Investigations into Anomalous Supersaturation in Cold Cirrus at the AIDA Cloud Chamber during the ISOCLOUD Campaigns

In recent years, in-situ instruments measuring water vapor in the UTLS have routinely observed anomalous supersaturations on the order of 10-20% in the presence of ice particles when temperatures were below 200 K. Experiments at the AIDA Cloud and Aerosol Chamber during the ISOCLOUD campaigns sought to reproduce this phenomenon in cold clouds at temperatures and pressures characteristic of the upper troposphere. We report on results from a series of cirrus formation experiments, involving both homogeneous nucleation of sulfate aerosols and heterogeneous nucleation with a variety of aerosol number densities and compositions, including mineral dust and organic aerosols with and without nitric acid coatings. Instruments measured particle number density, water vapor, total water, and water vapor isotopic concentrations, with multiple instruments providing simultaneous water measurements. We discuss the implications of these studies for ice deposition growth rates at the coldest UTLS temperatures.