ACCESS NWP Data
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. The ACCESS systems have been developed and tested by research staff from the Centre for Australian Weather and Climate Research (CAWCR) and formally replaced the GASP, LAPS, TXLAPS and MESOLAPS NWP models on Tuesday 17 August 2010. For more details about the ACCESS systems see the National Meteorological & Oceanographic Centre (NMOC) Operations Bulletin 83.
Available ACCESS-based models
The current roll-out of ACCESS models (version APS0) is designed to provide similar functionality to the GASP/LAPS family of NWP systems. The next version, APS1 (planned for release in 2011), will be a rationalised suite of models run at higher spatial resolutions with improved model physics. The following table describes the APS0 family of models and the legacy NWP models they have replaced.
| Model | Domain | Resolution | Legacy model equivalent |
|---|---|---|---|
| ACCESS-G | Global | Approximately 80km | Global Analysis and Prediction (GASP) |
| ACCESS-R | Regional | 0.375° (~37.5km) | Limited Area Prediction System (LAPS_PT375) |
| ACCESS-T | Tropical | 0.375° (~37.5km) | Tropical (Extended Domain) LAPS (TXLAPS_PT375) |
| ACCESS-A | Australia | 0.11° (~12km) | MesoLAPS (MESO_LAPS_PT125 & MA_LAPS_PT100) |
| ACCESS-C † | City | 0.05° (~5km) | City-based MesoLAPS variants (MESO_LAPS_PT050 models) |
| ACCESS-TC | Relocatable | 0.11° (~12km) | Tropical-cyclone LAPS (TCLAPS) |
| ACCESS-O3 | Global | Approximately 80km | A specialist model to replace the ozone and UV components of GASP |
† ACCESS-C consists of a set of models covering domains around Sydney, Melbourne, Brisbane, Perth and Adelaide.
NMOC has also implemented ACCESS-based wave and ocean models. Documentation of these systems will be available soon.
NWP data products
A range of NWP products, available via FTP for registered users, have been made available in NetCDF and GRIB edition 1 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 timestep. In addition to the native ACCESS model hybrid-height coordinates, data on pressure-levels and sigma-levels 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 timestep) as hours after base-time in the format HHH (e.g. 000, 048, 240), all = all timesteps 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, sigma) |
| ext: | file-type extension (e.g. grb, nc) |
Grid File ID Codes
| Product Code | Interpretation |
|---|---|
| IDY25000 series | ACCESS-G domains |
| IDY25100 series | ACCESS-T domains |
| IDY25200 series | ACCESS-A domains |
| IDY25300 series | ACCESS-R domains |
| IDY25400 series | ACCESS-C domains § |
| IDY25500 series | ACCESS-TC domains |
| IDY25600 series | ACCESS-O3 domains |
§ ACCESS-C domains consist of: Melbourne=IDY25400, Sydney=IDY25401, Brisbane=IDY25402, Perth=IDY25403 & Adelaide=IDY25404
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 | Radation 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 mositure 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. |
| sigma | Model data interpolated to a set of standard sigma levels. This grid-coordinate type is intended for backward compatibility with the LAPS/GASP family of models. Users of sigma level data are encouraged to migrate to model levels. |
| surface | Single-level fields. These share the same horizontal grid as all of the above multi-level coordinate 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 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). Raw data that has not undergone any interpolation may be made available on request.
Sample NWP data
Links are provided below to documentation for every ACCESS NWP product along with sample data files.
Data on hybrid height levels (model levels)
This data-set consists of ACCESS fields valid on all 50 ACCESS hybrid height levels.
| Fields.Levels | ACCESS-G | ACCESS-T | ACCESS-A | ACCESS-R | Melbourne | Sydney | Brisbane | Perth | Adelaide |
|---|---|---|---|---|---|---|---|---|---|
| all-flds.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 | HTML | PDF |
| pop-flds.lowest4-lvls | HTML | PDF | HTML | PDF | HTML | PDF | HTML | PDF | HTML | PDF | HTML | PDF | HTML | PDF | HTML | PDF | HTML | PDF |
| wind.rho-lvls | HTML | PDF | HTML | PDF | HTML | PDF | HTML | PDF | HTML | PDF | HTML | PDF | HTML | PDF | HTML | PDF | HTML | PDF |
| pop-flds.lowest15-lvls | HTML | PDF | ||||||||
| wind.rho-lvl-3 | 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). The interpolation is carried out using 3D cubic splines (in native model coordinate space). Physically constrained extrapolations are employed when required (e.g. when deriving data at 1000hPa for a location where surface pressure is 990hPa).
