Manual On The Global Data Processing And Forecasting System
The Global Forecast System (GFS) - Global Spectral Model (GSM) (GSM Version 13.0.2) (Updated May 2016 - Global Climate & Weather Modeling Branch). Post processor:. Variables:. (starting page 17).
Experimental/parallel configuration file/namelist variables: 1.0 The NCEP Global Forecast System (GFS) The NCEP’s Global Forecast System (GFS) is the cornerstone of NCEP’s operational production suite of numerical guidance. NCEP’s global forecasts provide deterministic and probabilistic guidance out to 16 days. The GFS provides initial and/or boundary conditions for NCEP’s other models for regional, ocean and wave prediction systems. The Global Data Assimilation System (GDAS) uses maximum amounts of satellite and conventional observations from global sources and generates initial conditions for the global forecasts. The global data assimilation and forecasts are made four times daily at 0000, 0600, 1200 and 1800 UTC. 1.1 Forecast model: The atmospheric forecast model used in the GFS is a global spectral model (GSM) with spherical harmonic basis functions.
The main purpose of the Global Data-processing and Forecasting Systems (GDPFS) shall be to prepare and make available to Members in the most cost-effective.
In response to increased computing resources and changing computer architecture at NCEP, the GFS has evolved to higher resolution, both horizontally and vertically, and a more modular code structure. The current operational horizontal resolution is T1534 (T574), or approximately 13 km (34km) at the equator for days 0-10 (days 10-16) forecasts.
In the vertical there are 64 hybrid sigma-pressure (Sela, 2009) layers with the top layer centered around 0.27 hPa (approximately 55 km). The current operational dynamical core of the GFS/GSM is based on a two time-level semi-implicit semi-Lagrangian discretization (Sela, 2010) with three dimensional Hermite interpolation (the dynamical core still supports three time-level Eulerian approach). The semi-Lagrangian advection calculations as well as treatment of physics are done on a linear, reduced (for computational economy) Gaussian grid in the horizontal domain. The semi-implicit treatment and implicit eighth order horizontal diffusion are performed in spectral space.
This requires the application of Fourier and Legendre transforms to convert between spectral and grid-point spaces. To improve the accuracy of associated Legendre function computation at higher wave numbers, an extended-range arithmetic (X-number – Juang, 2014) is used. To reduce noise in the stratosphere, additional second order divergence damping that increases with altitude is applied above 100hPa. Also, a correction is applied to the global mean ozone to account for the non-conservation during semi-Lagrangian advection step.
For the three time-level Eulerian option for dynamics a positive-definite tracer transport formulation (Yang et al., 2009) is used in the vertical. It is important to note that the same physical parameterization package is used across all horizontal and vertical resolutions (with slightly different tunable parameters). Upgrades to the physical parameterizations are ongoing and occur on the average of every other year. 1.2 Changes to physical parameterization since 2007 include: 1.2.1 Radiation: The longwave (LW) and the shortwave (SW) radiation parameterizations in NCEP's operational GFS are both modified and optimized versions of the Rapid Radiative Transfer Models (RRTMGLW v2.3 and RRTMGSW v2.3, respectively) developed at AER Inc. (Mlawer et al.
1997, Iacono et al., 2000, Clough et al., 2005). The LW algorithm contains 140 unevenly distributed g-points in 16 broad spectral bands, while the SW algorithm includes 112 g-points in 14 bands.
In addition to the major atmospheric absorbing gases of ozone, water vapor, and carbon dioxide, the algorithm also includes various minor absorbing species such as methane, nitrous oxide, oxygen, and up to four types of halocarbons (CFCs). To mitigate the unresolved sub-grid cloud variability when dealing multi layered clouds, a Monte-Carlo Independent Column Approximation (McICA) method is used in the RRTMG radiation transfer computations. A maximum-random cloud overlapping method is used in both LW and SW radiation calculations. Cloud condensate path and effective radius for water and ice are used for calculation of cloud-radiative properties. Hu and Stamnes' method (1993) is used to treat water clouds in both LW and SW parameterizations. For ice clouds, Fu's parameterizations (1996, 1998) are used in the SW and LW, respectively. In the operational GFS, a climatological tropospheric aerosol with a 5-degree horizontal resolution is used in both LW and SW radiations.
A generalized spectral mapping formulation was developed to compute radiative properties of various aerosol components for each of the radiation spectral bands. A separate stratospheric volcanic aerosol parameterization was added that is capable of handling volcanic events. In SW, a new table of incoming solar constants is derived covering time period of 1850-2019 (Vandendool, personal communication). An eleven-year solar cycle approximation will be used for time out of the window period in long term climate simulations.
The SW albedo parameterization uses surface vegetation type based seasonal climatology similar to that described in the NCEP Office Note 441 (Hou et. Al, 2002) but with a modification in the treatment of solar zenith angle dependency over snow-free land surface (Yang et al. Similarly, vegetation type based non-black-body surface emissivity is used for the LW radiation. Concentrations of atmospheric greenhouse gases are either obtained from global network measurements, such as carbon dioxide (CO2), or taking the climatological constants, such as methane, nitrous oxide, oxygen, and CFCs, etc. In the operational GFS, the actual CO2 value for the forecast time is an estimation based on the most recent five-year observations. In the lower atmosphere (.
