ACCESS-G: Hybrid-height (lowest20-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 National Operations Centre (NOC). This document describes the content of the ACCESS-G (version APS3) IDY25001.APS3.pop-flds.lowest20-lvls.YYYYMMDDHH.HHH.model 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-G covers a global domain, has a resolution of about 12 km and is run four times per day (00Z, 06Z, 12Z & 18Z basetimes) out to a forecast hour (HHH) of +240 (+84 for 06Z and 18Z). 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:

IDY25001.APS3.pop-flds.lowest20-lvls.YYYYMMDDHH.HHH.model.grb2 or IDY25001.APS3.pop-flds.lowest20-lvls.YYYYMMDDHH.HHH.model.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

Resolution
[Lon x Lat]
Domain limits
[W to E, S to N (Lon x Lat grid points)]
Parameters
[NC Vars]
0.176 by 0.117 95.010 to 169.893, -54.902 to 4.980 (427 x 512) 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 to 20 by 1
All fields lie on eta "theta" levels.
Refer to Appendix B for more information.

Time steps

Forecast hours of multi-level fields:
0 to 117 by 3, 120 to 240 by 6

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.

Multi-level fields

G2 d.c.n NetCDF var Steps G2 Units NC Units Description
0.0.6 dewpt All K K Dew point
0.3.5 geop_ht All gpm gpm Geopotential height above msl
0.2.3 merid_wnd All m s-1 m s-1 Meridional wind
0.0.0 air_temp All K K Temperature
0.2.9 vertical_wnd All m s-1 m s-1 Vertical velocity
0.2.2 zonal_wnd All m s-1 m s-1 Zonal wind

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 multi-level fields

G2 d.c.n NetCDF var Detailed description
0.0.6 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]
0.3.5 geop_ht Geopotential height of level (m above the geoid). [gpm]
0.2.3 merid_wnd Meridional (V) component of the wind velocity. [m s-1]
0.0.0 air_temp Air temperature. [K]
0.2.9 vertical_wnd Vertical (W) component of the wind velocity. Positive values indicate air moving upward. [m s-1]
0.2.2 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.
  • 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.
  • The geoid surface is at approximately mean sea level.

Appendix B - Hybrid Height Levels

Level index A [theta] B [theta] A [rho] B [rho]
70 80000.00000000 0.00000000 76066.67200000 0.00000000
69 72133.34400000 0.00000000 68660.28000000 0.00000000
68 65187.22400000 0.00000000 62123.60800000 0.00000000
67 59060.00000000 0.00000000 56359.72800000 0.00000000
66 53659.45600000 0.00000000 51280.76800000 0.00000000
65 48902.07200000 0.00000000 46807.21600000 0.00000000
64 44712.36000000 0.00000000 42867.37600000 0.00000000
63 41022.38400000 0.00000000 39396.71200000 0.00000000
62 37771.03200000 0.00000000 36337.28800000 0.00000000
61 34903.54400000 0.00000000 33637.26400000 0.00000000
60 32370.98400000 0.00000000 31250.37600000 0.00000000
59 30129.77600000 0.00000000 29135.48800000 0.00000000
58 28141.20800000 0.00000000 27256.11200000 0.00000000
57 26371.02400000 0.00000000 25580.04000000 0.00000000
56 24789.04800000 0.00000000 24078.89600000 0.00000000
55 23368.75200000 0.00000000 22727.84800000 0.00000000
54 22086.94400000 0.00000000 21505.20000000 0.00000000
53 20923.45600000 0.00000000 20392.11200000 0.00000000
52 19860.77600000 0.00000000 19372.30400000 0.00000000
51 18883.84000000 0.00000000 18431.78400000 0.00000000
50 17979.72800000 0.00060152 17558.57600000 0.00224440
49 17137.42400000 0.00493146 16742.52000000 0.00839963
48 16347.60800000 0.01278598 15975.03200000 0.01776593
47 15602.45600000 0.02356307 15248.94400000 0.02981912
46 14895.43200000 0.03681088 14558.28800000 0.04416431
45 14221.14400000 0.05218690 13898.15200000 0.06050034
44 13575.16000000 0.06942793 13264.53600000 0.07859300
43 12953.90400000 0.08832635 12654.20800000 0.09825544
42 12354.50400000 0.10871357 12064.60800000 0.11933256
41 11774.70400000 0.13044661 11493.72000000 0.14169087
40 11212.73600000 0.15339991 10939.99200000 0.16521013
39 10667.24800000 0.17745828 10402.24000000 0.18977850
38 10137.23200000 0.20251217 9879.60000000 0.21528775
37 9621.96000000 0.22845450 9371.43200000 0.24163253
36 9120.90400000 0.25518005 8877.30400000 0.26870724
35 8633.70400000 0.28258377 8396.92000000 0.29640685
34 8160.13600000 0.31056000 7930.08800000 0.32462663
33 7700.04000000 0.33900481 7476.68800000 0.35326258
32 7253.34400000 0.36781349 7036.67200000 0.38221036
31 6820.00000000 0.39688360 6610.00000000 0.41136875
30 6400.00000000 0.42611351 6196.66400000 0.44063777
29 5993.33600000 0.45540484 5796.66400000 0.46992007
28 5600.00000000 0.48466241 5410.00000000 0.49912144
27 5220.00000000 0.51379300 5036.66400000 0.52815145
26 4853.33600000 0.54270712 4676.67200000 0.55692090
25 4500.00000000 0.57131907 4330.00000000 0.58534697
24 4160.00000000 0.59954500 3996.66400000 0.61334673
23 3833.33600000 0.62730483 3676.66400000 0.64084168
22 3520.00000000 0.65452232 3370.00000000 0.66775644
21 3220.00000000 0.68112302 3076.66400000 0.69401952
20 2933.33600000 0.70703624 2796.66400000 0.71956113
19 2660.00000000 0.73219523 2530.00000000 0.74431532
18 2400.00000000 0.75653489 2276.66400000 0.76822004
17 2153.33600000 0.77999398 2036.66400000 0.79121490
16 1920.00000000 0.80251517 1810.00000000 0.81324336
15 1700.00000000 0.82404277 1596.66400000 0.83425283
14 1493.33600000 0.84452495 1396.66400000 0.85419230
13 1300.00000000 0.86391385 1210.00000000 0.87301465
12 1120.00000000 0.88216313 1036.66400000 0.89067675
11 953.33600000 0.89923042 876.66400000 0.90713696
10 800.00000000 0.91507727 730.00000000 0.92235760
9 660.00000000 0.92966677 596.66400000 0.93630497
8 533.33600000 0.94296594 476.66400000 0.94894683
7 420.00000000 0.95494578 370.00000000 0.96025493
6 320.00000000 0.96557879 276.66400000 0.97020499
5 233.33600000 0.97484139 196.66400000 0.97877419
4 160.00000000 0.98271404 130.00000000 0.98594368
3 100.00000000 0.98917861 76.66400000 0.99169863
2 53.33600000 0.99422098 36.66400000 0.99602561
1 20.00000000 0.99783101 10.00000000 0.99891521
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 (m) 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.