unfrozen_and_saturated

[tluettm]

The method unfrozen_and_saturated used in freezing_methods should check for saturation with respect to ice instead to saturation with respect to water.

I could rework the test while adding homogeneous freezing methods.

[slayoo]

Thank you @tluettm for reporting.

We follow Shima et al. 2020 paper, where (section 4.1.4) "i-th particle freezes immediately when the following three conditions are all satisfied: (1) the particle is a droplet, i.e., ri > 0; (2) the ambient water vapor is supersaturated over liquid water, i.e., ei > ews (Ti ); " (https://gmd.copernicus.org/articles/13/4107/2020/gmd-13-4107-2020.pdf)