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Non-hydrostatic Icosahedral Model (NIM)

Institution: NOAA Earth System Research Laboratory (ESRL), Boulder, CO

Model Metadata

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The Nonhydrostatic Icosahedral Model (NIM) formulates the latest numerical innovation of the three-dimensional finite-volume control volume on the quasi-uniform icosahedral grid suitable for ultra-high resolution simulations. NIM’s modeling goal is to improve numerical accuracy for weather and climate simulations as well as to utilize the state-of-art computing architecture such as massive parallel CPUs and GPUs to deliver routine high-resolution forecasts in timely manner.

NIM uses innovations in model formulation similar to its hydrostatic version of the Flow following Icosahedral Model (FIM) which has been tested and accepted for future use by the National Weather Service as part of their operational global prediction ensemble. Innovations from the FIM used in the NIM include:

  • A local coordinate system remapped spherical surface to plane for numerical accuracy [1]
  • Grid points in a table-driven horizontal loop that allow any horizontal point sequence [2]
  • Flux-Corrected Transport formulated on finite-volume operators to maintain conservative positive definite transport [3]
  • All differentials evaluated as finite-volume integrals around the cells [1]
  • Icosahedral grid optimization [4],

The accuracy and efficiency of these numerical schemes have been demonstrated in FIM with real-data simulations[5]. NIM has extended the two-dimensional finite-volume operators used in FIM for hydrostatic simulations into the three-dimensional finite-volume solvers designed to improve pressure gradient calculation and orographic precipitation over complex terrain. The NIM dynamical core has been successfully verified with various non-hydrostatic benchmark test cases such as warm bubble, density current, internal gravity wave, and mountain waves.  Physical parameterizations from GFS developed for real data simulations and YSU parameterizations[6] suitable for multiscale simulations have been incorporated into the NIM dynamic core and successfully tested with multimonth aqua-planet simulations.

(insert acronym here)
# of horizontal
grid points
Grid spacing at
the equator (km)
time step (s)
time step (s)
List of all dissipation coefficients
(with physical units)
 G6  40962  111  450  450  
 G7  163842  56  225  225  
 G8  655352  28  112.5  112.5  

Test Case Results

Information on the computational grid:

The hexagonal-icosahedral grid


[1] Lee J.-L. and A.E. MacDonald, 2009: A finite-volume icosahedral shallow water model on local coordinate, Mon. Wea. Rev. 137, 1422–1437.

[2] MacDonald, A.E., J. Middlecoff, T. Henderson, and J.-L. Lee, 2011: A general method for modeling on irregular grids. International Journal of High Performance Computing Applications, 25(4), 392–403N.

[3] Lee J.-L., R. Bleck, and A.E. MacDonald, 2010: A multistep flux-corrected transport scheme. J. Comput. Phys. 229, 9284–9298.

[4] Wang, N. and J.-L. Lee, 2011 : Geometric properties of the icosahedral-hexagonal grid on the two-sphere. SIAM J. Sci. Comput. 33(5): 2536-2559.

[5] R. Bleck, S. Benjamin, J.-L. Lee, and A.E. MacDonald, 2010: On the Use of an Adaptive,Hybrid-Isentropic Vertical Coordinate in Global Atmospheric Mode. Mon. Wea. Rev. 138, 2188–2210.

[6] Kim, J.-E., and S.-Y, Hong, 2012: A global atmospheric analysis data set downscaled from the NCEP-DOE reanalysis. J. Climate, 25, 2527–2534.

Members of this modeling group during DCMIP-2012 and room location

Name Institution Role
Dr. Lee, Jin NOAA/OAR/ESRL Mentor
Ms. Ka Yee Wong NOAA/OAR/ESRL Mentor
Mr. Chris Eldred Colorado State University


Mr. Mark Schlutow University Rostock/IAP


Miss Jacky Goddard University of Exeter



Last Update: Dec. 2, 2014, 11:04 a.m. by deleted user

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