NCEP Global Forecast System Upgrade Implementation

On August 22, NCEP Global Forecast System (GFS) was upgraded to correct several user-specific problem areas (particularly stratospheric ozone, Antarctic ice, and snow analyses).  The changes were made in the following aspects.

Forcing changes

• Orography and land sea mask

  • Labels shelf ice as land not ocean

  • Uses upgraded Antarctic orography

  •  Corrects other minor navigation errors

• Snow analysis processing

  • Removes double interpolation error

  • Particularly helps around the Alps

• Land property quality control

  • Guards against incompatible land states

Physics changes

• Naval Research Laboratory (NRL) ozone physics

  • Uses algorithms contributed by NRL through Joint Center for Satellite Data Assimilation (JCSDA) and adapted by Environmental Modeling Center (EMC)

  • Removes low tropical bias in total ozone in GFS

• Glacial ice

  • Uses new land model algorithm dealing with polar shelf ice

• Longwave radiation at surface

  • Corrects error in downward radiation at surface

Dynamics changes

• Time filter

  • Increases amount of time filtering (coefficient changed to 0.85 from 0.92)

  • Achieves greater stability without affecting forecast

• Allowance for more than 100 vertical layers

Infrastructure changes

• Full Earth System Modeling Framework (ESMF) compliance

  • Uses community software framework in operations

  • Enables GFS coupling; GFS is now enabled to couple to itself in ensemble mode in the future

• Consolidated I/O

  • Common GFS I/O package among GFS programs

  • Enables full precision restart files, and future hybrid sigma-pressure-isentropic and space environment versions of the GFS

The changes have minimum impact to most GFS customers (negligible effect on hemispheric scores, precipitation, or tropical storms) that were reviewed by Climate Prediction Center, Hydrometeorological Prediction Center,  Aviation Weather Center, and Tropical Prediction Center/National Hurricane Center.  All these centers recommended the implementation. 

GFS Upgrade Implementation Scientific Decision Briefing by Mark Iredell on 8/22/2006

Contact Mark Iredell