Radiative-dynamical feedbacks in low liquid water path stratiform clouds

When stratiform-cloud-integrated radiative flux divergence (heating) is dependent on liquid water path (LWP) and droplet concentration N _d, feedbacks between cloud dynamics and this heating can exist. These feedbacks can be particularly strong for low LWP stratiform clouds, in which cloud-integrated longwave cooling is sensitive to LWP and N _d. Large-eddy simulations reveal that these radiative-dynamical feedbacks can substantially modify low LWP stratiform cloud evolution when N _d is perturbed. At night, more rapid initial evaporation of the cloud layer occurs when N _d is high, leading to more cloud breaks and lower LWP values that both result in less total cloud longwave cooling. Weakened circulations result from this reduced longwave cooling and entrainment drying is able to counteract cloud growth. When N _d is low, the cloud layer is better maintained because cloud longwave cooling is still relatively strong. During the day, the addition of shortwave warming leads to reduced LWP for all values of N _d and, consequently, further reduced longwave cooling and weakened circulations. For high N _d, these reductions are such that the cloud layer cannot be maintained. For lower N _d, the reductions are smaller and the cloud layer thins but does not dissipate. These results suggest that low LWP cloud layers are more tenuous when N _d is high and are more prone to dissipating during the day. Comparison with other studies suggests the modeled low LWPcloud response may be sensitive to the initial thermodynamic profile and model configuration.