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.

For more details about the ACCESS systems see the following Bureau National Operations Centre (BNOC) Operations Bulletins:

Available ACCESS-based models

All of the ACCESS models have recently been upgraded from version APS1 to APS2. APS2 models assimilate more observational inputs and include improved model physics. APS2 ACCESS-G and city systems are also cofigured to run at higher horizontal spatial resolution compared to APS1.

The following table describes the APS2 family of models.

Model Domain Resolution
ACCESS-G Global Approximately 25km
ACCESS-R Regional 0.11° (~12km)
ACCESS-C § City 0.0135° (~1.5km)
ACCESS-TC Relocatable 0.11° (~12km)

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

The AUSWAVE model was also upgraded to align with the ACCESS APS2 upgrades. 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 (where vertical is with respect to the mean-sea-level surface). 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 these extra level types 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. APS2, APS1)
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
IDY25020 ACCESS-G (single-level subset only), full (global) domain
IDY25021 ACCESS-G (single-level subset only), subset to Australian region
IDY25300 ACCESS-R (single and multi-level data), full (greater Australian) domain
IDY25301 ACCESS-R (single and multi-level data), subset to Australian region
IDY25320 ACCESS-R (single-level subset only), full (greater Australian) domain
IDY25321 ACCESS-R (single-level subset only), subset to 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)
IDY25500 ACCESS-TC domain one §
IDY25501 ACCESS-TC domain two §
IDY25502 ACCESS-TC domain three §

§ Only runs for active named Tropical Cyclones. The order is determined by priority, and which tropical cyclone runs for each domain can vary from cycle to cycle.

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 over.
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 precipitations, 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)
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 labeled 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 available.

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 R R-AUS VicTas Sydney Brisbane Perth Adelaide Darwin
all-flds.slv HTML HTML HTML HTML HTML HTML HTML HTML HTML HTML
group1.slv HTML HTML HTML HTML HTML HTML HTML HTML HTML HTML
group2.slv HTML HTML HTML HTML HTML HTML HTML HTML HTML HTML
group3.slv HTML HTML HTML HTML HTML HTML HTML HTML HTML HTML
group4.slv HTML   HTML              
mask.surf HTML HTML HTML HTML HTML HTML HTML HTML HTML HTML
prec.surf HTML HTML HTML HTML HTML HTML HTML HTML HTML HTML
pres.msl HTML HTML HTML HTML HTML HTML HTML HTML HTML HTML
pres.surf HTML HTML HTML HTML HTML HTML HTML HTML HTML HTML
topog.surf HTML HTML HTML HTML HTML HTML HTML HTML HTML HTML
wind.10m HTML 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 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 R R-AUS 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 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 HTML            
wind.rho-lowest4-lvls HTML HTML HTML HTML HTML HTML HTML HTML HTML HTML
wind.rho-lvl-2 HTML HTML HTML HTML HTML HTML HTML HTML HTML HTML
wind.rho-lvl-4     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 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 R R-AUS VicTas Sydney Brisbane Perth Adelaide Darwin
all-flds.all-lvls HTML HTML HTML HTML HTML HTML HTML HTML HTML HTML
pop-flds.1000 HTML 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 HTML
pop-flds.500 HTML HTML HTML HTML HTML HTML HTML HTML HTML HTML
pop-flds.700 HTML HTML HTML HTML HTML HTML HTML HTML HTML HTML
pop-flds.850 HTML 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 netcdf | grb

Notes on specific NWP file-formats

Data files are made available in two formats, GRIB2 and NetCDF4. Meta-data for certain fields has changed with APS2. For details along with technical information bout the formats, please refer to GRIB2 format notes and NetCDF format notes.

Known metadata issues

The field "summed evaporation over open sea" from APS1 still exists in APS2, but is now actually the "average rate of evaporation over open sea", although the description metadata was not updated.

The soil temperature and moisture content at layer fields have incorrect depth information. The correct layer information is below.

Layer Listed depth Actual depth
layer 2 10 to 25 cm 10 to 35 cm
layer 3 25 to 65 cm 35 to 100 cm
layer 4 65 to 200 cm 100 to 300 cm

The fields "accumulated convective precipitation" and "accumulated large scale precipitation" should refer to "rainfall" instead of "precipitation". These fields refer only to water precipitation.

Other APS2 differences

  • New field "average total surface moisture flux" has been introduced.
  • APS1 versions of the fields "horizontal visibility" and "probability of horizontal visibility < 5km" omitted the effects of precipitation. These effects are included in APS2 modelling of these fields.

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. As such this field can be non-zero at the nominal analysis (base) time.
  • Some spurious artefacts exist near the domain edges of ACCESS-R, ACCESS-C and ACCESS-TC models. Care should be taken when using data points from the outer 10 grid-points of these models. This is the region that the parent model is directly influencing, acting as an inflow and outflow for information. This region generates divergence, and enhanced precipitation in particular can be evident near this boundary region.
  • Minor anomalies appear to be present in certain fields, including convective cloud base and cloud-top pressures as well as sensible heat fluxes which can appear excessive over small isolated regions at high latitudes).
  • 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.