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: 10/01/11 – 03/01/12
Background — The interaction of Earth's atmosphere with its geosphere through the planetary boundary layer (PBL) (i.e., land/inland water and ocean) via exchanges of energy and mass is a major driver of atmospheric phenomena and thus climate. Interaction between the ocean and the atmosphere, particularly the exchange of mass (moisture), momentum, and energy (heat) between the atmosphere and the ocean, controls atmospheric phenomena such as cyclones and hurricanes. Proper understanding of the coupling between the atmosphere and ocean is essential for accurately predicting hurricane wind intensity, trajectory, and likely landfall. As air flows over the ocean, wind stress generates surface gravity waves and drives local ocean currents and large-scale circulation. Analysis of smaller ocean mesoscale features suggests that the ocean mainly affects the atmosphere through heat exchange. Because of the importance of these two-way couplings, a fully coupled atmosphere-ocean model is necessary for accurate analysis of atmospheric phenomena.
Approach — A coupled atmosphere-ocean model has been developed using the Earth System Modeling Framework (ESMF), a general purpose software that facilitates coupling earth system modeling codes such as WRF (Weather Research and Forecasting) and HYCOM (HYbrid Coordinate Ocean Model). This coupled atmosphere-ocean model is created using the weather prediction model, Weather Research and Forecasting-CHEM (WRF-CHEM) and HYCOM. The coupled model is a flexible and efficient software framework designed to facilitate developing multicomponent Earth science modeling applications. Coupling is based on conservation of mass, momentum, and energy at the air-sea interface. The sea surface temperature (SST) is computed in the HYCOM model and passed to WRF-CHEM. SST is the primary controlling parameter that is passed from HYCOM to WRF-CHEM.
Accomplishments — A computational framework was established to carry out simulations of ocean and atmosphere dynamics. The computational framework can be used in subsequent projects to develop an atmosphere-ocean-wave model by including wave simulation software. The model also can be extended to investigate the effects of atmosphere dynamics on aerosol generation, aerosol transport, and cloud formation. Simulation of Hurricane Rita, demonstrated the importance of coupling the atmospheric and ocean model for intensity forecasts of hurricanes. The project also developed the ESMF-based computational platform necessary for simulating atmospheric dynamics and processes. The predicted intensity of Hurricane Rita was compared with the observed data. Simulations suggest that the storm intensity changes as a direct consequence of variations in the heat flux across the ocean-atmosphere interface. This showed that the coupling between WRF-CHEM and HYCOM correctly predicted the physics of the hurricane. Significant experience was gained using atmospheric modeling tools developed by the National Oceanic and Atmospheric Administration (NOAA), as well as with the ESMF computing platform and several NOAA-developed post-processing codes. This experience positions the staff to secure external projects from federal agencies, such as NOAA, National Science Foundation, and National Aeronautics and Space Administration. Two journal papers are being prepared for publication in the near future.
