ACCESS NWP Data Information

This web site provides an overview of the Australian Community Climate and Earth-System Simulator (ACCESS) Numerical Weather Prediction (NWP) data made available by the Bureau of Meteorology. This data is in a digital gridded binary format (GRIB edition 2 and NetCDF-4) and is made available to customers who have become Registered User subscribers.

The ACCESS models are being progressively upgraded from version APS2 to APS3. APS3 models are higher resolution, assimilate more observational inputs and include improved model physics compared with APS2 systems. More information about the APS3 ACCESS systems will be available soon in upcoming Analysis and Prediction Operations Bulletins.

For detailed information about APS2 products, please see this page.

The rest of this document describes the new APS3 systems, namely the first (and only currently available) model, APS3 ACCESS-G:

Model Domain Resolution
ACCESS-G Global Approximately 12km in the mid-latitudes

The AUSWAVE model continues to use ACCESS APS2. Information about the products available from this system can be found here.

NWP data products

A range of NWP products, available via FTP for Registered Users, has been made available in NetCDF4 and GRIB edition 2 formats.

The ACCESS models output meteorological parameters defined on three-dimensional grids for each forecast time-step. The grid structure is evenly spaced latitude/longitude in the horizontal and hybrid-height based in the vertical. As such the NetCDF and GRIB file products contain a range of gridded field values valid for a particular model time-step.

In addition to the native ACCESS model hybrid-height coordinates, data on pressure-levels (levels of constant atmospheric pressure) is also available. Note that data on this level type is derived entirely from the hybrid-height coordinate data via interpolation (or where necessary, extrapolation).

All product files conform to the following naming convention:

IDYnnnnn.version.fields.levels.base-time.forecast-hour.grid-coords.ext

File-name key

IDYnnnnngrid file ID code (defines the model and the domain)
versionmodel version number (e.g. APS3, APS2)
fieldsalphanumeric descriptor of fields (e.g. all-flds, pop-flds)
levelsalphanumeric descriptor of levels (e.g. all-lvls, pop-lvls)
base-timemodel run's UTC base time in the format YYYYMMDDHH, where YYYY = year, MM = month, DD = day, HH = hour (e.g. 2010122500)
forecast-hourproduct's validity time (model time-step) as hours after base-time in the format HHH (e.g. 000, 048, 240), all = all time-steps or Mhh = -hh hours (e.g. M02 = -02 hours). Note a HHH of 000 is the analysis time-step.
grid-coordsdescriptor of model grid co-ordinate level-type (e.g. surface, model, pressure)
extfile-type extension (e.g. grb, nc)

Grid File ID Codes

Product Code Interpretation
IDY25000 ACCESS-G (single and multi-level data), full (global) domain
IDY25001 ACCESS-G (single and multi-level data), subset to Australian region
IDY25006 ACCESS-G (single and multi-level data), subset to greater Australian region
IDY25020 ACCESS-G (single-level subset only), full (global) domain
IDY25021 ACCESS-G (single-level subset only), subset to Australian region
IDY25026 ACCESS-G (single-level subset only), subset to greater Australian region

Field descriptors

Field group Description
all-flds All meteorological fields available for the model, forecast-hour and grid-coords.
pop-flds "Popular fields"; a subset of all-flds that are most commonly requested.
group1 Twelve popular single-level fields including temperatures, moisture parameters, surface and mean-sea-level pressures, 10m winds, precipitation and total cloud cover.
group2 Eleven popular single-level technical fields including low-, middle- and high-level cloud covers, planetary boundary layer height, accumulated evaporation, precipitable water, first-layer soil moisture content, screen-level horizontal visibility and wind gusts at 10m.
group3 Radiation flux fields (including latent, sensible, long-wave and short-wave fluxes).
group4 A collection of single-level fields including accumulated convective and large-scale rainfall, snowfall, soil moisture and temperature, time-averaged mean-sea-level pressure and surface stresses, roughness length and friction velocity and a number of of other miscellaneous fields.
wind The zonal and meridional components of wind velocity.
prec Accumulated total precipitation amount at the surface.
pres Atmospheric pressure (at surface or mean-sea-level, depending on grid-coords).
syncld Synthetic infrared and water vapour satellite imagery
topog Height of topography.
mask Land mask used by the model.

Level group descriptors

Levels group Description
all-lvls All levels available for the grid-coords.
pop-lvls A popular subset of all-lvls. Currently applies only to pressure levels.
lowestN-lvls The lowest N levels, where N is an integer (e.g. 4 or 15).
surf The ground surface.
10m 10 meters above the ground surface.
msl The mean-sea-level surface.
slv Collection of single levels (e.g. a mix of surface, screen-level and 10m fields).
rho-lvls Data on model levels, half-way vertically between the normal heights. Winds on these levels will tend to be slightly more accurate than winds on other levels.
rho-lowestN-lvls The lowest N rho levels, where N is an integer (e.g. 4 or 15).
numeric A particular level; e.g. when the grid-coords is pressure, a levels group value of 1000 represents 1000hPa.

Grid-coordinate descriptors

grid-coords group Description
model Hybrid-height level data. Unless stated otherwise by the level group descriptor, data on these levels represents the so called "theta" hybrid-height levels on a uniform horizontal grid †.
pressure Model data interpolated (and extrapolated where necessary) to a set of standard pressure levels.
surface Single-level fields. These share the same horizontal grid as all of the above multi-level coordinates types and can thus be used alone or in conjunction with other level types. Note that not all parameters in files labelled with this grid-coordinate are valid at the surface (e.g. some are valid at screen-level height or at 10m). The sub-surface parameters soil moisture content and soil temperature have also been designated this grid-coords group.

