APS3 NetCDF Data File Notes

The format of ACCESS NetCDF files has undergone significant changes with APS3. NetCDF files now contain much richer metadata that is intended to be broadly compliant with CF 1.6 conventions while maintaining backward compatibility with the APS2 format.

Richer Metadata

NetCDF field variables now include the following additional attributes:

New Variable Attribute Convention Example Value
standard_name CF-1.6 air_pressure_at_sea_level
coordinates CF-1.6 forecast_reference_time
grid_mapping CF-1.6 latitude_longitude
cell_methods CF-1.6 time: mean
bounds (for coordinate vars) CF-1.6 time_bnds
coverage_content_type ACDD-1.3 modelResult
um_stash_source N/A m01s16i222
marsParam N/A 228202

New supporting variables (e.g. "forecast_reference_time", "latitude_longitude", "time_bnds", "lat_bnds" etc) have also been added in accordance with the CF conventions.

The following global NetCDF attributes have been added:

New Global Attribute Convention Example Value
title CF-1.6 ACCESS-Global Model Forecast
institution CF-1.6 Australian Bureau of Meteorology
summary ACDD-1.3 Global Numerical Weather Prediction Data
license ACDD-1.3 Bureau Express Licence
date_created ACDD-1.3 2019-10-22T02:32:43
standard_name_vocabulary ACDD-1.3 CF Standard Name Table v67
stash_vocabulary N/A http://reference.metoffice.gov.uk/um/stash

Other Changes

  • The following NetCDF fields have been renamed or replaced:
APS2 NetCDF Variable Name Units APS3 Name Units Change Note
accum_conv_prcp kg m-2 accum_conv_rain kg m-2 Renamed, field determined to be a rainfall quantity
accum_ls_prcp kg m-2 accum_ls_rain kg m-2 Renamed, field determined to be a rainfall quantity
accum_evap_sea kg m-2 av_evap_sea kg m-2 s-1 Replaced, accum_evap_sea field values were invalid
z0 m sfc_rough_len m Renamed/Replaced, see NWP Data Notes
  • The units of the "prob_vis_5km_ppt" field have been fixed from "m" to "1".
  • Subsurface level-depth metadata values (i.e. values in the "soil_lvl" NetCDF variable) were found to be incorrect in APS2 and have been corrected in APS3 to the following: 0.1, 0.35, 1, 3 (m). An accompanying cell boundary variable (soil_lvl_bnds) has also been provided. The description of temperature on soil levels field(s) have also been clarified as representing an average layer temperature (now reflected also in the cell_methods = "soil_lvl: mean" metadata).
  • Legacy "accum_value" variable attribute metadata values are now accurate but it is recommended users ignore this metadata and leverage CF compliant cell_methods and time bounds metadata instead.
  • "missing_value" and "_FillValue" variable attributes are now only defined for fields that actually contain missing values.
  • "valid_min" and "valid_max" variable attributes values better represent the actual min/max field value bounds.
  • The 962.5hPa level value in the "lvl" variable in pressure-level files is no longer rounded to the nearest integer.