An implementation of a leaping-point Two-step Shape-Preserving Advection Scheme in the high-resolution spherical latitude-longitude grid

A finite difference based Two-step Shape Preserving Advection Scheme (TSPAS) was ported into an Eulerian-Spectral dynamical core of National Center for Atmospheric Research (NCAR)-Community Atmospheric Model 5 (CAM5), to replace the original Semi-Lagrangian Transport (SLT) scheme for resolving the advection equation under different resolutions. A leaping-point TSPAS is designed to increase the time-step which is too short as limited by the extremely high zonal resolution in the high-latitude regions of a high-resolution model. The TSPAS can thus, accommodate to large time-step. The results of solid body rotation tests suggest: (1) the leaping-point TSPAS maintains the conservation, shape-preserving and numerical precision of the original TSPAS, but with a large increase on time-step; (2) although the numerical diffusion is larger in the TSPAS than that in the SLT, the TSPAS run is less time consuming and improves the conservation of the transported scalar. The simulation in CAM5 suggests: (1) the results are similar in leaping-point and original TSPAS runs, and there is no anomaly in high-latitude regions; (2) in high-resolution simulation, CAM5-TSPAS and CAM5-SLT also exhibit similar results, but CAM5-TSPAS shows an improvement of precipitation in the southern side of the Tibetan Plateau. This work ensures a stable large-time-step integration of CAM5-TSPAS in its high-resolution simulation, presents an enlightenment for using finite difference based advection scheme in a high-resolution model and lays a basis for improving model performance in East Asia.