Abstract. Ice crystal numbers can exceed the numbers of ice-nucleating
particles (INPs) observed in mixed-phase clouds (MPCs) by several orders of
magnitude, also at temperatures that are colder than −8 ∘C. This
disparity provides circumstantial evidence of secondary ice formation, also
other than via the Hallett–Mossop process. In a new approach, we made use of
the fact that planar, branched ice crystals (e.g. dendrites) grow within a
relatively narrow temperature range (i.e. −12 to −17 ∘C) and can
be analysed individually for INPs using a field-deployable drop-freezing
assay. The novelty of our approach lies in comparing the growth temperature
encoded in the habit of an individual crystal with the activation temperature
of the most efficient INP contained within the same crystal to tell whether
it may be the result of primary ice formation. In February and March 2018, we
analysed a total of 190 dendritic crystals (∼3 mm median size)
deposited within MPCs at the high-altitude research station Jungfraujoch
(3580 m a.s.l.). Overall, one in eight of the analysed crystals contained
an INP active at −17 ∘C or warmer, while the remaining seven most
likely resulted from secondary ice formation within the clouds. The ice
multiplication factor we observed was small (8), but relatively stable
throughout the course of documentation. These measurements show that
secondary ice can be observed at temperatures around −15 ∘C and
thus advance our understanding of the extent of secondary ice formation in
MPCs, even where the multiplication factor is smaller than 10.
A New Type of BTP/Zeolites Nanocomposites as Mixed-Phase Fire Suppressant: Preparation,Characterization and Extinguishing Mechanism Discussion
