Polar

SIMA has identified high resolution coupled modeling of high latitude regions as a critical frontier. Accordingly, we have developed high resolution refined mesh atmosphere models that are currently in the process of being put into the development version of CESM, which is publicly available.

Variable resolution CESM (VR-CESM) is supported for the spectral-element dynamical core. Two variable resolution grids have been introduced into SIMAv0, the ARCTIC grid, which is a 1 degree horizontal resolution grid with regional refinement of 1/4 degree resolution over the broader Arctic region. The ARCTICGRIS grid is similar to the ARCTIC grid, but additionally refines a patch covering the big island of Greenland with 1/8 degree resolution.

2x quare grid of the arctic
3x quare grid of the arctic

Note that what is depicted above is the element grid – the computational grid contains 3x3 unique grid points within each element. These grids are currently supported for an F compset, i.e., all major components of CESM are active except the ocean model, and the sea-surface temperature field is instead prescribed. In particular, the F2000climo and F1850 compsets, which consists of year 2000 and pre-industrial 1850 boundary conditions, respectively. The FHIST compset is also supported, which is a historical simulation with time varying boundary conditions starting at 1979, and with the Community Land Model is in BGC_CROP mode (i.e, has prognostic growth rates of the different plant functional types).

The CESM2topo software has been updated to consistently compute the topography for variable resolution grids, which is required to generate the correct sub-grid variance fields to drive CAM6's gravity wave drag and PBL form drag routines in the physics package. Here is a comparison of the topography over Greenland in the two grids, and compared with the default 1 degree resolution finite volume dynamical core grid:

Topo Greenland

The higher resolution topography is required to capture the steep elevation gradients of the ice margin that are important in determining ice sheet ablation (Pollard 2010) and facilitates a more realistic surface mass balance in the Community Ice Sheet Model. In addition, high resolution around the coastal margins of the Greenland Ice Sheet has been shown to be crucial for simulating the correct orographic precipitation patterns, particularly in southeast Greenland (van Kampenhout et al. 2019). In going from the 1/4 degree ARCTIC grid to the 1/8 degree ARCTICGRIS grid, the Nares Strait in northwest Greenland is resolved, and so the orographic channeling of winds are likely to be improved in ARCTICGRIS simulations.

Instructions for Running SIMAv0 Polar on the Cheyenne Supercomputer

  • Clone the repository
    git clone https://github.com/ESCOMP/CESM.git my_cesm_sandbox
  • Go into the newly created CESM repository and checkout the CESM2.2 tag
    cd my_cesm_sandbox
    git checkout cesm2_2_alpha06d
  • Run the script manage_externals/checkout_externals
    ./manage_externals/checkout_externals
  • Create a SIMAv0 Polar case on Cheyenne
    /cime/scripts/create_newcase -res ne0ARCTICne30x4_ne0ARCTICne30x4_mt12 ...
    for the ARCTIC grid, and
    /cime/scripts/create_newcase -res ne0ARCTICGRISne30x8_ne0ARCTICGRISne30x8_mt12 ...
    for the ARCTICGRIS grid
  • Setup, build and submit the executable to the cheyenne queue
    ./case.setup
    qcmd -- ./case.build
    ./case.submit

References

  • Leonardus van Kampenhout, Alan M. Rhoades, Adam R. Herrington, Colin M. Zarzycki, Jan T. M. Lenaerts, William J. Sacks, and Michiel R. van den Broeke. 2019. "Regional grid refinement in an Earth system model: impacts on the simulated Greenland surface mass balance." The Cryosphere, 13: 1547–1564. https://doi.org/10.5194/tc-13-1547-2019
  • David Pollard. 2010. "A retrospective look at coupled ice sheet–climate modeling." Climatic Change, 100: 173-194. https://doi.org/10.1007/s10584-010-9830-9