In order to describe the evolving chamber conditions during an expansion, a detailed microphysics size-resolving parcel model was modified to account for diabatic heat and moisture interactions with the chamber walls. The wall vapour flux is derived using the measured total water content which is now accurately measured when there are no large particles present.
Model results are shown for a series of expansions using desert dust as ice forming nuclei, over an initial chamber temperature which ranged from -20 to -60C. During each expansion, the initial formation of ice particles was clearly observed. For the colder expansions there were two clear ice nucleation regimes.
Firstly, ice particles were added to the model as a function of time so as to reproduce the observations of SID ice crystal concentration. The agreement between the model and the observations of chamber relative humidity and temperature, and of the ice particle concentration and average diameter improves the confidence in these measurements, and in the estimated wall flux of heat and water vapour. The time interval and chamber conditions over which ice nucleation occurs is therefore accurately known. By establishing the ability of the model to describe the evolving chamber conditions, it can then be used as a test bed for different representations of heterogeneous ice nucleation.