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Abstract:
Cloud droplet temperature plays a key role in fundamental cloud microphysical and radiative processes, affecting cloud radiative effects and remote sensing of cloud properties. The supercooled droplet temperature impacts cloud ice and precipitation formation via homogeneous freezing and activation of ice-nucleating particles through contact and immersion freezing. Most observational and numerical studies assume that the droplet temperature is uniform and equal to the ambient temperature. This is not always the case, especially when the droplet is exposed to strong relative humidity gradients at the edges of a cloud. This study investigates the spatiotemporal evolution of the droplet temperature, radius, and its environment under various initial droplet characteristics, and environmental conditions, including ambient pressure, temperature, and relative humidity. An advanced numerical model is used to solve Navier-Stokes and continuity equations, coupled with heat and vapor transport, to simulate the drop interior and the moving droplet boundary, including thermal and vapor density gradients in the ambient air domain. Results include the evolution of internal thermal gradients within the droplet and the impacts of evaporative cooling on decreasing droplet surface temperatures, by at least 10 degrees within a second under certain environments, and droplet evaporation rates. The study underscores the need to improve the existing ice nucleation parameterization schemes to consider the decrease in droplet temperature due to evaporative cooling and provides important benchmark results useful for direct numerical simulation and coarser resolution models. The modeling framework can also be adapted to study supercooled droplets freezing on a substrate or melting of hailstones.
