Sensitivity of aerosol-induced effects on numerically simulated squall lines to the vertical distribution of aerosols
Numerical simulations of idealized squall lines are performed to specifically analyze the sensitivity of the aforementioned effects to the vertical distribution of aerosols. The simulations suggest that low-level air tends to either be detrained at the bottom of the convective cores or remains in the convective cores throughout the troposphere and is then detrained in the anvil region of the cloud. This should come as no surprise since the maximum updraft velocity occurs between 8 and 10 km above ground level, thus suggesting that air parcels are accelerating through the mid levels, entraining mid-level environmental air in and around the mixed-phase region of the cloud. As a result, not only is it shown that an increase in low-level aerosols has little to no effect on latent heating rates, but also on the bulk cloud properties as well. In other words, the effects on supercooled liquid water (and the subsequent effects on graupel formation and rain drop production) are minimal. Thus additionally, no effects are observed on cold pool dynamics. This does however elude to the potential for mid-level aerosols to be entrained into the convective cores and, in the case of an increase in these aerosols, promote enhanced convection, increased supercooled liquid water and graupel formation, and ultimately a reduction in rain water but an increase in size that acts to reduce cold pool intensity. These effects are analyzed in the context of RKW theory to demonstrate that the effect on the storm as a whole is to produce a more optimal line. This key result suggests that low-level local pollution sources have little effect on squall line dynamics and instead, mid-level distant pollution sources can have an appreciable effect on the storm strength and precipitation.