Removal of unnecessary, expensive array initializations in the MPAS_ATM model_mod.f90

[mjs2369]

Description:

Removed unnecessary array initializations from get_close_state() and get_close_obs() subroutines in the MPAS_ATM model_mod.f90

close_ind = -99
if (present(dist)) dist = 1.0e9_r8 !something big and positive (far away) in radians

Their removal causes a significant reduction to the runtime (can be more than 20%) when running MPAS_ATM cases with large model_size.

See issue for more info.

Fixes issue

Fixes issue #405

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• Documentation update
• Performance improvement

Documentation changes needed?

• My change requires a change to the documentation.
  • I have updated the documentation accordingly.

Tests

Tested to be bitwise identical with both Intel and GNU Fortran.
MPAS_ATM was also built and run with all debugging flags, which did not produce any relevant errors or warnings.

For an execution of a high-memory case on Casper (96 ensemble members, 459,985 observations, model_size = 327,759,048), the runtime was reduced from 145 min. to 112 min. or about %23

For an execution of separate mpas_atm case that uses RTTOV observations (10 ensemble members, 77,042 observations, model_size = 109,118,772), the runtime is reduced from 1 min. 9 sec. to 55 sec. or about %20

These test cases are included under Testing Datasets.

Checklist for merging

• Updated changelog entry
• Documentation updated
• Update conf.py

Checklist for release

• Merge into main
• Create release from the main branch with appropriate tag
• Delete feature-branch

Testing Datasets

• Dataset needed for testing available upon request
• Dataset download instructions included
• No dataset needed

Test cases can be found in the following directories on Cheyenne, but any execution of filter with MPAS_ATM will work.

/glade/scratch/masmith/DART/models/mpas_atm/test_run_96ensmembers (will take over an hour to run)
/glade/scratch/masmith/DART/models/mpas_atm/test_run_5ensmembers (recommend using this smaller version)
These test cases must be run on the mega-mpas branch.

/glade/scratch/masmith/DART/models/mpas_atm/mpas_rttov_test
This test case can be run on main, but will need to use a specific build template and &preprocess_nml for the RTTOV obs. These can be found at /glade/scratch/masmith/DART/models/mpas_atm/work/rttov_input.nml and /glade/scratch/masmith/DART/build_templates/mkmf.template.rttov.intel

[hkershaw-brown]

Great stuff Marlee.

There's a good chance we can remove these initialization from all over the code (as you know), but mpas is a great start.

Let's bundle this in with the next release (probably #403)