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

It is known from previous research that differences exist in model simulations of convective mode as horizontal grid spacing is refined from 3-km to 1-km. It is of particular interest as to why 3-km model simulations depicting clusters of cells tend to adopt a more linear structure in 1-km simulations. One theory is that this increase in linear structures at finer horizontal grid spacings is due to stronger vertical motion along the leading edge of the MCS, while other theories hold that stronger cold pools play a more dominant role in the development of linear morphologies. To explore this further, CM1 was used to simulate an array of MCSs with varying wind profiles (no-wind, RKW u-wind, Weisman-Klemp Multicell u-wind) while holding the thermodynamic profile constant (Weisman-Klemp analytic sounding). Simulated composite reflectivity was used half-hourly to classify storms into one of nine modes: isolated cells, clustered cells, broken line, non-stratiform line, trailing-stratiform line, parallel-stratiform line, leading-stratiform line, bow echo, or non-linear. After categorization, updrafts that exceeded 10.5m/s (roughly the 95^th percentile and similar to the threshold used in Squitieri and Gallus 2022) were analyzed (counts, areas, intensities) and compared at each horizontal grid spacing and vertical level configuration. Analysis of parameters such as surface potential temperature and 10-m surface wind speed was performed at various segments of each MCS to uncover potential differences accounting for the discrepancies in morphologies at varying horizontal grid spacings. Preliminary results suggest that the change from 3-km to 1-km is more impactful on the number, cumulative area, and intensity of updrafts than the change in vertical spacing. Wind shear also appears to influence the results. The multi-bubble runs with stronger shear most clearly support the hypothesis that finer grid spacing in both the horizontal and vertical resolves stronger updrafts that may account for a more rapid organization into lines of convection.