Data on sigma-levels
Sigma-level data comprises fields interpolated to the traditional 29 sigma levels as used by GASP/LAPS and MESO_LAPS_PT125. This data-set is provided for those who require backward compatibility with the GASP/LAPS models. Users are encouraged to explore ways of migrating their applications to make use of data on model hybrid-height levels. As with the pressure-level data, the interpolation to sigma levels is carried out using 3D cubic splines (in native model coordinate space).
| Fields.Levels | ACCESS-G | ACCESS-T | ACCESS-A | ACCESS-R | Melbourne | Sydney | Brisbane | Perth | Adelaide |
|---|---|---|---|---|---|---|---|---|---|
| all-flds.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 | HTML | PDF |
| pop-flds.lowest4-lvls | HTML | PDF | HTML | PDF | HTML | PDF | HTML | PDF | HTML | PDF | HTML | PDF | HTML | PDF | HTML | PDF | HTML | PDF |
| Sample Data | netcdf | grb | netcdf | grb | netcdf | grb | netcdf | grb | netcdf | grb | netcdf | grb | netcdf | grb | netcdf | grb | netcdf | grb |
Single-level data
Single-level data is provided separately from other level-types. This data can be mixed with any of the other multi-level files (model, pressure-level or sigma-level) since the horizontal grid is consistent with the horizontal layout of each of these formats.
GRIB tables
The GRIB-1 sample data contains header data referenced against the Bureau's local GRIB tables. These tables are available for download below.
Table 128 | Table 228 | Table 229 | Table 231
Note: These are UNIX formatted text-files and thus notepad in Windows will not read these files correctly. Please use wordpad or another text editor if using Windows. The formatting is fixed width with a header line to label the columns.
Customised data feeds
While efforts have been made to find subsets of data suitable for most users, the Bureau appreciates that the bandwidth required to download some of the NWP products files on a routine basis may in some cases be prohibitively expensive. As such, in the short term, it may be possible to receive a customised data feed. Please make enquiries via NMOC's Operations Development section for any such requests. There is no guarantee however of new customised products being issued. In the long term a user-driven interface to select a subset of ACCESS data may become available. Via such an interface users could establish an automatic generation and notification of customised data subsets.
The current set of ACCESS NWP products deliberately excludes a number of multi-level parameters due to current processing and disk-space constraints. If there is demand for some of these fields they may potentially be made available for a selection of ACCESS model domains and level-types. The parameters currently excluded are:
| Parameter | GRIB code.table |
|---|---|
| Cloud area fraction | 82.128 |
| Liquid cloud fraction | 83.128 |
| Ice cloud fraction | 84.128 |
| Convective cloud condensed water (kg/m3) | 88.128 |
| Convective cloud cover | 185.128 |
Future releases
Updated sample data will be made available via this portal as the ACCESS NWP data content and/or format evolves. Future releases may see the number of derived fields expanded (e.g. to include CAPE and lifted-index). A model upgrade (APS1) expected in 2011 is likely to bring about higher resolution data, additional outputs and consolidation of model domains.
Depending on end-user requirements some sigma-level products are hoped to be gradually phased-out.
To further reduce bandwidth requirements it is likely a NWP format supporting modern lossless compression will be eventually be adopted, most likely JPEG-2000 compressed GRIB-2.
NMOC would like to hear from anyone with specific needs not met by the current set of data or anyone with suggestions on ways to improve this service.
Answers to frequently asked questions about ACCESS NWP data
- Accumulated fields (including precipitation) are continuously accumulated from the start of the assimilation cycle (rather than reset every 24 hours as was the case with GASP). As such this field can be non-zero at the nominal analysis (base) time.
- Vertical wind in m/s replaces vertical up-motion on sigma-levels in Pa/s (known commonly as omega). Note: while an omega field is being derived, it is recommended that this field be avoided as there are problems with the calculation of this field that have yet to be resolved.
- Some spurious artifacts exist near the domain edges of ACCESS-R, ACCESS-T and ACCESS-A. Care should be taken when using data points from the outer 10 grid-points of these models until this is rectified.
- Meta-data in GRIB and NetCDF files indicating step-sizes for averaged, accumulated or max/min fields is currently sometimes wrong. Please refer to the ACCESS NWP Data information documents for more information.
- 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
An overview of the scientific and technical details of the ACCESS models can be found in Operations Bulletin 83. 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.