Land Surface Effects on Shear Balance of Squall Lines

We explore whether and how the land characteristics, especially surface drag, affect the squall line, in an idealized modeling framework. We find that the balance between the ambient low-level shear and cold-pool-induced shear in the squall line can be modified by surface drag: it not only changes the ambient shear if near-surface environmental wind is nonzero, but also reduces the cold-pool-induced shear by both weakening the low-level wind and deepening the cold pool. The land surface impact on squall lines is larger with lower convective available potential energy (CAPE), partly because of stronger convection with higher CAPE. The cold pool intensity (vertically integrated negative buoyancy) could not explain the reduced cold pool shear induced by the land. Furthermore, land characteristics-such as roughness lengths-help maintain the shear balance and potentially make the squall line long-lived, suggesting that they be included in convective (or cold pool) parameterizations to improve climate and Earth system models.