Note: The raw ACCESS outputs are actually on a set of interleaved ("staggered") grids. To achieve a uniform grid for all parameters the wind components have been interpolated horizontally (and vertically in the case of theta level outputs).

Sample NWP data

Links are provided below to documentation for ACCESS NWP products along with sample data files. Blank entries in the tables below indicate a product that is not currently available, but can be added upon request.

Single-level data

Single-level data is provided separately from other level-types. This data can be used in conjunction with data from any of the other multi-level files (model or pressure-level) since the horizontal grid is consistent with the horizontal layout of each of these formats.

Fields.Levels G G-AUS G-REG
all-flds.slv HTML HTML HTML
group1.slv HTML HTML HTML
group2.slv HTML HTML HTML
group3.slv HTML HTML HTML
group4.slv HTML   HTML
mask.surf HTML HTML HTML
prec.surf HTML HTML HTML
pres.msl HTML HTML HTML
pres.surf HTML HTML HTML
syncld.slv HTML HTML HTML
topog.surf HTML HTML HTML
wind.10m HTML HTML HTML
Sample Data netcdf | grb netcdf | grb netcdf | grb

Note: single level products also include rho-level-2 and rho-level-4 products described in the "Data on hybrid-height levels" table below.

Data on hybrid-height levels (model levels)

This data-set consists of ACCESS fields valid on all 70 ACCESS hybrid-height levels.

Fields.Levels G G-AUS G-REG
geopht.all-lvls HTML HTML HTML
pop-flds.all-lvls HTML HTML HTML
pop-flds.lowest20-lvls   HTML HTML
pop-flds.lowest4-lvls HTML HTML HTML
wind.rho-lowest4-lvls HTML HTML HTML
wind.rho-lvl-2 HTML HTML HTML
wind.rho-lvl-4 HTML   HTML
Sample Data netcdf | grb netcdf | grb netcdf | grb

Data on pressure-levels

This data-set consists of ACCESS fields interpolated to 35 pressure levels (a super-set of the "standard" pressure levels). Physically constrained extrapolations are performed when required (e.g. when deriving data at 1000hPa for a location where surface pressure is 990hPa). The interpolation method used is a tri-linear mapping between native model coordinate space and logarithmic pressure-levels.

Fields.Levels G G-AUS G-REG
all-flds.all-lvls HTML HTML HTML
pop-flds.1000 HTML HTML HTML
pop-flds.200 HTML HTML HTML
pop-flds.250   HTML  
pop-flds.300 HTML HTML HTML
pop-flds.500 HTML HTML HTML
pop-flds.700 HTML HTML HTML
pop-flds.850 HTML HTML HTML
pop-flds.all-lvls   HTML HTML
Sample Data netcdf | grb netcdf | grb netcdf | grb

Notes on specific NWP file-formats

Data files are made available in two formats, GRIB2 and NetCDF4. Metadata for certain fields has changed with APS3. For details along with technical information about the formats, please refer to GRIB2 format notes and NetCDF format notes.

Main APS3 differences

  • The ACCESS-R model will not be a part of the APS3 suite as it has been superseded by ACCESS-G.
  • Product codes IDY25006 and IDY25026 are new. Products with these codes are intended to replace APS2 ACCESS-R products with product codes IDY25300 and IDY25320 respectively. Grid resolution is as per IDY25000 (i.e. approximately 12 km in the mid latitudes).
  • New fields "synthetic infrared satellite brightness temperature (K)" and "synthetic water vapour satellite brightness temperature (K)" are available.
  • Single-level forecast fields are available at hourly temporal resolution.
  • In APS3 ACCESS-G the time interval over which time-averaged fields are calculated is now hourly instead of 3-hourly as in APS2. Maximum and minimum screen-level temperature fields are similarly affected.
  • The fields "accumulated convective precipitation (kg m-2)" and "accumulated large scale precipitation (kg m-2)" in APS2 were labelled incorrectly. The field descriptions and accompanying metadata have been amended to be "accumulated convective rainfall (kg m-2)" and "accumulated large scale rainfall (kg m-2)" respectively.
  • Subsurface layer depth metadata values for soil temperature and soil moisture content fields were found to be incorrect in APS2 and have been corrected in APS3.
  • The field "summed evaporation over open sea" from APS2 has been replaced by "average rate of evaporation over open sea (kg m-2 s-1)".
  • The description of the ACCESS-G field "roughness length" has been clarified as "surface roughness length for momentum (m)". In APS2 the ACCESS-R "roughness length" field was found to represent a different field (a roughness length quantity over the ocean) and this variant is deprecated, replaced with the ACCESS-G "surface roughness length for momentum (m)" valid over both land and sea.

Future releases

Updated sample data will be made available via this portal as the ACCESS NWP data content and/or format evolves.

Answers to frequently asked questions about ACCESS NWP data

  • Accumulated fields (including precipitation) are continuously accumulated from the start of the assimilation cycle (i.e. 3 hours prior to the nominal base date/time of the model run). As such this field can be non-zero at the nominal analysis (base) time.
  • Fog, visibility & probability of visibility fields are experimental and have not been tuned for Australian conditions. They are included for evaluation purposes only.

Getting help and providing feedback

If you have a query about any information presented here or require further information or assistance about ACCESS NWP products please contact the Bureau's Real-time Data Services Section.