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         MISSION / VISION    |    About EMC

NOAA Environmental Modeling System


Quick NEMS Facts

  • Employs ESMF superstructure and utilities
  • Digital filtering capabilities
  • Separate dynamics and physics components for GFS; dynamics and physics combined for NMM-B
  • Adiabatic (dynamics only) simulation capability
  • Enhanced postprocessing capability
  • Digital filtering capabilities


NEMS uses standard ESMF (Earth System Modeling Framework) compliant software. For more information regarding ESMF, please refer to the following links:

NOAA Environmental Modeling System
(using standard ESMF compliant software)

NEMS ESMF Grid Component Scheme


NEMSIO is a package that has been created to support input/output in NEMS.
  • Currently handles binary and Grib-1 data, and will soon be capable of handling Grib-2 and NetCDF data
  • Contains serial and MPI versions
  • Uses standard meta data and user-defined meta data
  • Handles endianness for different machines in its parallel version
For more detailed information about the NEMSIO package, see the above tab, NEMSIO.

NEMS Component and Directory Structures

NEMS Component Structure

Below the large yellow box, the source codes are organized by the model developers.

The current directory structure of NEMS consists of five main directories:
  • /src
    • main program
    • source for the NEMS component and internal state (highest level governing component; creates EARTH)
    • source for the EARTH component and internal state (controls the atmosphere/hydrosphere system)
    • /atmos - the source for the ATM component and internal state
      • /gfs - all files directly related to GFS
      • /nmm - all files directly related to the NMM-B
      • /fim - all files directly related to the FIM
      • /gen - all files directly related to the GEN
      • /phys - intended to hold all physics science source code that is not core-specific and contains no ESMF (Currently holds only NMM-B routines. GFS routines under /gfs/phys.)
      • /share - holds files that are shared by any/all of the model cores
      • /post - contains only subroutines to connect NEMS and POST, no unified post source code included
    • /chem - GOCART source files
    • /ENS_Cpl - source for ensemble coupling
    • /conf - compile/build settings
  • /exe - NEMS and makedepf90 executables
  • /tests - examples of run scripts and NEMS regression tests

NEMS Source Code and Analysis (including data dictionary and flow chart):

NEMS revision #27084, click here.

Following are architecture graphs for NEMS version 11731:
Current hierarchy of NEMS components:

  1. NEMS
    • Couples ensemble
  2. EARTH
    • Couples atm/ocn
  3. ATM
    • Couples gfs/nmm
  4. NMMdriver
    • Couples nests
  5. NMMinstance
    • Couples dyn/phys
  6. PHYS
    • Couples phys/chemistry/land
  7. CHEM

NMM-B with Nests

  • The 12km NAM will still run to 84 hr, with current output.
  • Fixed domain nests run to 60 hr - Implemented & operational
    • 4 km CONUS
    • 6 km Alaska
    • 3 km HI & PR
  • Single locatable 1.33 km (CONUS) or 1.5 km (Alaska) nest to 36 hr - Implemented & operational
  • Nests
    • Static, 1-way
    • Boundaries from parent every time-step
    • Nest is "grid-associated" with parent (same orientation w.r.t. earth)
    • 1-way and 2-way moving nests including multiple and telescoping moving nests

NEMS GFS Aerosol Component

  • Dynamics, physics and chemistry run on the same grid in the same decomposition
  • GOCART does not own aerosol tracers (i.e, do not allocate aerosol tracer fields)
  • PHY2CHEM coupler component transfers/converts data from physics export state to GOCART import state
    • Converts units (e.g., precip rate, surface roughness)
    • Calculations (e.g., soil wetness, tropopause pressure, relative humidity, air density, geopotential height)
    • Flips the vertical index for 3D fields from bottom-up to top-down
  • CHEM2PHY coupler component transfers data from GOCART export state to physics export state
    • Flips vertical index back to bottom-up
    • Updates 2d aerosol diagnostic fields
To view experimental T126 L64 NRT dust forecasts from NEMS GFS aerosol component (NGAC), click here. Only 3-hr AOD animation (after June 11) is posted. More results (forecast and verification) will be added as development continues.

Workflows & Merging

Program Flow (WRF)

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NCEP Version of Program Flow (NMM-B)

? are pieces that are functional but not used at NCEP (click to enlarge)

NEMS Workflow

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NCEP NEMS Ensemble Workflow

Click to enlarge