Decoding Radiosonde Code

Radiosonde observations are usually separated into several sections. The 3 most widely used sections are:

TTAA - mandatory level data
TTBB - significant level data
PPBB - standard level wind data

Click one of the above links for information about decoding those observations.

TTAA's - Observations of thermodynamic data at the mandatory levels - levels that must be included in the sounding.

Example of TTAA section of sounding:

TTAA  81001 72518 99030 08863 33004 00263 10464 34016
92904 04461 00518 85585 00079 01526 70138 04182 32526 50572
17372 31549 40736 28766 31052 30935 45763 30055 25054 55158
29568 20193 63557 28573 15371 58560 27071 10624 62164 28053
88192 64957 28579 77182 28581 41314 51515 10164 00021 10194
36018 34526=

Decoding the TTAA section

data are orgainized in groups of 5 characters, and 3 groups per atmospheric level

data identification (level): symbolically, TTAA DDHHF IIIII

TTAA  - signals the start of the data identification (level) of the mandatory level data
DD    - day of month (GMT) plus 50                 ; e.g., 81 decodes to the 31st day of month, 81 - 50 = 31
HH    - hour GMT                                   ; e.g., 00 decodes to 00 GMT
F     - wind level flag or level of last wind group; e.g., 1  decodes to 100 mb and above
IIIII - block and station number                   ; e.g., 72518 is Albany, New York

each mandatory level (data): symbolically, CCLLL TTTDD WWWSS

follows the data indentification section

first group: CCLLL

CC  - a code for the level and signals the start of data at that level; e.g., 00 decodes to 1000 mb
LLL - the level, either pressure (at the surface) or height (otherwise); see table below

CC     level           LLL decoding
99     surface         pressure in whole millibars, without a thousands digit. 
			  030 decodes to 1030 mb (992 would decode to 992 mb).
00     1000 mb         height in whole meters.
92      925 mb         height in whole meters.
85      850 mb         height in whole meters, without a thousands digit of 1. 
			  585 decodes to 1585 m.
70      700 mb         height in whole meters, without a thousands digit of 2 or 3. 
			  138 decodes to 3138 m. 
			  the 3 produces a result closer to average conditions.
50      500 mb         height in whole dekameters (10 meters)
                            572 decodes to 5720 m.
40      400 mb         height in whole dekameters
                            736 decodes to 7360 m.
30      300 mb         height in whole dekameters
                            935 decodes to 9350 m.
25      250 mb         height in whole dekameters, without a leading 1.
                            054 decodes to 10540 m.
20      200 mb         height in whole dekameters, without a leading 1.
                            193 decodes to 11930 m.
15      150 mb         height in whole dekameters, without a leading 1.
                            371 decodes to 13710 m.
10      100 mb         height in whole dekameters, without a leading 1.
                            624 decodes to 16240 m.
88      tropopause     pressure in whole millibars.
                            192 decodes to 192 mb.
77      max wind       pressure in whole millibars.
                            182 decodes to 182 mb.

second group: symbolically, TTTDD

TTT is the temperature in tenths of a degree Celcius. An odd tenths digit indicates a negative value; 
    an even tenths digit indicates a positive value. 
    041 decodes to - 4.1 C. 046 decodes to + 4.6 C.
DD  is the dewpoint depression in degrees Celcius. 
    A DD of 50 or less is in tenths of a degree Celcius.                  48 decodes to 4.8 C. 
    A DD above 55 is in whole degrees Celcius, and 50 must be subtracted. 59 decodes to 9 C.

    To find the dewpoint temperature, subtract the DD from the temperature.

third group: symbolically, WWWSS

WWW - wind direction to the nearest 5 degrees.
SS  - wind speed in whole knots; tens and units digits only. 
      If speed is over 100, 1 is added to the wind direction.

at the max wind level, the second group is the wind group and the temperature group is omitted.

51515 is a code that signals the end of the TTAA

If the TTAA example is reformated with one level per line:

TTAA  81001 72518 	data ident info		day = 31; station idn = 72518
99030 08863 33004 	surface level		P = 1030 mb; T = + 8.8 C; DD = 13 C; dir = 330; spd =  4
00263 10464 34016	1000 mb level		Z =  263 m ; T = +10.4 C; DD = 14 C; dir = 340; spd = 16
92904 04461 00518 	 925 mb level		z =  904 m ; T = + 4.4 C; DD = 11 C; dir = 005; spd = 18
85585 00079 01526 	 850 mb level		z = 1585 m ; T =   0.0 C; DD = 29 C; dir = 015; spd = 26
70138 04182 32526 	 700 mb level		z = 3138 m ; T = - 4.1 C; DD = 32 C; dir = 325; spd = 26
50572 17372 31549 	 500 mb level		z = 5720 m ; T = -17.3 C; DD = 22 C; dir = 315; spd = 49
40736 28766 31052 	 400 mb level		z = 7360 m ; T = -28.7 C; DD = 16 C; dir = 310; spd = 52
30935 45763 30055 	 300 mb level		z = 9350 m ; T = -45.7 C; DD = 13 C; dir = 300; spd = 55
25054 55158 29568 	 250 mb level		z =10540 m ; T = -55.1 C; DD =  8 C; dir = 295; spd = 68
20193 63557 28573 	 200 mb level		z =11930 m ; T = -63.5 C; DD =  7 C; dir = 285; spd = 73
15371 58560 27071 	 150 mb level		z =13710 m ; T = -58.5 C; DD = 10 C; dir = 270; spd = 71
10624 62164 28053	 100 mb level		z =16240 m ; T = -62.1 C; DD = 14 C; dir = 280; spd = 53
88192 64957 28579    tropopause level 		P =  192 mb; T = -64.9 C; DD =  7 C; dir = 285; spd = 79
77182 28581 41314    max wind   level		P =  182 mb; T & DD not included ! ; dir = 285; spd = 81
51515 10164 00021    end of level data flag	stop here
10194 36018 34526=   ignore

