The Impacts of Elevated Aerosol Layers on the Dynamics and Microphysical Characteristics of Deep Convective Storms

Variations in the altitude of aerosol layers influencing deep convective storms may impact the storm dynamics and microphysics through a number of different processes. These include the following: (1) the absorption of radiation by elevated aerosol layers may produce significant local enhancements in atmospheric stability that might influence the initial convective development, as well as secondary convection spawned by the cold pool; and (2) the vertical location of an aerosol layer may have substantial impacts on the amount of aerosol ingested by the storm, with subsequent implications for aerosol indirect effects. For example, while very high number concentrations of aerosol may be located several kilometers above cloud base, aerosol number concentrations within the storm system will be highly dependent on the location and rate of entrainment of aerosol at cloud base and the lateral edges of the updraft. Therefore, the goal of the research to be presented here has been to quantify the impacts of such elevated layers on the storm strength and surface precipitation through their modulation of aerosol ingestion and their production of local stable layers.

This goal has been achieved through the use of high-resolution, idealized numerical simulations of convection conducted using the Regional Atmospheric Modeling System (RAMS). Convection was initiated through the use of a warm, thermal perturbation, and a relatively clean, homogeneous aerosol background was utilized in the control simulation. A number of sensitivity tests were then conducted in which the location and concentrations of aerosols were varied, including (1) a linearly decreasing profile of aerosol concentrations starting with 400/cc at the surface; and (2) three simulations in which enhanced aerosol concentrations were located from 0-2km, 2-5km and 5-8km. The aerosol number concentration was varied within each of these three layers in order to ensure that the optical depth was the same as that in the linearly decreasing case. The aerosol within the simulations may serve as cloud condensation nuclei and/or ice nuclei based on the prognosed environmental conditions, and fully interacts with the radiation scheme. The impacts of such elevated layers on the development, characteristics and surface precipitation of the evolving deep convection has been analyzed through the use of microphysical process budgets, aerosol tracking and trajectory analysis, and will be presented.