Large-eddy simulations of the stratocumulus to cumulus transition in the Northeast Pacific using ICON

The Northeast Pacific stratocumulus deck is one of the well-known subtropical semipermanent stratocumulus decks that transitions into shallow cumuli along the sea surface temperature gradient away from the Californian coast line. In this study we use observational data from the Marine ARM GPCI Investigation of Clouds (MAGIC) ship campaign to evaluate stratocumulus to cumulus transitions (SCTs) in idealised large-eddy simulations (LESs) with the ICOsahedral Nonhydrostatic Model (ICON). The simulations are conducted with a horizontal resolution of 50 m and a vertical resolution of at most 10 m in the lowest 3 km of the atmosphere. 
From previous studies of SCTs, including MAGIC and in particular Leg15A, it is well known that entrainment processes drive an important, and likely dominant role in forcing the transition. However, recent studies have shown that microphysical effects like sedimentation or precipitation can significantly alter the course of the SCT. Suppressed precipitation through a higher number of cloud droplets often leads to a delayed SCT. On the other hand, this is counteracted by the associated increase in entrainment, which benefits the transition. This raises the question of the mechanism of this interaction and the overall strength of microphysical effects. 
Here we present the evaluation of ICON LES and the characterisation of nine selected transitions from the MAGIC campaign, including the well analysed Leg15A.