2.6      Using hierarchical time-stepping to utilize MPAS-A computational resources for customized extreme variable-resolution meshes.

Ng, Ka-Ki, Kwan-Shu Tse, Yuk Sing Lui, Wai-Nang Leung, and Chi Chiu Cheung, ClusterTech Limited, Hong Kong

High-resolution regional/local weather forecast has long been a simulation challenge due to limited computational resources. In order to achieve higher accuracy within a limited budget, focusing computational resources on the region of interest is desired. The use of unstructured spherical centroidal Voronoi tessellation in the Model for Prediction Across Scales - Atmosphere (MPAS-A) gives flexibility to use customized variable-resolution meshes with refinements for regions of interest. However, time integration becomes expensive when using a small globally-constant time-step determined by CFL condition on the smallest cell.

We have implemented hierarchical time-stepping (HTS) to save computational resources by using inhomogeneous time-step. MPAS-A integrations with and without HTS were carried out on both standard and customized variable-resolution meshes for three historical cases. By comparing with reanalysis and station data, it was discovered that simulations with and without HTS have comparable performance. With HTS, computational cost is reduced considerably and it is more practical to use customized extreme variable-resolution meshes.