Simulating surface energy fluxes using the variable-resolution Community Earth System Model (VR-CESM)

摘要

Recent advances in variable-resolution (VR) global models provide the tools necessary to investigate local and global impacts of land cover by embedding a high-resolution grid over areas of interest in a seamless and computationally efficient manner. We used two eddy covariance tower clusters in the Eastern USA to evaluate surface energy fluxes (latent heat, lambda E; sensible heat, H; net radiation, R-n; and ground heat, G) and surface properties (aerodynamic resistance to heat transfer, r(aero); Bowen ratio, beta; and albedo, alpha) by uncoupled point simulations of the land-only Community Land Model (PTCLM4.5) and two coupled land-atmosphere Community Earth System Model (CESM1.3) simulations. The CESM simulations included a 1 degrees uniform grid global simulation and global 1 degrees simulation with a 0.25 degrees refined VR grid over the Eastern USA. Tower clusters included the following plant functional types-broadleaf deciduous temperate (hardwood) forest, C3 non-Arctic grass (grass), a cropland, and needleleaf evergreen temperate (pine) forest. During the growing season, diurnal cycles of lambda E and H for grass and the cropland were simulated well by PTCLM4.5 and VR-CESM1.3; however, lambda E (H) was biased low (high) at the hardwood and pine forested sites, contributing to biases in beta. Growing season R-n was generally well simulated by CLM4.5 and VR-CESM1.3; however, modeled elevated albedo (indicative of snow cover) persisted longer in winter and spring leading to large biases in R-n and alpha. The introduction of a VR grid does not adversely impact surface energy fluxes compared to 1 degrees uniform grids and highlights the usefulness of this approach for future efforts to predict land-atmosphere fluxes across heterogeneous landscapes.