ACCESS-DN: Hybrid-height (rho-lvl-4) "wind" 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.wind.rho-lvl-4.YYYYMMDDHH.HHH.model and IDY25425.APS3.wind.rho-lvl-4.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-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.wind.rho-lvl-4.YYYYMMDDHH.HHH.model.nc4 or

IDY25425.APS3.wind.rho-lvl-4.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

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.

Vertical levels

Eta-level index values:
4
All fields lie on eta "rho" levels.
Refer to Appendix B for more information.

Time steps

Forecast hours of multi-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.

Multi-level fields

G2 d.c.n NetCDF var Steps G2 Units NC Units Description
0.2.3 merid_wnd All m s-1 m s-1 Meridional wind
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
0.2.3 merid_wnd Meridional (V) component of the wind velocity. [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.

Appendix B - Hybrid Height Levels

Level index A [theta] B [theta] A [rho] B [rho]
80 38500.00000000 0.00000000 37771.77250000 0.00000000
79 37044.54215000 0.00000000 36351.59990000 0.00000000
78 35658.65380000 0.00000000 34997.77820000 0.00000000
77 34336.90260000 0.00000000 33706.01465000 0.00000000
76 33075.12285000 0.00000000 32472.27060000 0.00000000
75 31869.41450000 0.00000000 31292.77305000 0.00000000
74 30716.13160000 0.00000000 30163.98770000 0.00000000
73 29611.84380000 0.00000000 29082.61510000 0.00000000
72 28553.38255000 0.00000000 28045.57525000 0.00000000
71 27537.77180000 0.00000000 27050.01145000 0.00000000
70 26562.24725000 0.00000000 26093.24025000 0.00000000
69 25624.23325000 0.00000000 25172.78610000 0.00000000
68 24721.33510000 0.00000000 24286.33130000 0.00000000
67 23851.32750000 0.00000000 23431.74680000 0.00000000
66 23012.16225000 0.00000000 22607.04600000 0.00000000
65 22201.92590000 0.00000000 21810.39245000 0.00000000
64 21418.86285000 0.00000000 21040.09600000 0.00000000
63 20661.33300000 0.00000000 20294.59355000 0.00000000
62 19927.85410000 0.00000000 19572.44520000 0.00000000
61 19217.04015000 0.00000000 18872.32655000 0.00000000
60 18527.61680000 0.00000000 18193.02485000 0.00000000
59 17858.43290000 0.00033824 17533.42360000 0.00131448
58 17208.42200000 0.00292895 16892.51025000 0.00511000
57 16576.60235000 0.00789405 16269.34925000 0.01118031
56 15962.10000000 0.01503696 15663.09745000 0.01933777
55 15364.09490000 0.02417879 15072.98100000 0.02941112
54 14781.86325000 0.03515562 14498.29920000 0.04124341
53 14214.73130000 0.04781717 13938.42065000 0.05469007
52 13662.11000000 0.06202431 13392.77555000 0.06961739
51 13123.44495000 0.07764869 12860.84800000 0.08590121
50 12598.25490000 0.09457027 12342.17215000 0.10342571
49 12086.09325000 0.11267726 11836.33605000 0.12208212
48 11586.57885000 0.13186391 11342.96625000 0.14176817
47 11099.35365000 0.15203105 10861.73165000 0.16238703
46 10624.10580000 0.17308439 10392.33580000 0.18384681
45 10160.56195000 0.19493402 9934.52075000 0.20605965
44 9708.48340000 0.21749382 9488.06320000 0.22894117
43 9267.64300000 0.24068210 9052.75140000 0.25241116
42 8837.85980000 0.26441926 8628.41210000 0.27639167
41 8418.96440000 0.28862917 8214.89130000 0.30080760
40 8010.82205000 0.31323744 7812.05810000 0.32558604
39 7613.29800000 0.33817312 7419.79700000 0.35065648
38 7226.29215000 0.36336634 7038.00405000 0.37595074
37 6849.71210000 0.38874963 6666.59840000 0.40140201
36 6483.48085000 0.41425727 6305.50305000 0.42694588
35 6127.52910000 0.43982561 5954.66410000 0.45251885
34 5781.80295000 0.46539237 5614.02765000 0.47805979
33 5446.25620000 0.49089700 5283.55135000 0.50350900
32 5120.85035000 0.51628065 4963.20055000 0.52880838
31 4805.55460000 0.54148597 4652.94830000 0.55390134
30 4500.34200000 0.56645742 4352.76765000 0.57873333
29 4205.19330000 0.59114084 4062.64320000 0.60325087
28 3920.09310000 0.61548370 3782.56109000 0.62740228
27 3645.02831000 0.63943522 3512.50707500 0.65113782
26 3379.98584000 0.66294654 3252.47345500 0.67440911
25 3124.96184000 0.68596985 3002.45522500 0.69716936
24 2879.94899500 0.70845952 2762.44661000 0.71937373
23 2644.94384000 0.73037141 2532.44376000 0.74097903
22 2419.94329500 0.75166317 2312.44436500 0.76194377
21 2204.94543500 0.77229419 2102.44727000 0.78222815
20 1999.94910500 0.79222559 1902.45132000 0.80179422
19 1804.95353500 0.81142029 1712.45613000 0.82060576
18 1619.95834000 0.82984297 1532.46054500 0.83862844
17 1444.96236500 0.84746022 1362.46456500 0.85582964
16 1279.96676500 0.86424018 1202.46857500 0.87217849
15 1124.97077000 0.88015304 1052.47257500 0.88764599
14 979.97438000 0.89517070 912.47618000 0.90220500
13 844.97798000 0.90926683 782.47977500 0.91583009
12 719.98118500 0.92241700 662.48297500 0.92849775
11 604.98438000 0.93459852 552.48578000 0.94018622
10 499.98718000 0.94579057 452.48819000 0.95087555
9 404.98958500 0.95597413 362.49062850 0.96054759
8 319.99171050 0.96513196 282.49267200 0.96918605
7 244.99363350 0.97324864 212.49447450 0.97677643
6 179.99531550 0.98031060 152.49603600 0.98330603
5 124.99675650 0.98630603 102.49735650 0.98876398
4 79.99791800 0.99122498 62.49839750 0.99314121
3 44.99883850 0.99505929 32.49915900 0.99643049
2 19.99948335 0.99780262 12.49967565 0.99862635
1 4.99987180 0.99945043 2.49993513 0.99972520
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.