A historical upper air-data set for the 1939-44 period

Historical upper-air data from radiosonde ascents and weather flights were re-evaluated in order to study the circulation of the upper troposphere and lower stratosphere during the 1939-44 period. Temperature and geopotential height data from 132 records, comprising around 26 500 single atmospheric profiles and 1750 monthly mean profiles, were compiled, digitized, controlled, adjusted, and assessed. The data stem from a number of countries in the extratropical Northern Hemisphere, including Germany and occupied areas, Sweden, the UK, the former Soviet Union, and the USA. In this paper, the principal procedures used to correct the historical radiosonde data for the effects of lag and radiation errors are presented and ways of assessing the accuracy and precision of the data are discussed. The results show that the specified quality criteria are generally met by most data records. Some of the records had to be corrected for systematic errors; a few were rejected. Many series, however, were too short for a reasonable assessment. Also, individual ascents may have a larger error. Monthly anomaly maps of upper-level temperature and geopotential height based on the re-evaluated data show clear spatial patterns that are consistent with each other and with corresponding anomaly fields from the Earth's surface. The re-evaluated data can be used to study synoptic to interannual variability, but they are not suitable for long-term trend analysis. Copyright (C) 2003 Royal Meteorological Society.