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:
- 83. Operational Implementation of the ACCESS Numerical Weather Prediction systems
- 93. APS1 upgrade of the ACCESS-G Numerical Weather Prediction system
- 98. APS1 upgrade of the ACCESS-R Numerical Weather Prediction system
- 99. APS1 upgrade of the ACCESS-C Numerical Weather Prediction system
Available ACCESS-based models
The original roll-out of ACCESS models (version APS0) was designed to provide similar functionality to the old GASP/LAPS family of NWP systems which were decommissioned in 2010.
The current version, APS1, is a rationalised suite of models run at higher spatial resolutions with improved model physics. ACCESS-A and ACCESS-T became redundant with the release of the APS1 version of ACCESS-R.
The following table describes the APS1 family of models and the legacy NWP models they have replaced.
| Model | Domain | Resolution | Legacy model equivalent |
|---|---|---|---|
| ACCESS-G | Global | Approximately 40km | Global Analysis and Prediction (GASP), ACCESS-T |
| ACCESS-R | Regional | 0.11° (~12km) | Limited Area Prediction System (LAPS_PT375), ACCESS-A, ACCESS-T |
| ACCESS-C § | City | 0.036° (~4km) | City-based MesoLAPS variants (MESO_LAPS_PT050 models) |
| ACCESS-TC | Relocatable | 0.11° (~12km) | Tropical-cyclone LAPS (TCLAPS) |
§ ACCESS-C consists of a set of models covering domains around Sydney, Melbourne, Brisbane, Perth and Adelaide.
BNOC has also implemented the ACCESS-based AUSWAVE model. 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. For each output forecast-hour the ACCESS models output various meteorological parameters defined on three-dimensional grids. 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.fields.levels.base-time.forecast-hour.grid-coords.ext
File-name key
| IDYnnnnn | grid file ID code (defines the model and the domain) |
|---|---|
| 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, full (global) domain |
| IDY25001 | ACCESS-G, subset to Australian region |
| IDY25300 | ACCESS-R full (greater Australian) domain |
| IDY25301 | ACCESS-R, subset to Australian region |
| IDY25400 | ACCESS-C, "VicTas" domain (ACCESS-VT) |
| IDY25401 | ACCESS-C, "Sydney" domain (ACCESS-SY) |
| IDY25402 | ACCESS-C, "Brisbane" domain (ACCESS-BN) |
| IDY25403 | ACCESS-C, "Perth" domain (ACCESS-PH) |
| IDY25404 | ACCESS-C, "Adelaide" domain (ACCESS-AD) |
| IDY25500 series | ACCESS-TC domains |
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. |
| 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 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.
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 | Melbourne | Sydney | Brisbane | Perth | Adelaide |
|---|---|---|---|---|---|---|---|---|---|
| all-flds.all-lvls | HTML | PDF | HTML | PDF | HTML | PDF | HTML | PDF | HTML | PDF | ||||
| geopht.all-lvls | HTML | PDF | HTML | PDF | HTML | PDF | HTML | PDF | HTML | PDF | HTML | PDF | HTML | PDF | HTML | PDF | HTML | PDF |
| pop-flds.all-lvls | HTML | PDF | HTML | PDF | HTML | PDF | HTML | PDF | HTML | PDF | HTML | PDF | HTML | PDF | HTML | PDF | |
| pop-flds.lowest20-lvls | HTML | PDF | HTML | PDF | |||||||
| pop-flds.lowest4-lvls | HTML | PDF | HTML | PDF | HTML | PDF | HTML | PDF | |||||
| wind.rho-lvl-2 | HTML | PDF | HTML | PDF | HTML | PDF | HTML | PDF | |||||
| wind.rho-lvl-4 | HTML | PDF | ||||||||
| 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 employed 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.
Notes on specific NWP file-formats
Data files are made available in two formats, GRIB2 and NetCDF4. For technical notes about the GRIB2 encoding of ACCESS data, please refer to GRIB2 format notes. For technical notes about the NetCDF4 encoding of ACCESS data, please refer to NetCDF format notes.
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 and ACCESS-C models. Care should be taken when using data points from the outer 10 grid-points of these models until this is rectified.
- Metadata in NetCDF files indicating step-sizes for averaged, accumulated or max/min fields is currently sometimes wrong and a technical limitation prevented correct encoding of similar metadata for accumulated GRIB2 fields. Please refer to the notes on specific NWP file-formats for more information (NetCDF format notes and GRIB2 format notes).
- Minor anomalies are present in some fields including friction velocity (under strong wind conditions at high altitudes) and convective cloud base and cloud-top pressures. There may be anomalies in sensible heat fluxes (some small areas appear to have values too large 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 Registered User Services section.