Response of Arctic Mixed-phase Clouds to Upper Layer Clouds

Description

Multilayered, mixed-phase clouds are frequently present in the Arctic atmosphere. The upper cloud layers can impact the lower clouds by precipitating ice particles into them and reducing their cloud-top radiative cooling rate. The Large-Eddy Simulation (LES) version of the Regional Atmospheric Modeling System (RAMS) is used to study the response of the lower cloud layers to the perturbations introduced by the upper layer clouds through the aforementioned mechanisms. The results show that both ice precipitation and downwelling longwave radiation from the upper layer clouds contribute to the dissipation of the lower cloud layers. As the liquid in the lower cloud deck is reduced, differential heating between the region directly perturbed by the upper level cloud and the adjacent region generates a circulation in the cloud-topped boundary layer and dissipates the low-level liquid cloud beyond the directly perturbed region. A broad updraft forms in the gap formed after the dissipation of the low-level liquid cloud, which can lead to the reformation of a liquid cloud in the center of the gap, the results of which is to reduce the magnitude of the differential heating, and limit the significance of this response. However, even with this reformation, the warm air in the gap lowers the cloud top height and reduce the liquid water path of nearby clouds and potentially change their radiative effects.