GSI2DART

Overview

The GSI2DART converter was contributed by Craig Schwartz and Jamie Bresch of the Mesoscale & Microscale Meteorology Lab at NSF NCAR. Thanks Craig and Jamie!

This converter is designed to convert observation files created by the Gridpoint Statistical Interpolation (GSI) system maintained by the National Oceanic and Atmospheric Administration (NOAA) into DART observation sequence files. The files created by GSI are ‘BIG_ENDIAN’ and have filenames such as:

  • diag_amsua_metop-a_ges.ensmean

  • diag_amsua_metop-a_ges.mem001

  • diag_amsua_metop-a_ges.mem002

  • diag_amsua_n18_ges.ensmean

  • diag_amsua_n18_ges.mem001

  • diag_amsua_n18_ges.mem002

  • diag_amsua_n19_ges.ensmean

  • diag_amsua_n19_ges.mem001

  • diag_amsua_n19_ges.mem002

  • diag_conv_ges.ensmean

  • diag_conv_ges.mem001

  • diag_conv_ges.mem002

The DART converter uses routines from the GSI system that use the Message Passing Interface (MPI) to process observations in parallel (even when converting a small amount of observations) so MPI is required to execute this observation converter.

Due to these prerequisites, we provide a detailed description of this directory to guide the user.

This directory contains copies of several source code files from GSI. The GSI source code is available via a Github repository managed by NOAA’s Environmental Modeling Center (EMC):

https://github.com/NOAA-EMC/GSI

To differentiate between the sets of code, we refer to the root directory of the NOAA-EMC repository as GSI and refer to the root directory of this observation converter as GSI2DART.

GSI2DART/enkf copies seven files from GSI/src mostly without modification:

  1. GSI2DART/enkf/constants.f90 from GSI/src/gsi/constants.f90

  2. GSI2DART/enkf/kinds.F90 from GSI/src/gsi/kinds.F90

  3. GSI2DART/enkf/mpi_readobs.f90 from GSI/src/enkf/mpi_readobs.f90

  4. GSI2DART/enkf/readconvobs.f90 from GSI/src/enkf/readconvobs.f90

  5. GSI2DART/enkf/read_diag.f90 from GSI/src/gsi/read_diag.f90

  6. GSI2DART/enkf/readozobs.f90 from GSI/enkf/readozobs.f90

  7. GSI2DART/enkf/readsatobs.f90 from GSI/enkf/readsatobs.f90

Note that within GSI the source file kinds.F90 has an upper-case F90 suffix. Within the GSI2DART observation converter, it gets preprocessed into mykinds.f90 with a lower-case f90 suffix. Case-insensitive filesystems should be banned … until then, it is more robust to implement some name change during preprocessing.

The following three files had their open() statements modified to read ‘BIG_ENDIAN’ files without the need to compile EVERYTHING with the -convert big_endian compiler option. Using the DART open_file() routine also provides some nice error handling.

  • original: open(iunit,form="unformatted",file=obsfile,iostat=ios)

  • modified: iunit = open_file(obsfile,form='unformatted',action='read',convert='BIG_ENDIAN')

  1. GSI2DART/enkf/readconvobs.f90

  2. GSI2DART/enkf/readozobs.f90

  3. GSI2DART/enkf/readsatobs.f90

DART Modifications

Within GSI2DART

The source files within GSI2DART are:

  1. gsi_to_dart.f90: the main program.

  2. dart_obs_seq_mod.f90: the DART obs_seq output subroutine.

  3. params.f90: the same module name as GSI/src/enkf/params.f90 but with different content. This version is used to avoid modifying GSI2DART/enkf/read*.f90.

  4. radinfo.f90: the same module name as GSI/src/gsi/radinfo.f90 but with different content. This version is used to avoid modifying GSI2DART/enkf/read*.f90.

  5. mpisetup.f90: the same module name as GSI/src/enkf/mpisetup.f90 but with different content. This version is used to avoid dependency on GSI.

Elsewhere in the repository

This observation converter required modifying two files and adding a module for radiance observation types.

  • Modified ../../forward_operators/DEFAULT_obs_def_mod.F90

  • Modified ../../DEFAULT_obs_kind_mod.F90

  • Added ../../forward_operators/obs_def_radiance_mod.f90 which has radiance observation types

Additional files and directories

  1. satinfo is a file read by radinfo.f90 and must exist in the GSI2DART/work directory.

  2. datapath specifies the directory containing the data to be converted – it is specified in the gsi_to_dart_nml namelist in GSI2DART/work/input.nml.

  3. submit.csh is contained in GSI2DART/work/ – it runs the gsi_to_dart converter once it has been compiled. Again, since GSI requires MPI, multiple processors must be requested to run the gsi_to_dart executable.

Issues

1. The converter requires an ensemble size greater than one and will MPI_Abort() if only one ensemble member is requested.

The following are issues previously recorded in the README:

  1. Radiance and surface pressure bias correction

  2. Surface pressure altimeter adjustment?

  3. Specific humidity obs are transformed to relative humidity. What to do? [Just run EnSRF with psuedo_rh=.false. and assimilate RH obs]

  4. DART must use W and PH as control variables [okay, EnSRF can do this too (nvars=6 for WRF-ARW)]

  5. Does DART not do vertical localization for surface obs?

! If which_vert has no vertical definition for either location do only horizontal
if(loc1%which_vert == VERTISUNDEF .or. loc2%which_vert == VERTISUNDEF) comp_h_only = .true.
! If both verts are surface, do only horizontal
if(loc1%which_vert == VERTISSURFACE .and. loc2%which_vert == VERTISSURFACE) comp_h_only = .true.

Running with 32 bit reals

The converter has been tested with 64-bit reals as well as 32-bit reals (i.e. r8=r4 and -D_REAL_4). The answers are different only at the roundoff level.

This requires changes in two places:

  1. DART/assimilation_code/modules/utilities/types_mod.f90 change required: r8 = r4

  2. GSI2DART/work/quickbuild.sh change required: -D_REAL4_

If these are not set in a compatible fashion, you will fail to compile with the following error (or something similar):

../../../../observations/obs_converters/GSI2DART/dart_obs_seq_mod.f90(213): error #6284:
There is no matching specific function for this generic function reference.   [SET_LOCATION]
location = set_location(lon, lat, vloc, which_vert)
-----------------^