IDY25000: single-level "group2" 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-G (version APS0) IDY25000.group2.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-G covers a global domain, has a resolution of about 80 km and is run twice per day (00Z and 12Z basetimes) out to a forecast hour of +240. This model 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:

IDY25000.group2.slv.YYYYMMDDHH.HHH.surface.grb or IDY25000.group2.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]
1.250 by 0.833 0.000 to 358.750, 90.000 to -90.000 (288 x 217) 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 240 by 3

Parameters

Single-level fields

Par NetCDF var Steps Units Description
057.228 accum_evap All kg m-2 Accumulated evaporation
058.228 accum_evap_sea All kg m-2 Accumulated evaporation over open sea
188.128 hi_cld All 0-1 High cloud cover
186.128 low_cld All 0-1 Low cloud cover
187.128 mid_cld All 0-1 Middle cloud cover
159.128 abl_ht All m Planetary boundary layer height
137.128 precwtr All but steps: 123 to 237 by 6 kg m-2 Precipitable water
140.128 soil_mois All kg m-2 Soil moisture content layer 1

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
057.228 accum_evap Evaporation from land soil surface. [kg m-2]
058.228 accum_evap_sea Evaporation from the open sea. It is weighted by the total sea (i.e. open sea and sea-ice) fraction. [kg m-2]
188.128 hi_cld High cloud cover, calculated under maximum overlap assumption between ICAO 500hPa and 150hPa levels (5574m and 13608m above mean sea level). [0-1]
186.128 low_cld Low cloud cover, calculated under maximum overlap assumption between ICAO 1000hPa and 800Pa levels (111m and 1949m above mean sea level). [0-1]
187.128 mid_cld Middle cloud cover, calculated under maximum overlap assumption between ICAO 800hPa and 500Pa levels (1949m and 5574m above mean sea level). [0-1]
159.128 abl_ht Height above ground level of the top of the planetary boundary layer (i.e. boundary layer depth). [m]
137.128 precwtr Total column precipitable water. [kg m-2]
140.128 soil_mois Total (frozen and unfrozen) soil moisture content in soil layer 1 (surface to 0.1m depth). [kg m-2]

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.