Using Variable-Resolution Meshes to Model Tropical Cyclones in the Community Atmosphere Model

Abstract

A statically nested, variable-mesh option has recently been introduced into the Community Atmosphere Model's (CAM's) Spectral Element (SE) dynamical core that has become the default in CAM version 5.3. This paper presents a series of tests of increasing complexity that highlight the use of variable-resolution grids in CAM-SE to improve tropical cyclone representation by dynamically resolving storms without requiring the computational demand of a global high-resolution grid. As a simplified initial test, a dry vortex is advected through grid transition regions in variable-resolution meshes on an irrotational planet with the CAM subgrid parameterization package turned off. Vortex structure and intensity is only affected by grid resolution and no spurious artifacts are observed. CAM-SE model simulations using an idealized tropical cyclone test case on an aquaplanet show no numerical distortion or wave reflection when the cyclone interacts with an abrupt transition region. Using the same test case, the authors demonstrate that a regionally refined mesh with significantly fewer degrees of freedom can produce the same local results as a globally uniform grid. Additionally, the authors discuss a more complex aquaplanet experiment with meridionally varying sea surface temperatures that reproduces a quasi-realistic global climate. Tropical cyclogenesis is facilitated without the need for vortex bogusing in a high-resolution patch embedded within a global grid that is otherwise too coarse to resolve realistic tropical cyclones in CAM.

TempestExtremes: a framework for scale-insensitive pointwise feature tracking on unstructured grids

“…Here, we show two deterministic forecasts (initialized at 00Z on 21 and 22 October 2012) for Hurricane Sandy using the Community Atmosphere Model (CAM) with a 0.125 • (14 km) grid spacing over the North Atlantic basin. Details about the model setup, forecast skill of CAM, and a case study of Hurricane Sandy results can be found in Zarzycki and Jablonowski (2015). Both forecasts were initialized prior to the National Hurricane Center declaring Sandy as a tropical depression, which occurred at 12Z on 22 October (Blake et al, 2013).…”

“…Tropical cyclone trajectories and associated intensities as obtained from the simulation of a single hurricane season in CAM 3.5 using (top) native spectral element grid data and (bottom) data regridded to a regular latitude-longitude grid with 0.25 • grid spacing. Zarzycki et al, 2014a;Zarzycki and Jablonowski, 2015). Since VR-CAM-SE uses an unstructured mesh with degrees of freedom stored at spectral element Gauss-Lobatto (GL) nodes, data are typically analyzed only after being regridded to a regular latitude-longitude mesh of approximately equal resolution.…”

High-Resolution Multi-decadal Simulation of Tropical Cyclones

“…8.2 (bottom) contains 13,340 elements, compared to 86,400 for a globally uniform mesh of the same resolution (25 km). Assuming a variable-resolution model that is able to scale with the number of grid cells (as CAM-SE has demonstrated (Zarzycki et al 2014a)), regional tropical cyclone studies can be dramatically improved by decreasing the computational cost to simulate at a particular horizontal resolution. In the case above, the variableresolution simulation only cost one-sixth of the CPU hours of an equivalent simulation utilizing high-resolution over the entire global domain.…”

Analyzing the Adaptive Mesh Refinement (AMR) Characteristics of a High-Order 2D Cubed-Sphere Shallow-Water Model

“…Application examples for static (nonmoving) mesh adaptations are provided in Zarzycki et al (2014), Rauscher and Ringler (2014), Zarzycki and Jablonowski (2015), and Huang et al (2016) (see also further references therein). Our paper focuses on dynamically adaptive grids, which track features of interest during the model simulation by locally adding or removing grid points as needed.…”