WMO, and NWP centres, want radiosonde stations to move towards sending high-resolution reports in BUFR. Extra levels, and detailed position information, improves NWP forecasts.
For more details see Ingleby et al (2016, BAMS, http://journals.ametsoc.org/doi/abs/10.1175/BAMS-D-15-00169.1) 'Progress towards high-resolution, real-time radiosonde reports'.
There are various templates available, summarised here for convenience along with notes on when they should be used (these notes have no official standing).
Full documentation of the templates, and other coding issues, is at https://community.wmo.int/activity-areas/wis/wis-manuals
(309050 is BUFR PILOT format - pressure coordinate, if there are both pressure and height measurements I would suggest using 309052 or 309057)
309051 is BUFR PILOT format - height coordinate, use for wind-only ascents without a pressure sensor
309052 is BUFR TEMP ascent format (original template, 309057 is slightly better now)
309053 is BUFR dropsonde format
(509055 is BUFR TEMP ascent format with height coordinate but not pressure, not used in practice)
309056 is BUFR TEMP descent format
309057 is latest BUFR TEMP ascent format (compared to 309052 there is higher precision for height and pressure, plus extra metadata)
These are sometimes written with spaces, eg. 3 09 057.
There should be no need to provide reports in multiple templates: if 309057 is provided then it is better to stop sending 309052.
It is important that there should be one report containing all data from the ascent, although there can be earlier partial reports (particularly up to 100 hPa) for timeliness reasons.
Usually these BUFR reports are produced by the software from the radiosonde manufacturers. (Attempts to convert alphanumeric TEMP reports to BUFR are very problematic, and do not provide the higher resolution that WMO GBON will require shortly.)
Ideally there should be an overlap of 2-6 months between good quality BUFR made available over the GTS and the withdrawal of TAC reports - with notification of these changes via https://community.wmo.int/news/operational-newsletter .
Following approval of the plans for the Global Basic Observing Network (GBON) in October 2021, radiosonde data should be reported at high vertical resolution from January 2023 and details of the horizontal/time sampling required were set out. See https://public.wmo.int/en/events/constituent-bodies/cg-ext2021 and https://meetings.wmo.int/Cg-Ext-2021/SitePages/Session%20Information.aspx .
ECMWF provides a BUFR validator which can be used to check the content of BUFR messages.
It also provides ecCodes including a customised program for reading/printing BUFR radiosonde reports (bufr_read_tempf, available in Python or Fortran - ecCodes needs setting up first).
Example output is provided below. There is an option to print all levels or just standard levels.
Descriptors: [309057]
Ob: 1 65344 20220223 103600 6.356 2.388 6.0 nan 154 132
RS number/software/balloonwt 20127-028462 5.16.4.11 0.0
level dtime dlat dlon pressure geopotH airTemp dewPtT windDir windSp signif
1 0.0 0.000 0.000 101180.0 6.0 303.45 298.75 240.00 4.00 145408
2 21.0 0.001 0.001 100000.0 110.6 300.52 297.52 247.00 7.20 65536
3 21.0 0.001 0.002 99980.0 112.4 300.49 297.51 247.00 7.20 8192
4 57.0 0.002 0.004 97896.0 300.0 298.62 296.89 245.00 7.00 2048
5 59.0 0.002 0.004 97766.0 311.5 298.50 296.83 245.00 7.00 4096
6 99.0 0.003 0.006 95714.0 498.3 297.57 295.40 226.00 6.80 4096
7 121.0 0.004 0.006 94612.0 600.0 296.92 294.66 223.00 6.20 2048
8 161.0 0.006 0.008 92500.0 797.9 295.98 292.93 212.00 5.10 65536
9 181.0 0.007 0.008 91421.0 900.0 295.46 291.91 204.00 4.30 2048
10 259.0 0.008 0.008 87262.0 1305.1 293.78 288.90 125.00 2.10 4096
11 285.0 0.008 0.007 85934.0 1438.3 293.58 289.28 25.00 1.60 2048
12 300.0 0.008 0.007 85190.0 1513.3 293.18 289.43 11.00 2.50 4096
13 303.0 0.008 0.007 85000.0 1532.6 293.08 289.27 9.00 2.70 65536
...
129 5365.0 -0.031 -0.888 1220.0 29499.1 224.88 201.47 280.00 15.10 2048
130 5365.0 -0.031 -0.887 1220.0 29500.4 224.88 201.47 280.00 15.10 4096
131 5441.0 -0.033 -0.668 1132.0 30000.0 225.25 201.33 286.00 9.40 2048
132 5442.0 -0.033 -0.666 1132.0 30001.1 225.25 201.33 286.00 9.30 14336
Finishing normally. Number of BUFR records read: 1