3D-Land Energy and Moisture Exchanges: Harnessing High Resolution Terrestrial Information to Refine Atmosphere-to-Land interactions in Earth System Models

All comprehensive Earth System models (ESMs) include Land components, which simulate
canopy temperature and humidity; soil moisture, ice, and temperature; snow as well as many
biogeochemical fluxes between atmosphere, plants and soils. ESMs capture sub-grid land
heterogeneities, which arise from land-use, geomorphology, fires and vegetation dynamics.
Typically, all sub-units within a land grid receive the same downward fluxes of radiation and
precipitation from an atmospheric grid. ESMs assume that the canopy air is clean and ignore tracers
that may be present in the canopy air (e.g. dust or fire emissions). Parameterizations have been
developed to capture effects of mountains, vegetation structures and snow impurities on the surface
radiation budget. Such parameterizations have been evaluated in stand-alone land, regional, and
global atmospheric models. However, no complete and inherently consistent land surface radiation
transfer treatment (e.g. mountains, multi-layer canopy, and snow) has been implemented in any
CMIP6-class ESMs.

Summary of work to be completed. We propose to advance the representation of atmosphere-
to-land radiation exchange processes in the NOAA/GFDL ESM4, DOE/E3SM, and NCAR/CESM2,
including:
i) Radiation flux parameterization accounting for the effects of mountain shading and multiple
reflections between mountains and snow;
ii) Parameterizations for black carbon and dust mixing in snow and associated light absorption
and scattering processes;
iii) Multi-layer canopy energy transfer accounting for the tracers (e.g dust and black carbon) in
the canopy air space; and
iv) Interactions of the above improvements with sub-grid land-heterogeneity (e.g., different
vegetation/plant functional types, elevation bands, mountain aspects, hydrological hill-slopes,
etc.).

These new representations of land radiation treatments will be evaluated and constrained through
rigorous and detailed comparisons (e.g. ILAMB) with existing and new observational datasets.
This Land CPT proposal meets four criteria: Relevance: Current land components of ESMs
ignore orography, vertical canopy structures, and tracers in canopy air and snow in radiation
exchanges. Readiness: Prior studies have demonstrated that parameterizations for 3D radiation
scaling and snow impurities are transferable to climate models. Focus: The proposed CPT will
focus on a set of processes governing energy transfer from the atmosphere to land, with explicit
treatments of orography-vegetation-snow interactions. Model independence: The set of processes
is of great interest to developers in three climate centers. Proposed improvements will contribute
to NOAA’s capacity-building activities through advancing our understanding of the Earth’s
climate system, particularly hydro-climate and land ecosystems.