Friday, 11 July 2014: 11:45 AM
Essex Center/South (Westin Copley Place)
Aerosol as a short-lived climate forcer has large spatio-temporal variability. The climate impact of aerosol can be rapidly communicated to the human-earth system through changing regional energy budget and water cycle. The vertical distribution of aerosols is also important. It affects the interactions with liquid and/or ice clouds. For light-absorbing aerosols like black carbon, the vertical distribution also influences local radiative heating profile and, consequently, the thermodynamic structure and circulation. Thus it is necessary to have accurate global three-dimensional distributions of aerosols to fully assess their radiative and microphysical impacts in climate models. However, many global aerosol-climate models have large biases in the prediction of aerosol distributions, particularly over remote regions. Aerosol wet scavenging processes (i.e., aerosol activation, cloud processing, re-suspension and removal, etc.), which affect aerosol residence time, spatial distribution, and impact on clouds/precipitation in the atmosphere as well as deposition onto the snow/ice surface, remain key sources of uncertainty in global aerosol-climate models. With increasing computational power, climate models have been achieving higher resolution but have not yet reached global cloud-resolving resolution. The representation of the coupled aerosol-cloud-radiation system, including these wet scavenging processes, in climate models still relies on parameterization schemes that use a variety of assumptions to relate subgrid-scale quantities to grid-scale variables. We recently found that the representation of in-cloud wet scavenging plays a key role in determining the amount of aerosols transported from sources to remote regions and the consequent impact on clouds in a global climate model (the Community Atmosphere Model version 5). Our improvements to the model give better agreement with observations of aerosols and clouds. Uncertainty in the treatment of wet scavenging processes in coarse-resolution climate models and the impact on global aerosol spatial distributions and climatic effects will be discussed. We also explore how the wet scavenging processes in warm and mixed-phase clouds, respectively, affect the horizontal and vertical distribution of aerosols in shallow boundary layer as well as in deep convective systems using cloud-resolving model simulations. Preliminary analysis of the simulations shows that the interactions between ice particles and supercooled liquid droplets in mixed-phase clouds induce an additional level of complexity to the wet scavenging and aerosol effects. We will perform in-depth analysis of the fine-resolution modeling results to provide new insights for representing wet scavenging processes in climate models.
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