There is a new paper that examines the role of aerosols on thunderstorms (h/t to Dev Niyogi of Purdue). Aerosols, of course, have both natural and human sources. The latter include vehicular and industrial emissions, as well as from biomass burning and blowing dust from landscape degradation.
The paper is
Storer, Rachel L., Susan C. van den Heever, Graeme L. Stephens, 2010: Modeling Aerosol Impacts on Convective Storms in Different Environments. J. Atmos. Sci., 67, 3904–3915. doi: 10.1175/2010JAS3363.1
The abstract reads
“Aerosols are known to have both direct and indirect effects on clouds through their role as cloud condensation nuclei. This study examines the effects of differing aerosol concentrations on convective storms developing under different environments. The Regional Atmospheric Modeling System (RAMS), a cloud-resolving model with sophisticated microphysical and aerosol parameterization schemes, was used to achieve the goals of this study. A sounding that would produce deep convection was chosen and consistently modified to obtain a variety of [Convective Available Potential Energy] CAPE values. Additionally, the model was initiated with varying concentrations of aerosols that were available to act as cloud condensation nuclei. Each model run produced long-lived convective storms with similar storm development, but they differed slightly based on the initial conditions. Runs with higher initial CAPE values produced the strongest storms overall, with stronger updrafts and larger amounts of accumulated surface precipitation. Simulations initiated with larger concentrations of aerosols developed similar storm structures but showed some distinctive dynamical and microphysical changes because of aerosol indirect effects. Many of the changes seen because of varying aerosol concentrations were of either the same order or larger magnitude than those brought about by changing the convective environment.”
An excerpt from the conclusions reads
The results presented here have shown that differences both in the initial CAPE and in the available aerosol concentration will lead to important changes in both microphysical and dynamic properties of convective storms. The relative importance of these differences is something that has not previously been examined. For the range of CAPE (491–2828 J kg**-1) and aerosol concentrations (100–6400 [per] cm**3) examined here, the total precipitation produced by the storms is primarily driven by CAPE, but an increase in the concentration of available aerosols from 100 to 6400 [per] cm**3 leads to a decrease in total precipitation amount by 30%–40% (if considering only a 400% change in aerosol concentration to better compare with the range in CAPE, the decrease is still ~15%).
Since, for example, other climate forcings and feedbacks, such as landscape change and the effects variability and long-term change of atmospheric circulation features, alters both CAPE and aerosol composition, this is yet another complex interaction among the components of the climate system. To claim prediction skill for clouds and precipitation decades into the future fails to account for the actual real world difficulty in skillfully simulating these complex interactions as well as how they will change in the future.
Climate Science: Roger Pielke Sr. 