1. Overview

GSI History and Background

The Gridpoint Statistical Interpolation (GSI) system is a unified data assimilation (DA) system for both global and regional applications. It was initially developed by the National Centers for Environmental Prediction (NCEP) Environmental Modeling Center (EMC) as a next generation analysis system based on the then operational Spectral Statistical Interpolation (SSI) analysis system. Instead of being constructed in spectral space like the SSI, the GSI is constructed in physical space and is designed to be a flexible, state-of-art system that is efficient on available parallel computing platforms. Starting with a three-dimensional variational (3DVar) data assimilation technique, the current GSI can be run as a data assimilation system of 2DVar (for surface data analysis), 3DVar, 3D ensemble-variational (3D EnVar), 4D EnVar, 3D/4D hybrid EnVar, or 4DVar (if coupled with an adjoint model from a GSI supported forecast system).

After initial development, the GSI analysis system became operational as the core of the North American Data Assimilation System (NDAS) for the North American Mesoscale (NAM) system in June 2006 and the Global Data Assimilation System (GDAS) for the Global Forecast System (GFS) in May 2007 at National Oceanic and Atmospheric Administration (NOAA). Since then, the GSI system has been adopted in various operational systems, including the National Aeronautics and Space Administration (NASA) Goddard Earth Observing System Model (GEOS), the United States Air Force (USAF) mesoscale data assimilation system, the NOAA Real-Time Mesoscale Analysis (RTMA) system, the Hurricane Weather Research and Forecasting (WRF) model (HWRF), and the Rapid Refresh (RAP) and High Resolution Rapid Refresh (HRRR) systems. The current version of GSI is also used as the data assimilation system in coming Finite-Volume Cubed-Sphere Dynamical Core (FV3) GFS system (Fv3GFS).

GSI Becomes Community Code

In 2007, the Developmental Testbed Center (DTC) began collaborating with major GSI development groups to transform the operational GSI system into a community system and support distributed development. The DTC complements the development groups in providing GSI documentation, porting GSI to multiple platforms, and testing GSI in an independent and objective environment, while maintaining equivalent functionality to what used in the operational centers. Since 2009, due to the NOAA security constraints, the DTC has been maintaining a community GSI code repository, which mirrors the EMC operational GSI code repository and facilitates community users to develop GSI. In 2017, the DTC and EMC worked together to build a unified GSI code repository for both operational and community developers and users. The unified repository facilitates direct communication among developers and helps accelerate transitions between research and operations. Based on this unified repository, the DTC releases this version of the GSI code with updated documentation.

The first community version of the GSI system was released in 2009. This users guide describes the release of GSI (v3.7) in October 2017. The DTC provides user support through the GSI Helpdesk (gsi-help@ucar.edu), tutorials, and workshops. More information about the GSI community services can be found at the DTC GSI webpage (http://www.dtcenter.org/com-GSI/users/index.php).

GSI Code Management and Review Committee

The GSI code development and maintenance are managed by the Data Assimilation Review Committee (DARC). It was originally formed as the GSI Review Committee in 2010, with the goal of incorporating all major GSI development teams in the United States within a unified community framework. In 2014, EMC and DTC decided to merge their GSI code repository with the code repository of the NOAA ensemble Kalman filter (EnKF) data assimilation system. This merge enabled coordinated development of both systems and joint community support. Following the repository merging, the GSI Review Committee was transitioned to DARC, incorporating new members representing EnKF development and applications. Currently, DARC contains members from NCEP/EMC, NASAs Goddard Global Modeling and Assimilation Office (GMAO), NOAA’s Earth System Research Laboratory (ESRL), the Joint Center for Satellite Data Assimilation (JCSDA), the National Center for Atmospheric Research (NCAR) Mesoscale & Microscale Meteorology Laboratory (MMM), the National Environmental Satellite, Data, and Information Service (NESDIS), USAF, the University of Maryland, and the DTC. The DTC also releases the EnKF system annually (along with GSI). Please refer to the community EnKF users webpage (http://www.dtcenter.org/EnKF/users/index.php) for more information.

