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)

[tluettm]

While liquid water droplets of a certain minimum size are present, the ambient saturation ratio will be close to water saturation. However, I don't see a physical reason why we should force saturation with respect to water as a requirement for freezing. Ideally, the model physics itself would resolve this. This might also be relevant for when we add individual ambient temperature and water vapor density for each droplet (different to the background field).