton flux levels no greater than 10 MeV (10+0).

7.) Background x-ray flux levels of A0 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 aurora 
absorption/unpredictable refraction or scattering of medium frequency RF 
signals, when the Kp is above 3.

10.) A -10 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 is best.

11.) Galactic cosmic rays decrease to -3 units below zero and trending 
towards zero.

12.) Energetic electrons no greater than 2 MeV (2+0).

13. A solar wind speed of less than 300 km/s for several days consecutively.

73 & GUD DX,
Thomas F. Giella W4HM
Lakeland, FL, USA
thomasfgiella at gmail.com