IDY25402: Hybrid-height (lowest4-lvls) "pop-flds" 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 BRISBANE (version APS0) IDY25402.pop-flds.lowest4-lvls.YYYYMMDDHH.HHH.model 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 BRISBANE covers the South-East QLD 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:

IDY25402.pop-flds.lowest4-lvls.YYYYMMDDHH.HHH.model.grb or IDY25402.pop-flds.lowest4-lvls.YYYYMMDDHH.HHH.model.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 0.050 148.000 to 155.950, -22.050 to -31.000 (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.

Vertical levels

Eta-level index values:
1, 2, 3, 4
All fields lie on eta "theta" levels.
Refer to Appendix C for more information.

Time steps

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

Parameters

Multi-level fields

Par NetCDF var Steps Units Description
017.228 dewpt All K Dew point
156.128 geop_ht All m Geopotential height
132.128 merid_wnd All m s-1 Meridional wind
130.128 air_temp All K Temperature
134.228 vertical_wnd All m s-1 Vertical velocity
131.128 zonal_wnd All m s-1 Zonal wind

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

For native (hybrid-height) level data, a GRIB-1 message will include a list of vertical coordinate parameters ("PV") values corresponding to "A" and "B" values for either "rho" or "theta" levels. Level parameters 1..50 are the A(k) values and level parameters 51..100 are the B(k) values listed in Appendix C.

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 multi-level fields

Par NetCDF var Detailed description
017.228 dewpt Dewpoint temperature. Calculated by (iteratively) finding the temperature at which the partial pressure due to water vapour equals the saturated water vapour partial pressure where 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. [K]
156.128 geop_ht Geopotential height of level (m above the geoid). [m]
132.128 merid_wnd Meridional (V) component of the wind velocity. [m s-1]
130.128 air_temp Air temperature. [K]
134.228 vertical_wnd Vertical (W) component of the wind velocity. [m s-1]
131.128 zonal_wnd Zonal (U) component of the wind velocity. [m s-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.
  • The geoid surface is at approximately mean sea level.

Appendix C - Hybrid Height Levels

Level index A [theta] B [theta] A [rho] B [rho]
50 62918.64700000 0.00000000 59968.64960862 0.00000000
49 57018.64592538 0.00000000 54506.41131237 0.00000000
48 51994.17669936 0.00000000 49855.77951937 0.00000000
47 47717.38863124 0.00000000 45895.45337006 0.00000000
46 44073.51810888 0.00000000 42516.86044718 0.00000000
45 40960.20278548 0.00000000 39623.48354624 0.00000000
44 38286.76430699 0.00000000 37130.13081919 0.00000000
43 35973.49733139 0.00000000 34962.21850189 0.00000000
42 33950.94596425 0.00000000 33055.09139267 0.00000000
41 32159.23052923 0.00000000 31353.28041235 0.00000000
40 30547.32400360 0.00000000 29809.82308279 0.00000000
39 29072.32216198 0.00000000 28385.54625438 0.00000000
38 27698.77663865 0.00000000 27048.35512528 0.00000000
37 26397.93990378 0.00000000 25772.52855260 0.00000000
36 25147.11090956 0.00000000 24537.99548795 0.00000000
35 23928.88006635 0.00000000 23329.66174791 0.00000000
34 22730.44342948 0.00000000 22136.66757401 0.00000000
33 21542.89171854 0.00000000 20951.69552760 0.00000000
32 20360.49933666 0.00000000 19770.26580102 0.00000000
31 19180.03226537 0.00000000 18590.01265313 0.00000000
30 17999.99933275 0.00000000 17409.99859611 0.00000000
29 16819.99785946 0.00114844 16249.99896069 0.00443934
28 15680.00006192 0.00987402 15130.00300104 0.01715025
27 14579.99964829 0.02642257 14049.99813342 0.03724613
26 13520.00291041 0.04992301 13009.99694156 0.06387166
25 12499.99726457 0.07953637 12009.99942547 0.09620329
24 11520.00158636 0.11445445 11049.99929327 0.13344941
23 10579.99700018 0.15390196 10130.00283684 0.17484966
22 9680.00238163 0.19713380 9249.99747243 0.21967618
21 8819.99885511 0.24343826 8410.00207566 0.26723123
20 7999.99900435 0.29213375 7609.99777092 0.31685076
19 7220.00282936 0.34257095 6849.99714194 0.36790059
18 6479.99774639 0.39413311 6130.00018873 0.41977890
17 5780.00263106 0.44623297 5450.00061941 0.47191604
16 5119.99860776 0.49831768 4809.99843399 0.52377363
15 4499.99826022 0.54986368 4209.99992433 0.57484440
14 3920.00158845 0.60038002 3649.99879858 0.62465380
13 3380.00230057 0.64940801 3130.00134858 0.67275785
12 2880.00039659 0.69652009 2650.00128248 0.71874541
11 2420.00216837 0.74131978 2209.99860028 0.76223643
10 2000.00132405 0.78344345 1809.99959384 0.80288190
9 1619.99786363 0.82255856 1449.99797130 0.84036573
8 1279.99807897 0.85836360 1130.00002453 0.87440222
7 980.00197008 0.89058931 849.99946165 0.90473866
6 719.99695322 0.91899952 610.00257453 0.93115265
5 500.00190398 0.94338632 410.00307131 0.95345487
4 319.99794678 0.96357758 250.00095199 0.97148696
3 179.99766534 0.97942938 130.00250843 0.98512152
2 80.00105966 0.99083087 50.00144877 0.99426426
1 20.00183788 0.99770358 9.99777301 0.99885182
Notes:
  • [theta] and [rho] denote the level types on which the parameters A and B are valid.

  • A values represent the height of the hybrid levels above the geoid assuming zero topography.

  • B values represent the fraction of the topographic height included in the hybrid levels.

  • The height of a hybrid-height level can be calculated via:

    z(k, i, j) = A(k) + B(k)*topo(i, j)
    where k denotes the level index,
    z(k, i, j) is the height above the geoid at grid-point (i, j, k),
    topo(i, j) is the height of the surface above the geoid at (i, j) and
    A(k) & B(k) are the values of A and B at level k.