A New Look at Radiosonde Data prior to 1958

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Abstract
Historical radiosonde data are known to suffer from inhomogeneities. The first radiosonde intercomparison was made at Payerne, Switzerland, in 1954, and a major international effort to standardize the network, including launch times, was made for the International Geophysical Year (IGY) in 1957–58. Data from before this period, in some cases extending back as far as 1934, have been viewed with even more suspicion than recent data. These early data are scattered among numerous archives with a variety of station identifier schemes and quality-control procedures, and some of the data have only recently been digitized from paper records. Here, the first systematic compilation of pre-IGY data is made, and a novel quality-assessment technique is applied, which reveals that much of the early data have uncorrected radiation and lag errors, especially in the former Soviet Union. Incorrect geopotential height units and problematic time stamps were also found. The authors propose corrections and present corrected hemispheric fields that show large changes and improved internal consistency in height and temperature across Eurasia compared with uncorrected data. The corrections are important, especially as they have a clear spatial structure that interferes with the planetary wave structure. These corrected data are useful for climate studies and considerably enhance the length and quality of the upper-air record but may not be suitable for trend analysis. Assimilation of the uncorrected data has led to a widespread warm bias in NCEP–NCAR reanalysis in the 1950s