As part of the Climate Process Team (CPT) project, “Coupling of Land and Atmospheric Subgrid Parameterizations (CLASP)” (Lead PI: Nathaniel Chaney at Duke University; See www.clasp.earth), the main objective of this project is to develop improved parameterization for the heterogeneous subgrid exchange between the land and atmosphere in the U.S. Department of Energy’s Energy Exascale Earth System Model (E3SM) and to characterize its implications for surface climate, variability, and extremes.

The complexity of spatial patterns overland across a range of scales plays a key role in convection, mesoscale circulations, hydrologic extremes, biodiversity, and ecosystem resilience. For this reason, a recurring emphasis on representing its role in climate and earth system models (ESMs) has led to significant advances in the representation of subgrid land heterogeneity over the last few decades. However, these advances have not been met with complementary advances in modeling the communication of land heterogeneous states to the planetary boundary layer (PBL). This leads to model deficiencies, including:

1. a limited influence of land models within contemporary subgrid turbulence/convection schemes;
2. deficient subgrid redistribution of key land surface states;
3. challenges when evaluating modeled surface fluxes using observations; and
4. unrealistic model feedbacks between the PBL and the heterogeneous land.

To address these deficiencies in E3SM, we will implement improved treatment to account for the effects of surface heterogeneity on atmospheric turbulence characteristics. The newly developed parameterization will be evaluated and constrained using large-eddy simulations (LES) and observations of surface fluxes and other relevant variables. The impacts of surface heterogeneity on the climate will be assessed.

The parameterization development, evaluation, and analysis will leverage advances in the representation of subgrid heterogeneity in other ESMs in the CLASP project, including NCAR’s Community Earth System Model version 2 (CESM2), GFDL’s Climate Model version 4 (CM4), and GMAO’s Goddard Earth Observing System Model (GEOS). The CPT combines experimentalists, process modelers and diagnosticians, theoreticians, and model developers, aiming to improve modeling of the land/atmosphere interface and thus advance our understanding of the earth system and to use this knowledge to improve the resilience of our nation.