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
elve.
The main sources for low latitude Sporadic-E include wind shear, internal
buoyancy/gravity waves (IBGW's), and traveling ionosphere disturbances, most
of which are produced by severe thunderstorm cell complexes tied to tropical
cyclones.
The forecasting of Sporadic-E has long been considered to be impossible.
However it is possible to identify certain troposphere level meteorological
conditions that can lead to the formation of Sporadic-E. One is as mentioned
above the severe thunderstorm cell complex.
Sporadic-E have been observed to occur within approximately 150 km/90 mi to
the left of a severe thunderstorm cell complex in the northern hemisphere,
with the opposite being observed in the southern hemisphere. To complicate
matters is the fact that Sporadic-E clouds not only have been observed to
move from west to east but at times also east to west. So one has to look
for Sporadic-E on either side of a severe thunderstorm cell complex.
Not all thunderstorm cell complexes reach severe levels and not all severe
thunderstorm cell complexes produce Sporadic-E. This is where knowledge in
tropospheric physics and weather forecasting is necessary. Coincidentally I
have a B.S. in Meteorology and an M.S. in Space Plasma Physics and am
qualified to identify which severe thunderstorm complexes are most likely to
produce Sporadic-E.
Some but not all key elements in identifying which severe thunderstorm cell
complexes have the potential to produce Sporadic-E via wind shear, internal
buoyancy/gravity waves, traveling ionosphere disturbances, sprites and elves
include:
1.) Negative tilted mid level long wave troughs.
2.) Approximate 150 knot/170 mph jet stream jet maxes that produce
divergence and therefore create a sucking vacuum effect above thunderstorm
cells, that assist thunderstorm cells in reaching and penetrating the
tropopause into the stratosphere.
3.) 500 mb temperatures of -20 deg. C or colder, which produce numerous
positive and negative lightning bolts and inter-related sprites and elves.
4.) Approximate 150-175 knot/172-200 mph updrafts within thunderstorm cells
that create overshooting tops that penetrate the tropopause into the
stratosphere (See definition #20 on Stratospheric Warming), launching
upwardly propagating internal buoyancy/gravity waves, traveling ionosphere
disturbances and wind shear.
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
kn4lf@arrl.net
Contesting Propagation eReflector:
http://lists.contesting.com/mailman/listinfo/propagation
HC-DX Propagation Channel:
http://www.hard-core-dx.com/index.php?topic=Propagation
KN4LF Daily Solar Space Weather & Geomagnetic Data Archive:
http://www.kn4lf.com/kn4lf5.htm
KN4LF Daily LF/MF/HF Radio Propagation Outlook:
http://www.kn4lf.com/kn4lf6.htm
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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