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TTBB's - Observations of thermodynamic data at the significant levels - levels where the vertical change of either temperature of moisture exceed critical values.

Example of TTBB section of sounding:

TTBB  81000 72518 00030 08863 11012 11264 22925 04461
33856 00571 44831 01886 55823 03086 66793 01884 77677 05980
88662 05768 99572 12964 11554 14368 22540 14971 33527 15962
44506 16575 55467 20166 66300 45763 77250 55158 88187 64957
99176 60758 11142 58161 22100 62164 31313 45202 82321 41414
00900=

Decoding the TTBB section

data identification (level): symbolically, TTBB DDHHF IIIII

same as TTAA

each significant level (data): symbolically, CCLLL TTTDD

2 groups per level
first group: CCLLL

CC  - a code for the level and signals the start of data at that level;
      values are 00, 11, 22, ...
LLL - the pressure in whole millibars.

second group: TTTDD

same as TTAA

31313 signals end of TTBB

If the TTBB example is reformated with one level per line:

TTBB  81000 72518  	data ident info		day = 31; station idn = 72518
00030 08863 		sig level		P = 1030 mb; T = + 8.8 C; DD = 13 C
11012 11264 		sig level		P = 1012 mb; T = +11.2 C; DD = 14 C 
22925 04461 		sig level		P =  925 mb; T = + 4.4 C; DD = 11 C
33856 00571  		sig level		P =  856 mb; T = - 0.5 C; DD = 21 C
44831 01886  		sig level		P =  831 mb; T = + 1.8 C; DD = 36 C
55823 03086  		sig level		P =  823 mb; T = + 3.0 C; DD = 36 C
66793 01884  		sig level		P =  793 mb; T = + 1.8 C; DD = 34 C
77677 05980 		sig level		P =  677 mb; T = - 5.9 C; DD = 30 C
88662 05768  		sig level		P =  662 mb; T = - 5.7 C; DD = 18 C
99572 12964  		sig level		P =  572 mb; T = -12.9 C; DD = 14 C
11554 14368  		sig level		P =  554 mb; T = -14.3 C; DD = 18 C
22540 14971  		sig level		P =  540 mb; T = -14.9 C; DD = 21 C
33527 15962 		sig level		P =  527 mb; T = -15.9 C; DD = 12 C
44506 16575  		sig level		P =  506 mb; T = -16.5 C; DD = 25 C
55467 20166  		sig level		P =  467 mb; T = -20.1 C; DD = 16 C
66300 45763  		sig level		P =  300 mb; T = -45.7 C; DD = 13 C
77250 55158  		sig level		P =  250 mb; T = -55.1 C; DD =  8 C
88187 64957 		sig level		P =  187 mb; T = -64.9 C; DD =  7 C
99176 60758  		sig level		P =  176 mb; T = -60.7 C; DD =  8 C
11142 58161  		sig level		P =  142 mb; T = -58.1 C; DD = 11 C
22100 62164  		sig level		P =  100 mb; T = -62.1 C; DD = 14 C
31313 45202  		end of level data flag	stop here
82321 41414		ignore
00900=			ignore

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PPBB's - Observations of wind data at standard levels.

Example of PPBB section of sounding:

PPBB  81000 72518 90012 33004 34520 35018 90346 00518 02021
36028 90789 34527 34026 33525 91024 32525 32031 31539 9167/
31043 31550 9205/ 31050 30553 93025 30055 29555 29571 9405/
28580 27071 9503/ 27565 28056=

Decoding the PPBB section

data identification (level): symbolically, PPBB DDHHF IIIII

same as TTAA

each standard level (wind data): symbolically, 9TABC WWWSS WWWSS WWWSS

4 groups per section; if A B or C are a "/", then that group is omitted

first group: symbolically, 9TABC

9 - signals the start of a 4 group section.
T - the base height, in 10,000's of feet MSL, of the following 3 observations.
A - the height relative to the base, in 1000's ft, of the first observation.
B - the height relative to the base, in 1000's ft, of the second observation.
C - the height relative to the base, in 1000's ft, of the third observation.

Example, 90012:
the base height is 0 * 10,000 = 0 ft MSL.
the height of the first level is  0 + ( 0 * 1000 ) = 0 ft, or the surface.
the height of the second level is 0 + ( 1 * 1000 ) = 1000 ft MSL.
the height of the third level is  0 + ( 2 * 1000 ) = 2000 ft MSL.

		second, third, and fourth groups: symbolically, WWWSS

same as TTAA

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