Topband: Improving Topband Conditions?!
Thomas Giella KN4LF
kn4lf at tampabay.rr.com
Mon Feb 16 22:20:37 EST 2004
On my "KN4LF MF Radio Propagation Theory Notes" website at http://www.kn4lf.com/kn4lf8.htm is posted the following:
..........15.) Sudden Stratospheric Warming (STRATWARM ALERT)-
Sudden stratospheric 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, lasting for many days at a time and characterized by a warming of the stratospheric temperature by some tens of degrees (temperature inversion).
Another way to explain stratospheric warming is a major disturbance of the winter polar middle atmosphere from the Tropospause to D-region which is at the base of the Mesophere resulting from a breakdown of the polar 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 gasses resulting in an increase in electron density and producing strong MF and HF absorption.
A little inter-related Troposphere Meteorology:
Interrelated with the splitting and shifting of the Arctic Circumpolar Vortex, is a Tropospheric 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 stratospheric warming effect medium frequency propagation in any way BUT medium frequency signals do propagate off of temperature inversions and moisture discontinuities and a temperature inversion is involved with stratospheric 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.
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 seems to be less pronounced.
16.) D Region Mid Winter Absorption Anomaly-
A period of increased MF 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 Region Mid Winter Absorption Anomaly. See definition #15.) Sudden Stratospheric Warming (STRATWARM ALERT)..........
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On 02/17/04 Thomas KN4LF Says:
We have had allot of stratospheric warming during the heart of this winter season and therefore allot of extra NIGHT TIME D layer absorption of MF transmitted signals. However as the global jet stream pattern has now changed, this phenomena is now diminishing in frequency of occurrence. By the way the STRATWARM's have coincided with repeated cross polar flow of bitter Arctic airmasses from Siberian Russia into Canada and the NE U.S., Great Lakes and Northern Plains regions. You can almost always correlate the coldest weather with poor medium frequency propagation conditions.
Also we are now moving out of the "D Region Mid Winter Absorption Anomaly" so MF Radio propagation always improves in beginning in February and extending into March before the QRN returns.
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Also on my "KN4LF MF Radio Propagation Theory Notes" website at http://www.kn4lf.com/kn4lf8.htm is posted the following:
Here are some general guidelines concerning correlation off propagation indices to actual expected propagation conditions.
1.) Dropping indices numbers are better.
2.) For medium frequencies a solar flux under 150, under 100 better, 70 is best for E layer multi hop.
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 background x-ray flux. See #7 below.
3.) Solar flux of at least 100 for 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) for 160/120 meters and no greater then (10-1) on MF broadcast band.
7.) Background x-ray flux levels less than C1 for several days consecutively for 160/120 meters and less then B9 for MF broadcast band, A9 or less is best.
8.) No current STRATWARM alert.
9.) IMF Bz with a (+) sign, indicates a lesser chance of high latitude path auroral absorption/unpredictable refraction or scattering of MF RF signals, when the Kp is above 3.
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On 02/17/04 Thomas KN4LF Says:
The 9 rules above can be put into practice by looking at the observed space weather indices below.
Between 01/20-01/29 2004 the daily solar flux levels were high enough to support the E-Valley/F Layer ducting mechanism. Also the background x-ray flux was in the low B range to high A range. There were very few C class solar flares. It all adds up to good night time MF propagation. Look in your logs and/or check the OH and JA 160 spots and you will see many more contacts occurring during this period.
The same holds for the 02/10-02/16 2004 period and all the other periods this season before it. AND on nights where the radio Aurora is contracted poleward (low Kp values) even high latitude propagation paths are open.
Let's face it 160 meters is to far removed from the daily MUF to be able to use HF propagation prediction concepts BUT openings are predictable. Many a day I see posts on the Topband Reflector where people grumble about 160 propagation being impossible to predict, "black magic" it's called. I rarely respond because of flaming but all it takes is reading and understanding the information on my website and applying it. The answers to the seemingly mysterious MF propagation occurrences are contained within.
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# Sunspot Stanford GOES12
# Radio SESC Area Solar X-Ray ------ Flares ------
# Flux Sunspot 10E-6 New Mean Bkgd X-Ray Optical
# Date 10.7cm Number Hemis. Regions Field Flux C M X S 1 2 3
#---------------------------------------------------------------------------
2004 01 20 129 94 540 1 -999 B3.9 0 1 0 1 1 1 0
2004 01 21 130 104 560 0 -999 B3.3 2 0 0 1 0 0 0
2004 01 22 122 76 400 0 -999 B2.5 0 0 0 0 0 0 0
2004 01 23 115 62 260 0 -999 B1.9 0 0 0 0 0 0 0
2004 01 24 108 47 230 0 -999 B1.8 0 0 0 0 0 0 0
2004 01 25 102 48 130 0 -999 B1.6 1 0 0 2 0 0 0
2004 01 26 98 38 30 0 -999 B1.5 1 0 0 0 0 0 0
2004 01 27 94 00 00 0 -999 B1.2 0 0 0 0 0 0 0
2004 01 28 89 00 00 0 -999 A8.7 0 0 0 0 0 0 0
2004 01 29 87 25 70 2 -999 A7.5 0 0 0 0 0 0 0
2004 02 10 117 78 520 0 -999 B2.0 0 0 0 0 0 0 0
2004 02 11 114 91 430 1 -999 B1.9 0 0 0 0 0 0 0
2004 02 12 112 65 420 0 -999 B1.9 0 0 0 0 0 0 0
2004 02 13 108 71 270 2 -999 B1.7 0 0 0 0 0 0 0
2004 02 14 104 64 210 1 -999 B1.3 0 0 0 0 0 0 0
2004 02 15 000 75 270 2 -999 B1.1 0 0 0 0 0 0 0
2004 02 16 99 81 190 0 -999 A9.0 1 0 0 1 0 0 0
73 & GUD DX,
Thomas F. Giella, KN4LF
Retired Space & Atmospheric Weather Forecaster
SKYWARN Observer HIL-249
SWFWMD Observer #574
Plant City, FL, USA
EL87WX
Yaesu FT-840 & PSK31 Digital Mode E Group http://groups.yahoo.com/group/yaesu_ft840
160-10 Meter Amateur Radio Resources http://www.kn4lf.com/kn4lf.htm
Daily Solar Space Weather & Geomagnetic Data Archive http://www.kn4lf.com/kn4lf5.htm
Daily MF Radio Propagation Outlook http://www.kn4lf.com/kn4lf6.htm
MF Radio Propagation Theory Notes http://www.kn4lf.com/kn4lf8.htm
Florida Space & Atmospheric Weather Institute http://www.kn4lf.com/fsawi.htm
Florida Daily Weather Discussion http://www.kn4lf.com/sub/fmci17.htm
Friend Website Design Studio http://www.kn4lf.com
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