NEMS/GFS Overview
Mark Iredell, Software Team Lead
NEMS/GFS Overview topics.
GFS nomenclature
 GFS history
 GFS resolution
 GFS in NCEP production
 GFS & GDAS workflow
 GSM time split
 NEMS motivation
 NEMS structure
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GFS nomenclature (obsolete)
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MRF
Medium Range Forecast
 Once per day late 10-day global forecast
 Obsolete when merged into GFS
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AVN
Aviation forecast
 Twice per day early 72-hour global forecast
 Obsolete when merged into GFS
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GFS nomenclature (GFS)
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GFS
Global Forecast System
 Applies to entire suite of jobs from
observation processing to data assimilation
to forecast model to product generation,
including ensemble (GEFS) and aerosol
(NGAC) components, but not seasonal
component.
 GFS runs four times per day, with “early”
(GFS) and a “late” (GDAS) analysis cycles.
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GFS nomenclature (GDAS)
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GDAS
Global Data Assimilation System
 Applies to portion of GFS which waits to
run well after real-time, assimilates all
available observations, cycles upon itself
with 9-hour forecasts, has no customer
products, but is the backbone for nearly
all NCEP numerical prediction guidance.
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GFS nomenclature (apps)

GSM
Global Spectral Model
 “Only” the numerical atmospheric prediction
forecast model application
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UPP
Unified Post Processor (aka NCEP post)
 Downstream application creating the master
file from which all GFS products are made
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GSM & UPP combined in NEMS/GFS
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GFS nomenclature (NEMS)
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NEMS
NOAA Environmental Modeling System
 Applies to the software framework
containing NCEP’s numerical models
 Contains both GSM and UPP components
 Also contains NGAC and GEFS
 Also contains NMM-B and FIM
 Soon will contain HYCOM and MOM5
 Uses ESMF and NUOPC to help couple
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GFS history (timeline)
Find full history timeline at
http://www.emc.ncep.noaa.gov/gmb/STATS/html/model_changes.html
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GFS resolution (horizontal)
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What the heck does “T574” mean?
T is triangular, the domain shape in spectral
space. Triangular is isotropic on a sphere.
 574 is the maximum number of waves
around a great circle in any direction, so the
shortest wavelength is 40000/574=70 km.
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The Eulerian GSM uses 3 gridpoints per
wave, so T574 is on a 1760 x 880
reduced Gaussian grid, or about 23 km.
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GFS resolution (vertical)
Hybrid sigma-pressure vertical
coordinate
 Pressure on interface k equals
Ak + Bk ps
(linear function of surface pressure)
 At bottom, A=0, B=1 (sigma)
 At top, A=0, B=0 (pressure)
 Pure pressure above 70 mb
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pressure (Pa)
GFS resolution (vertical function)
thickness (Pa)
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GFS resolution (vertical section)
pressure (Pa)
GFS 64 hybrid levels on a cross-section along 90 E
thickness (Pa)
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GFS in NCEP production
CLIMATE
CFS
GFS + MOM3/4
Oceans
Hurricane
HYCOM
GFDL
HWRF (NMM)
WaveWatch III
~3.5B Obs / Day
‘Mostly’
Satellite
+Radar
Global Data
Assimilation
Global
Forecast
System
Dispersion, Ash,
Smoke & Dust
North American
Mesoscale
ARL’s HYSPLIT
NMM
Severe Weather
Regional Data
Assimilation
NMM + ARW
Short-Range
Ensemble Forecast
Air Quality
NMM + ARW +
ETA + RSM
NAM + EPA/
ARL’s CMAQ
North American Ensemble
Forecast System
GEFS + Canadian Global +…
Very Short Range
Ensemble Forecasts
Rapid Refresh
for Aviation
ARW + GSI
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Time-Lagged
RR+NAM
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GFS & GDAS workflow
(timing and dependencies)
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GFS & GDAS workflow (jobs)
N
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N
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GSM time split concept
GSM does numerical prediction by
integrating a series of timesteps.
 T574 Eulerian has a 2 minute timestep.
 Each timestep in the GSM is split by
computing and integrating “Dynamics”
processes first and then computing and
integrating “Physics” processes.
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GSM time split Dynamics
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Ideal gas law
 Conservation of mass
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Conservation of momenturm
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Pressure gradient force (including mountain torque)
Coriolis force
Gravity (indirectly in hydrostatic approximation)
Conservation of energy (1st law)
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Transport (aka advection)
Energy conversion term
Cascade to unresolved scales (2nd law)
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GSM time split Physics
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Radiation (solar and terrestrial)
Surface exchange (land, sea, ice)
Turbulence (surface, boundary, and free)
Subscale gravity waves
Tracer sources and sinks
Moist processes
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Large-scale condensation
Shallow convection
Deep convection
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NEMS, what is that?
NOAA Environmental Modeling System
 A shared, portable, high performance
software superstructure and
infrastructure
 For use in operational prediction models
at NCEP
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NEMS motivation
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Develop a common superstructure for all NCEP
models.
Modularize large pieces of the models with ESMF
components and interfaces, and couple using
NUOPC layers and wrappers.
Divide atmospheric models down into Dynamics
and Physics components but no further.
Take history file I/O outside the science parts and
into a common Write component.
Keep science code and parallelization code in the
respective models the same as before.
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NEMS structure
MAIN
NEMS
All boxes represent
ESMF components.
EARTH(1:NM)
Atm
Ocean
Wrt
nemsio, …
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Ensemble
Coupler
NEMS
superstructure
Ice
NEMS
library
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NEMS components
NAM mesoscale
GFS global
GSM
NMM
FIM
Model components:
Domains(1:ND)
Dyn
Solver
Phy
Chem
Physics parameterizations
Postprocessor
Physlib
Post
Other components:
GFS Phy
column physics
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libpost.a
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NEMS/GFS Overview is over.
Thanks.
 Questions?
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