Topband: 160 Propagation & Weather

[Michael Keane, K1MK]

Hi Chuck,

At 07:00 AM 11/2/02, Charles Hutton wrote:

>But the original subject that I was discussing is:

I understood. This has become become a rather lengthy and convoluted 
thread. And I was attempting to comment on several of its disparate 
aspects, perhaps not as clearly as I might have.

>         "Thomas KN4LF Says: As a retired Meteorologist and Space Weather 
> Forecaster
>I can say that temperature and moisture discontinuities in the vicinity of a
>cold front can refract 160 meter signals in unpredictable ways."

Chuck, I'll agree with you that there's absolutely nothing in the 
Kazimirovsky & Kokourov review that's even peripherally related to a 
physical mechanism that is based upon refraction at discontinuities.

A simple check of the order of magnitude of the possible effects shows why 
refraction is simply the wrong place to be looking. The maximum difference 
in the radio index of refraction between cold/dry air and warm/wet air is 
less than 1 part in 1000. If such a discontinuity is placed approximately 
perpendicular to the direction of propagation then the maximum angular 
deviation one expects to see across the discontinuity is thousandths a degree.

>The Russian paper didn't touch on that subject, if my attention didn't
>wander too much while scanning it. I'm still curious as to whether there are
>studies on the long term effects of cold fronts, as opposed to the short
>term effects of lightning which is what some of the comments so far have
>been about.

Even though the specific mechanism of refraction is clearly not very 
significant, it should not be surprising to eventually find some 
correlation between fronts and ionospheric conditions. The effect may be 
causal with fronts acting as a source of dynamic disturbances that generate 
upwardly propagating waves. Or the effect may be indirect, with fronts 
serving as surrogates for changes in the state of the lower atmosphere. 
Both of these possibilities are hinted at by research that's referenced in 
Kazimirovsky & Kokourov.

73,
Mike K1MK

Michael Keane, K1MK
k1mk@alum.mit.edu