A Three-Dimensional Icosahedral Grid Advection Scheme Preserving Monotonicity and Consistency with Continuity for Atmospheric Tracer Transport

A tracer advection scheme for a three-dimensional icosahedral grid model is developed. Then, its tracer transport performance is evaluated using realistic flow fields. The consistency with continuity (CWC) scheme is newly introduced to a three-dimensionally monotonic scheme using existing techniques of an upwind-biased scheme and the intermediate density method. The CWC guarantees mass conservation and Lagrangian conservation, both of which are important properties for tracer transport. In addition, the scheme is positive definite. This transport scheme is implemented with the nonhydrostatic icosahedral atmospheric model and transport simulations are performed. A comparison with radon observations reveals that the proposed method reproduces high-concentration events more realistically than the original method does. Furthermore, results show that the proposed method has less numerical diffusion and is superior to the original method in terms of a sharper gradient.