ACOM Modeling (MODELING)

ACOM’s atmospheric chemistry modeling activities span the whole extent of the atmosphere from the troposphere up to the mesosphere and cover timescales from minutes to decades. The ACOM Lab works on simulating and predicting the chemical processes and interactions within the atmosphere, the impacts of these processes on climate, weather, and air quality, and the influence of human and natural emissions. Together with the community ACOM has been developing, supporting and using a wide variety of community models to cover the different spatial and temporal scales:

For regional to local applications the main modeling system has been the Weather Research and Forecast model with Chemistry (WRF-Chem), which simulates the emissions, transport, mixing, and chemical transformation of trace gases and aerosols simultaneously with the meteorology. WRF-Chem also can be run in Large Eddy Simulation (LES) mode, enabling chemistry simulations at turbulence resolved scales.

For global and large-scale atmospheric composition applications as well as chemistry-climate research, the main modeling systems are the Community Atmosphere Model with Chemistry (CAM-chem) and the Whole Atmosphere Community Climate Model (WACCM), both part of NSF NCAR’s Community Earth System Model (CESM). They enable simulating emission, transport, mixing, and chemical transformation of trace gases and aerosols within a fully coupled Earth System Model. CAM-Chem is considered the low-to-mid top model for applications spanning the troposphere and lower stratosphere, whereas the high-top WACCM allows simulating processes from the surface up to the lower thermosphere.  Due to its higher model top, WACCM is the only model that fully resolves the middle stratospheric dynamics. A special version of WACCM, WACCM-X extends to the upper thermosphere and includes processes important to the ionosphere.

Gas phase chemistry is represented in WRF-Chem, CAM-chem and WACCM by the family of MOZART chemical mechanisms, which includes hundreds of reactions describing chemical reactions covering the troposphere, stratosphere, mesosphere, and lower thermosphere. For representing photolysis rates in the models, ACOM has been developing the Tropospheric Ultraviolet Radiation model (TUV-x). Detailed chemistry studies using the explicit gas-phase chemical mechanism generator GECKO-A aid in the development of chemical mechanisms.

A major new initiative that ACOM together with the atmospheric chemistry community has been undertaking is the development of a new community modeling infrastructure: The Multi-Scale Infrastructure for Chemistry and Aerosols (MUSICA). MUSICA is moving atmospheric chemistry modeling towards a unification of the range of scales inherent in the Earth System, allowing for the exploration of the couplings across space, time and ecosystems in a consistent manner. It will offer a modular model architecture and will provide flexibility for users to adapt the modeling framework for their own needs. MUSICA design will be model-independent and can be connected to any atmosphere model, or to any single column or 0-D box model (e.g. MusicBox).

In order to facilitate model evaluation, ACOM together with NOAA is developing the python-based modular community framework MELODIES MONET which allows users to compare atmospheric chemistry model output with observations from a variety of platforms including surface monitors, satellite observations, and aircraft campaigns.

NSF NCAR Atmospheric Chemistry Transport and Process Models and Example Applications