Upper Air Data Conversion

The upper air data conversion program called uacvt reformats and collates the data into a compact form. The upper air data is broadcast twice a day (observed at 0000 GMT and 1200 GMT) with special soundings taken at 0600 and 1800 GMT. Upper air data for a station is sent in up to 8 parts:

• TTAA -- contains lower atmosphere (below 100 mb) mandatory level data that normally arrives within an hour after observation. These data give height, temperature, dewpoint, wind directions and speed data for set pressure levels:
  surface, 1000, 925, 850, 700, 500, 400, 300, 250, 200, 150 and 100 millibars plus   tropopause and maximum wind level data.
• TTCC -- contains upper atmosphere (above 100 mb) mandatory level which arrives shortly after the TTAA data. These data give height, temperature, dewpoint, wind directions and speed data for set pressure levels:
  70, 50, 30, 20 and 10 millibars
• TTBB -- contains lower atmosphere significant level data. Significant level data contain temperature and dewpoint information at pressure levels other than the mandatory levels where changes in the temperature and dewpoint profiles occur.
• TTDD -- contains upper atmosphere significant level data. Significant level data contain temperature and dewpoint information at pressure levels other than the mandatory levels where changes in the temperature and dewpoint profiles occur
• PPAA -- contains lower atmosphere mandatory level wind information.   This information is included in the TTAA data but some stations only report wind data and thus the PPAA is more appropriate
• PPCC -- contains upper atmosphere mandatory level wind information.   This information is included in the TTCC reports but like the PPAA is for stations that only report winds.
• PPBB -- contains lower atmosphere (below 50,000 feet) significant wind data at heights.  These data only contain wind direction and speed information at heights in between mandatory levels reported at even multiples of 1000 feet.
• PPDD -- contains upper atmosphere (above 50,000 feet) significant wind data at heights.  These data only contain wind direction and speed information at heights in between mandatory levels reported at even multiples of 1000 feet.

The conversion process performed on these various reports takes two steps. The first step is to parse consecutive hourly data files for the occurrence of upper air data, since these data are generally captured over a two to four hour period. Once the appropriate upper air data is found (either a TTAA, TTBB, TTCC, TTDD, PAA, PPBB, PPCC or PPDD report) within one of the files, it is decoded and placed into a structured array for all reporting stations. Significant levels are then sorted and duplicate levels removed. This gives three arrays of data for a particular station. The first contains all the mandatory levels to 10 millibars plus the tropopause and maximum wind level. The second contains all the significant level information and the third contains the significant wind levels. The three arrays for each station are saved in a single file in either ASCII WXP or netCDF format with the file name representing the hour of the report.