The Global Forecast System (GFS) - Global Spectral Model (GSM) (GSM Version 13.0.2) (Updated May 2016 - Global Climate & Weather Modeling Branch). Post processor:. Variables:.
(starting page 17). Experimental/parallel configuration file/namelist variables: 1.0 The NCEP Global Forecast System (GFS) The NCEP’s Global Forecast System (GFS) is the cornerstone of NCEP’s operational production suite of numerical guidance. NCEP’s global forecasts provide deterministic and probabilistic guidance out to 16 days. The GFS provides initial and/or boundary conditions for NCEP’s other models for regional, ocean and wave prediction systems. The Global Data Assimilation System (GDAS) uses maximum amounts of satellite and conventional observations from global sources and generates initial conditions for the global forecasts.
The global data assimilation and forecasts are made four times daily at 0000, 0600, 1200 and 1800 UTC. 1.1 Forecast model: The atmospheric forecast model used in the GFS is a global spectral model (GSM) with spherical harmonic basis functions. In response to increased computing resources and changing computer architecture at NCEP, the GFS has evolved to higher resolution, both horizontally and vertically, and a more modular code structure. The current operational horizontal resolution is T1534 (T574), or approximately 13 km (34km) at the equator for days 0-10 (days 10-16) forecasts. In the vertical there are 64 hybrid sigma-pressure (Sela, 2009) layers with the top layer centered around 0.27 hPa (approximately 55 km). The current operational dynamical core of the GFS/GSM is based on a two time-level semi-implicit semi-Lagrangian discretization (Sela, 2010) with three dimensional Hermite interpolation (the dynamical core still supports three time-level Eulerian approach). The semi-Lagrangian advection calculations as well as treatment of physics are done on a linear, reduced (for computational economy) Gaussian grid in the horizontal domain.
The semi-implicit treatment and implicit eighth order horizontal diffusion are performed in spectral space. This requires the application of Fourier and Legendre transforms to convert between spectral and grid-point spaces. To improve the accuracy of associated Legendre function computation at higher wave numbers, an extended-range arithmetic (X-number – Juang, 2014) is used.
To reduce noise in the stratosphere, additional second order divergence damping that increases with altitude is applied above 100hPa. Also, a correction is applied to the global mean ozone to account for the non-conservation during semi-Lagrangian advection step. For the three time-level Eulerian option for dynamics a positive-definite tracer transport formulation (Yang et al., 2009) is used in the vertical. It is important to note that the same physical parameterization package is used across all horizontal and vertical resolutions (with slightly different tunable parameters). Upgrades to the physical parameterizations are ongoing and occur on the average of every other year. 1.2 Changes to physical parameterization since 2007 include: 1.2.1 Radiation: The longwave (LW) and the shortwave (SW) radiation parameterizations in NCEP's operational GFS are both modified and optimized versions of the Rapid Radiative Transfer Models (RRTMGLW v2.3 and RRTMGSW v2.3, respectively) developed at AER Inc.
(Mlawer et al. 1997, Iacono et al., 2000, Clough et al., 2005). The LW algorithm contains 140 unevenly distributed g-points in 16 broad spectral bands, while the SW algorithm includes 112 g-points in 14 bands. In addition to the major atmospheric absorbing gases of ozone, water vapor, and carbon dioxide, the algorithm also includes various minor absorbing species such as methane, nitrous oxide, oxygen, and up to four types of halocarbons (CFCs).
To mitigate the unresolved sub-grid cloud variability when dealing multi layered clouds, a Monte-Carlo Independent Column Approximation (McICA) method is used in the RRTMG radiation transfer computations. A maximum-random cloud overlapping method is used in both LW and SW radiation calculations. Cloud condensate path and effective radius for water and ice are used for calculation of cloud-radiative properties. Hu and Stamnes' method (1993) is used to treat water clouds in both LW and SW parameterizations. For ice clouds, Fu's parameterizations (1996, 1998) are used in the SW and LW, respectively. In the operational GFS, a climatological tropospheric aerosol with a 5-degree horizontal resolution is used in both LW and SW radiations.
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A generalized spectral mapping formulation was developed to compute radiative properties of various aerosol components for each of the radiation spectral bands. A separate stratospheric volcanic aerosol parameterization was added that is capable of handling volcanic events. In SW, a new table of incoming solar constants is derived covering time period of 1850-2019 (Vandendool, personal communication).
An eleven-year solar cycle approximation will be used for time out of the window period in long term climate simulations. The SW albedo parameterization uses surface vegetation type based seasonal climatology similar to that described in the NCEP Office Note 441 (Hou et. Al, 2002) but with a modification in the treatment of solar zenith angle dependency over snow-free land surface (Yang et al. Similarly, vegetation type based non-black-body surface emissivity is used for the LW radiation. Concentrations of atmospheric greenhouse gases are either obtained from global network measurements, such as carbon dioxide (CO2), or taking the climatological constants, such as methane, nitrous oxide, oxygen, and CFCs, etc. In the operational GFS, the actual CO2 value for the forecast time is an estimation based on the most recent five-year observations. In the lower atmosphere (.