Effects of Increased Horizontal and Vertical Grid Spacing on Mixing in a Simulated Continental Squall Line

English Abstract:

The sensitivity of an idealized squall line to horizontal (and vertical) grid spacing is investigated using a new approach. Simulations are first performed at a modest horizontal resolution. Once the storm reaches a quasi-steady state, model output is interpolated to a higher resolution domain and the model is restarted using the interpolated state. This framework allows for investigating both the response and sensitivity of the simulated squall line to horizontal grid spacing (Δ). The results demonstrate that there are two resolution-dependent regimes; the transition between regimes occurs for Δ between 250 and 500 m. This transition is found to be independent of the vertical resolution. Mixing in the context of varying resolution is also investigated via passive tracers that are initialized 1 hr after restarting the simulations at higher resolution. The state of the tracer field at the end of the simulations reveals that entrainment and detrainment at mid-levels are suppressed in the simulations with Δ ≥ 500 m. For smaller Δ, entrainment and detrainment at mid levels become substantially more important, limiting the flux of low-level tracer to the upper-troposphere, which has important implications for modeling studies of atmospheric transport from the boundary layer to the free-troposphere.