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A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
Re: Horizon refraction: photos of changes
From: Marcel Tschudin
Date: 2013 Apr 20, 12:25 +0300
From: Marcel Tschudin
Date: 2013 Apr 20, 12:25 +0300
Frank, you wrote:
"No. I don't think that has any significant impact on the refraction phenomena here. They're not chimneys. The temperature difference is not great, and there's very little convection above them. The tops of those towers, by the way, are 500 feet up, well above the phenomena we've been talking about. Besides those are sixteen miles away! Don't forget the compression of distances that occurs in telephoto images."
Our evaluation of the situation is obviously not quite the same and we appear to *think* differently. The cooling towers are heat exchangers making use of the chimney effect, thus producing locally a forced air circulation which involves more than only the visible water vapour escaping at the top from where it disperses "somehow". The refraction phenomena require only small temperature differences and the large distance may even enhance the effect due to the small angle (difference) of incidence of a visible ray passing a discontinuity. This does not contradict that your two photos are very good examples for showing the variability of terrestrial refraction. I only wanted to indicate that the selected location may be one where the view could be more susceptible to changing refractions than at a "normal" location.
Marcel
"No. I don't think that has any significant impact on the refraction phenomena here. They're not chimneys. The temperature difference is not great, and there's very little convection above them. The tops of those towers, by the way, are 500 feet up, well above the phenomena we've been talking about. Besides those are sixteen miles away! Don't forget the compression of distances that occurs in telephoto images."
Our evaluation of the situation is obviously not quite the same and we appear to *think* differently. The cooling towers are heat exchangers making use of the chimney effect, thus producing locally a forced air circulation which involves more than only the visible water vapour escaping at the top from where it disperses "somehow". The refraction phenomena require only small temperature differences and the large distance may even enhance the effect due to the small angle (difference) of incidence of a visible ray passing a discontinuity. This does not contradict that your two photos are very good examples for showing the variability of terrestrial refraction. I only wanted to indicate that the selected location may be one where the view could be more susceptible to changing refractions than at a "normal" location.
Marcel
