Development of a Coupled Mechanistic Model to Examine Aerosol Migration in the Atmosphere, 20-R8182
Principal Investigators
Todd Mintz
Debashis Basu
Kaushik Das
Marla Roberts
Michael Muller
Tim Michaels
Inclusive Dates: 10/01/10 – 10/01/11
Background — Aerosols, which are suspensions of solid or liquid particles in the atmosphere, affect Earth's climate directly by scattering and absorbing radiation, particularly by scattering incoming shortwave radiation back to space. In addition, aerosols indirectly affect Earth's climate by modifying the microphysical and radiative properties of clouds. The resulting effect of aerosols is to cool the atmosphere. Accurate estimates of the indirect radiative effects require an understanding of the role of aerosols in influencing cloud properties. This is considered one of the most uncertain aspects of current global climate models. Sea-salt aerosol emission, migration and removal also are affected by atmosphere and ocean properties. Interaction between the ocean and the atmosphere plays a crucial role in the atmosphere-ocean momentum flux exchange and heat and mass exchange. The interaction, particularly the exchange of heat, momentum and moisture between the atmosphere and the ocean, controls atmospheric phenomena such as cyclones and hurricanes. Proper understanding of the coupling among the atmosphere and ocean is essential for predicting large-scale circulation of the ocean and the atmosphere and the role circulation plays in atmospheric and oceanic transfer of momentum, heat and mass. The present work aims at developing an efficient computational tool for more accurate estimations of sea-salt aerosol effect on cloud formation by coupling ocean and atmospheric models. The efficiency of the developed computational tool is achieved through the coupling and also by modeling the effects of scattering, radiation and nucleation on cloud formation.
Approach — The project encompasses two major tasks. The first involves developing a coupled atmosphere and ocean model. At each time step, the individual models will calculate the environmental parameters and then pass this information to the other model to be used as boundary conditions. The second task will evaluate the coupled model against the uncoupled model. This will be accomplished by comparing cloud formation in the coupled model to cloud formation in the uncoupled model over the Gulf of Mexico region. The two models will be compared with actual cloud formation using satellite imagery, which can be obtained from either the National Oceanic and Atmospheric Administration Geostationary Satellite Server or the National Aeronautics and Space Administration Moderate Resolution Imaging Spectroradiometer instruments. Comparisons will include area coverage and cloud patterns. In addition to examining the fully coupled model, sensitivity analyses will evaluate the influence of coupled boundary conditions on aerosol effect and subsequent cloud formation. This will be accomplished by only coupling certain boundary conditions for a given simulation and observing the resulting outcome.
Accomplishments — SwRI researchers have successfully simulated several cases with weather research and forecasting chemistry model (WRF-CHEM) and hybrid coordinate ocean model (HYCOM) in the system. The results have been analyzed and post-processed with National Center for Atmospheric Research Command language (NCL) post-processing software. Simulations with WRF-CHEM tested the nested grid capability. Initial simulations used a coarse grid; subsequently, the nested grid was used. The domain was chosen for the central gulf coast region. This region will be used in subsequent simulations, because observational data and prior computational data for atmospheric aerosol distributions are available. Simulations using HYCOM have also been carried out. The project team has implemented the Earth System Modeling Framework (ESMF) software to couple WRF-CHEM and HYCOM. The plan is to use the ESMF superstructure and associated coupling mechanism. Work is under way to formulate how to include the effect of nucleation on aerosol and cloud formation.
