ACCESS-DN: single-level "group1" fields

A number of raw and post-processed NWP products are available as outputs from the Australian Community Climate Earth-System Simulator (ACCESS) suite of Numerical Weather Prediction models which are run routinely by the Bureau National Operations Centre (NOC). This document describes the content of the ACCESS-C DARWIN (version APS3) IDY25405.APS3.group1.slv.YYYYMMDDHH.HHH.surface and IDY25425.APS3.group1.slv.YYYYMMDDHH.HHH.surface series of products.

For background information about ACCESS please refer to the top-level ACCESS NWP technical data documentation page.

If you require further information or assistance about ACCESS NWP products contact the Bureau's Real-time Data Services Section.

Model summary

ACCESS-C DARWIN covers the Darwin domain, has a resolution of about 1.5 km and is run four times per day (00Z, 06Z, 12Z & 18Z basetimes) out to a forecast hour (HHH) of +36 (+42 for 18Z). This model is nested in the ACCESS-G model and consists of both an assimilation and forecast component.

NWP data filename convention

All NWP files in this product series have names that conform to the following convention:

IDY25405.APS3.group1.slv.YYYYMMDDHH.HHH.surface.grb2 or IDY25405.APS3.group1.slv.YYYYMMDDHH.HHH.surface.nc4 or

IDY25425.APS3.group1.slv.YYYYMMDDHH.HHH.surface.grb2 or IDY25425.APS3.group1.slv.YYYYMMDDHH.HHH.surface.nc4

where

YYYYMMDDHHBase-date of model run in UTC time. YYYY = year, MM = month, DD = day, HH = hour
HHHForecast hour. A HHH of 000 is the analysis time-step.

Horizontal grid geometries

Variant
[IDY code]
Resolution
[Lon x Lat]
Domain limits
[W to E, S to N (Lon x Lat grid points)]
Parameters
[NC Vars]
IDY25405
 0.014 by 0.013 127.000 to 139.029, -18.000 to -7.970 (892 x 744) All
IDY25425
 0.014 by 0.013 127.000 to 139.029, -18.000 to -7.970 (892 x 744) All

Please note that

  • Latitude values in GRIB and NetCDF files are ordered North to South while longitude values are ordered West to East.
  • Longitudes always lie in the range 0.0 to 360.0 degrees. Longitudes can be transformed to lie between -180 and +180 degrees by subtracting 360 degrees from any longitude values greater than 180.

Time steps

Forecast hours of single-level fields:
0 to 36 by 1

Parameters

The following fields are included in this product series. Note that the "G2 d.c.n" table column refers to a field's GRIB2 'discipline'.'parameterCategory'.'parameterNumber' metadata. For more information see GRIB2 format notes.

Single-level fields

G2 d.c.n NetCDF var Steps G2 Units NC Units Description
0.2.2 u10 All m s-1 m s-1 10m wind u component
0.2.3 v10 All m s-1 m s-1 10m wind v component
0.1.8 accum_prcp All kg m-2 kg m-2 Accumulated precipitation
0.3.1 mslp All Pa Pa Mean sea level pressure
0.0.6 dewpt_scrn All K K Screen level dewpoint temperature
0.0.4 tmax_scrn 1... K K Screen level max temperature
0.0.5 tmin_scrn 1... K K Screen level min temperature
0.1.1 rh2m All % % Screen level relative humidity w.r.t. water
0.0.0 temp_scrn All K K Screen level temperature
0.3.0 sfc_pres All Pa Pa Surface pressure
0.0.0 sfc_temp All K K Surface temperature
0.6.1 ttl_cld All % 1 Total cloud cover

Explanation of steps column terms

AllParameter available at all time-steps
All but stepsParameter available at all time-steps except as specified
hhh...Parameter available from fhr onward

Notes on specific NWP file-formats

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.

Appendix A - Extended Field Descriptions

Extended description of single-level fields

G2 d.c.n NetCDF var Detailed description
0.2.2 u10 Zonal (U) component of the wind velocity at 10m above ground level. [m s-1]
0.2.3 v10 Meridional (V) component of the wind velocity at 10m above ground level. [m s-1]
0.1.8 accum_prcp Accumulated total precipitation amount at the surface. This is the sum of rainfall and snowfall at the surface. [kg m-2]
0.3.1 mslp Atmospheric pressure at mean sea level. [Pa]
0.0.6 dewpt_scrn Dewpoint temperature at 1.5m above ground level (screen level). [K]
0.0.4 tmax_scrn Maximum (over a time window) atmospheric air temperature at 1.5m above ground level (screen level). [K]
0.0.5 tmin_scrn Minimum (over a time window) atmospheric air temperature at 1.5m above ground level (screen level). [K]
0.1.1 rh2m Relative humidity at 1.5m above ground level (screen level). Calculated as 100*water_vapour_pressure/saturation_partial_pressure_of_water_vapour where the the saturation partial pressure of water vapour represents the saturation vapour pressure over liquid water for temperatures above the triple point, over ice for temperatures 20 degrees below the triple point, and a linear combination of the two for temperatures in-between. [%]
0.0.0 temp_scrn Atmospheric temperature at 1.5m above ground level (screen level). Calculated by integrating the similarity equations from the surface to 1.5m. [K]
0.3.0 sfc_pres Atmospheric pressure at the surface. [Pa]
0.0.0 sfc_temp Temperature of the land or sea/sea-ice surface. On land points this is the surface "skin" temperature. On ice-free sea points it is the temperature of the sea surface, and on sea points with ice it is a gridbox mean given by: [(ice fraction)*(temperature of top ice layer computed by the atmosphere surface/boundary layer scheme)] + [(1 - ice fraction)*(freezing point of sea water)]. [K]
0.6.1 ttl_cld Total cloud coverage calculated with a maximum-random overlap assumption. [1]

Please note:

  • Fields in the above tables are listed in the same order as shown in the Parameters section of this document.
  • Units in the above table refer to NetCDF fields. In some cases the GRIB2 equivalent field has had values scaled/offset to convert to SI units for WMO GRIB2 compliance.
  • The nature of fields can not always be deduced easily from their NetCDF variable names. It is always safest to refer to the detailed description of a parameter.
  • All accumulated fields are accumulated from the start of the model assimilation window. Hence any of these fields can be non-zero at the model base-time (which is a time-step at the center of the assimilation window).
  • Maximum and minimum screen-level temperatures represent a maximum/minimum value over the period from the last model output time-step to the field's nominal forecast-hour.