ACME is a modeling project launched by DOE in July 2014 to advance a set of science questions for the near-term time horizon (1970-2050). Over 100 researchers are involved in ACME model development, with most of them from eight DOE Laboratories. While there are many scientists working on an individual component (e.g., the atmosphere) of an Earth system model (such as ACME), there are far fewer scientists working on the (land-atmosphere, ocean-atmosphere, land-ocean, and snow-sea ice) interface processes partly due to our traditional disciplinary education. For ACME, two critical knowledge gaps and challenges are: (a) what are the major deficiencies of the (land-atmosphere, ocean-atmosphere, land-ocean, and snow-sea ice) interface processes in ACME? and (b) how can we improve the treatment of these deficiencies in ACME?

Our objectives are to address the first overarching question using a variety of DOE and other datasets, and to address the second overarching question based on our extensive experiences in interface processes in other global and regional models. We will address the above objectives through four tasks. Code tests, model evaluations, and uncertainty quantifications will be integrated parts of each task.

Task 1 (land-atmosphere coupling): ACME intends to run the atmosphere and land models on different grids, including up to 12 elevation classes per atmospheric grid box,  up to 4 topographic units per land grid box (based on watersheds), and dynamic topography over land ice sheets. However, such a land-atmosphere coupling approach presents two technical challenges and hence has not been implemented in ACME. We will use an innovative method (that conserves quantities through the flux coupler precisely) to address the two challenges and implement and test this coupling approach in ACME.  

Task 2 (ocean-atmosphere coupling): Both ocean skin temperature and surface turbulent fluxes are important parts of the ocean-atmosphere interactions. To improve this coupling, we will implement and test a physically-based prognostic skin temperature scheme in ACME. We will also revise the bulk algorithm for computing ocean surface turbulent fluxes in ACME under stable and weak wind conditions.

Task 3 (land-ocean coupling): The only interaction between the land and ocean components of ACME is one-way through the river network (and ocean water, even with sea level rise, cannot flow into the land model). We will improve the river transport model, and then couple it with the ACME ocean model to allow for a two-way exchange of water between the ACME land and ocean components.

Task 4 (snow-sea ice coupling): While much work has been devoted to including an accurate representation of other processes (e.g., melt ponds) into sea ice models, snow complexity is not yet widely represented in sea ice. We will implement and test a new snow density model into the ACME sea ice model.

The final deliverables include: (a) a better understanding of interface processes in ACME; and (b) improved treatments of interface processes for implementation in ACME. This project will directly address “Component coupling” – one of the six focus areas of this FOA. It will also directly address the goal “Synthesize new process knowledge and innovative computational methods, advancing next-generation, integrated models of the human-Earth system” of the DOE Earth and Environmental Systems Sciences Division (EESSD). Through this project, we hope to become the go-to team on scientific issues of the atmosphere-land-ocean-ice interface processes in ACME. We will also adjust our effort level in individual tasks following our interactions with ACME developers to fit our efforts into the overall ACME annual deliverables.