A turbulence-informed parameterization of phase partitioning in stratiform mixed-phase clouds for the ICOLMDZ model
Résumé
High-latitude clouds, present over the Arctic Ocean, the Southern Ocean and the Antarctic continent, are very often. Despite being essential for the climate of the poles, they remain a major modelling challenge for climate models. In this study, we present a new cloud phase partitioning parameterization developed for the ICOLMDZ atmospheric model. This parameterization is based on the theory of the evolution of supersaturation in a turbulent environment and is inspired by previous theoretical and modelling works. This scheme completely abandons the standard temperature dependent phase partitioning used in the model to predict the amount of supercooled liquid water in clouds as a function of turbulent kinetic energy, resolved vertical velocity and pre-existing ice crystal properties. This new scheme is evaluated over the Southern Ocean with observation from the MARCUS campaign and results show an improvement in the simulation of the cloud phase spatial variability. The sensitivity to the crystal number concentration determined by a prescribed concentration of ice nucleating particles is also assessed. A second evaluation is performed in the Arctic region with observations collected in mid-level frontal during the RALI-Thinice campaign and a perturbed parameter ensemble experiment is conducted to assess the parametric sensitivity. The new scheme suppresses the systematic overestimation of liquid far from cloud top and shows the ability to simulate patches and thin layers of supercooled liquid water as commonly observed in polar frontal clouds.
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