Volker et all,
On my website KN4LF LF/MF/HF Radio Propagation Theory Notes at
http://www.kn4lf.com/kn4lf8.htm I have published the following:
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
Sporadic-E (Es). Sporadic-E clouds occur at approximately 100 km/60 miles in
altitude and generally move from west to east but at times east to west.
Like stratospheric level warming and troposphere level temperature and
moisture discontinuities, Sporadic-E can depending on the circumstances
absorb, block and refract medium, high and very high frequency RF signals in
an unpredictable manner.
The main source for high latitude Sporadic E is radio aurora activity.
The main sources for mid latitude Sporadic-E include wind shear, internal
buoyancy/gravity waves (IBGW's), and traveling ionosphere disturbances
(TID's), most of which are produced by severe thunderstorm cell complexes.
The tie in between Sporadic-E and a severe thunderstorm is the sprite and
The main sources for low latitude Sporadic-E include wind shear, internal
buoyancy/gravity waves (IBGW's), and traveling ionosphere disturbances, most
of which are produced by severe thunderstorm cell complexes tied to tropical
The forecasting of Sporadic-E has long been considered to be impossible.
However it is possible to identify certain troposphere level meteorological
conditions that can lead to the formation of Sporadic-E. One is as mentioned
above the severe thunderstorm cell complex.
Sporadic-E have been observed to occur within approximately 150 km/90 mi to
the left of a severe thunderstorm cell complex in the northern hemisphere,
with the opposite being observed in the southern hemisphere. To complicate
matters is the fact that Sporadic-E clouds not only have been observed to
move from west to east but at times also east to west. So one has to look
for Sporadic-E on either side of a severe thunderstorm cell complex.
Not all thunderstorm cell complexes reach severe levels and not all severe
thunderstorm cell complexes produce Sporadic-E. This is where knowledge in
tropospheric physics and weather forecasting is necessary. Coincidentally I
have a B.S. in Meteorology and an M.S. in Space Plasma Physics and am
qualified to identify which severe thunderstorm complexes are most likely to
Some but not all key elements in identifying which severe thunderstorm cell
complexes have the potential to produce Sporadic-E via wind shear, internal
buoyancy/gravity waves, traveling ionosphere disturbances, sprites and elves
1.) Negative tilted mid level long wave troughs.
2.) Approximate 150 knot/170 mph jet stream jet maxes that produce
divergence and therefore create a sucking vacuum effect above thunderstorm
cells, that assist thunderstorm cells in reaching and penetrating the
tropopause into the stratosphere.
3.) 500 mb temperatures of -20 deg. C or colder, which produce numerous
positive and negative lightning bolts and inter-related sprites and elves.
4.) Approximate 150-175 knot/172-200 mph updrafts within thunderstorm cells
that create overshooting tops that penetrate the tropopause into the
stratosphere (See definition #20 on Stratospheric Warming), launching
upwardly propagating internal buoyancy/gravity waves, traveling ionosphere
disturbances and wind shear.
73 & GUD DX,
Thomas F. Giella, KN4LF
Retired Space & Atmospheric Weather Forecaster
Plant City, FL, USA
Grid Square EL87WX
Lat & Long 27 58 33.6397 N 82 09 52.4052 W
Contesting Propagation eReflector:
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KN4LF Daily Solar Space Weather & Geomagnetic Data Archive:
KN4LF Daily LF/MF/HF Radio Propagation Outlook:
KN4LF HF/MF Radio Propagation Theory Notes: http://www.kn4lf.com/kn4lf8.htm
KN4LF Amateur & SWL Radio History: http://www.kn4lf.com/index.htm
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