Impacts of moisture profile on the evolution and organization of midlatitude squall lines under various shear conditions

The interaction between surface cold-air pool and ambient vertical wind shear is commonly recognized as an important mechanism for the development and organization of squall lines, and has been extensively investigated for decades. In addition to the cold pool-vertical shear interaction, the static stability is expected to significantly affect the organization modes of mesoscale convective systems. This study explores the impacts of tropospheric moisture profiles (which have close ties with the stability) in various shear environments on the structure, evolution, and organization of midlatitude squall lines. For this purpose, we have performed an extensive set of cloud-resolving simulations in conditions of a wide spectrum of moisture and shear profiles. The main conclusions from our experiments are: (1) As the boundary layer becomes drier, the interaction between the squall-line cold pool and low-level ambient shear is more critical to the development of strong convection; (2) In moister conditions, a stronger shear is favorable for stronger convective systems in terms of precipitation intensity so long as the shear layer is below 5 km; (3) A moister condition in the boundary layer is more favorable for the squall-line strength than a moister condition above the boundary layer, as long as available column moisture content is almost the same; (4) The ratio of cold-pool strength and shear presented by Rotunno et al. well predicts the strength of squall lines in a wide range of moisture conditions, especially in drier environments; (5) The amount of precipitable water vapor content as well as CAPE regulates the strength and organization of squall lines. (c) 2006 Elsevier B.V. All rights reserved.