IDY25403: 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 of Meteorology's National Meteorological & Oceanographic Centre (NMOC). This document describes the content of the ACCESS-C PERTH (version APS0) IDY25403.group1.slv.YYYYMMDDHH.HHH.surface series of products.

An overview of the scientific and technical details of the ACCESS models can be found in NMOC's Operations Bulletin 83 http://www.bom.gov.au/nwp/doc/bulletins/apob83.pdf

If you require further information or assistance about ACCESS NWP products contact the Bureau's Registered User Services section.

Model summary

ACCESS-C PERTH covers the Perth/Southwest WA domain, has a resolution of about 5 km and is run twice per day (00Z and 12Z basetimes) out to a forecast hour of +36. This model is nested in the ACCESS-R model and consists of only a forecast component.

NWP data filename convention

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

IDY25403.group1.slv.YYYYMMDDHH.HHH.surface.grb or IDY25403.group1.slv.YYYYMMDDHH.HHH.surface.nc

where

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

Horizontal grid geometries

Resolution
[Lon x Lat]
Domain limits
[W to E, N to S (Lon x Lat grid points)]
GRIB parameters
[code.table]
0.050 by 0.050 112.000 to 119.950, -28.050 to -37.000 (160 x 180) 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

Single-level fields

Par NetCDF var Steps Units Description
165.128 u10 All m s-1 10m wind u component
166.128 v10 All m s-1 10m wind v component
061.228 accum_prcp All kg m-2 Accumulated precipitation
151.128 mslp All Pa Mean sea level pressure
168.128 dewpt_scrn All K Screen level dewpoint temperature
201.128 tmax_scrn All K Screen level max temperature
202.128 tmin_scrn All K Screen level min temparature
101.128 rh2m All % Screen level relative humidity
167.128 temp_scrn All K Screen level temperature
134.128 sfc_pres All Pa Surface pressure
125.128 sfc_temp All K Surface temperature
164.128 ttl_cld All 0-1 Total cloud cover

Explanation of steps column terms

AllParameter available at all time-steps
fhr...Parameter available from fhr onward

Appendix A - Notes on specific NWP file-formats

GRIB-1

ACCESS data in GRIB-1 format is defined relative to the Bureau's local GRIB tables. A copy of these tables in plain-text format is available for download from the ACCESS NWP web data interface.

Local extensions are also present in the GRIB-1 message headers. The following tables summarise these.

Section 1 octet Value Remarks
29-30 Stash ID 16-bit UM STASH ID.
31 4V offset Number of hours from start of 4V assimilation window to nominal analysis time.
19 P1 period of time Be aware that currently this is sometimes being set incorrectly for averaged, accumulated and max/min quantities (at certain timesteps only).
APS0 Model name GeneratingProcessIdentifier (ID of model)
ACCESS-G 1
ACCESS-T 10
ACCESS-R 20
ACCESS-A 30
ACCESS-VT 50
ACCESS-SY 54
ACCESS-BN 58
ACCESS-AD 62
ACCESS-PH 66
ACCESS-TC 80
ACCESS-O3 90

NetCDF

  • ACCESS NetCDF files aim to be broadly compliant with CF 1.4 conventions (http://cf-pcmdi.llnl.gov/documents/cf-conventions/1.4/cf-conventions.html)
  • NetCDF data is of the "classic format" variant (compatible with the unidata NetCDF library version 3.6.x+)
  • Please ignore the accum_value metadata value. This parameter is not always set correctly for non-instantaneous fields.
  • Longitudes in the NetCDF files lie in the range [0.0 degrees, 360.0 degrees]. The NetCDF files somewhat misleadingly describe the valid range attribute for this dimension as -180 to +360.

Appendix B - Extended Field Descriptions

Extended description of single-level fields

Par NetCDF var Detailed description
165.128 u10 Zonal (U) component of the wind velocity at 10m above-ground-level. [m s-1]
166.128 v10 Meridional (V) component of the wind velocity at 10m above-ground-level. [m s-1]
061.228 accum_prcp Accumulated total precipitation amount at the surface. This is the sum of the large scale rainfall, convective rainfall and snowfall at the surface. [kg m-2]
151.128 mslp Atmospheric pressure at mean sea level. [Pa]
168.128 dewpt_scrn Dewpoint temperature at 1.5m above ground level (screen level). [K]
201.128 tmax_scrn Maximum atmospheric air temperature at 1.5m above ground-level (screen level). [K]
202.128 tmin_scrn Minimum atmospheric air temperature at 1.5m above ground-level (screen level). [K]
101.128 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. [%]
167.128 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]
134.128 sfc_pres Atmospheric pressure at the surface. [Pa]
125.128 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]
164.128 ttl_cld Total cloud coverage calculated with a maximum-random overlap assumption. [0-1]

Please note:

  • Fields in the above tables are listed in the same order as shown in the Parameters section of this document.
  • 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.