Technical Note: A numerical test-bed for detailed ice nucleation studies in the AIDA cloud simulation chamber

[摘要] The AIDA (Aerosol Interactions and Dynamics in the Atmosphere) aerosol andcloud chamber of Forschungszentrum Karlsruhe can be used to test the iceforming ability of aerosols. The AIDA chamber is extensively instrumentedincluding pressure, temperature and humidity sensors, and optical particlecounters. Expansion cooling using mechanical pumps leads to icesupersaturation conditions and possible ice formation. In order to describethe evolving chamber conditions during an expansion, a parcel model was modified to account for diabatic heat andmoisture interactions with the chamber walls. Model results are shown for aseries of expansions where the initial chamber temperature ranged from−20°C to −60°C and which used desert dust as ice formingnuclei. During each expansion, the initial formation of ice particles wasclearly observed. For the colder expansions there were two clear icenucleation episodes.

In order to test the ability of the model to represent the changing chamberconditions and to give confidence in the observations of chamber temperatureand humidity, and ice particle concentration and mean size, ice particleswere simply added as a function of time so as to reproduce the observationsof ice crystal concentration. The time interval and chamber conditions overwhich ice nucleation occurs is therefore accurately known, and enables themodel to be used as a test bed for different representations of iceformation.

[学科分类] 大气科学