Using variable resolution meshes to model tropical cyclones in NCAR's CAM general circulation model

Modeling of tropical cyclones in General Circulation Models (GCMs) has traditionally proved challenging due to issues such as relatively small storm sizes and intense convective processes. Tropical cyclones are significantly under-resolved, if not completely unresolved, at traditional GCM grid resolutions of 50-300 km. However, recent gains in computational ability and advances in GCM model design now allow for GCM simulations with grid spacings as small as 15-30 km. At these resolutions, models are able to more effectively capture key features of tropical cyclones. This paper evaluates the potential of GCMs at very high horizontal resolutions to simulate tropical cyclones. In particular, we explore a novel variable-resolution mesh approach that allows for high spatial resolutions in areas of interest, such as low-latitude ocean basins where tropical cyclones are prevalent. Such GCM designs with variable-resolution meshes have the potential to become a future tool for regional climate assessments.

A statically-nested, variable-mesh option has recently been introduced into the National Center for Atmospheric Research (NCAR) Community Atmosphere Model's (CAM) Spectral Element (SE) dynamical core that is slated to become the NCAR default in future CAM releases. We present preliminary CAM-SE model simulations using an idealized tropical cyclone test case with a variety of grid sizes and refinement scales. We evaluate the evolution of tropical cyclones initialized at various locations in or near grid scale transition regions. Additionally, we investigate the sensitivity of storm intensity in these areas to variables such as initial vortex strength and radius. Specific focus is centered on factors crucial to storm cyclogenesis and maintenance such as air-sea interaction and vertical development. We also consider potential computational consequences of using such a setup in either process or climate studies..163 on 11-17-2011-->