[NLRS] Tropo Maps

[Ford Peterson]

>I don't want to be taken as totally negative, just that I'm sure there are more 
> weather phenomena showing at VHF than at MF to affect propagation. 

I think it was Albert Einstein who quipped.  "Every Tom, Dick, and Harry says he knows what a Quantum is (a photon), but they are wrong...  Albert E in 1926

The statement is just as true today as back in 1926.  The closest definition to reality that I've been able to locate is one by Gilbert, who wrote:

"A photon is what a photon detector detects..."

Hardly a definition.  But it does explain how hams use them to good effect every day.  Until we understand what the heck our buddy Al's Quantum is, we won't know all the implications.

...snip...

> I wish that for severe weather forecasting and for understanding of odd 
> none precip radar echoes (like the blobs of summer evenings) that there 
> were thousands more soundings and that they were every few minutes. 

I am fairly certain that the NOAA would not be interested in more frequent soundings.  I don't know how much it costs to send up a balloon with a payload that just gets abandoned, but it has to be $200 or more with the Helium involved.  While I have no idea what all they do with the data, I can speculate that these soundings become input into their weather models.  As the Jet Stream moves about, they track the info to model how this induces a change in the lower atmosphere.

> There are some UHF vertical sounders that return data continuously, but I've 
> neglected to remember all their operational characteristics.

I would be very interested in any resource of data collected on this topic.  It may prove WAY more interesting than the wx info.

> As we've just been discussing on the microwave list, it may well be important 
> to look at IR satellite images for clouds of cold crystals (though there's no 
> elevation information other than temperature and the satellite temperature 
> includes surface through thin clouds or clear skies) and to look at storm tops 
> (as K0SM is doing for predicting rain and snow scatter opportunities at 10 
> GHz) from radar data.

My thinking is the best we can hope for is a general indication of conditions that may be present above 40km.  The upper atmosphere is a not nearly as variable as the lower atmosphere.  It is simply too thin.  The Jet Stream is an indication, but will likely not be the entire picture.  It is hoped that the lower atmosphere can be some day viewed with an understanding of what is going on above the mesosphere.  

> It appears to me that most of the accepted phenomena at MF come from 
> solar (e.g. UV) ionization of layers too high above the ground for balloon 
> observations. I can't discount there being pressure variations on those 
> heights and ionization intensities. Most often VHF and up requires a great 
> deal greater intensity of ionization that is very uncommon so other factors are 
> predominant.

At MF, I am told that even in the depths of the solar duldrums, MUF does NOT play a role on MF since the ionization levels are more than adequate to support MF propagation.  Only rarely do the MUF's approach 2mHz.  

...snip...

> To me, it sounds like path skewing, spotlighting, path nulls, terminator effects, 
> and reverberations are characteristics of ducts created by solar ionization or 
> varying air densities or humidities. 

Some sort of ducting is the traditional explanation.  But difficult to visualize or predict as it sometimes works and sometimes doesn't work--and it seems to work in peculiar ways.  Understanding the data inputs needed for prediction could prove to be very useful.

...snip...

> Don't discount the possibilities that a duct might be from ionization some 
> places, from temperature gradients in other places and from humidity 
> gradients in other places and a random collection of all three (and probably 
> a couple I've not mentioned) are required to make a particular path.

The notion of ducting is greatly debated on MF.  Everyone believes that it does happen.  But the mechanisms involved with why it happens today and not next Friday is a bit of a mystery.  On MF, the D layer plays a significant role.  The refractions actually occur on the E layer, but the D layer gets in the way as the gyro frequency of the molecules of air is about 1.5mHz.  Topband is only 300kHz away at 1.8mHz.  If the D layer serves to block signals from arriving at the E layer, and block signals returning back from the E layer, the attenuation is greatly increased in the path of interest.  However, if you consider how holes in the D layer can form, and these 'holes' extend up into the E layer, E to F ducting can occur.  Does weather play a role?  Quite possibly.

> I've not studied it but it seems like the same ionized particles that create 
> aurora can accumulate in the atmosphere to make charged and refractive 
> layers, most often thin for VHF propagation, but one can't rule out MF 
> propagation either. A lot depends on the ionization intensity and weather 
> balloon soundings won't show that and its unlikely the ionization will cause 
> any weather shift, but its worth looking.

I have pondered the notion of star dust before.  Many weather observers feel that the solar wind does make it down into the atmosphere.  Some believe these particulates are needed to form rain as the particulates begin to accumulate water on the surface of a particle to form droplets of rain.  More intense solar activity is traced to increases in rainfall.  So maybe these particulates play a role too.  Central Canada and the upper Midwest are known by the term "black hole" in MF circles.  Aurora can (but not always) induce considerable attenuation of MF signals.  While attributed to the close proximity to the north magnetic pole, perhaps these are also the areas that accumulate star dust in the atmosphere.  How this affects MF propagation is speculation.

> Then for unexpected directions at MF, what about polarization shifts in 
> propagation? Many long wire antennas have significant cross and angle 
> polarized lobes well off the main axis from the preferred signal polarization 
> that can confuse the observer of the apparent incoming direction.
> 
> 73, Jerry, K0CQ

The stations able to report direction at MF are not the peanut whistle variety.  K9DX has 9 - 130' towers in a huge circle to form a directional phased array.  Many use a set of 4 - 130' tall 1/4wL verticals set in a square and phase them.  There are others using a series of 800' to 1000' long beverage antennas to provide some indication as to direction.  Mammoth structures actually.  W0AIH in WI is one of the stations that experience the skewing effects.  These are not localized effects, which would be easily explained with backscatter.  Whole areas of the country will experience similar results.

> -- 
> Entire content copyright Dr. Gerald N. Johnson, electrical engineer.
> Reproduction by permission only.

I shamelessly copied the above references without the permission of anybody.  Presumably, the author, by posting his response in this public forum, provides permission assumptions?  If not, forgive me...

Ford-N0FP
ford at cmgate.com