Modeling Cloud Responses to Global Atmospheric Circuit Variability

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Prior work has shown consistent correlations between changes in atmospheric circulation and current flow in the global atmospheric electric circuit. The current in this circuit is modulated by external factors, such as variations in the solar wind, and internal factors, such as the variation of ionospheric electrical potential due to variation in occurrence of thunderstorms and other highly electrified cloud generators. The nature of these correlations eliminates several proposed sun- earth weather links, and requires a mechanism that also explains atmospheric responses to global circuit changes due to internal processes. The proposed mechanism is that changes in cloud processes are produced by the effect of varying electrical charge in the atmosphere on rates of aerosol scavenging processes in liquid water and ice clouds. Variations in this electrical space charge are associated with variations in the vertical current density of the global circuit.This project will extend previously published models describing this ion-cloud interaction. It will result in creation of a comprehensive data base of collision rate coefficients for scavenging of aerosol particles by cloud droplets and ice particles. The outcome will be improved parameterization of electrical effects on aerosol scavenging that will be suitable for introduction into a range of cloud and atmospheric circulation models. Once incorporated into these models, these parameterizations will improve quantitative treatment of electrical effects on precipitation, atmospheric radiation balance, and other aspects of atmospheric behavior in which clouds are involved. This project also will enhance an existing model of the global atmospheric electric circuit by better accounting for the resistive effects of clouds in the total ionosphere-earth column resistance. Better treatment of processes responsible for charging of layer clouds will be developed that include the effects of turbulence in distributing the charge within the cloud, and better describe of charge exchange between droplets, aerosol particles, and ions. The global variation of cloud responses to changes in cosmic ray flux will be evaluated using this global circuit model. Model results will be compared with available observations and laboratory work.The broader impact of the work includes improved understanding of the role of scavenging and processing of aerosol particles in clouds. Electrical effects on scavenging are not a part of present cloud models. Electrical processes are likely to be responsible for some of the present lack of agreement between models and observations, especially for primary ice nucleation in clouds. Better treatment of these processes will lead to improvements in forecasting weather, and to better understanding of weather and climate changes due to human aerosol production and due to changing solar activity inputs. The project includes the training of graduate students in computer modeling techniques. The subject of human and solar influences on climate is of wide community interest, and project scientists will continue educating University of Texas-Dallas students and faculty, the community, and the media on this topic.