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Die Entwicklung unserer Anschauungen über atmosphärische Eisbildung seit Wegener

Alfred Wegener Institute for Polar and Marine Research & German Society of Polar Research
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  • Chemistry


Die Entwicklung unserer Anschauungen über atmosphärische Eisbildung seit Wegener Helmut Weickmann ':. Abstract. Alfred Wegener developed h is ideas on ice formation in the atmosphere on the basis of his profound experience of observations in the arctic. He postulated that "Eiskerne" (ice nuclei) are particles which cause sublimation of water vapor directly into the solid phase. They TTIUst be characterized by a sirnilar, "isornorphtc", crystal structure as iee and must consequently be solid particles, while particles w hich cause the condensation of water vapor must be liquid particles. Subsequently and Iogicalt the ice nuclei were called sublimation nuclei. These views remained essentially unchanged tor 30 years in spi te of physicochemist Ostwald's "Stufenregel" (step rule) which postulated that in phase transitions that phase forms first whose surface energy with the vapor is a minimum. In the systern water vapor-water-ice water would be the phase forming first, and then through a crystallisation process ice would form. The whole problern received a theoreticai basis in 1939 through Volmers theory of the kinetics of phase transitions, and experimental support through the observation of the activity of "freezing riuclei''. Nowadays, the existence of sublimation nuciei can hardly be defended in view of energetic considerations which make the detour condensation-water-freezing nucleus-ice more probable, in view of very strict requirements for isomorphy between ice and a sublimation nucleus w htch are not even met »v silver iodide or other excellent ice nuclei, in view of the fact that ail phenomena of ice formation can be explained by invoking the sole existence of freezing nuciei, and in view of the homogeneaus freezing point of water at a temperature of -40 Q C which was unknown to w egencr-s time. Freezing nuclei can initiate ice formation during the condensation process at or near water saturation, during the evaporation process, through contact with a supercooled droplet, or whe

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