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 have been upgraded to APS4. APS4 global model assimilates more observational inputs and includes improved model physics compared with APS3 global system.The upgrade to ACCESS-C and ACCESS-CE systems is limited to the technical upgrade only. Products from all ACCESS NWP systems remain unchanged from APS3 to APS4.

Model Domain Resolution
ACCESS-G/GE Global ACCESS-G: 0.17578125° longitude by 0.1171875° latitude (~12km in the mid-latitudes, ~17km in tropics) ACCESS-GE: ~33km
ACCESS-C § City 0.0135° (~1.5km)
ACCESS-CE City Ensemble 0.0198° (~2km)

§ ACCESS-C and ACCESS-CE consists of a set of models covering domains around Sydney, Victoria and Tasmania, Brisbane, Perth, Adelaide, Darwin and North Queensland.

The AUSWAVE model has also been upgraded to use APS4 data as inputs. 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

IDYnnnnn grid file ID code (defines the model and the domain)
version model version number (e.g. APS3, APS2)
fields alphanumeric descriptor of fields (e.g. all-flds, pop-flds)
levels alphanumeric descriptor of levels (e.g. all-lvls, pop-lvls)
base-time model run's UTC base time in the format YYYYMMDDHH, where YYYY = year, MM = month, DD = day, HH = hour (e.g. 2010122500)
forecast-hour product'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-coords descriptor of model grid co-ordinate level-type (e.g. surface, model, pressure)
ext file-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
IDY25400 ACCESS-C (single and multi-level data), "VicTas" domain (ACCESS-VT)
IDY25401 ACCESS-C (single and multi-level data), "Sydney" domain (ACCESS-SY)
IDY25402 ACCESS-C (single and multi-level data), "Brisbane" domain (ACCESS-BN)
IDY25403 ACCESS-C (single and multi-level data), "Perth" domain (ACCESS-PH)
IDY25404 ACCESS-C (single and multi-level data), "Adelaide" domain (ACCESS-AD)
IDY25405 ACCESS-C (single and multi-level data), "Darwin" domain (ACCESS-DN)
IDY25420 ACCESS-C (single-level subset only), "VicTas" domain (ACCESS-VT)
IDY25421 ACCESS-C (single-level subset only), "Sydney" domain (ACCESS-SY)
IDY25422 ACCESS-C (single-level subset only), "Brisbane" domain (ACCESS-BN)
IDY25423 ACCESS-C (single-level subset only), "Perth" domain (ACCESS-PH)
IDY25424 ACCESS-C (single-level subset only), "Adelaide" domain (ACCESS-AD)
IDY25425 ACCESS-C (single-level subset only), "Darwin" domain (ACCESS-DN

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).
helicity Updraft helicity.
radar Derived radar reflectivity.
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 VicTas Sydney Brisbane Perth Adelaide Darwin
all-flds.slv HTML HTML HTML HTML HTML HTML HTML HTML HTML
group1.slv HTML HTML HTML HTML HTML HTML HTML HTML HTML
group2.slv HTML HTML HTML HTML HTML HTML HTML HTML HTML
group3.slv HTML HTML HTML HTML HTML HTML HTML HTML HTML
group4.slv HTML   HTML            
helicity.slv       HTML HTML HTML HTML HTML HTML
mask.surf HTML HTML HTML HTML HTML HTML HTML HTML HTML
prec.surf HTML HTML HTML HTML HTML HTML HTML HTML HTML
pres.msl HTML HTML HTML HTML HTML HTML HTML HTML HTML
pres.surf HTML HTML HTML HTML HTML HTML HTML HTML HTML
radar.slv       HTML HTML HTML HTML HTML HTML
syncld.slv HTML HTML HTML            
topog.surf HTML HTML HTML HTML HTML HTML HTML HTML HTML
wind.10m HTML HTML HTML HTML HTML HTML HTML HTML HTML
Sample Data netcdf | grb netcdf | grb netcdf | grb netcdf | grb netcdf | grb netcdf | grb 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 for ACCESS-G, and all 80 ACCESS hybrid-height levels for ACCESS-C.

Fields.Levels G G-AUS G-REG VicTas Sydney Brisbane Perth Adelaide Darwin
all-flds.all-lvls       HTML HTML HTML HTML HTML HTML
geopht.all-lvls HTML HTML HTML HTML HTML HTML HTML HTML HTML
pop-flds.all-lvls HTML HTML HTML HTML HTML HTML HTML HTML HTML
pop-flds.lowest20-lvls   HTML HTML            
pop-flds.lowest4-lvls HTML HTML HTML            
wind.rho-lowest4-lvls HTML HTML HTML HTML HTML HTML HTML HTML HTML
wind.rho-lvl-2 HTML HTML HTML HTML HTML HTML HTML HTML HTML
wind.rho-lvl-4 HTML   HTML HTML HTML HTML HTML HTML HTML
wind.rho-lvls         HTML        
Sample Data netcdf | grb netcdf | grb netcdf | grb netcdf | grb netcdf | grb netcdf | grb 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 VicTas Sydney Brisbane Perth Adelaide Darwin
all-flds.all-lvls HTML HTML HTML HTML HTML HTML HTML HTML HTML
pop-flds.1000 HTML HTML HTML           HTML
pop-flds.200 HTML HTML HTML HTML HTML HTML HTML HTML HTML
pop-flds.250   HTML              
pop-flds.300 HTML HTML HTML HTML HTML HTML HTML HTML HTML
pop-flds.500 HTML HTML HTML HTML HTML HTML HTML HTML HTML
pop-flds.700 HTML HTML HTML HTML HTML HTML HTML HTML HTML
pop-flds.850 HTML HTML HTML HTML HTML HTML HTML HTML HTML
pop-flds.all-lvls   HTML HTML HTML HTML HTML HTML HTML HTML
Sample Data netcdf | grb netcdf | grb netcdf | grb netcdf | grb netcdf | grb netcdf | grb 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 APS4 differences

APS4 represents a significant upgrade to the Bureau's global NWP capability and results in an overall increase in forecast skill.

There are major changes to the physics of the global model and the ensemble generation compared to ACCESS-G3/GE3.

Key enhancements include:

  • An upgrade of the model configuration from GA6/GL6 (global atmosphere/land version 6) to GA8/GL9 (global atmosphere version 8; land version 9). This represents significant physics changes affecting most areas of model science, but especially as related to the convection scheme and the representation of the land surface.
  • An improved method of ensemble generation – ensemble of four-dimensional ensemble-variational (En4DEnVar) data assimilation (DA) – which is more closely aligned with the DA system of ACCESSG and produces more reliable probability forecasts.
  • Improved land surface DA with the inclusion of analyses of soil-, skin- and snow temperature

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 for ACCESS-G , 30 minutes for ACCESS-C). As such this field can be non-zero at the nominal analysis (base) time.
  • ACCESS-C domains do not have 'group3' products available at the analysis timestep because it only has 'average' products. ACCESS-C does not generate minimum, maximum and average fields at the nominal analysis 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.