PNNL

The Science                                 

The land surface plays a crucial role in regulating the water and energy cycles in the lower atmosphere. The land component of Earth system models can represent a variety of landform types and their respective status in a single grid cell. However, the model only communicates the grid mean with the overlying atmosphere. This neglects the land surface diversity within grid cells in land-atmosphere interactions. A new study reveals that including land diversity in land-atmosphere interactions changes the heat and moisture transport in the lower atmosphere and increases low-level clouds.

The Impact

This research offers an initial assessment of representing land surface diversity in the land-atmosphere interactions of a state-of-the-art Earth system model. The results show that a new mathematical representation, or parameterization, improves the mechanistic understanding of atmospheric responses to complex land surface conditions. Since clouds play an essential role in the climate system, the significant impact of this parameterization on the low-level clouds highlights the importance of better representing diverse landform types in land-atmosphere interactions in next-generation Earth system models.

Summary

Researchers implemented a new parameterization into the Energy Exascale Earth System Model (E3SM) to better represent land surface heterogeneity at a subgrid scale. They performed two single-column model simulations over the Atmospheric Radiation Measurement Southern Great Plains site during the summer. The comparison between the new treatment and default model representation showed that under the new treatment, the land surface demonstrates considerably more subgrid variability in temperature and humidity. This discrepancy can extend through half of the atmospheric boundary layer, affecting the turbulent transport of heat and moisture. As land surface diversity increases, so does the amount of shallow clouds. These results emphasize the importance of correctly representing land surface conditions and their interaction with the atmosphere in next-generation Earth system models.

This research used resources of the National Energy Research Scientific Computing Center, a Department of Energy Office of Science User Facility.

PNNL Contact

Po-Lun Ma, Pacific Northwest National Laboratory, po-lun.ma@pnnl.gov

Funding

This research is supported by the Coupling Land Atmosphere Subgrid Parameterizations (CLASP) project, funded by the Department of Energy, Office of Science, Biological and Environmental Research program, Earth System Model Development program area, as part of the Climate Process Team CLASP project.