NAT-rock formation by mother clouds: A microphysical model study

S. Fueglistaler, B. P. Luo, C. Voigt, K. S. Carslaw, Th Peter

Research output: Contribution to journalArticlepeer-review

47 Scopus citations


Polar stratospheric clouds (PSCs) of type 1a or 1a-enh containing high number densities of nitric acid trihydrate (NAT) particles, can act as mother clouds for extremely large NAT particles, termed NAT-rocks, provided the air below the clouds is supersaturated with respect to NAT. Individual NAT particles at the cloud base fall into undepleted gas phase and rapidly accelerate due to a positive feedback between their growth and sedimentation. The resulting reduction in number density is further enhanced by the strong HNO3 depletion within a thin layer below the mother cloud, which delays subsequent particles. This paper introduces the basic microphysical principles behind this mother cloud/NAT-rock mechanism, which produces 10-4 cm-3 NAT-rocks with radii around 10 μm some kilometers below the mother cloud. The mechanism does not require selective nucleation and works even for a monodisperse particle size distribution in the mother cloud.

Original languageEnglish (US)
Pages (from-to)99-101
Number of pages3
JournalAtmospheric Chemistry and Physics
Issue number2
StatePublished - 2002
Externally publishedYes

All Science Journal Classification (ASJC) codes

  • Atmospheric Science


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