Inadvertent Weather Modification Resulting From Anthropogenic Emissions and Photochemistry

The emissions of gases and particles from human activities results in atmospheric particulate matter concentrations higher than would occur in the natural environment. These particles affect the weather, through several mechanisms. The particles directly alter the radiative balance of the atmosphere through scattering and/or absorbing incident light from the sun (aerosol direct effect). Particles may also act as cloud condensation nuclei – depending on their composition, the particles provide sites for water condensation, hence cloud droplet growth. The aerosols may thus affect the radiative balance, through altering the location and radiative properties of clouds (aerosol indirect effect).

Both the aerosol direct and indirect effect have been known to be of importance on the climatological time scales, and for this reason, parameterizations for these effects are included into climate models. On shorter synoptic time scales, and on the local scale, these aerosol effects may also be responsible for inadvertent weather modification. In this work, a 2.5 km horizontal resolution fully coupled air-quality model (GEM-MACH) was used to investigate the impacts of feedbacks between chemically created aerosols and weather. The potential for inadvertent weather modification was investigated through the comparison between simulations in which the model-generated aerosols were used to modify the aerosol direct and indirect effect, to simulations in which simplified climatological parameterizations were used. The domain chosen includes a region of urban and industrial emissions in Canada.

The model results show that the local emissions and chemistry may modify local weather, particularly in regions where the emissions are large, with modifications to short wave radiation reaching the surface, surface temperatures, surface pressures, precipitation and cloud water variables. The feedbacks between the chemically created particles and weather also modify the dispersion and transport of the chemical species. The impact of these simulation differences relative to observations will be discussed.