Improving Understanding of the Role of Anthropogenically-generated Sulfate in Convective Cloud and Precipitation Processes Using Observations and Multiscale Modeling

Understanding daily-to-weekly variability in local weather impacts (e.g., floods, severe storms, hurricanes, heat waves, fires) as well as monthly-to-interannual earth climate system variability, is key to development and implementation of climate adaptation strategies that are a high priority within NOAA. Central to improving understanding of ECS variability is improving our understanding of cloud systems, particularly how changes in aerosol composition and concentration affect cloud properties at all scales from global- to cloud-scale.

While first principle approaches to predicting cloud droplet number concentration based on the aerosol size distribution are being incorporated into atmospheric models at various scales, the crossing of disciplinary boundaries is needed in order to obtain a more complete understanding and ability to simulate. Interdisciplinary research in the early stages at the University of North Dakota (UND) has the potential to make substantial advances to our knowledge of aerosol-cloud-trace gas-climate interactions, particularly on the regional scales for which our knowledge is most lacking. Specifically, work in nanoscale computational chemistry, chemical engineering, aerosol-cloud microphysical interactions, parameterization of cloud processes, convective transport, and regional numerical weather/climate prediction is at a stage where a synergistic focus of resources and effort can yield substantive advance to the current state of knowledge.

In this poster presentation, we present an overview of the planned interdisciplinary efforts involving multiscale modeling from the nanoscale to the regional scale. The methodologies that will be used in the realm of computational chemistry (with respect to the nucleation process), cloud microphysics and storm-scale simulation are discussed. Further, preliminary results will be shown from a pilot effort to use aircraft observations to define a new functional formulation for cloud condensation nuclei based on a modal representation for sulfate aerosols generated by a coal-fired power plant in western North Dakota. In such a modal representation, the aerosol size distribution is specified as a series of log-normal distributed modes, with each mode characterized by aerosol number concentration as well as geometric mean diameter and standard deviation. The new functional formulation will be incorporated into the Weather Research and Forecasting (WRF) model double-moment microphysics schemes (WDM5). Results from test WRF simulations of a weakly forced convective event with the modified WDM5 scheme will be compared with a control simulation utilizing the standard WDM5 scheme. We anticipate that the comparison will provide give an indication of how sulfate aerosols can affect the resulting precipitation amount for weak convective events, which have less notoriety but occur at greater frequency than severe weather events.