Regional Climate Simulations With the Community Earth System Model

Abstract

The spectral element (SE) variable‐resolution (VR) mesh dynamical core is tested in developmental versions of the Community Earth System Model version 2 (CESM2). The SE dynamical core is tested in baroclinic wave, aquaplanet and full physics configurations to evaluate variable‐resolution simulations against uniform high and uniform low‐resolution simulations. Different physical parameterization suites are also evaluated to gauge their sensitivity to resolution. Dry dynamical core variable‐resolution cases compare well to high‐resolution tests. More recent versions of the atmospheric physics, including cloud schemes for CESM2, are less sensitive to changes in horizontal resolution. Most of the sensitivity is due to sensitivity to time step and interactions between deep convection and large‐scale condensation, which is expected from the closure methods. The resulting full physics SE‐VR model produces a similar climate to the global low‐resolution mesh and similar high‐frequency statistics in the high‐resolution region. The SE‐VR simulations are able to reproduce uniform high‐resolution results, making them an effective tool for regional climate simulations at lower computational cost. Some biases are reduced (orographic precipitation in Western United States), but biases do not necessarily go away at high resolution (e.g., summertime surface temperatures). Variable‐resolution grids are a viable alternative to traditional nesting for regional climate studies and are available in CESM2.

NCAR Release of CAM‐SE in CESM2.0: A Reformulation of the Spectral Element Dynamical Core in Dry‐Mass Vertical Coordinates With Comprehensive Treatment of Condensates and Energy

“…Consequently, any updates to the HOMME code base would have to be imported into CAM and pass regression tests in both HOMME and CAM. We refer to this setup as CAM‐HOMME, which has been extensively tested in AMIP‐style climate simulations (e.g., Bacmeister et al, ; Evans et al, ; Gettelman et al, ; Reed et al, ; Rhoades et al, ; Zarzycki & Jablonowski, ). CAM‐SE's code base is in CAM and not HOMME.…”

Exploring a Variable‐Resolution Approach for Simulating Regional Climate Over the Tibetan Plateau Using VR‐CESM

“…Other studies have found their way around the resolution-computation conundrum by implementing variable resolution (VR) models to simulate climate phenomena (e.g., Fox-Rabinovitz et al, 2006;Harris & Lin, 2012, 2014Hourdin et al, 2006;McGregor, 1996;Sabin et al, 2013;Sakaguchi et al, 2015;Zhou & Li, 2002). Specifically, VR versions of CESM have been used to study tropical cyclones (Zarzycki et al, 2013;Zarzycki & Jablonowski, 2014), snowpack, and hydroclimate in the western United States Rhoades et al, 2016Rhoades et al, , 2018Wu et al, 2017Wu et al, , 2018Zarzycki et al, 2015) and to examine their capability for regional climate simulations (Gettelman et al, 2017). This process generally makes use of a "regional refinement" of the horizontal grid to very high horizontal resolutions of a domain of interest, which coarsens to large horizontal grid spacings away from the domain of interest.…”

The Impact of Rimed Ice Hydrometeors on Global and Regional Climate

“…That is why global climate models typically forego the representation of rimed ice. However, increases in computational power have allowed global models to simulate features at higher resolution, and new methods for variable mesh simulations have enabled regional climate modeling at resolutions more typical of mesoscale models (10–25 km; e.g., Gettelman et al, ; Huang et al, ; Rauscher et al, ; Zarzycki & Jablonowski, ). There are also ongoing efforts at unification of weather and climate models (Brown et al, ).…”