DARC primarily steers distributed GSI/EnKF development, community code management, and support. The responsibilities of the committee are divided into two major aspects: coordination and code review. The purpose and guiding principles of the review committee are as follows:

  • Coordination and advisory
    • Propose and shepherd new development
    • Coordinate on-going and new development
    • Establish and manage a code review and transition process
    • Community support recommendation
  • Code review
    • Establish and manage a unified coding standard followed by all GSI/EnKF developers
    • Review proposed modifications to the unified code repository
    • Make decisions on whether code change proposals are accepted or denied for inclusion in the repository
    • Manage the repository
    • Oversee the timely testing and inclusion of code into the repository

Community Code Contributions

GSI is a community data assimilation system, open to contributions from scientists and software engineers from both the operational and research communities. DARC oversees the code transition from prospective contributors. This committee reviews proposals for code commits to the GSI repository and ensures that coding standards and tests are being fulfilled. Once the committee approves, the contributed code will be committed to the GSI code repository and available for operational implementation and public release.

To facilitate this process, the DTC is providing code transition assistance to the general research community. Prospective code contributors should contact the DTC GSI helpdesk (gsi-help@ucar.edu) as early as possible. It is contributor’s responsibility to ensure the proposed code change is correct, meeting GSI coding standards, and well documented. The DTC will help the contributor run regression tests and merge the code with the top of the repository. Prospective contributors can also apply to the DTC visitor program for their GSI research and code transition. The visitor program is open to applications year-round. Please check the visitor program webpage (www.dtcenter.org/visitors/) for the latest announcement of opportunity and application procedures.

About This GSI Release

As a critical part of the GSI user support, this document is provided to assist users in applying GSI to data assimilation and analysis studies. It was composed by the DTC and reviewed by the DARC members. Please note that the major focuses of the DTC are currently on testing and evaluation of GSI for regional numerical weather prediction (NWP). GSI for global and chemical applicaitons are briefly discussed in the document. The document is based on GSI v3.7 release. Active users can contact the DTC (gsi-help@ucar.edu) for developmental versions of GSI and access to the GSI code repository.

What Is New in This Release Version

The following lists some of the new functions and changes included in the v3.7 release of the GSI versus v3.6:

Observational aspects:

  • Further code generalization on all-sky radiance assimilation
  • Added the capability of assimilating satellite hydrometeor retrievals (integrated liquid-water content (LWC) and integrated solid-water content (SWC)) into GSI
  • Added assimilation of KOMPSAT5 GPSRO data
  • Modifications and improvements for CrIS and CrIS-FSR analysis
  • Update CRTM library and coefficients to version 2.3

Code optimization and refactoring:

  • Add wrf interface a library (wrflib). No need to compile WRF with GSI and EnKF
  • Added code to read in multiple-time level ARW ensemble forecast to get 4D perturbations

Application specific updates:

  • Applicaiton for FV3
    • Added FV3GFS interface
    • Added regional GSI interface with single FV3 tile
    • Added new scripts and fix files for using global and regional FV3 applications
  • RTMA
    • Updated mesonet uselist
    • The use of mesonet visibility data

Other enhancements and updates:

  • Remove GOTO statements from the code.
  • Added capability to read GFS ensemble member nemsio files in parallel simultaneously
  • Remove srw data type option
  • Clean up the output and add a “verbose” namelist flag.
  • Updated surface pressure observation error
  • Added Safeguard to filter out bad data in the radiance bias correction.
  • Utility updates such as radar data plotting.
  • Bug fixes

Besides the above-mentioned changes, this version release code have a unified cmake-based build system. This cmake buidl ssytem has been tested on mupltiple platform by DTC and EMC and released as the only building utility for thie release version of GSI.

