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Shift time coordinates in climate model data

Source: R/htr_shift_years.R
htr_shift_years.Rd

This function adjusts time coordinates in climate model files, particularly useful for paleoclimate data where model years need to be shifted to correspond to actual calendar years. It uses CDO (Climate Data Operators) to shift time coordinates and updates filenames accordingly.

Usage

htr_shift_years(indir, outdir, adjust_value)

Arguments

indir

Character string. Directory containing input NetCDF files with time coordinates that may need shifting.

outdir

Character string. Directory where time-adjusted files will be saved.

adjust_value

Numeric. Number of years to add to the time coordinates. Can be positive or negative. For example, use 1653 to shift model years 347-1006 to calendar years 2000-2659.

Value

No return value. The function creates time-adjusted files in the specified output directory. Files with years < 1200 are shifted and renamed with new year ranges, while others are copied unchanged.

Details

Some climate models, particularly paleoclimate simulations, use arbitrary year numbering that doesn't correspond to actual calendar years. This function shifts the time coordinates to align with real calendar years for proper temporal analysis.

The function:

  1. Extracts metadata from input filenames to determine current year ranges

  2. Checks if years are less than 1200 (indicating they need adjustment)

  3. For files needing adjustment:

    • Calculates new year ranges by adding the adjustment value

    • Uses cdo shifttime,Nyears to shift the time coordinates

    • Updates filenames with the new year ranges

  4. For files not needing adjustment: Simply copies them to the output directory

The CDO command used for shifting is: cdo shifttime,adjust_value years input_file output_file

Note

  • Requires CDO (Climate Data Operators) to be installed and accessible from the system PATH

  • Input files must follow CMIP6 naming conventions for proper metadata extraction

  • The threshold of 1200 years is used to identify files needing time adjustment

  • Uses parallel processing with (number of CPU cores - 2) workers

  • Filenames are automatically updated to reflect the new time ranges

  • Progress messages show which files are being processed

References

CDO User Guide: https://code.mpimet.mpg.de/projects/cdo/embedded/cdo.pdf CDO shifttime operator: https://code.mpimet.mpg.de/projects/cdo/embedded/cdo.pdf#page=143

Author

Tin Buenafe

Examples

if (FALSE) { # \dontrun{
# Shift paleoclimate model years to modern calendar years
htr_shift_years(
  indir = file.path(base_dir, "data", "proc", "regridded", "yearly", "tos"),
  outdir = file.path(base_dir, "data", "proc", "shifted", "yearly", "tos"),
  adjust_value = 1653  # Shift model years 347-1006 to 2000-2659
)

# Shift backwards (negative adjustment)
htr_shift_years(
  indir = file.path(base_dir, "data", "proc", "regridded", "yearly", "tos"),
  outdir = file.path(base_dir, "data", "proc", "shifted", "yearly", "tos"),
  adjust_value = -50  # Shift 50 years backwards
)
} # }