its slope) is represented sufficiently well. This leads to the conclusion that details of the nucleation rate are less important for simulating ice nucleation in bulk models as long as the main feature of the nucleation rate (i.e. The nucleation events are sensitive to the slope of the nucleation rate but only weakly affected by changes in its absolute value. We use a state-of-the-art bulk ice microphysics model to investigate nucleation events as driven by constant cooling rates the key variables are the final ice crystal number concentration and the maximum supersaturation during the event.
The nucleation rate can be adjusted, and the formulation can be simplified to a threshold description. In this study we investigate the formulation of the nucleation rate of homogeneous freezing of solution droplets (1) to link the formulation to the nucleation rate of pure water droplets, (2) to derive a robust and simple formulation of the nucleation rate, and (3) to determine the impact of variations in the formulation on nucleation events. It is not clear how nucleation events are influenced by the exact formulation of the nucleation rate or even their inherent uncertainty. The nucleation rate can be parameterized as a function of water activity, based on empirical fits and some assumptions on the underlying properties of super-cooled water, although a general theory is missing. Homogeneous freezing of solution droplets is an important pathway of ice formation in the tropopause region.
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