Cloud-resolving model simulations of multiply-banded frontal clouds

An idealized two-dimensional cloud-resolving model is used to investigate the formation and temporal evolution of multiply-banded clouds in frontal zones. Radar observations often show both upright and slantwise convection in the circulations associated with such bands. The aim is to examine the interaction between upright and slantwise convection and to determine the mechanisms leading to multiple banding. A warm bubble is used to initiate convection in the frontal zone, which has an initial thermodynamic profile based on observations. Further triggering occurs and banded clouds evolve. The initially upright plumes become tilted due to the so-called AM adjustment process (upscale development). Observed multiple bands in frontal zones are frequently attributed to the release of conditional symmetric instability (CSI). However, in these simulations, there is no evidence of the release of CSI despite the fragmentation of slantwise bands into multiple layers in the mid-troposphere. Successive triggering of upright convection is instead associated with a spreading cold pool driven by evaporative cooling in the slanted downdraughts. Triggering can occur on both the warm- and cold-air sides of the frontal zone, and is sensitive to the microphysical parametrization used.