Contact freezing: a review

Abstract

Abstract. This manuscript compiles both theoretical and experimental information on contact freezing with the aim to better understand this potentially important but still not well quantified heterogeneous freezing mode. There is no complete theory that describes contact freezing and how the energy barrier has to be overcome to nucleate an ice crystal by contact freezing. Experiments on contact freezing indicate that it can initiate ice formation at the highest temperatures. A difference in the freezing temperatures between contact and immersion freezing has been found using different instrumentation and different ice nuclei. There is a lack of data on collision rates in most of the reported data, which inhibits a quantitative calculation of the freezing efficiencies. Thus, new or modified instrumentation to study this heterogeneous freezing mode in the laboratory and in the field are needed. Important questions concerning contact freezing and its potential role for ice cloud formation and climate are also summarized.