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The ice crystal number concentration (N-i) is a key property of ice clouds, both radiatively and microphysically. Due to sparse in situ measurements of ice cloud properties, the controls on the N-i have remained difficult to determine. As more advanced treatments of ice clouds are included in global models, it is becoming increasingly necessary to develop strong observational constraints on the processes involved.

This work uses the DARDAR-Nice N-i retrieval described in Part 1 to investigate the controls on the N-i at a global scale. The retrieved clouds are separated by type. The effects of temperature, proxies for in-cloud updraft and aerosol concentrations are investigated. Variations in the cloud top N-i (N-i(top)) consistent with both homogeneous and heterogeneous nucleation are observed along with differing relationships between aerosol and N-i(top) depending on the prevailing meteorological situation and aerosol type. Away from the cloud top, the N-i displays a different sensitivity to these controlling factors, providing a possible explanation for the low N-i sensitivity to temperature and ice nucleating particles (INP) observed in previous in situ studies.

This satellite dataset provides a new way of investigating the response of cloud properties to meteorological and aerosol controls. The results presented in this work increase our confidence in the retrieved Ni and will form the basis for further study into the processes influencing ice and mixed phase clouds.