Observations Used by This Version

GSI is used by various applications on multiple scales. The types of observations GSI can assimilate vary from conventional to aerosol observations. Users should use observations with caution to fit their specific applications. The GSI v3.7 can assimilate, but is not limited to, the following types of observations:

Conventional observations (including satellite retrievals):

  • Radiosondes
  • Pilot ballon (PIBAL) winds
  • Synthetic tropical cyclone winds
  • Wind profilers: USA, Jan Meteorological Agency (JMA)
  • Conventional aircraft reports
  • Aircraft to Satellite Data Relay (ASDAR) aircraft reports
  • Meteorological Data Collection and Reporting System (MDCRS) aircraft reports
  • Dropsondes
  • Moderate Resolution Imaging Spectroradiometer (MODIS) IR and water vapor winds
  • Geostationary Meteorological Satellite (GMS), JMA, and Meteosat cloud drift IR and visible winds
  • European Organization for the Exploitation of Meteorological Satellites (EUMETSAT) and GOES water vapor cloud top winds
  • GEOS hourly IR and cloud top wind
  • Surface land observations
  • Surface ship and buoy observations
  • Special Sensor Microwave Imager (SSMI) wind speeds
  • Quick Scatterometer (QuikSCAT), the Advanced Scatterometer (ASCAT) and Oceansat-2 Scatterometer (OSCAT) wind speed and direction
  • RapidScat observations
  • SSM/I and Tropical Rainfall Measuring Mission (TRMM) Microwave Imager (TMI) precipitation estimates
  • Velocity-Azimuth Display (VAD) Next Generation Weather Radar ((NEXRAD) winds
  • Global Positioning System (GPS) precipitable water estimates
  • Sea surface temperatures (SSTs)
  • Doppler wind Lidar
  • Aviation routine weather report (METAR) cloud coverage
  • Flight level and Stepped Frequency Microwave Radiometer (SFMR) High Density Observation (HDOB) from reconnaissance aircraft
  • Tall tower wind

Satellite radiance/brightness temperature observations (instrument/satellite ID):

  • SBUV: NOAA-17, NOAA-18, NOAA-19
  • High Resolution Infrared Radiation Sounder (HIRS): Meteorological Operational-A (MetOp-A), MetOp-B, NOAA-17, NOAA-19
  • GOES imager: GOES-11, GOES-12
  • Atmospheric IR Sounder (AIRS): aqua
  • AMSU-A: MetOp-A, MetOp-B, NOAA-15, NOAA-18, NOAA-19, aqua
  • AMSU-B: MetOp-B, NOAA-17
  • Microwave Humidity Sounder (MHS): MetOp-A, MetOp-B, NOAA-18, NOAA-19
  • SSMI: DMSP F14, F15, F19
  • SSMI/S: DMSP F16
  • Advanced Microwave Scanning Radiometer for Earth Observing System (AMSR-E): aqua
  • GOES Sounder (SNDR): GOES-11, GOES-12, GOES-13
  • Infrared Atmospheric Sounding Interferometer (IASI): MetOp-A, MetOp-B
  • Global Ozone Monitoring Experiment (GOME): MetOp-A, MetOp-B
  • Ozone Monitoring Instrument (OMI): aura
  • Spinning Enhanced Visible and Infrared Imager (SEVIRI): Meteosat-8, Meteosat-9, Meteosat-10
  • Advanced Technology Microwave Sounder (ATMS): Suomi NPP
  • Cross-track Infrared Sounder (CrIS): Suomi NPP
  • GCOM-W1 AMSR2
  • GPM GMI
  • Megha-Tropiques SAPHIR
  • Himawari AHI

Others:

  • GPS Radio occultation (RO) refractivity and bending angle profiles
  • Solar Backscatter Ultraviolet (SBUV) ozone profiles, Microwave Limb Sounder (MLS) (including NRT) ozone, and Ozone Monitoring Instrument (OMI) total ozone
  • Doppler radar radial velocities
  • Radar reflectivity Mosaic
  • Tail Doppler Radar (TDR) radial velocity and super-observation
  • Tropical Cyclone Vitals Database (TCVital)
  • Particulate matter (PM) of 10-um diameter, 2.5-um diameter or less
  • MODIS AOD (when using GSI-chem package)
  • Significant wave height observations from JASON-2, JASON-3, SARAL/ALTIKA and CRYOSAT-2

Please note that some of these above mentioned data are not yet fully tested and/or implemented for operations. Therefore, the current GSI code might not have an optimal setup for these data.