One thought on “The Hail Cannon

  1. For your interest,

    Sixty years ago we carried out experiments with French antihail rockets urged on by Dr Kritzinger from Stellenbosh University South Africa. The public reactions were the same as yours plus mothers of young children. The trials were very amateurish and the results contentious but some of us thought the rockets did have a positive effect especially the occasional fall of soft hail which was practically unknown before. Rockets also cause the green colour if present to disappear immediately( colour due to sun shining into cavity) and also the roar. Changes which can occur naturally but not as frequently as wished.

    It does not matter how many times you get successful results it will always be coincidence or imagination. An approach to change the experts opinion may be to question the official theory, whatever that is. It is a very plausible one, but not supported by any proven facts. One aspect is that the amount of heat produced at a considerable height during the production of a particularly large fall of hail would about put the top of the storm into orbit. Also at these heights the atmosphere is much thinner and there is much less water vapor about. Another aspect that could be investigated is small hail which occurs in northwest U.S.A., no vertical development in those clouds.

    As I understand it the idea began during the Crimean War when the effect of artillery barrages was seen to ‘disperse’ hail storms and the idea spread west across Europe to France, particularly in the valleys of the Alps. By 1900 rockets and hail cannon were extensively used in some areas with uncertain results, in Northern Italy acetylene gas was tried instead of black gun powder which was difficult to light in a wild storm the reason for often enough failures.

    In 1902 a World Meteorological Conference in Vienna declared that rockets/cannon had some ameliorating effect on hail

    Storms. Two committees were formed to investigate one/ hail rockets (which I understand had no hope of coming to a statistical result) and two/ to investigate soft hail. To me the result seemed to indicate that they did. (Soft hail, the first hail to fall is hard but at a specific moment the hail turns soft and for the rest of the life of the storm it does no damage.)

    I don’t know if that resolution is still on the minutes.

    During World War One the same effect was noted on hail storms as in the Crimean War. After the war a French air Force General Ruby studied the problem with the use of an aircraft and emphasized that Flying into storms was very dangerous. He published a book “La Grale”. He pointed out that in his opinion the method was right but the means were poor. He also suggested a theory which seemed to me half baked but on the right track. This was described as ingenious and whimsical.

    To me it appears most of the action takes place in the lower part of the storm. A possible explanation is that the hail is produced by a

    horizontal vortex forming below the freezing level. As the storm develops a strong vertical up draught forms, encouraged by an isothermal layer and then a downdraught develops behind it. By chance or naturally a minor horizontal vortex forms sufficient to cause a slight reduction in pressure (gas to liquid) /temperature causing some water vapour to condense thus producing more condensation and a rapid escalation of the drop in temperature/pressure until a horizontal vortex forms spitting out hail. This is a very unstable structure, held together by centrifugal force. The shock wave from the antihail device very briefly breaks this bond allowing the vortex to collapse. Possibly also upsetting the up draught at the same time.

    Another approach may be an enquiry into why a number of aircraft come to grief upon flying into the lower part of a storm.

    Kind Regards
    Tom Archer
    QLD Australia


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