Causes of Differences in Depiction of Convective Lines in 1-km and 3-km CM1 Simulations

Abstract Previous research has shown that 3-km horizontal grid spacing simulations depicting clusters of cells often change to showing linear structures when grid spacing is refined to 1 km. This increase in linear structures at finer horizontal grid spacings may be due simply to the resolving of stronger vertical motion along the leading edge of the MCS cold pool resulting in more continuous zones of convection in higher-resolution runs. However, prior work has suggested that the cold pools themselves are stronger with finer grid spacing, enhancing lift to grow linear morphologies faster. In the present study, Cloud Model 1 was used to simulate an array of MCSs with varying wind profiles and a constant thermodynamic profile (Weisman–Klemp analytic sounding) at both 1- and 3-km horizontal grid spacings and with 50 and 100 vertical levels. A line of seven randomly spaced warm bubbles was used to initiate convection. In 1-km Δ x simulations, gravity waves dominated in initiating new convection for growth into lines, and the ascent associated with them was much greater than in 3-km runs. Upscale growth into lines in 3-km Δ x simulations was driven more by ascent caused by the collision of convective cold pools.