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GEOS model

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The Goddard Earth Observing System (GEOS) model consists of a group of model components that can be connected in a flexible manner in order to address questions related to different aspects of Earth Science.

Resolution

GEOS uses a spherical cube to as discretization of the earth. Resolution is usually given in the form Cxxx / Lxx, e.g. C1120 / L191, where L denotes the number of vertical levels and C encodes the horizontal resolution as number of grid points per axis on a cube side. Sticking with the example of C1120 / L191, we have

  • 1120 grid points per horizontal axis
  • 1120 x 1120 grid points per cube side
  • 6 x 1120 x 1120 grid points for the full cube
  • and 191 vertical levels (for all sides of the cube)

The following table "translates" Cxxx to approximate horizontal resolution in kilo meters and GEOS common resolutions. Production runs marked with *.

{ 
    'C12'  : 773.91
    'C24'  : 386.52
    'C48'  : 193.07
    'C90'  : 102.91
    'C180' : 51.44
    'C270' : 40
    'C360' : 25.71
    'C540' : 19
    'C720' : 12.86 *
    'C1080': 10    *
    'C1120': 8.26  *
    'C1440': 6.43
    'C1539': 6
    'C2160': 5
    'C2880': 3.21
    'C5760': 1.61
}

Vertical pressure level data ("eta files")

FV3, the dynamical core in GEOS, requires so called "eta files" as input to run. These files contain pressure at every level. According to Lucas Harris,

the values are typically hard-coded as there is no real formula for generating "good" level setups.

NDSL ships two eta files (79 and 91 levels) in its test data, which are required to run NDSL tests and re-used in PyFV3 tests and examples. FV3 has many more pre-defined pressure-level configurations. If we ever get to a point that we need them, start re-reading in this issue on how to extract that information from the fortran files.